Fishing for Females

Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 1076

Fishing for Females

Sensory Exploitation in the Swordtail Characin

MIRJAM AMCOFF

ACTA UNIVERSITATIS UPSALIENSIS ISSN 1651-6214 ISBN 978-91-554-8758-4 UPPSALA urn:nbn:se:uu:diva-207334 2013 Dissertation presented at Uppsala University to be publicly examined in Ekmansalen, Norbyvägen 14, Uppsala, Thursday, October 31, 2013 at 09:00 for the degree of Doctor of Philosophy. The examination will be conducted in English.

Abstract Amcoff, M. 2013. Fishing for Females: Sensory Exploitation in the Swordtail Characin. Acta Universitatis Upsaliensis. Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 1076. 43 pp. Uppsala. ISBN 978-91-554-8758-4.

Mate choice plays an important role in sexual selection and speciation. The evolution of mate choice is intriguing in cases where choosy individuals gain little except for genetic material from the mate and where the trait used as a criterion for the choice is costly to its bearer. The sensory exploitation hypothesis is an interesting idea that applies to such cases because it suggests that sexual preferences may arise as side-effects of preferences that are under selection in other contexts. The role of mate choice in speciation is strong but is debated because the reasons for population divergence in mate preferences and sexual traits are sometimes hard to explain. Also in this context sensory exploitation offers a potential explanation in that a link between natural and sexual selection may result in divergence in sexual selection whenever populations differ in natural selection. In this thesis, I test several aspects of this hypothesis in a species of fish, the swordtail characin (Corynopoma riisei). In this species males display a flag-like ornament that grows from the operculum. Because females respond to this ornament by biting at it, it has been proposed to act as a food-mimic. By manipulating female food type and quantity, and testing the resulting female preference for the male ornament, I find support for the theory that the preference has evolved through sensory exploitation and that females indeed appear to relate the ornament to a food item. Furthermore, I show that sensory exploitation can lead to morphological divergence among natural populations in this species. Apart from the flag-ornament, other courtship signals are also investigated. The results show that the relative importance of different signals may vary depending on receiver motivation. This suggests that various aspects of both male courtship signals and the conditions during which they are being signalled should be considered to gain a full understanding of mate choice and its role in sexual selection and speciation.

Keywords: Sexual selection, Mate choice, Courtship, Sensory bias, Plasticity, Corynopoma riisei, Mulitiple signalling

Mirjam Amcoff, Uppsala University, Department of Ecology and Genetics, Animal ecology, Norbyvägen 18 D, SE-752 36 Uppsala, Sweden.

ISSN 1651-6214 ISBN 978-91-554-8758-4 urn:nbn:se:uu:diva-207334 (http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-207334)

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List of Papers

This thesis is based on the following papers, which are referred to in the text by their Roman numerals.

I Amcoff, M. and Kolm, N. (2013) Does female feeding motivation affect the response to a food-mimicking male ornament in the swordtail characin Corynopoma riisei? Journal of Fish Bi- ology, 83:343–354.

II Amcoff, M., Lindqvist, C. and Kolm, N. (2013) Sensory exploitation and plasticity in female mate choice in the swordtail characin. Animal Behaviour, 85:891–898.

III Kolm, N., Amcoff, M., Mann, R. P. and Arnqvist, G. (2012) Diversification of a food-mimicking male ornament via sensory drive. Current Biology, 22:1440–1443.

IV Amcoff, M., Kolm, N. and Arnqvist, G. (2009) Courtship signalling with a labile bilateral signal: males show their best side. Behavioural Ecology and Sociobiology, 63:1717–1725.

V Amcoff, M. and Kolm, N. Multiple male sexual signals and female responsiveness in the swordtail characin (Corynopoma riisei). Submitted manuscript.

Reprints were made with permission from the respective publishers.

Cover photo: Niclas Kolm

The following papers were written during the course of my doctoral studies but are not part of the present dissertation.

Amcoff, M. and Kolm, N. A test of sensory exploitation in the swordtail characin (Corynopoma riisei) based on colour matching between female prey and a male ornament. Environmental Biology of Fishes, In Press.

Amcoff, M., Gonzalez-Voyer, A. and Kolm, N. Evolution of egg dummies in Tanganyikan cichlid fishes: the roles of parental care and sexual selection. Journal of Evolutionary Biology, In Press.

Amcoff, M.*, Hallsson, L. R.*, Winberg, S. and Kolm, N. Male courtship pheromones affect female behaviour in the swordtail characin (Corynopoma riisei). Submitted manuscript. [*These authors contributed equally to this work.]

Contents

Introduction...... 9 Communication in sexual selection...... 9 Selection on mate preferences...... 10 Evolution of mate preferences...... 11 Sensory exploitation ...... 12 Study species...... 14 Aim...... 16 Methods ...... 17 Experimental design...... 17 Behaviour and morphology...... 18 Results and Discussion ...... 21 Ornament size and shape...... 21 Female motivation...... 23 Ornament size and male display behaviour...... 26 Effect of morphology and behaviour...... 28 Conclusions and Future Challenges...... 29 Sammanfattning på svenska...... 33 Resultat...... 34 Slutsats ...... 34 Tack ...... 36 Literature Cited ...... 40

Introduction

Extant organisms display amazing variation in physical appearance and behaviour. Some of this variation is attributed to adaptation in the struggle for survival, while some can be assigned to intra- and interspecific communication. Signals used in communication can, for instance, be vocalisations, physical contact, body postures, activity and colour patterns, vibrations, light emissions, and chemical cues. In all forms of communication, regardless of mode, there is a signaller (or transmitter) that emits a signal, and a receiver that receives and interprets that signal. Attributes of the signaller, the signal itself, the ambient conditions during signal transmission, and the sensory system of the receiver together determine the effectiveness of a given signal (Endler & McLellan 1988; Ryan 1990; Endler 1992, 1993). The evolutionary history, morphology, physiology and cognitive ability of both the transmitter and the receiver will place limits on what signals the transmitter will be able to emit and the receiver able to receive (Ryan 1990). At the same time, natural and sexual selection pressures acting on both the transmitter and the receiver will affect which signals are effective, in terms of both transmission and reception. Selection will favour signals that most efficiently transmit the received message to the recipient, and the optimal signal will differ depending on the environmental conditions, both with regards to ambient noise and recipient susceptibility. The evolution of different signals will therefore be directed or biased by environmental conditions, as well as by physical and neurological limitations in the receiver (Ryan 1990; Endler 1992). Because of the interre- lationship between how signals are transmitted and received, these factors are not evolutionary independent of each other but are likely to coevolve (Endler 1992).

Communication in sexual selection Sexual selection arises through competition between members of one sex over mating opportunities with the other sex (intra-sexual competition) and through specific preferences expressed by one sex for various traits expressed in the other sex (mate choice; Darwin 1859; 1871). Any trait that gives rise to variation among individuals in mating success may be subject to sexual selection. The signals that have arisen in response to sexual selection

9 are often exaggerated and extravagant. Furthermore, sexual selection often drives traits to be expressed in ways that are in direct opposition with natural selection. Signals used in intra-sexual competition, such as weapons or status badges, can be used to convey information about the competing individuals’ respective vigour (Andersson 1994; Berglund et al. 1996). These signals may be used by both same-sex rivals to assess competitive ability of the bearer, as well as by potential partners to gauge the individual’s quality (Berglund et al. 1996; Qvarnström & Forsgren 1998). Signals used in mate choice may convey information about both direct and indirect benefits that may be gained by the choosy sex in mating with a specific individual (Andersson 1994). Direct benefits may come in the form of e.g. nuptial gifts, parental care, high quality territory, defence etc. and the indirect benefits may be genetic material for the offspring (reviewed in Kirkpatrick & Ryan 1991; Andersson 1994).

Selection on mate preferences In cases where there are direct benefits to be gained from mating with a particular mate, there is direct selection on mate preferences. What those benefits are can be evident from direct inspection (for example nuptial gift, territory size etc.). In other cases, direct benefits can be signalled through for instance plumage colouration or courtship intensity (Berglund et al. 1996). Apart from when there are direct benefits involved, there are two alternative bodies of theory pertaining to when mate preferences are under direct selection: sexual conflict theories and sensory bias theories (Kokko et al. 2003). Sexual conflict arises when the fitness curves of males and females have different optima. For example, in many species, male fitness increases in- definitely with increasing number of matings while the female fitness curve displays a sigmoid or bell shaped relationship in relation to number of matings (Arnqvist & Rowe 2005). This can lead to a conflict of interest between the sexes, where males will try to coerce matings with females while females will be under direct selection to try to resist matings (Arnqvist & Rowe 2005). The sensory bias theory proposes that signals may evolve by exploiting an already existing sensory bias (West-Eberhard 1984; Kirkpatrick 1987; Endler & McLellan 1988; Basolo 1990; Ryan 1990, 1998; Ryan et al. 1990; Ryan & Rand 1990; Christy 1995). The sensory bias may be related to food acquisition, predator detection/avoidance or similar; and because individuals with this bias have higher survival and/or fecundity, there is direct selection on the receiver to express that particular preference (Kirkpatrick 1987). In this way, a sexual preference may evolve as a side-effect of an already existing sensory bias (West-Eberhard 1984; Endler & McLellan 1988; Basolo

10 1990; Ryan 1990, 1998; Ryan et al. 1990; Ryan & Rand 1990). There are biases in the neural system resulting from the evolutionary history of both receivers and transmitters and any of these may be targeted for coincidental evolution of mate preferences (Kirkpatrick & Ryan 1991; Arak & Enquist 1993). The nature of the bias affects how strong the resulting mate preference can be: if the initial preference is under strong direct natural or sexual selection this will have the side-effect of generating strong direct selection also on the novel signal (Christy 1995). In many cases, the choosy sex does not receive any apparent benefits apart from genetic material from the partners they choose to mate with (Fisher 1915, 1930; Lande 1981). Traditionally, signals that convey indirect benefits have been divided into those that convey honest information about the quality of the signaller (indicator signals; Fisher 1915; Zahavi 1975), and those where there exists a correlation between the signal expression and the preference (Fisher’s runaway process; Fisher 1915, 1930). In the latter case, the choosy sex gets an indirect benefit in having more attractive offspring (rather than superior survivors as in the case of indicator signals). Thus, there may be both direct and indirect selection for a preference in the choosy sex.

Evolution of mate preferences It is relatively simple to understand evolution of preferences for characters that indicate direct benefits to the receiver. However, the question about how sexual preferences related to traits that are not directly related to male quality have evolved is still highly debated. Both the honesty of many signals (Dawkins & Guilford 1991) and the importance of indirect benefits to the choosy sex have been questioned (see Kokko et al. 2003; Kotiaho & Puurtinen 2007; Hettyey et al. 2010 for re- views). Hence, why females prefer some males over others when they appear not to gain any substantial benefits remains problematic. In addition, the fact that there are not only costs associated with eliciting signals, but also with receiving and processing them (e.g. Pomiankowski 1987; Dawkins & Guil- ford 1991), was initially ignored. Such costs include time lost while assessing the signal and increased risk of predation by being in proximity to a displaying mate (Dawkins & Guilford 1991). The sensory bias theory, where the observed preference is a side-effect of a preference that is (or was) under direct selection in another context, offers an interesting explanation for situations where selection for indirect benefits seems to be at work (Boughman 2002; Kokko et al. 2003). A number of closely related hypotheses have been formulated to describe different parts of this process while trying to explain not only the initial evolution of a preference but also the direction of the preference (West-Eberhard

11 1984; Endler & McLellan 1988; Ryan 1990; Proctor 1991; Endler 1992; Endler & Basolo 1998). The term sensory bias has been used to include all aspects of this process, explaining why both ornaments and preferences have evolved (Fuller et al. 2005). From here on, I will focus on the role of sensory bias in the evolution of mate preferences and will therefore refer to it as sensory exploitation (Ryan 1990; Ryan et al. 1990; Ryan & Rand 1990; Endler & Basolo 1998; Fuller et al. 2005).

Sensory exploitation Models of preference evolution through sensory exploitation have often been given names with negative connotations, such as sensory trap and sensory exploitation (West-Eberhard 1984; Ryan 1990). This may lead the reader to believe that the evolving preference is implicitly negative and that responding to the novel signal is detrimental for the receiver. Although this is sometimes the case, it need not be so (Christy 1995; Dawkins & Guilford 1996; Arnqvist 2006). Responding to the new sexual signal can be beneficial, for instance, by reducing the costs of mate search. However, responding to a signal could be detrimental, for example if it leads to mating with suboptimal mates that the receiver would otherwise discriminate against, or if it inter- feres with receiving and responding to other signals (Dawkins & Guilford 1996). Just as there can be both positive and negative consequences for the receiver, the resulting selection on the signal trait has no inherent direction as long as the net benefit of responding to the signal is positive (Christy 1995; Rodriguez 2009). This means that the preference can lead to reduced, exaggerated or stabilising selection on trait expression, in the same way as Fisher's runaway process. Although the sensory exploitation theory is often discussed as an alternative to other hypotheses for the evolution of mate preferences, these different theories are not mutually exclusive (Basolo 1990; Endler & Basolo 1998; Fuller et al. 2005). For instance, if a genetic correlation between the signal and the preference arises, the trait and preference may develop further through Fisher’s runaway process (Endler & Basolo 1998; Arnqvist 2006). Alternatively, if there are costs associated with producing the signal, it may become an honest signal of individual quality (Macías Garcia & Ramirez 2005). Finally, if it is costly to respond to the signal, the receiver will be selected to increase discrimination between the signal and the original model. The signal will, in turn, be selected to develop into a better mimic (Bradbury & Vehrencamp 2000; Macías Garcia & Ramirez 2005; Arnqvist 2006). Thus further refinement of the signal and the receiver may occur through sexual conflict (Bradbury & Vehrencamp 2000; Macías Garcia & Ramirez 2005; Arnqvist 2006). Below, I have outlined two tests that can be employed to test the sensory exploitation hypothesis. The first test, which addresses the evolution of the

12 preference, makes it possible to distinguish sensory exploitation from other models of preference evolution (Basolo 1990; Ryan 1990; Shaw 1995; Endler & Basolo 1998; Fuller et al. 2005). The second test investigates the expected direction of the preference, and therefore its proximal function. This test does not necessarily distinguish sensory exploitation from other models. However, understanding how mate preferences work mechanisti- cally can help us understand how selection works in general and to explain the observed or expected effects the preference has on the trait (Fuller et al. 2005). The first test examines the prediction that the preference preceded the trait in evolutionary time (Basolo 1990; Ryan 1990; Shaw 1995). To make infer- ences about evolutionary events, phylogenetic analyses must be used. The use of such techniques is subject to inherent limitations, as well as limitations imposed by the study system. Importantly, phylogenetic comparative analyses are only as good as the phylogeny on which they are based (Shaw 1995; Ryan 1996; Martins 2000), though recent developments now allow for better control for uncertainty in both the phenotypic data and the phylogeny (Pagel et al. 2004; Pagel & Meade 2006). Another issue is that tests of pre- existing mate preferences using phylogenetic techniques make a number of assumptions regarding the study system, for instance the presence of the signal and trait in the phylogeny and the relative speed of signal and preference evolution (Christy 1995; Endler & Basolo 1998; Fuller et al. 2005). Observations indicating that a preference has originated by means of one mechanism do not mean that the preference is still under the same selective forces as when it evolved and vice versa (Endler & Basolo 1998; Fuller et al. 2005). It is therefore useful to have information about both past and present evolutionary forces acting on the preference. The second test therefore aims at exploring the evolutionary forces acting on the preference in the present. This is a more direct way of testing for evidence of sensory exploitation that involves investigating the link between the original selection pressure and the resulting mate preference (Christy 1995; Fuller et al. 1995; Fuller 2009). Although evidence of a direct link between the original selective pressure and the mate preference arguably constitutes strong evidence in favour of evolution through sensory exploitation, there may be alternative explana- tions. For instance, a preference for red food items (resulting in mate preference for red ornaments) will be expected to coincide with a mate preference for red ornaments also if the preference evolved through any other model of preference evolution and this may have preceded or even driven the inclu- sion of red food in the diet (original selective pressure). The same is true for the observation that a signal matches the maximal sensitivity of the receiver’s sensory system; it is possible that the trait evolved first, and that the receiver’s sensory system subsequently evolved to match the trait. Tests of present evolutionary forces acting on the preference can consist of exploring indirect evidence in the form of correlations between signal and

13 preference. More direct evidence can be gathered, from experimentally altering the selective pressure on the preference the signaller is thought to home in on, and investigating the effect on the mate preference (Fuller et al. 2005). In some systems, long term selection experiments can be performed to artifi- cially alter selection on the preference (Fuller et al. 2005). Alternatively, a neural network approach can be adopted (Fuller 2009). Thus, in the absence of appropriate data to perform phylogenetic comparative analyses, tests of the current function in signal-receiver systems can provide important hints about the evolution of mate preferences.

Study species The swordtail characin (Corynopoma riisei), subfamily Glandulocaudinae (but see Weitzman et al. 2005), is a small (30-50 mm standard length) freshwater fish native to Venezuela and Trinidad. It is a very suitable study species for research of sensory exploitation: it has pronounced sexual dimor- phism and relatively easily observed courtship behaviours. The sexual di- morphism between the sexes is pronounced with the male having enlarged anal and dorsal fins and the lower lobe of the caudal fin is also clearly elongated (Kutaygil 1959; Nelson 1964a). The most extreme secondary sexual character in the male is a thin paddle-like structure extending from the operculum that is enlarged at the end into a flag (Kutaygil 1959; Nelson 1964a; Figure 1, 2). Courting in this species is time consuming and may extend over several days (Kutaygil 1959). During courtship the male extends the flag in front of the female (Kutaygil 1959; Nelson 1964a, b; Figure 1, 2). When the flag is presented to the female, she frequently responds by attempting to bite at it. Fertilization is internal in C. riisei but the males lack external genitalia (Ku- taygil 1959) and it is still unknown exactly how and when sperm transfer takes place in this species. However, it has been proposed that the male’s flag display serves to lure the female closer to him and to position her for successful insemination (Kutaygil 1959; Nelson 1964). The fact that the female attempts to bite at the flag has led to the suggestion that she might think it is a food item (Kutaygil 1959; Nelson 1964; Wickler 1968). It has therefore been suggested that it may have evolved through sensory exploitation where the pre-existing bias relates to female food-acquisition (Kutaygil 1959; Wickler 1968, Arnqvist 2006).

Figure 1. Male swordtail characin (right) displaying his flag ornament in front of a female (left). Photo: Niclas Kolm.

Damage to the ornament, for example through bites from other individuals, may lead to temporary loss of smaller portions of the flag or even the complete removal of the entire flag (the flag grows back within a few weeks if left undisturbed; Kutaygil 1959; own obs.). A larger ornament is expected to function as a stronger signal that may be seen from farther away and elicit a stronger response in the female (Endler 1992). Furthermore, it is possible that females could use the degree of damage to a male’s flag to extract information about male quality, for instance if he is preferred by other females, his dominance rank etc. There exists great variation in flag shape across natural populations of C. riisei (Arnqvist & Kolm 2010). This variation in ornament shape correlates with habitat characteristics (water depth and amount of shading vegetation) of the populations. Furthermore, it has been shown that stream width, current velocity and canopy cover correlate with female diet composition across populations (Kolm & Arnqvist 2011). If the male flag ornament is indeed a food mimic, it is possible that there is also a link between female diet and the shape of the male ornament.

15 Aim The focus of this thesis lies in testing the general hypothesis that sensory exploitation acts in the evolution of mate preferences by examining the function of the C. riisei flag ornament. Specifically, the stages preceding fertilization are studied to test the proposed function of the ornament as a food mimic (Wickler 1968). First, I investigated the effect of flag morphology (size and shape; papers I and III) and the link between female feeding motivation and the male ornament (papers I-III). In paper III, I also investigated the relationship between flag morphology and female diet among natural populations. In paper IV, I explored the within-individual variation in flag size in both a laboratory population and in natural populations. In the same paper, I investigated the males’ ability to adjust behaviourally to this variation. Finally, in paper V, I used a multivariate approach to study the relationship between female behaviour and male morphology and courtship behaviour.

16 Methods

To investigate the evidence for sensory exploitation in the swordtail characin a series of behavioural experiments were conducted. The fish used in all experiments were either captive bred fish purchased from aquarium fish wholesalers, or their laboratory-reared descendants. Juveniles were initially kept in groups of ~50 individuals in 100 L stock-tanks. To ensure that females were virginal prior to experiments, they were physically and visually isolated in individual 50 L (W46 x L36 x H30 cm) tanks before or at first sign of sexual maturation. In both sexes, this occurs at about 25 mm standard length (Kutaygil 1959). In captivity, males isolated from females show higher courtship intensity when paired with a female (Kutaygil 1959). Therefore, males were also kept isolated from conspecifics. This also served to prevent any damage to the paddle ornament caused by male or female biting of the ornament. All tanks were equipped with motor driven filters and were manually cleaned once a week by removing food residuals and algae. In addition, approximately 20% of the water was changed weekly. The water consisted of 50% tap water and 50% deionised water and water temperature was kept at 24±2ºC. At each cleaning and water change, the water quality was main- tained through use of water conditioner (Sera Aquatan) and pH was kept at a stable level (pH 6.5-7) using a pH-reducing agent (Sera pH-Minus). In 2011, all tanks were equipped with a layer of coarse sand. From then, it was not necessary to manually clean the tanks weekly, only to change the water once a week. The fish were fed dry flake food ad libitum daily. All tanks were kept on a 12:12h light-dark cycle with one hour dusk/dawn period in between, using daylight fluorescent lighting. The behavioural experiments took place in 50 L tanks, except in paper II, where female response to the computer animation was tested in 24 L tanks.

Experimental design To investigate the effect of the various aspects of male morphology and behaviour and the effect of prior foraging experience, a series of behavioural studies was performed. Male swordtail characins use a number of different signals during courtship: Apart from displaying the flag, they also display several stereotypical

17 courtship behaviours (Nelson 1964a, b). To investigate the effects of these behaviours, I investigated female response to real males allowed to interact freely with the female (papers II, IV and V). However, in other chapters, where the effect of flag morphology on female behaviour was specifically investigated, other behaviours in the complex courtship ritual of C. riisei may have confounded or obscured the effects of male flag morphology. Therefore, in the experiments where flag morphology (e.g. size and shape) were investigated, I wanted to isolate this effect from other male characters. To this end, I used several different approaches: i) artificial flags (paper I), ii) computer animations (paper II), iii) real male flags with no visual access by females to other male characters (papers I and III) and iv) real male flags with visual access by females to the rest of the male body (paper II). In papers I and III, where the effects of flag shape and size were being investigated, a manipulation of real males’ flags, similar to that done in paper IV would have been a possibility. However, as shown in paper IV, the males may alter their display behaviour following manipulation of the flag which would have complicated the interpretation of the results. Limitations in laboratory space as well as in number of sexually mature fish available at any one time have led to somewhat reduced sample sizes. Therefore, the experimental design to isolate the effect of the trait of interest was, in all cases, optimised to obtain the clearest possible effect.

Behaviour and morphology The behaviour of C. riisei was thoroughly described by Nelson (1964a, b). In my thesis, I have focussed on the most common courtship-related male and female behaviours. The behaviours relating directly to the flag ornament were flag display and flag bites. Both total number of and latency to first flag display and bite were recorded. In the investigation of the relative size of the left and right flag (paper IV), relative number of displays using the right and left flag was also recorded. When artificial flags were used, or when the male was confined to a box, either number of bites directed at the flag or female proximity to the flag was investigated (paper I-III). Although it is not yet confirmed when exactly fertilisation takes place in this species, the most likely candidate behaviour is what Nelson (1964) referred to as ‘quivering’. During this part of the courtship, the male is swimming next to the female with his anal and lower caudal lobe wrapped around the ventral side of the female (Nelson 1964; Figure 2). Of all described courtship behaviours, the male is closest to the female during quivering and, considering the male’s lack of an external gonopodium, it is therefore likely to be the moment when fertilisation takes place (own obs.). This is further corroborated by the important role that the hooks on the anal fin have in

18 fertilisation (Kutaygil 1959; see below). This behaviour is referred to as mating attempt in my thesis and is measured in papers II and V.

Figure 2. From top to bottom: male swordtail characin displaying his left and right flag ornament in front of a female and engaging in mating attempt (‘quivering’ as described by Nelson 1964). From Nelson 1964, reprinted with permission from University of California Press.

In paper V, where a more extensive investigation of male and female courtship behaviours was conducted, I also measured zigzagging behaviour. This behaviour is one of the most commonly observed behaviours in the C. riisei courtship repertoire (own obs.). The female is the dominant sex in C. riisei and female aggression can se- verely hamper male courtship (Nelson 1964; own obs.). Females are highly variable in aggression level, but why some females are more aggressive than others is not known. Potential factors might be stress or unwillingness to mate. In any case, aggression is an important explanatory variable when investigating courtship behaviour in this species. Therefore, number of and latency to first aggressive bite was investigated in papers II and V. In addition, latency to first chase was recorded in paper V. Various expressions of stress are also often observed during courtship (own obs.). The most common stress behaviour is thigmotaxis (Simon et al. 1994) which is when the fish swims rapidly against the wall at a 90° angle or swimming along the wall with the head pressed against it. This was investigated in paper V.

19 Apart from the paddle ornament, males differ morphologically from females in that they are slightly smaller, they have a narrower and elongated caudal peduncle and the unpaired fins are elongated. Male morphology was measured by sedating and photographing the male ornaments on both sides. Male body size (snout to posterior end of last vertebra), caudal fin length (dark glandular spot to caudal fin tip) and flag related measures (total ornament length: operculum to flag tip; flag length: base to tip; flag area) on both sides were measured using image processing software. Ornament shape was investigated using geometric morphometrics (paper III).

20 Results and Discussion

Ornament size and shape In papers I and III, we investigated the effects of ornament size and shape on female response. With regards to flag size, all females were expected to respond more strongly to a larger flag. If the flag ornament is solely a sensory exploitation signal we predicted no particular preference with regards to damaged or undamaged flag shape, as all females in these experiments had been fed the same diet consisting of flake food, which is highly variable in shape. We found no effect of ornament size on female response to the artificial flag, or to the real male ornament. However, when female feeding motivation was increased (see below) females bit more often at the large ornament and there was also a tendency towards a faster response by females towards the larger ornament when tested on the artificial ornament but not on the real male ornaments. As predicted, females showed no preference for damaged or undamaged flags. We found that there was a strong correlation between flag shape and female diet composition across natural populations (Figure 3). We then tested the causality of this relationship in two separate laboratory experiments. Of all food types, ants were the most abundant across all natural populations investigated (Kolm & Arnqvist 2011). Therefore, we trained one group of laboratory reared females on ants while the other group was fed other food items (flake food in experiment 1 and Drosophila larvae in experiment 2). We presented the females with a choice between a male flag from one of two natural populations: a typical ‘ant-population’ or a typical ‘generalist- population’. We found that females trained on ants showed a stronger preference for the more ant-like flag than did females trained on the other food items (Figure 4). The hypothesis that the flag is an ant mimic was further supported by the fact that the similarity between the shape of the male ornament and the shape of an ant increased with increasing proportion of ants in the diet across the natural populations surveyed.

21 1.5

1.0 ) Y

0.5

0.0

-0.5

Male ornament shape (CV1 -1.0

-1.5 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 Female food utilization (CV1 ) X Figure 3. Relationship between female food utilization index and male ornament shape across 17 natural populations on Trinidad. The shape of the points shows the mean outline of male ornament shape in each population. The shape at the lower right, outside the plot represents the average shape of an ant.

We found a significant effect of female body size suggesting that larger females showed a stronger preference for the larger ornaments than did smaller females. The sizes of the large artificial flags used in paper I were within the natural range of flag areas observed in this laboratory population, but it is possible that these ornaments were at the large end of the scale of food size for this species. This supports the idea that the large ornaments mimicked a prey item that was too large, at least for the smaller females. This would explain the observation that larger females responded more strongly to the ornament than did small females. That the preference for larger ornaments increased in females with a stronger feeding incentive agrees with what Gill & Hart (1994) found in threespine sticklebacks (Gasterosteus aculeatus). They found that an individual’s willingness to eat larger prey increased with their hunger level, even though larger prey require longer handling time (Gill & Hart 1994). The artificial ornaments differed in size by approximately 6 mm2 compared to the smaller 0.8 mm2 difference in the real male ornaments. The smaller difference in flag size in real males may explain the reduced response seen in this experiment.

Figure 4. Proportion female bites directed at the flag ornament of a male coming from a population where the diet was rich in ants in females that had been fed ants or other food objects (flake food; black symbols or Drosophila larvae; white symbols).

The lack of preference for ornaments of damaged or undamaged shape supports the idea that there is a direct link between female feeding experience and preference for the male ornament. As such, any female preference for ornament shape is limited when females are kept on a diet where food items vary in shape. This idea is further supported by our findings in paper III, where female diet was shown to affect female preference for ornament shape (Figure 4). Given that the female responds to the male ornament by biting at it, Wickler (1968) suggested that the C. riisei flag ornament may be a food mimic. He went on to suggest that it may be mimicking Daphnia or other ‘water fleas’. In support of Wickler’s (1968) theory we showed that there is a relationship between ornament shape and female diet (Figure 3). However, we refute the suggestion that the flag is mimicking water fleas by showing that the ornament instead appears to be an ant-mimic.

Female motivation To investigate the link between the female’s internal motivation relating to food and her response to the male flag, we manipulated female feeding experience with regards to quantity (paper I) and quality (colour; paper II) of food. If females respond to the male flag as if it were a food item, hungry females would be expected to respond more strongly to the flag than fed

23 females. We investigated this by comparing the response to a male ornament between females that had been fed at normal level and females that had been starved. The internal motivation with regards to food quality was also manipulated by exposing females to a novel, red-coloured food. The response of these females to a red-coloured male flag was compared with that of females trained on standard coloured food. We found that hungry females responded more strongly to the artificial ornament (as measured by latency to first flag bite) than did fed females. For total number of bites directed at the ornament, the number of bites tended to increase with female body size in the food-deprived females, while it decreased with female body size in the fed females. No effect of female hunger level was detected in female response to the real male ornament. When presented with animated pictures, preference for the male with the red-coloured flag increased with female body size in females that had been trained on red-coloured food while it decreased with female body size in the control females. In the test of female response to red-coloured real flags of the male confined to the box, there was a tendency towards a greater response in the red trained females in that they directed on average twice as many bites at the male ornament compared to the control females. When the male was free to interact with the female, females trained on red food again directed more than twice as many bites at the flag compared to control females (Figure 5). In addition, females trained on red food were more likely to engage in mating attempts (15 red-trained females compared to nine in the control treatment), although the average number of mating attempts did not differ significantly between the treatments.

24 Bites at flag-ornament Bites 23456789

Red Control Treatment

Figure 5. Total number of flag bites directed at the male with red-coloured flags by the females in the red and control treatment groups (mean±SE).

The increase in response observed in the females with a higher feeding incentive is consistent with the suggestion that females perceive the flag as a food object. Furthermore, the increased response in females trained on red food to the red-coloured flag shows that there is a direct link between what the females have eaten and their response to the flag. This response was very fast (following only ten days of food training), which suggests that female preferences may be labile and change rapidly in response to changes in the composition of the available food. It makes sense that, in order to survive, individuals must be able to rapidly adapt to changes in food abundance or type. However, it would be impossible for the evolution of male flag morphology to track such rapid changes in female preference. Unless the female preference is stable over long periods of time, the male flag would not have time to evolve in response to female mate choice (Mead & Arnold 2004; Chaine & Lyon 2011). The correlation between female diet composition and environmental variables indicates that the food composition is indeed stable over time in the natural habitat of C. riisei (Kolm & Arnqvist 2011; but see Owens 2010). In species where males offer nuptial gifts to females, it has been shown that unfed females are more likely to accept the gift and to mate compared to fed females (Thornhill 1984; Bilde et al. 2007; Fox & Moya-Laraño 2009). The nutritional value of the male flag is probably limited, even if the female manages to bite off the whole flag. Therefore, any direct advantages to responding to the flag are probably marginal.

25 Ornament size and male display behaviour In paper IV, we investigated patterns of ornament asymmetry and whether male display behaviour was affected by the relative size of the male ornament. First we showed that there was substantial within- and between-individual variation in both paddle length and flag area in C. riisei, both in our laboratory population and in wild populations. The pattern of asymmetry was investigated and we showed that the pattern did not conform to that expected if it were a case of fluctuating asymmetry, nor was there any evidence of direc- tional asymmetry (Palmer 1996). Furthermore, both in the laboratory population and wild populations the level of asymmetry was higher than that expected in cases of fluctuating asymmetry (laboratory population: 5.9% in paddle length and 20% in flag area; across all wild populations: 4% in paddle length and 17.2% in flag area). This suggests that the asymmetries in ornament length and flag area are not the result of developmental instability but may instead be the result of damage inflicted on the ornament (damage asymmetry; Uetz & Taylor 2003) in the wild populations. In the laboratory population, the males had been kept in isolation preventing damage to the flag inflicted by other individuals. Therefore the asymmetry seen in this population is probably due to developmental instability. We then investigated the effect of this asymmetry on male display behaviour. To display a large flag could be beneficial to the male as a larger flag can be seen from farther away and thus acts as a stronger stimulus (Endler 1992). We found that asymmetrical males indeed preferentially displayed the larger flag (Figure 6). Moreover, after manipulation of the relative size of the flags, the males were shown to change their display behaviour accordingly (Figure 6).

26 Proportion displays with manipulated paddle 0.3 0.4 0.5 0.6 0.7 Before manipulation After manipulation

Figure 6. Proportion displays with the more manipulated paddle before and after manipulation (mean±SE).

In a similar study by Gross et al. (2007), it was shown that male guppies (Poecilia reticulata) also tend to show their more colourful side. However, in that study the effect disappeared after removing the effect of female behaviour. When female cues were removed, males showed both sides equally often (Gross et al. 2007). In our study, we found no evidence that male display behaviour was mediated by behavioural cues given by the female. In- stead the males appeared to be aware of the state of the flags and actively chose to display the larger one. The ornament investigated in P. reticulata may vary over time, depending on availability of carotenoid rich food (Grether et al. 1999). Changes in the flag shape and size in C. riisei may occur on a moment to moment basis due to biting by males or females (Kutaygil 1959; Nelson 1964a) and although the flag regenerates, this takes weeks (Kutaygil 1959). In response to such changes, male swordtail characins may be able to assess the state of their flags visually by extending the flag on each side or by assessing drag. We showed in paper I that more feeding motivated females show a stronger response to larger flags than smaller ones. By preferentially displaying the larger flag to the female, the male may maximise the female response to the ornament.

27 Effect of morphology and behaviour In paper V, the relationship between female behaviour, male morphology and courtship behaviour was investigated. We found that an earlier onset and higher courtship intensity was associated with more flag bites, more mating attempts and a reduced level of aggression towards males. Interestingly, neither body size, caudal fin length nor any trait describing the flag ornament were found to have an effect on female behaviour. Male flag morphology was shown to have a strong effect on female response (papers I-III). However, in those cases, female preference for the male ornament was driven by the quality and quantity of the food the females had been fed. For instance, preference for increased flag size was found only in hungry females, whilst preference for a certain flag shape was found only in females that had been fed food items that matched the flag shape. In the current study, all females were well fed on a diet consisting of flake food (which is highly variable in size and shape). It is therefore possible, in the absence of any manipulation of female motivation, that female attention, at least during certain phases of courtship, is focussed on flag display frequency rather than flag morphology. That the male displays the flag is probably central to attracting the attention of the female. Displaying the flag is probably also very important in providing opportunity for the female to assess the shape and size of the flag, so this behaviour necessarily constitutes a vital part of the sensory exploitation process of this preference and trait. A common behaviour in the C. riisei courtship ritual is the zigzagging behaviour. The zigzagging movement is very similar to the movement both males and females perform when feeding on particles suspended in the water column (Nelson 1964a; own obs.). We propose that zigzagging may also be intended to trigger a feeding response in the female (own obs.). If this is the case, this behaviour may interact with the flag display behaviour by ensuring that the females’ sensory system is prepared for receiving information related to food. This corresponds to the context and attention-altering hypotheses presented by Hebets & Papaj (2005). They suggest that in a signal dyad, one signal may serve to prime the receiver’s motivation towards the context of the second signal, or to direct the receiver’s attention towards the second signal (Hebets & Papaj 2005). Thus the zigzagging movement may serve to increase the females’ response when presented with the flag.

28 Conclusions and Future Challenges

Using direct experimental manipulations, I have demonstrated a strong and direct link between female feeding experience and male flag morphology in the swordtail characin. Moreover, I demonstrate that there is remarkable plasticity in female preference for the male flag that can be directly linked to environmental variation. This lends strong support to the hypothesis that the preference for this ornament has evolved through sensory exploitation by acting as a food mimic and that females respond to it as if it was food. To confirm that the preference indeed evolved through sensory exploitation, the evolutionary aspects of the female preference for the flag ornament in C. riisei must be investigated. In recent years, several robust molecular phylogenies including several species of the Stevardiinae have been con- structed (Weitzman et al. 2005; Javonillo et al. 2010; Oliveira et al. 2011). However, behavioural data is lacking for all other closely related species. One caveat is that when the original preference in question relates to some- thing as broad as food acquisition, as is the case in the swordtail characin, it may be hard to define the evidence required to support evolution through sensory bias (Christy 1995; Fuller et al. 2005). That females have a preference for food in species lacking the flag can hardly be used as evidence in favour of evolution through sensory exploitation. Nevertheless, the case of parallel evolution of flag-like ornaments – with seemingly similar function in several species of the Stevardiinae (Figure 7) – certainly suggests that they may indeed be independently derived morphological solutions to similar selective pressures. Therefore, I think that it would be very interesting to investigate whether the same selective pressures as I have demonstrated in C. riisei are influencing male secondary sexual trait morphology in these species. Another important aspect that has not been directly tested in this thesis is whether variation in the strength of the female response to the ornament affects fitness. In paper II, the females whose prior foraging experience best matched the physical appearance of the flag engaged in more mating attempts. But it would be more powerful to have a direct measurement of both male and female fitness benefits associated with signalling and responding to the flag.

Figure 7. Males of five species of the Corynopomini. Four of these species display a flag-like ornament. From top to bottom: Corynopoma riisei, Pterobrycon landoni, Pterobrycon myrnae, Gephyrocharax sp. and Gephyrocharax atricaudata. From Burns & Weitzman 2005, reprinted with permission from the Smithsonian Insititu- tion Division of Fishes; illustaration by Tamara Clark.

As shown in paper V, multiple signals may interact and their relative importance may vary depending on the circumstances. For instance, seasonal variations in food composition and abundance (Owens 2010) may affect female responsiveness to various aspects of the male courtship. These interactions should be further explored. Furthermore, any interactions between sensory exploitation and other possible signalling mechanisms is a hitherto unexplored avenue in this species. In the Goodeinae fishes, it was recently demonstrated that an ornament that had evolved through sensory exploitation subsequently evolved into an honest indicator signal (Macías Garcia & Ra- mirez 2005; Macías García & Lemus 2012). It is possible that expressing the flag in C. riisei is costly in terms of its production, maintenance and display and thus, that the flag also is an indicator of male quality. In that case, mating with individuals carrying a large flag may confer direct or indirect benefits to the females. The strong link between female foraging and the male flag seen in this species also sets the stage for potential direct costs in responding to the ornament. It could be very costly for the females if they were

30 unable to distinguish between the ornament and the food and, in doing so, missed out on opportunities to forage in favour of responding to the male ornament (Macías García & Lemus 2012). It is well known that geographically isolated populations may diverge phenotypically over time, such that they become reproductively isolated, and that sexual traits and preferences often are responsible for pre-mating isolation (Panhuis et al. 2001; Turelli et al. 2001). However, what drives this divergence in isolated populations is still debated. Because habitats often differ between geographically isolated populations, the sensory exploitation hypothesis offers an appealing explanation to why divergence occurs. If there is a link between natural and sexual selection through sensory exploitation, then changes in the environment will result in changes in the natural selection which in turn will result in direct changes in sexual selection (Fuller et al. 2005). If different populations are subject to different natural selection pressures, this will lead to differentiation also in sexual selection (Boughman 2002). If two populations experience different environments the differences in the environments need not be large in order to lead to differences in signal transmission, perception and preference (Boughman 2002). Examples where ambient conditions have had effects on expression of the trait, female perception and female preference have been documented in several species (for example in guppies, Endler & Houde 1995; Godin & Briggs 1996; sticklebacks, Boughman 2001; cichlids; Maan et al. 2006, 2010; Seehausen et al. 2008). The variation in flag shape and female diet found among natural populations of C. riisei (Arnqvist & Kolm 2010; Kolm & Arnqvist 2011), suggests that there is potential for ongoing speciation. The freshwater systems of Trinidad are currently under strong pressure from anthropogenic disturbance, including pollution and perturbations due to urban land developments and quarrying activities (Phillip 1998; Maharaj & Alkins-Koo 2007). Apart from direct effects on survival, disturbance in the form of increased turbidity may prevent transmission of signals. Furthermore, changes in the surrounding vegetation may result in changes in the available prey types and thus in al- tered female preference. The information on ornament form and female diet used in paper III was collected in 2005 (Arnqvist & Kolm 2010; Kolm & Arnqvist 2011). Earlier this year (summer 2013), I collected data from the same populations. Given the short time span between these studies (eight years), I find it unlikely that any changes in ornament shape will be found, though changes in the diet might be detected. Furthermore, to test the potential for speciation by investigating mate choice in natural populations, I collected behavioural data from wild-caught fish. It will be interesting to ana- lyse the behavioural data further to assess the possibility for assortative mating across populations. In conclusion, strong evidence in favour of preference evolution through sensory exploitation has been found in the swordtail characin. A link be-

31 tween female feeding experience and male ornament morphology was demonstrated. As predicted by the sensory exploitation hypothesis, this directly links natural and sexual selection and sets the stage for speciation driven by this link.

32 Sammanfattning på svenska

De signaler som hanar använder för att attrahera honor tillhör några av de mest varierande och spektakulära karaktärerna inom djurvärlden. Forskning har visat att olika partnervalsprocesser kan utgöra mycket viktiga bakomlig- gande faktorer till hur skillnader mellan populationer uppkommer och fak- tiskt också driva artbildning. Sexuellt urval genom partnerval är därmed en mycket stark evolutionär drivkraft, som dessutom kan utgöra en promotor i evolutionen av reproduktiv isolering och artbildning (Boughman 2002; Ful- ler et al. 2005). Därför är det mycket viktigt att vi förstår hur samspelet mellan honlig preferens och hanlig signal startar. Trots omfattande teoretiska och empiriska satsningar för att förstå evolutionen av partnerval, så är vår förståelse över hur honliga preferenser för olika hanliga drag uppkommer fortfarande begränsad. En hypotes gällande detta är ‘sensoriskt utnyttjande’ (sensory exploitation hypothesis på engels- ka; Endler & McLellan 1988; Basolo 1990; Ryan 1990, 1998; Ryan et al. 1990; Ryan & Rand 1990). Enligt denna hypotes kan honliga preferenser för en hanlig signal uppkomma som resultat av en preferens de redan hade för något som, initialt, var helt orelaterat till den hanliga signalen (West- Eberhard 1984; Endler & McLellan 1988; Basolo 1990; Ryan 1990, 1998; Ryan et al. 1990; Ryan & Rand 1990; Christy 1995). Betänk, till exempel, att en art livnär sig på en viss typ av föda. Om hanarna hos denna art utveck- lar ett ornament som råkar likna födan de äter så kan honorna, genom preferensen de har för födan, också börja föredra hanarna som har detta ornament. Detta leder till att det finns ett unikt samband mellan naturligt och sexuellt urval vilket, i sin tur, gör att sensoriskt utnyttjande potentiellt kan vara en mycket stark evolutionär mekanism. Studieorganismen som jag använt för att testa sambandet mellan honliga preferenser och hanliga signaler är sötvattensfisken dvärgdrakfenan (Cory- nopoma riisei). Denna fisk lever naturligt på Trinidad och i norra Venezuela. Hanarna hos denna art har en flagglik struktur som sticker ut från gällocket på båda sidor om kroppen (Kutaygil 1959; Nelson 1964). Hanarna viftar med detta ornament framför honorna under parningsleken (Kutaygil 1959; Nelson 1964). Honorna svarar på ornamentet genom att bita på det och det har därför föreslagits att honorna tror att det är mat (Kutaygil 1959; Nelson 1964; Wickler 1968). Denna art utgör därmed potentiellt ett utmärkt exempel på hur en honlig preferens för ett hanligt ornamentet kan evolvera genom sensoriskt utnyttjande. I min avhandling har jag, i en rad beteendeförsök,

33 undersökt den potentiella länken mellan den honliga preferensen och den hanliga signalen hos dvärgdrakfenan.

Resultat I de tre första kapitlen undersöker jag honornas svar på ornament som varie- rade i form, storlek och färg. Jag manipulerade också honornas födosöksmo- tivation antingen genom att variera tillgången på mat eller genom att ge dem olika typer av mat (kapitel I-III). Jag fann att det inte fanns någon inbyggd preferens för ornament av en viss form eller storlek. Däremot kunde preferenser både för ornamentens storlek, form och färg induceras genom att honornas motivation manipulerades. Hungriga honor svarade starkare på stora ornament än mätta honor (kapitel I), honor som tränats på röd mat svarade starkare på ett rött ornament än de som tränats på grön mat (kapitel II) och, slutligen, honor som tränats på en viss typ av mat svarade starkare på ett ornament vars form stämde överens med formen på denna mat än honor som tränats på annan typ av mat (kapitel III). Dessa experiment visar att honornas preferenser är plastiska. Till exempel i kapitel II, där jag introducerade en ny typ av mat som var rödfärgad, så svarade honorna som tränats på röd mat mer än dubbelt så starkt på det hanliga ornamentet jämfört med en kon- trollgrupp som ätit den vanliga, grönfärgade maten. Denna förändring i preferens påvisades efter en träningsperiod som endast varat i tio dagar. I kapitel IV undersökte jag den naturligt förekommande variationen i storlek mellan höger och vänster ornament, både i naturliga populationer av dvärgdrakfenan på Trinidad, och i laboratoriepopulationen och hur denna variation påverkade hanarnas eget beteende. Det finns påtaglig variation i ornamentsstorlek både hos naturliga populationer och i laboratoriepopulationen. Jag visade att hanarna föredrar att visa det stora ornamentet för honorna och att, om ornamentens storlek manipuleras, så anpassar hanarna sig och fortsätter att visa det största ornamentet. Detta tyder på att hanarna kan avgö- ra vilket ornament de visar för honorna och att de därmed kan lura honorna att tro att de har större ornament än de egentligen har och därmed kan väcka ett maximalt starkt svar hos honorna. I det sista kapitlet undersökte jag hur andra hanliga signaler påverkar ho- nans beteende. Jag undersökte då sambandet mellan honornas beteende och en rad av hanarnas olika morfologiska karaktärer liksom olika uppvakt- ningsbeteenden.

Slutsats I min avhandling har jag visat att det finns en stark och direkt länk mellan vad honorna ätit och hur de svarar på hanarnas ornament (kapitel I-III). Det-

34 ta stöder hypotesen att honornas preferens uppkommit och bibehålls genom sensoriskt utnyttjande. Vidare visar mina resultat att när man studerar sambandet mellan honligt val och hanligt ornament så är det viktigt att undersö- ka honornas svar på ornamentet under olika förhållanden och vid olika tid- punkter. Detta för att honornas svar kan påverkas av deras egen motivation vilken kan förändras över tid (kapitel I-III). Jag visade också att hanarna själva har möjlighet att påverka hur ornamentet visas för honorna och att det är viktigt att undersöka så många aspekter av hanarnas uppvaktningsbeteen- de som möjligt för att till fullo förstå honligt val och dess roll i sexuellt urval (kapitel IV och V). Därmed har ett direkt samband mellan naturlig och sexuell selektion illu- strerats. Just ett sådant samband har föreslagits som en möjlig drivande kraft till varför isolerade populationer kan börja skilja sig i honlig preferens och hanliga signaler vilket i sin tur kan leda till att nya arter bildas. Därmed kan sensoriskt utnyttjande fungera som en viktig drivkraft både i sexuellt urval och i artbildning, båda mycket viktiga evolutionära krafter bakom variation inom och mellan arter.

35 Tack

First of all, I would like to thank my supervisor Niclas. I was Niclas’ first PhD-student and I was told by many that this could be both good and bad. It was possible that Niclas would be ‘too supportive’, that he would not dare to let me make mistakes and that he would be looking over my shoulder at all times and thus making it more difficult for me to become an independent researcher. Another possible scenario was that he would not know what kind of support you need as a PhD-student. As it turned out Niclas did it all per- fectly. He did let me make mistakes, all of which I learned immensely from. He managed to give me just the right amount of support; his office door was always open for me to come in and have an emergency meeting. No matter what he was doing at the time, he would drop everything and would some- how know exactly what I was doing at the moment. Then he would either help me directly or give me the nudge I needed to go solve the problem my- self. Truly, I could not have wished for a better supervisor! I have enjoyed working, discussing, agreeing and disagreeing with you for more than five years and I am confident that it will continue like this during any future pro- jects we may have together. I am also grateful to my assistant supervisor Göran. I have always found him equally supportive, regardless if his role was to patiently describe some statistics to me or to share his insight into how the Corynopoma flag ornament might work and I am very grateful for this! I love to learn and I think that doing a PhD was the greatest thing I ever did. Even though it certainly has its ups and downs, I have enjoyed it enor- mously. This is not least because of the people at the Department of Animal Ecology. Even when I was going through tough times, I was always looking forward to going to work because I knew that my colleagues and friends at work would be ready to offer encouraging words and support. Special among those was Josefin who turned out not to be just another Swedish girl starting her PhD at about the same time as I did, but who I would soon con- sider a great friend with whom I shared all kinds of problems. I am also grateful to Amber for her never ending enthusiasm, friendliness, awesome- ness…, Björn for being a great friend who is always up for a beer and who has an unbelievable story about a friend of a friend for every occasion, Kasia for being the most unfalteringly positive person I have ever met, Paolo for his refreshing attitude, Mårten for his unforgettable first words to me at the department fika: ‘so… do you come here often?’. I am also grateful to Fer-

36 nando, Teddy and Alex K for sharing their dance moves, to David for being such a great person and for having a YouTube video up his sleeve at all times, to Isobel for always being up for going out partying and to Arild for always being ready to dress up (in Josefin’s clothes) and attend to the afore mentioned parties. I would like to thank Alejandro, Alex, Teddy and Masa- hito with whom I shared not only research group but also lots of great parties. Special thanks to Lára who first introduced me to Niclas when I was a prospecting master student and then went on to introduce me to the whole department thus making sure I became part of it. I am also grateful to Sandra with whom I shared an office for several years and who, not only made me privy to the secrets of mosquito rearing, but also inspired me to work hard. I am grateful also to Simon, my new office mate, for our many interesting discussions that would more often that not be so lively that half of the department would be able to hear them! Thanks also to Johanna, Andreas, Murielle, Karo, Hwei-Yen, Elina, Julieta, Elena, Martyna, Karl, Eryn, Fo- teini, Rado, Jakub, Martin, David, Magnus, Niclas V, Takashi, Felix, Olivia, Sara, Hanna, Emma, Marnie, David, German, Yvonne, Friederike, Thomas, Leanne, Matt, Erem, Simone, Peter, Richard, Jessica, Hanne and all the others who made or are still making the department such a nice place to work at. I am also very grateful to all the more ‘senior’ staff at the department: Mats, Ingrid, Alexei, Anna, Anders Ö, Anders B, Fredrik, Lars, Ted, Göran, Anssi and Jakob for their willingness to share their experience and expertise. Special thanks to Peter Eklöv for agreeing to be my opponent when I de- fended my licentiate thesis and to Maria and Omar, Violeta, Rosa, Philipp, Pia, Cristian and Hannes who were members of other departments at the EBC during various times and with whom I shared not only many a Friday pub but also other nice experiences! I have needed lots of practical help during the various stages of my PhD, I owe the following people many thanks; the guys in the basement for all the help with the work in the laboratory, Anders Ö for helping me with the spec- trophotometer when I needed it, Björn, Arild and Göran for helping me, on multiple occasions, with the statistics, Fernando, Göran, Ingrid, Anna, An- ders, Björn, Simone, Amber, Simon and many other people for reading and giving constructive criticism on many manuscripts, Ingela for help with administrative stuff and to Charlie, Piotr and Alberto, the master students who performed studies with me in the lab. Over the past few years I have had the opportunity to teach and I would like to thank Niclas, Fredrik, Emma D, Andreas, Norbert, Daniel, Josefin, Fia and Froukje for the great times we had on Klubban and Brita, Fia and Emma R for teaching me about nature conservation! I am grateful to the people with whom I spent my six month sabbatical in Seville. I owe special thanks to Alejandro for supervising me during this period and to Carles and Jennifer for welcoming me to their group, but also

37 to Violeta, Marga, Leti, Marcello, Jorge and all the other good people at the Estación Biológica de Doñana. For some reason, during the last couple of years of my PhD, I was under the impression that I had oceans of time. Therefore, Niclas suggested that I get involved in his guppy project so that I could get experience working with a new system and learn some new techniques. I am grateful to Alex for teaching me how to work with the guppies and to Sofia, Reija and Gunilla for introducing me to the mysteries of microsatellites and genetic analyses. During my PhD, I met a few people who do not work at the EBC (all bi- ologists, naturally!) among those I would like to thank Lisa and the more recent Uppsala-inhabitants Belén and Nacho for being great friends! This year, I finally made it to Trinidad! This was a wonderful trip and I would like to thank Fernando, Josefin and Alex for being the best field assis- tants ever, Amy and Indar for helping us with absolutely everything both before and during the trip, Heather for helping us setting up the lab and last but certainly not least Atkin, for being a great assistant, guide, and chauffeur and whose services I would recommend to anyone. I also managed a few other memorable trips during my PhD, most of these I did together with all of or parts of the following crew: Fernando, Josefin, Mårten and Björn. Thank you for all the wonderful memories! I love travelling with you guys and I can barely wait for the next trip, whenever and wherever that may be. During my PhD I have had the opportunity to travel a fair bit. I attended to several conferences, spent a 6 month sabbatical in Seville and a field trip in Trinidad. This would not have been possible without the generous grants I received from the following foundations: Stiftelsen för Zoologisk Forskning, Helge Ax:son Johnsons Stiftelse, Liljewalchs, Rektors resebidrag från Wallenbergstiftelsen, Sederholms, Selma Andersons, Letterstedts and the British Ecological Society. I saved the most important people to last: these being my family. Durante los últimos cuatro años mi novio Fernando ha sido una parte muy importante de mi vida. Fernando, eres mi compañero, mi colega y, sobre todo, mi amigo. Ni siquiera sé cómo empezar a agradecerte todo el apoyo que me has dado, pero lo voy a intentar: Gracias por enseñarme a querer a los animales como una bióloga de verdad, por viajar conmigo alrededor del mundo, por compartir mi vida, por hacerme querer ser una persona mejor, por animarme y por hacerme reír a todas horas, y por ser tú y sólo tú pase lo que pase. También quiero agradecer a tu familia, Fernando Grande, María Auxiliadora Rita (también conocida como Jenny o simplemente Mami), Pilar y Jhoani (conocido como Joan por el gobierno español), por acogerme en vuestra familia con los brazos abiertos y por perdonarme el que me haya llevado a Fernando tan lejos. När jag var liten fick jag lära mig att älska och respektera naturen. Jag skulle inte vara den jag är eller där jag är om det inte vore för mamma och

38 pappa. Jag är evigt tacksam för allt stöd ni alltid gett mig och för att ni alltid uppmuntrat mig att göra det jag helst vill, även när det innebar att utbilda mig till biolog med små utsikter att få ett ‘riktigt jobb’ och att jag måste resa hit och dit, till den ena platsen längre bort och farligare än den andra. Jag vill också särskilt tacka Birgitta och Frans för att jag fick bo och känna mig som hemma hos er under mina första år i Uppsala. Jag vill också tacka min mor- bror trollkarlen, Örjan, för all insikt han gett mig i livet som akademiker, för många trevliga middagar på Turken och för att jag fick vara med på den årliga julfesten på Geologen. Ibland har jag känt behovet av att behöva få komma bort ett tag, då har ett hus i Bollnäs alltid stått öppet och jag har kun- nat få lite lugn och ro hos Gunlög och Anders. Sedan vill jag tacka Helena och Armel (mina föräldrar), Kristina och Sören, Cecilia och Erik, Emelie, Cyrill, Lars och Elisabeth, Sara och Kalle, Jonas och Monica, Erik och Mar- kus för allt stöd.

39 Literature Cited

Andersson, M. 1994: Sexual Selection. Princeton Univ. Press, Princeton. Arak, A. & Enquist, M. 1993: Hidden preferences and the evolution of signals. Phil. Trans. R. Soc. Lond. B 340, 207–213. Arnqvist, G. 2006: Sensory exploitation and sexual conflict. Phil. Trans. R. Soc. Lond. B 361, 375–386. Arnqvist, G. & Kolm, N. 2010: Population differentiation in the swordtail characin (Corynopoma riisei): a role for sensory drive? J. Evol. Biol. 23, 1907–1918. Arnqvist, G. & Rowe, L. 2005: Sexual Conflict. Monographs in Behavior and Ecol- ogy. Princeton Univ. Press, Princeton. Berglund, A., Bisazza, A. & Pilastro, A. 1996: Armaments and ornaments: An evolutionary explanation of traits of dual utility. Biol. J. Linn. Soc. 58, 385–399. Basolo, A. L. 1990: Female preference predates the evolution of the sword in swordtail fish. Science 250, 808–810. Bilde, T., Tuni, C., Elsayed, R., Pekar, S. & Toft, S. 2007: Nuptial gifts of male spiders: sensory exploitation of the female’s maternal care instinct or foraging motivation? Anim. Behav. 73, 267–273. Boughman, J. W. 2001: Divergent sexual selection enhances reproductive isolation in sticklebacks. Nature 411, 944–948. Boughman, J. W. 2002: How sensory drive can promote speciation. Trends Ecol. Evol. 17, 571–577. Bradbury, J. W. & Vehrencamp, S. L. 2000: Economic models of animal communication. Anim. Behav. 59, 259-268. Burns, J. R. & Weitzman, S. H. 2005: Insemination in ostariophysan fishes. In: Vi- viparous Fishes (Uribe M. C. & Grier H. J. eds). New Life Publ., Florida, pp. 105–132. Chaine, A. S. & Lyon, B. E. 2008: Adaptive plasticity in female mate choice damp- ens sexual selection on male ornaments in the lark bunting. Science 319, 459– 462. Christy, J. 1995: Mimicry, mate choice, and the sensory trap hypothesis. Am. Nat. 146, 171–181. Darwin, C. 1859: On the Origin of Species: By Means of Natural Selection. John Murray, London. Darwin, C. 1871: The Descent of Man and Selection in Relation to Sex. John Murray, London. Dawkins, M. & Guilford, T. 1991: The corruption of honest signalling. Anim. Be- hav. 41, 865–873. Dawkins, M. S. & Guilford, T. 1996: Sensory bias and the adaptiveness of female choice. Am. Nat. 148, 937–942. Endler, J. A. 1992: Signals, signal conditions, and the direction of evolution. Am. Nat. 139, S125–S153. Endler, J. A. 1993: Some general comments on the evolution and design of animal communication systems. Phil. Trans. R. Soc. Lond. B 340, 215–225.

40 Endler, J. A. & Basolo, A. L. 1998: Sensory ecology, receiver biases and sexual selection. Trends Ecol. Evol. 13, 415–420. Endler, J. A. & Houde, A. E. 1995: Geographic variation in female preferences for male traits in Poecilia reticulata. Evolution 49, 456–468. Endler, J. A. & McLellan, T. 1988: The process of evolution: Toward a newer hypothesis. Ann. Rev. Ecol. Syst. 19, 395–-421. Fisher, R. A. 1915: The evolution of sexual preference. Eugen. Rev. 7, 184–192. Fisher, R. A. 1930: The Genetical Theory of Natural Selection. Clarendon Press, Oxford. Fox, C. & Moya-Laraño, J. 2009: Diet affects female mating behaviour in a seed- feeding beetle. Physiol. Entomol. 34, 370–378. Fuller, R. C. 2009: A test of the critical assumption of the sensory bias model for the evolution of female mating preference using neural networks. Evolution 63, 1697–1711. Fuller, R. C., Houle, D. & Travis, J. 2005: Sensory bias as an explanation for the evolution of mate preferences. Am. Nat. 166, 437–446. Gill, A. B. & Hart, J. B. 1994: Feeding behaviour and prey choice of the threespine stickleback: the interacting effects of prey size, fish size and stomach fullness. Anim. Behav. 47, 921–932. Grether, G. F., Hudon, J. & Millie, D. F. 1999: Carotenoid limitation of sexual coloration along an environmental gradient in guppies. Proc. R. Soc. Lon. B 266, 1317–1322. Godin, J.-G. J. & Briggs, S. E. 1996: Female mate choice under predation risk in the guppy. Anim. Behav. 51, 117–130. Gross, M. R., Suk, H. Y. & Robertson, C. T. 2007: Courtship and genetic quality: asymmetric males show their best side. Proc. R. Soc. Lon. B 274, 2115–2122. Hebets, E. A. & Papaj, D. R. 2005: Complex signal function: Developing a frame- work of testable hypotheses. Behav. Ecol. Sociobiol. 57, 197–214. Hettyey, A., Hegyi, G., Puurtinen, M., Hoi, H., Torok, J. & Penn, D. 2010: Mate choice for genetic benefits: time to put the pieces together. Ethology 116, 1–9. Javonillo, R., Malabarba, L. R., Weitzman, S. H. & Burns, J. R. 2010: Relationships among major lineages of characid fishes (Teleostei: Ostariophysi: Characifor- mes), based on molecular sequence data. Mol. Phylogenet. Evol. 54, 498–511. Kirkpatrick, M. 1987: Sexual selection by female choice in polygynous animals. Ann. Rev. Ecol. Syst. 18, 43–70. Kirkpatrick, M. & Ryan, M. J. 1991: The evolution of mating preferences and the paradox of the lek. Nature 350, 33–38. Kokko, H., Brooks, R., Jennions, M. & Morley, J. 2003: The evolution of mate choice and mating biases. Proc. R. Soc. Lon. B 270, 653–664. Kolm, N. & Arnqvist, G. 2011: Environmental correlates of diet in the swordtail characin (Corynopoma riisei, Gill). Environ. Biol. Fish. 92, 159–166. Kotiaho, J. & Puurtinen, M. 2007: Mate choice for indirect genetic benefits: scrutiny of the current paradigm. Funct. Ecol. 21, 638–644. Kutaygil, N. 1959: Insemination, sexual differentiation and secondary sex characters in Stevardia albipinnis Gill. In: Istanbul University Fen Fakultesi Mecmuasi, Series B, pp. 93–128. Lande, R. 1981: Models of speciation by sexual selection on polygenic traits. Proc. Natl. Acad. Sci. USA 78, 3721–3725. Maan, M., Hofker, K., Alphen, J. V. & Seehausen, O. 2006: Sensory drive in cichlid speciation. Am. Nat. 167, 947–954.

41 Maan, M., Seehausen, O. & Alphen, J. V. 2010: Female mating preferences and male coloration covary with water transparency in a Lake Victoria cichlid fish. Biol. J. Linnean Soc. 99, 398–406. Macíac García, C. & Lemus, Y. S. 2012: Foraging costs drive female resistance to a sensory trap. Proc. R. Soc. Lond. B 279, 2262–2268. Macías García, C. & Ramirez, E. 2005: Evidence that sensory traps can evolve into honest signals. Nature 434, 501–505. Maharaj, L. D. & Alkins-Koo, M. 2007: Use of Benthic Macroinvertebrates to As- sess Anthropogenic Impacts in the Rivers of Trinidad and Tobago. Report to the Environmental Management Authority. Martins, E. P. 2000: Adaptation and the comparative method. Trends Ecol. Evol. 15, 296–299. Mead, L. S. & Arnold, S. J. 2004: Quantitative genetic models of sexual selection. Trends Ecol. Evol. 19, 264–271. Nelson, K. 1964a: Behavior and morphology in the Glandulocaudine fishes (Ostariophysi, Characidae). In: University of California Publications in Zool- ogy, vol. 75 (Davis J., Marler P. R. & Smith R. I., eds). Univ. of California Press, Berkley and Los Angeles, pp. 59–152. Nelson, K. 1964b: The temporal patterning of courtship behaviour in the glandulocaudine fishes (Ostariophysi, Characidae). Behaviour 24, 90–146. Oliveira, C., Avelino, G. S., Abe, K. T., Mariguela, T. C., Benine, R. C., Ortí, G., Vari, R. P., Corrêa e Castro, R. M. 2011: Phylogenetic relationships within the speciose family Characidae (Teleostei: Ostariophysi: Characiformes) based on multilocus analysis and extensive ingroup sampling. BMC Evol. Biol. 11, 275. Owens, D. C. 2010: Seasonal Variation in Terrestrial Insect Subsides to Tropical Streams and Implications for the Diet of Rivulus hartii. MSc thesis, University of Nebraska. Pagel, M. & Meade, A. 2006: Bayesian analysis of correlated evolution of discrete characters by reversible-jump Markov chain Monte Carlo. Am. Nat. 167, 808– 825. Pagel, M., Meade, A. & Barker, D. 2004: Bayesian estimation of ancestral character states on phylogenies. Syst. Biol. 53, 673–684. Palmer, A. R. 1996: Waltzing with asymmetry. Bioscience 46, 518–532. Panhuis, T. M., Butlin, R., Zuk, M. & Tregenza, T. 2001: Sexual selection and speciation. Trends Ecol. Evol. 16, 364–371. Phillip, D. A. T. 1998: Biodiversity of Freshwater Fishes of Trinidad and Tobago, West Indies. PhD thesis, University of St. Andrews. Pomiankowski, A. 1987: The cost of choice in sexual selection. J. Theor. Biol. 128, 195–218. Proctor, H. C. 1991: Courtship in the water mite Neumania papillator: males capi- talize on female adaptations for predation. Anim. Behav. 42, 589–598. Qvarnström, A. & Forsgren, E. 1998: Should females prefer dominant males? Trends Ecol. Evol. 13, 498–501. Rodríguez, R. L. 2009: Trait duplication by means of sensory bias. Behav. Ecol. 20, 1376–1381. Ryan, M. J. 1990: Sexual selection, sensory systems, and sensory exploitation. Oxf. Surv. Evol. Biol. 7, 157–195. Ryan, M. J. 1996: Phylogenetics and behavior: some cautions and expectations. In: Phylogenies and the Comparative Method in Animal Behavior (E. Martins ed.). Oxford Univ. Press, Oxford, pp. 1–21. Ryan, M. J. 1998: Sexual selection, receiver biases, and the evolution of sex differences. Science 281, 1999–2003.

42 Ryan, M. J., Fox, J., Wilczynski, W. & Rand, A. 1990: Sexual selection for sensory exploitation in the frog Physalaemus pustulosus. Nature 343, 66–67. Ryan, M. J. & Rand, A. 1990: The sensory basis of sexual selection for complex calls in the túngara frog, Physalaemus pustulosus (sexual selection for sensory exploitation). Evolution 44, 305–314. Seehausen, O., Terai, Y., Magalhaes, I. S., Carleton, K. L., Mrosso, H. D. J., Miyagi, R., van der Sluijs, I., Schneider, M. V., Maan, M. E., Tachida, H., Imai, H. & Okada, N. 2008: Speciation through sensory drive in cichlid fish. Nature 455, 620–626. Shaw, K. 1995: Phylogenetic tests of the sensory exploitation model of sexual selection. Trends Ecol. Evol. 10, 117–120. Simon, P., Dupuis, R. & Costentin, J. 1994: Thigmotaxis as an index of anxiety in mice. Influence of dopaminergic transmissions. Behav. Brain Res. 61, 59–64. Thornhill, R. 1984: Alternative female choice tactics in the scorpion fly Hylobittacus apicalis (Mecoptera). Am. Zool. 24, 367–383. Turelli, M., Barton, N. H. & Coyne, J. A. 2001: Theory and speciation. Trends Ecol. Evol. 16, 330–343. Uetz, G. W. & Taylor, P. W. 2003: Developmental instability and animal communication: fluctuating asymmetry as a signal and as an influence on the signalling process. In: Developmental Instability: Causes and Consequences. (Polak, M. ed.). Oxford Univ. Press, New York, pp. 213–230. Weitzman, S. H., Menezes, N. A., Evers, H.-G., Burns, J. R. 2005: Putative relationships among inseminating and externally fertilizing characids, with a description of a new genus and species of Brazilian inseminating fish bearing an anal-fin gland in males (Characiformes: Characidae). Neotrop. Ichthyol. 3, 329–360. West-Eberhard, M. J. 1984: Sexual selection, competitive communication and species-specific signals in insects. In: Insect Communication (Lewis, T., ed.). Aca- demic Press, New York, pp. 283–324. Wickler, W. 1968: Mimicry in Plants and Animals. McGraw-Hill, NewYork. Zahavi, A. 1975: Mate selection – a selection for a handicap. J. Theor. Biol. 53, 205–214.

43 Acta Universitatis Upsaliensis Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 1076 Editor: The Dean of the Faculty of Science and Technology

A doctoral dissertation from the Faculty of Science and Technology, Uppsala University, is usually a summary of a number of papers. A few copies of the complete dissertation are kept at major Swedish research libraries, while the summary alone is distributed internationally through the series Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology.

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