The Plasticity and Geography of Host Use and the Diversification Of

The plasticity and geography of host use and the diversiﬁcation of butterﬂies

Jessica Slove Davidson c Jessica Slove Davidson, Stockholm 2012

Front cover: Green earth c Kounadeas Ioannhs, "orange" butterﬂies c MarkMirror Morpho & Aptus c Aleksandr Kurganov, Gonepteryx c Zhu Difeng Back cover: Photo c Jens Voepel, Vanessa cardui c Hedwig Storch

ISBN 978-91-7447-440-4

Printed in Sweden by US-AB, Stockholm 2011 Distributor: Department of Zoology, Stockholm University To all who soldier on in the name of science, your dedication continues to inspire me.

List of Papers

The following papers, referred to in the text by their Roman numerals, are included in this thesis.

PAPER I: The relationship between diet breadth and geographic range size in the butterﬂy subfamily Nymphalinae – a study of global scale. Slove, J. & Janz, N. (2011) PLoS ONE, 6(1): e16057.

PAPER II: Phylogenetic analysis of the latitude-niche breadth hypothesis in the butterﬂy subfamily Nymphalinae. Slove, J. & Janz, N. (2010) Ecological Entomology, 35: 768–774.

PAPER III: Validity of the subspecies paradigm – a case study of the nymphalid butterﬂy Polygonia faunus. Kodandaramaiah, U., Weingartner, E., Janz, N., Leski, M., Slove, J., Warren, A. & Nylin, S. Submitted

PAPER IV: Exploring a complex trait – the effect of larval feeding ability and unequal transition costs on the dynamics of host range evolution in two groups of related butterﬂies. Slove, J., Eriksson, T., Nylin, S. & Janz, N. Manuscript,

PAPER V: Host range oscillations in nymphalid butterﬂies: a phylogenetic investigation. Nylin, S., Slove, J. & Janz, N. Manuscript

Reprints were made with permission from the publishers. Paper II c John Wiley and Sons

Contents

List of Papers v

1 The diversity of butterﬂies 9

2 Host use changes driving diversiﬁcation 11 2.1 Diversity via host shifts ...... 11 2.2 Diversity via host range oscillations ...... 12

3 Geographic aspects of host use 15 3.1 Host range in relation to distribution size ...... 15 3.2 Host range in relation to latitude ...... 16 3.3 Host range in relation to phylogeography ...... 18

4 Plasticity in host use 21 4.1 Host use is a complex trait ...... 21 4.2 Host use expansions are transient ...... 24

5 Concluding remarks 27

Sammanfattning xxix

Acknowledgements xxxi

References xxxiii

1. The diversity of butterﬂies

Although the number of species on earth is imprecisely known, estimates suggest that at least half of all living species are insects (Strong et al., 1984). Owing to their conspicuousness and beauty butterflies are the best described group of insects and, of the estimated 17,500 species of butterflies, the vast majority have scientific names (Robbins & Opler, 1997). The diversity of butterflies is many times greater than other well-known taxonomic groups such as birds and mammals. Sadly, the diversity of all these groups is in rapid decline (Pimm et al., 1995) and butterflies are the fastest receding group of species in Britain (Thomas et al., 2004).

(a) (b)

Figure 1.1: Two of the redlisted butterﬂies in Sweden, a) Euphydryas maturna and b) Lycaena helle. Photos c Alslutsky & Roger Meerts

With unprecedented levels of urbanisation and intensification of agricul- ture, loss of habitat is causing substantial loss of butterfly diversity. The high human population density in Belgium has provided a worst case scenario for butterflies in Europe, with the extinction of 30 percent of indigenous butterfly species in the 20th century (Maes & Van Dyck, 2001). In Sweden there are nine endangered or critically endangered butterfly species, including the Scarce Fritillary, Euphydryas maturna and the Violet Copper, Lycaena helle (Fig. 1.1), and another 24 species are vulnerable or near threatened (Gär-

9 denfors, 2010). While early conservation measures largely ignored insects in favour of vertebrates and plants, butterflies are now paving the way for insect conservation as charismatic “flagship” species (New, 1997). Much of butterfly biology is well understood as a result of extensive am- ateur observations and considerable scientific investigation and their distributions (Kerr, 2001), host ranges (Ackery, 1988) and habitat demands (e.g. Thomas et al., 1992) are relatively well characterised. On a side note, studies using butterflies as a research model have led to advances of important ideas, such as, mimicry (Müller, 1879), coevolution (Ehrlich & Raven, 1964) and metapopulations (Hanski, 1991). Some possible mechanisms to explain the diversity of butterflies, and insects in general, have also been advanced, commonly invoking some aspect of the host plant interaction. The family of brush-footed butterflies, Nymphalidae, studied in this thesis is the most species rich family of butterflies, comprised of about 6000 species. They are common around the world and often rich in colour, especially orange with notable rare cases of iridescent blues. Many well known butterflies belong to this family, such as, Danaus plexippus, Aglais io, Vanessa atalanta and V. cardui more commonly known as the monarch, peacock, red admiral and painted lady.

10 2. Host use changes driving diversiﬁcation

The host plant plays an integral role in the life of a butterfly. More specifically, the host plant may provide shelter for the butterfly, supply necessary precursors for pheromone production or even be the location where the sexes encounter each other and mating occurs, in addition to being the source of food for the growing larvae and nectar for the adult (Jermy, 1984). Butterflies as a group are almost entirely plant-feeding with a few exceptions of species feeding on fungi, lichens, ants and other diets (Ehrlich & Raven, 1964). The combined diversity of herbivorous insects and the plants they feed on make up more than half of the diversity on earth (Fig. 2.1; Strong et al., 1984), and the ecosystem services they provide, as for example pollinators, make it important to understand the source of this diversity (Kim, 1993). Although herbivorous insects are species rich, herbivory has only evolved in 9 of 30 extant insect orders (Kristensen, 1981), which suggests that there is some barrier, such as the low nutritional content or production of toxic metabolites, hindering the use of plants (Schoonhoven et al., 2005). Overcoming these hurdles would allow the herbivore access to a rich and diverse resource and there is evidence that changes in host use may be relevant to explaining insect diversity (Farrell, 1998; Mitter et al., 1988).

2.1 Diversity via host shifts

Ehrlich & Raven (1964) remarked upon the pervasive pattern of related butter- ﬂies feeding on related plants and concluded that patterns of host use are driven by the secondary metabolites of plants. The evolution of a novel substance re- leases the plant from the pressure of herbivory and enables the plant to radiate as a result. This will lead to families of plants characterised by particular secondary metabolites. The herbivore, in turn, evolves tolerance to these defences and shift onto the previously protected plant group where it is be able to di- versify in the absence of competitors. This process of reciprocal escape and radiation could thereby explain both the pattern of related butterﬂies feeding on related plants and the diversity of plants and herbivorous insects.

11 Figure 2.1: The proportions of plant and animal taxa (excl. fungi, algae & mi- crobes) showing the diversity of herbivorous insects and the plants they feed on. From Schoonhoven et al. 2005, Images c Potapov Alexander, Slobodan Zivkovic & MarkMirror

There is some evidence that host shifts have promoted the diversity of her- bivores. Fordyce (2010), for example, identified a number of butterfly groups that showed an increased diversification rate following an inferred major host shift, as opposed to the more constant rates of diversification in groups lacking such host shifts. In a few cases the key innovation that enabled the host shift has even been identified, linking detoxification of particular plant defence to colonisation of and subsequent radiation (Berenbaum et al., 1996; Wheat et al., 2007). The prevailing pattern of host use in butterflies is highly conservative with few shifts to distantly related plant taxa (Winkler & Mitter, 2008). Most host shifts, in fact, appear to involve closely related plants (Janz & Nylin, 1998) and are unlikely to open up new adaptive zones that could facilitate rapid diversification.

2.2 Diversity via host range oscillations

Frequent colonisations of the same plant families in the butterfly tribe Nympha- lini, as well as a possible trend toward host range expansion, led Janz et al. (2001) to suggest an alternative mechanism whereby oscillations in the host ranges of butterflies drive diversification. The colonization of one or more host plants causes a host range expansion. The cumulative distribution of these added host plants allows the butterfly species to increase its geographical range. A wider geographic range will likely encompass an increased heterogeneity and with time there will be local adaptation to fit the local conditions.

12 Spatial variation in the preferred host will cause specialisation on different host plants in different parts of the range. Thereby, the oscillation comes full circle with re-specialisation coupled with population fragmentation and speciation. Compared to the radiations resulting from shifts to new adaptive zones, the oscillation hypothesis does not necessarily predict rapid radiation so much as an increased diversification rate. There is evidence of host range oscillations promoting diversity in that groups of butterflies with diverse host use, indicating recent historical polyphagy, are more species rich than those restricted to ancestral hosts (Janz et al., 2006; Weingartner et al., 2006). The importance of host range expansions is emphasised by the realisation that all host shifts must include a plastic period of ability to feed on (at least) the ancestral and the novel host, that is, an expansion in host range. In addition, major host shifts, such as the colonisation of a novel host plant family, appear to be related to polyphagy (Janz et al., 2001; Winkler & Mitter, 2008). Both shifts and oscillations of host ranges are likely to have contributed to the diversity of butterflies, although determining their relative importance may prove challenging (Janz, 2011). Either way it is clear that changes in host use are important for explaining the diversity of butterflies. This thesis though mainly focuses on the latter ideas as I study geographic aspects and plasticity of host use and discuss implications for butterfly diversity.

13 14 3. Geographic aspects of host use

The oscillation hypothesis, as outlined in the previous chapter (see Janz & Nylin, 2008, for more details), predicts increases in geographic range as a result of expansions in host range, with subsequent fragmentation and specialisation leading to speciation. The prevalence of specialist feeding habits among butterﬂies has caused a lot of attention to be aimed solely at specialisation as a driving force of diversity. It has, for example, been suggested that specialisation may explain the conspicuous diversity of tropical species (e.g. Scriber, 1973). The more stable environment in the tropics, it is argued, would favour more specialised host use and allow tighter species packing as more species can coexist for a given resource (MacArthur & Levins, 1967). In other words, from these suggested mechanisms for the diversity of herbivorous and tropical species we expect to ﬁnd that host range is correlated with both latitude and geographic range.

3.1 Host range in relation to distribution size

There are two ways in which an increased host range could lead to an increased distribution size. The first is that insects that feed on a wide range of plants are more abundant and therefore fill a larger proportion of their potential distribution. The second is that using more host plants increases the combined distribution of the host plants, allowing the insect a larger potential distribution (Quinn et al., 1998). That is, as different host plants are unlikely to have identical distributions, the combined distribution of a wider host range should on average be larger than any individual host plants distribution. A study of the butterflies of the United Kingdom suggested that distribution size is correlated to host range and that it is due to the increased size of the host plants’ combined distributions (Quinn et al., 1998). Although the distribution of the host plants sets an upper limit of the insect’s potential distribution, other factors may cause the potential distribution not to be completely filled, and the actual distribution will be a result of several compounding factors (Dennis et al., 2000). Brändle et al. (2002) found that the importance of different factors varies depending on the scale at which the distributions are studied. For example, increasing the scale from Germany to

15 Europe causes the effect of host range on distribution to decrease. Most studies showing a correlation between host range and distribution size have been done at a local scale (Brändle et al., 2002; Dennis et al., 2000; Päivinen et al., 2005; Quinn et al., 1998). However, the global perspective on this relationship is of particular importance in the case of butterfly diversity, as it appears that most of the processes involved in the oscillation hypothesis act on a global level in butterflies, although this may vary among groups. A study of the butterfly subfamily Nymphalinae at a global scale showed that species with wider host ranges also had larger distributions; although the effect was not very strong the correlation was still highly significant (paper I). Most of the species analysed had specialised host ranges, with half of the species only feeding on one or two plant genera. This is consistent with the pattern in general among insects, where the majority of species are specialised (Schoonhoven et al., 2005). However, there is still considerable variation within the group with many species being able to feed on several genera from different plant families. The geographic ranges, similarly, are generally very restricted yet range to worldwide distributions (Fig. 3.1). The painted lady (Vanessa cardui), for example, has an exceptionally wide host range and can be found almost globally (Fig. 3.1 b). Reanalysis of the data excluding this exceptional butterfly did not change the result that distribution size is related to host range (paper I). Host range and distribution were also tested for sta- tistical dependence due to phylogenetic relationships, so called phylogenetic signal, this indicated that there is an effect of phylogeny on the covariance of host range, but not for distribution. However, a correlation between host range and distribution size was found regardless of whether data was analysed phylogenetically or using cross species comparisons. More studies on the relationship between host range and distribution size in different taxa, especially at a global scale, are necessary, but the general corroboration among studies so far suggest that there is indeed a correlation. Most likely this effect is strongest at a local scale but still significant at global scale. This lends support for one of the steps leading to increased species richness as proposed by the oscillation hypothesis, that is, that an expansion in host range might lead to geographic expansion.

3.2 Host range in relation to latitude

Latitude has been found to be positively correlated to host range in a number of studies on butterﬂies and moths (Dyer et al., 2007; Loder et al., 1998; Scriber, 1973), but similar studies have found no correlation (Fiedler, 1997; Novotny et al., 2006) and there is even evidence in the case of beetles for a negative correlation (Beaver, 1979). These studies have employed a variety

16 (a) (b)

Figure 3.1: Distribution maps for two butterflies with contrasting geographic ranges and host plant ranges: a) Vanessa gonerilla only feeds on plants within the genus Urtica and is endemic to New Zealand (as implied by the name New Zealand red admiral), and b) the painted lady Vanessa cardui which is found worldwide and has been observed using over sixty different host plant genera in different orders. Photos c Tony Wills & Hedwig Storch of measures in the search of a latitudinal gradient in host range, and results may vary depending on if host range is measured as the number of host taxa, proportion of specialists or taxonomic diversity of hosts used (Krasnov et al., 2008). Studies also differ in whether they make comparisons of tropical and temperate forests or measure the latitude of the species distribution, as well as varying in scale from a local (Loder et al., 1998) to a global perspective (e.g. Scriber, 1973). An important conceptual difference in methodology is whether comparisons are made between communities or within a taxonomic group. The first case restricts sampling geographically, looking at the specificity of the species found in the community, while in the second case sampling is restricted to a taxonomic group and analysed throughout the latitudinal range. If a difference in host range along a latitudinal gradient were found within a taxonomic group, this would indicate that host range has evolved as a response to a shift in the latitude. The same difference found in a comparison between communities, could on the other hand also be a result of sorting of species with different host ranges. Determining if some effect of latitude allows species to evolve a more specialised feeding habit therefore requires comparative studies within taxonomic groups. Although a number of taxonomic groups have been investigated for such a latitudinal gradient in host range, very few have rigorously accounted for phylogeny. The significant phylogenetic signal in both latitude and host range, however, suggests that phylogenetic consideration is called for (paper II). Us- ing a simple model including only host range and latitude resulted in a positive

17 correlation, suggesting that species at higher latitudes have broader host ranges than species in more tropical environments. Interestingly, when the geographic range sizes of the butterﬂies were also included in the model this effectively reversed the relationship so that host range became negatively correlated with latitude. This result, however, was dependent on the measures of latitude and host range, indicating that the inconsistent results of studies may partly be due to varying methodology. The lack of universal pattern in host range and latitude suggests that specialisation is unlikely to be the explanation for the greater diversity of the tropics. Vázquez & Stevens (2004) suggested that the inconsistent results between studies may be because different environmental variables are likely to be important for different groups of organisms. For example, although the temperature in the tropics is stable rainfall is more variable than in temperate areas. This could explain the disparate results between studies. Beaver (1979) similarly suggested that the spatial heterogeneity in the tropics might hinder specialisation. Indeed the greater plant diversity in the tropics could hinder specialisation if it makes it harder to ﬁnd a particular host plant. An alternative explanation is that host range oscillations, as opposed to specialisation in itself, have lead to the diversity in the tropics. The greater species richness might then be a result not of a different process but rather different rates in the same process. That is, the greater diversity of host plants and possible interactions in the tropics might allow more rapid oscillations in host range, leading to slightly higher speciation rates. If so, host range evolution may prove to be important in explaining the diversity of both herbivorous and tropical insects.

3.3 Host range in relation to phylogeography

Given that host range expansions can lead to geographic range expansion we turn brieﬂy to population fragmentation within this extended range and the causes of speciation. Across the distribution of a given species, populations will often vary in their host plant preferences, with local specialisation on different hosts (Thompson, 1994). These differences in host plant preference are commonly associated with different subspecies, suggesting that these might be insipient species, in the early stages of ecological speciation whereby divergent selection on different ecological environments leads to population fragmentation (Schluter, 2009). In order for host plant specialisation to be the driver of such ecological speciation there must be phylogeographic differentiation between such subspecies, that is, there must be genetic structuring between individuals sampled from the distributions of the respective subspecies. There are ﬁve commonly recognised subspecies of Polygonia faunus with local specialisation in host use and distinct morphologies (Fig 3.2). However, an extensive

18 Figure 3.2: Subspecies of Polygonia faunus and their distributions. Diamonds indicate the sampling location of the individuals shown. study using a combination of mitochondrial and microsatellite data as well as Wolbachia infection found no evidence to support the status of subspecies as incipient species (paper III). Rather the phylogeography indicated a recent rapid geographic expansion with no genetic differentiation in relation to host plant use. These results are in accordance with those found in the sister species Poly- gonia c-album which also failed to find any evidence of host use variation being related to genetic differentiation (Kodandaramaiah et al., 2011). Stud- ies in other herbivorous insect species on the other hand have found distinct phylogeographic patterns in host plant use (Brown et al., 1997; Fordyce & Nice, 2003) and rapid genetic change as result of a host shift (Singer et al., 1993), indicative of incipient ecological speciation. One possibility then is that the lack of phylogeographic pattern in host use in Polygonia faunus and P. c- album reflects very recent adaptations where genetic divergence has not had a chance to occur yet. Another possibility is that the inconsistent results among taxa reflect different likelihoods of ecological speciation. Whereas some taxa are likely incipient ecological species we should not always expect ecological speciation. Although a a considerable degree of speciation events do apear to be associated with divergence in host use, a majority of speciation events must have other explanations (Nyman et al., 2010; Winkler & Mitter, 2008). Given that no phylogeographic pattern is found in the distinct Polygonia

19 faunus subspecies, this implies that the differences in host plant use are the result of a plastic response to environmental variation (paper III). As mentioned this local specialisation provides a basis for future divergent selection that may, or may not, lead to ecological speciation, either way this plasticity is an important aspect in explaining the dynamics of host use evolution.

20 4. Plasticity in host use

Most butterflies have very specialised host plant use. A study in Costa Rica, for example, showed that half of all butterflies and moths were extreme specialists that feed on a single plant species (Janzen, 1988) and it is estimated that less than 10 percent of herbivorous insects feed on plants from more than three families (Bernays & Graham, 1988). In addition, local specialisation will inflate the estimated host range of the species and underestimate the prevalence of specialists (Thompson, 1994). This prevalence of specialist butterflies taken together with the previously mentioned strong host use conservatism, where related butterflies feed on related plants, depicts host use evolution as static with rare changes in host use. In contrast we see evidence of frequent colonisations, both historical and on-going. Phylogenetic studies have inferred historical change in the hosts used (Janz & Nylin, 1998) as well as the size of the range (Janz et al., 2001; Nosil, 2002; Stireman, 2005). Changes are not only historically inferred, but can also commonly be "seen", for example, in the rapid colonisations of introduced plants (Carroll & Boyd, 1992; Gillespie & Wratten, 2011; Groman & Pellmyr, 2000). These opposing patterns may be explained by restricted plasticity in host use. Host use is adapted to changed environmental conditions without genetic change. These plastic responses will be limited to novel plants that are similar enough that they are at least partly encompassed by the existing metabolic machinery. Polyphagous species will be more plastic, as they are likely to have broader machinery, and will therefore be more likely to make more "radical" shifts (Janz et al., 2001; Nylin & Janz, 2009). Therefore, understanding the dynamics of host range evolution is partly dependent on understanding the dynamics of host plant colonisation.

4.1 Host use is a complex trait

The readiness and rapidity with which novel plants are often colonised is coun- terintuitive not only due to the conservative nature of host use, but also considering the inherent complexity involved in colonising a new plant. "Host use" is actually the synthesis of several physiological and behavioural traits. The ability to use a particular plant requires the female to recognise and accept it

21 as a host; the result of a sequence of behavioural steps regulated by a multi- tude of chemical cues, some repellent others attractants (Schoonhoven et al., 2005). Following successful ovipostition the larva must be able to feed, grow and survive on the plant or it is not a viable host. In addition to plants being a generally poor nutritional resource, the larva must also be able to deal with any chemical and physical defences that may deter feeding, interfere with diges- tion or even have toxic effects on the larva (Schoonhoven et al., 2005). Even if all the mechanisms are in place in the butterfly host use may still be impeded by competitors or parasitoids (Gratton & Welter, 1999). The plant may not be accessible to the butterfly because of asynchrony in the timing of development (Hodkinson, 1997), assuming that their distributions overlap in the first place. Taking this complexity into account suggests that the colonisation of a novel plant should be an unlikely event. When host use is reconstructed in order to study patterns of shifts and colonisations, this complexity is seldom accounted for, more often it is con- sidered as a simple yes-or-no trait. One way of accounting for complexity when reconstructing complex traits is to use unequal transition costs. The argument being that acquiring a complex trait such as the vertebrate eye or even the use of a new host plant, is likely to require considerable more evolutionary change than the loss of the same trait (Agnarsson & Miller, 2008). We should therefore expect an asymmetry in the transitions between states, with losses being easier than gains. The problem lies in selecting the appropriate transitions rates. Rather than making explicit assumptions regarding transitions, many studies assume the default equal transitions. With gains and losses of host use weighed equally, however, the resulting number of inferred colonisations seems disproportionate to the number of butterfly taxa. For example, within the Polygonia-Nymphalis group there is, on average, one colonisation per branch (paper IV). Increasing the cost of gaining host use causes the number of colonisations to decrease in favour of multiple losses. The use of the same host plant genus by butterflies in different parts of the tree will then be inferred as the result of one ancestral colonisation with subsequent losses of host use in butterflies that are not observed to use the plant, rather than the an- cestor not having used the host followed by independent colonisations by the butterflies that do use the plant (Fig. 4.1 a & b). Increasing the cost of gaining the use of a host to three times the cost of loosing host use was enough to in- fer most plant genera as colonised just once within the Polygonia-Nymphalis group (Paper IV). A ratio of three losses to each gain of host use may be rea- sonable considering the complexity of host use and the relatively small amount of evolutionary change necessary to cause a loss in host use. Host use may be lost as a result of an increased abundance of a preferred host, or a slight change in geographic range whereby the butterfly no longer encounters the plant.

22 (a) (b)

Figure 4.1: Alternative explanations for a pattern of apparent independent colonisations as suggested by observations of host plant use (shown in the tips of the tree and in dark green). Unobserved partial abilities are indicated by light green branches. The alternatives are a) actual independent colonisations, b) one colonisation followed by multiple partial losses, c) one colonisation followed by a partial loss with some retained ability for use of the plant facilitating later recolonisation and c) preadaptation followed by parallel, non-independent, colonisations.

If the loss of availability of a plant is not immediately followed by the loss of preference and feeding ability then we may find evidence of such ancestral host use in the potential host ranges (c.f. Wiklund, 1975) of extant butterflies. For most butterflies this type of data is lacking for most host plants. Inclu- sion of available data on larval feeding ability on Urtica within the Polygonia- Nymphalis group, however, supported a pattern of multiple partial losses rather than independent colonisations (paper IV). Similarly, larval feeding ability in Humulus revealed a likely recolonisation following such a partial loss. With at least some retained machinery for using an ancestral host plant the recolonisation (Fig. 4.1 c) requires substantially less evolutionary change than colonising a completely novel host plant. The frequency of reversals to ancestral host plants (Berenbaum & Passoa, 1999; Funk et al., 1995; Futuyma et al., 1993)

23 could thereby be explained by these potentially common partial losses. Even where no feeding response is found in the larva, developmental pathways may have been retained that allow recurrence of host use (West-Eberhard, 2003). Possibly there is little selection against retained ability to feed on ancestral hosts as evidence for trade-offs for the ability to feed on different plants is scarce (Futuyma et al., 1993; Keese, 1998; Scriber & Feeny, 1979). Con- versely, there may be selection for retaining many of the genes if they are involved in the metabolism of other plants in the repertoire (c.f. Heidel-Fischer et al., 2009). Overlapping gene expression patterns could also allow novel host plant associations to arise (West-Eberhard, 2003). The ability of some species in the Nymphalini tribe to feed on Laportea, for example, may be a result of overlapping biochemical pathways with the related and ancestrally used Urtica (c.f. Fig. 4.1 d; paper IV). Overall, even the limited data available on larval feeding ability on non-hosts suggests a considerable degree of potential ﬂexibility although limited mainly to a common set of ancestral plants. Plasticity in host use could thereby reconcile a dynamic host use evolution with frequent changes and large scale patterns of conservative host use.

4.2 Host use expansions are transient

There are exceptions to this large scale conservatism with some butterflies feeding on "odd" hosts, for example, Kaniska canace feeding on Smilaceae, a plant family that is not used by any other butterfly in the Nymphalini tribe. Interestingly Janz et al. (2001) noted that all such cases within Nymphalini had occurred in more polyphagous parts of the tree. This makes sense in the above mentioned plasticity scenario, as polyphagous species are likely to have more encompassing machinery for dealing with their wide range of host plants, and therefore would be more likely to show some ability to feed on more chem- ically different plants (Janz, 2011). A similar pattern may be found within Nymphalidae with the host shift to monocotyledon plant orders Arecales and Poales (paper V), which may have played an important role in the extensive radiation of satyrine butterflies (Peña et al., 2011; Peña & Wahlberg, 2008). Even within Nymphalidae, despite the large time span involved and the large diversity of species, there is a remarkable degree of conservatism in host use with only a handful of plant orders being used by most genera in the family (paper V). The prevalence of specialists is also a pattern reflected in the Nymphalidae family with few butterflies feeding on more than one plant order (paper V). Of 6000 described species only 249 species were found with records of feeding on more than one order and only 79 of these have been observed feeding on at least

24 Figure 4.2: Phylogeny of the tribes within the butterfly family Nymphalidae; if any of the species in the tribe feed on three or more plant orders this is indicated in black. three plant orders. Evidence suggests that there is hidden dynamic to this pattern in a similar way to that of the conservative pattern. Most changes in host range within the family were increases in host range, and these changes were occurring right at the tips of the tree (Fig 4.2; paper V). There are a number of different ways this pattern could be explained. The literal interpretation is that something in the environment has changed, causing a previously universal monophagous host plant use to suddenly expand. This is unlikely considering that a number of significant host plant shift are inferred closer to the base of the tree and these are, as mentioned, likely to have been associated with broader host ranges. Another explanation follows the argument of independent colonisations; the polyphagous state may be the ancestral state followed by multiple specialisations (Stireman, 2005). Although this is a possible scenario it is less likely as the different polyphagous taxa feed on different combinations of host plant orders, suggesting that they have separate origins (paper V). The most likely scenario is that host range expansions are transient, and that ancestral polyphagy has been erased by subsequent losses and recolonisations. Plasticity in host use not only allows butterflies to adapt their repertoire to local and changing environmental conditions, but inclusion of novel host plants will widen the range of this plasticity sometimes leading to truly generalist host use. These will be transient phases as selection in the long term is likely to favour specialisation (Agosta et al., 2010).

25 26 5. Concluding remarks

The papers presented in this thesis are in line with the mechanisms proposed in the oscillation hypothesis of host range driven diversification (Janz & Nylin, 2008). Patterns of host range evolution in the butterfly family Nymphalidae suggests that polyphagy is a transient phase in host range evolution, which tends to be rapidly followed by re-specialisation (paper V). Host range expansion in turn starts with the colonisation of novel host plants. Many colonisations may not be as independent as they first appear, rather they are facilitated by some already existing ability to feed on the plant as a result of historical host use or overlap with pathways used for other plants in the repertoire (paper IV). As more hosts are added to the repertoire, more diverse plants are encompassed by the existing metabolic pathways, and so might lead to further expanded host range and truly generalist host use. These host range expansions will enable the butterfly to spread, as shown for the butterfly subfamily Nymphalinae (paper I). The next steps in the oscillation hypothesis predict speciation resulting from adaptation to local conditions. Although no genetic differentiation was found between locally specialised subspecies of Polygonia faunus (paper III) such differentiation has been found for other taxa (Brown et al., 1997; Fordyce & Nice, 2003). The geographic variation in host plant use in P. faunus has potential for future divergent selection. Furthermore, speciation caused by other factors than host plant use, such as, geographic isolation will be more likely in larger geographic ranges. In fact, within P. faunus there are a few populations that show some genetic differentiation. The lack of clear pattern in host range in relation to latitude within Nympha- linae (paper II) suggests that the diversity of tropical species is not simply explained by specialisation allowing more species to coexist on a given resource. An alternative explanation is that increased rates of host range evolution in the tropics, fuelled by the greater diversity of plants, might lead to further increased rates of speciation. This warrants further study. The main insights gained from this thesis are that although butterflies appear to frequently colonise new plants these changes are seldom independent and their historical use can be more accurately traced by including data on larval feeding abilities. These non-independent processes explain how host use can be both dynamic and conserved. Further, truly generalist host use is rare

27 and most likely an evolutionarily transient phase. When host range expansions do occur they allow the butterfly to spread over larger areas. As mentioned these findings lend support for the oscillation hypothesis and thereby further our understanding of the diversification of butterflies.

28 Sammanfattning

Dagfjärilarna är en artrik grupp med fler arter än fåglar och däggdjur samman- lagt. Fjärilarna är dock hotade av både habitatförlust och klimatförändringar, och i Sverige har vi över 40 rödlistade dagfjärilsarter varav 9 är starkt eller akut hotade. Det är därför viktigt att förstå ursprunget till denna minskande di- versitet. Eftersom växtätande insekter är anmärkningsvärt artrika jämfört med deras närmast besläktande insekter som är icke-växtätande antas värdväxt an- vändning och framförallt förändringar i vilka växter som används, ha främjat artbildning. Denna avhandling studerar sambandet mellan värdväxtanvändandet och olika aspekter av fjärilars utbredningar, och undersöker förändringar i värdväx- tanvändandet i ett evolutionärt perspektiv. Studiearterna hör till den artrikaste familjen av fjärilar, Nymphalidae eller Praktfjärilar, vilka återfinns över hela världen. Vi visar att fjärilar i underfamiljen Nymphalinae, Vinterpraktfjärilar, som livnär sig på ett flertal värdväxter har större utbredningsområden än arter som utnyttjar färre växter. Sambandet mellan värdväxtbredd och latitud är inte lika enkelt. Vid en första anblick verkar tropiska fjärilar vara mer specialiserade än arter i tempererade områden men detta mönster försvinner när vi kontrollerar för skillnader i utbredningsområdets storlek. Enligt Oscillations hypotesen kan de större utbredningsområdena som hålls av generalistiska fjärilsarter leda till ökad artbildning eftersom sannolikheten att populationer blir ekologiskt eller geografiskt isolerade ökar. Det är i så fall tänkbart att underarter som använder sig av olika värdväxter är begynnande nya arter. Trots att morfologiskt distinkta underarter av Poly- gonia faunus utnyttjar olika värdväxter fann vi ingen genetisk differentiaering som stöder att de skulle vara begynnande arter. Detta tyder på att den obser- verade variationen är ett resultat av fenotypisk plasticitet i värdväxtanvänd- ningen. Fjärilarna kan alltså anpassa sin värdväxtanvändning till den lokala tillgången av olika växter utan en genetisk anpassning. Rekonstruktioner av det historiska värdväxtanvändandet i fjärilsgrupperna Polygonia-Nymphalis och Vanessa visar att plasticitet är viktigt för att för- stå mönstret i värdväxtanvändandet mellan arter såväl som inom en art. Vad som framstår som oberoende koloniseringar av samma växt är troligare ett resultat av historisk förmåga att använda växten. Historisk förmåga har sedan följts av flera förluster och eventuella återkoloniseringar, och partiella historiska förmågor har följts av parallella koloniseringar. Vi argumenterar för att kolonisationer kan antas vara ovanligare än förluster och finner stöd för dessa processer när vi inkluderar information om larvers förmåga att äta växter som inte används i naturen. Dessa processer, som leder till flexibilitet i användandet av ett begränsat antal växter, återspeglas även i den konservativa användningen av växtord- ningar inom fjärilsfamiljen Nymphalidae. Få fjärilar äter växter från mer än en ordning, och sådant generalistiskt värdväxtutnyttjande uppkommer tillsynes väldigt sent i evolutionen, vilket i vår mening visar att generalistisk värdväx- tanvändning är evolutionärt kortvarigt och snabbt övergår i ett mer specialiserat tillstånd. Avhandlingen ger insikter i hur värdväxtandvändning kan vara både specialiserat och konservativt och samtidigt dynamiskt med förändringar som kan ske över kort tid. Vi finner även stöd för att större breddningar i värdväxtan- vändningen är tillfälliga, men när de sker kan de leda till att fjärilen kan sprida sig geografiskt. Det är möjligt att dessa processer kan leda till en ökad artbild- ningshastighet, och detta arbete är på så sätt ett steg mot att förklara den stora artrikedommen av dagfjärilar och andra växtätande insekter. Acknowledgements

This is the final chapter of my PhD and there are people to be thanked for the contributions they made to the story. The biggest thanks goes to Niklas who played the part of my supervisor. You have all the qualities one could ask for in a supervisor, you are enthusi- astic, patient and insightful. Through you I have learnt a lot about butterflies, science, teaching, writing and presenting as well as a thing or two about my- self. Thank you for getting me here. Sören, my assistant supervisor and head of department, your extensive knowledge on the nymphalid butterflies, their ecology and evolution has contributed greatly to this thesis. I also enjoyed the many lunchtime discussion on the philosophy of science and science fiction. Thank you Bertil for always making time to read and comment on manu- scripts, your suggestions are appreciated. And thanks for some good laughs at the Friday pub. Berit, Anette and Siw, thank you for helping me with all the administrative necessities. You always had an answer even when I was not sure what my question was. Ulf, thank you for always being available to help with IT issues, including those that magically dissipated at your mere presence. Minna, always ready to lend an ear when I needed to mull over exam correcting or make excuses for how I lost the key card, again. I will miss comparing bruises with you. Room mates have come and gone through the years, mostly gone. At the beginning of my story at the department the room was bustling, and I enjoyed the company of Maria, Adde, Martin, Professorn and Alex. Öh, Alex, I am in awe of you grasp of classical music, physics and the workings of animals dressed in silly hats. As the story comes to a close I can enjoy more peace and quiet, with Marianne there to keep me from getting lonely. As the number of room mates has dwindled, the number of group members has steadily increased. Lisa and Josefin, thank you for taking me into the field and showing me what the butterflies look like IRL. Lina, you are always brim- ming with energy and your ability to stay positive regardless of the volumes of vanilla sauce is inspirational. Alex, your diligence and focus is something to aspire to, whenever I’m struggling to get started with something I will hear a voice saying "just do it". Maria, Micke, Hélèn and Karin, thank you for all the interesting group meetings and good times at after works. Aleksandra, my fellow PhD student, teaching colleague, rowing buddy and friend. I trust that the end of our PhD stories is not the end of movie dates, games nights etc. Thank you for all the fun (and for not letting me forget to take my lactose tablets). Marina, your no-nonsense attitude is very refreshing, keep telling it like it is. Marianne, you always offer help and support, you even managed to make me feel included when I first arrived and feeling a bit anonymous. Jeannette, I clearly remember the confidence you exuded as we waited to be let in to present our project plans. I was impressed then, and your strength has continued to impress me since. Ullasa, I hope there are more skiing trips in our future. Carlos, we had many good times, I miss you. Marianne, always see where you are heading and stay out of the reeds. To Gabriella, Titti, Kenneth, Helena, Tomas, Martin, Martin, Lina (thank you for the delicious "left overs"), Lina (a.k.a. Prof. Drosophila), Kerstin, Lily, Agata, Neval, Mija, Sibylle and all the others at the department who contribute to what must one of the most inspiring, enlightening and fun workplaces to be found. To all my friends whom I have sorely neglected while working on this story. No more excuses. Let there be fikas, movie dates, karate, billiards, rowing, new years celebrations, skiing trips, and so on, and so on, I have time to make up for! Thank you Magnus for the support and encouragement you have given me. To my Nan, for always making me feel special. My bestest little brother, for caring even when you could not be less interested. Mum, for believing in me and always being there, puss och kram. Dad, I listen to you and appreciate your opinion, perhaps more than you realise, thank you for all your help. Ian, thank you for helping at all stages of writing and taking such good care of me, I could not have done this without you. References

Ackery, P. 1988. Hostplants and classiﬁcation - a review of Nymphalid butterﬂies. Biological Journal of the Linnean Society 33(2):95–203.

Agnarsson, I. & Miller, J. 2008. Is ACCTRAN better than DELTRAN? Cladistics 24(6):1032–1038.

Agosta, S., Janz, N., & Brooks, D. 2010. How specialists can be generalists: resolving the "parasite paradox" and implications for emerging infectious disease. Zoologia 27(2):151–162.

Beaver, R. 1979. Host speciﬁcity of temperate and tropical animals. Nature 281:139–141.

Berenbaum, M., Favret, C., & Schuler, M. 1996. On deﬁning ”key innovations” in an adaptive radiation: Cytochrome P450s and papilionidae. American Naturalist 148:S139–S155.

Berenbaum, M. & Passoa, S. 1999. Generic phylogeny of North American Depressariinae (Lepidoptera: Elachistidae) and hypotheses about coevolution. Annals of the Entomological Society of America 92:971–986.

Bernays, E. & Graham, M. 1988. On the evolution of host speciﬁcity in phytophagous arthropods. Ecology 69(4):886–892.

Brändle, M., Öhlschläger, S., & Brandl, R. 2002. Range sizes in butterﬂies: correlation across scales. Evolutionary Ecology Research 4(7):993–1004.

Brown, J., LeebensMack, J., Thompson, J., Pellmyr, O., & Harrison, R. 1997. Phylogeography and host association in a pollinating seed parasite Greya politella (Lepidoptera: Prodoxidae). Molecular Ecology 6(3):215–224.

Carroll, S. & Boyd, C. 1992. Host race radiation in the soapberry bug - natural-history with the history. Evolution 46(4):1052–1069.

Dennis, R., Donato, B., Sparks, T., & Pollard, E. 2000. Ecological correlates of island incidence and geographical range among British butterﬂies. Biodiversity and Conservation 9(3):343–359.

Dyer, L., et al. 2007. Host speciﬁcity of Lepidoptera in tropical and temperate forests. Nature 448(7154):696–699.

Ehrlich, P. & Raven, P. 1964. Butterﬂies and plants: A study in coevolution. Evolution 18:586–608.

Farrell, B. 1998. "Inordinate fondness" explained: Why are there so many beetles? Science 281(5376):555– 559.

Fiedler, K. 1997. Geographical patterns in life-history traits of Lycaenidae butterﬂies - ecological and evolutionary implications. Zoology-Analysis of Complex Systems 100(4):336–347.

Fordyce, J. 2010. Host shifts and evolutionary radiations of butterﬂies. Proceedings of the Royal Society B- Biological Sciences 277:3735–3743. Fordyce, J. & Nice, C. 2003. Contemporary patterns in a historical context: Phylogeographic history of the pipevine swallowtail, Battus philenor (Papilionidae). Evolution 57(5):1089–1099.

Funk, D., Futuyma, D., Orti, G., & Meyer, A. 1995. A history of host associations and evolutionary diversiﬁcation for Ophraella (Coleoptera, Chrysomelidae) - New evidence from mitochondrial-DNA. Evolution 49(5):1008–1017.

Futuyma, D., Keese, M., & Scheffer, S. 1993. Genetic constraints and the phylogeny of insect-plant associations - responses of Ophraella communa (Coleoptera, Chrysomelidae) to host plants of its congeners. Evolution 47(3):888–905.

Gärdenfors, U. 2010. Rödlistade arter i Sverige 2010. ArtDatabanken SLU, Uppsala.

Gillespie, M. & Wratten, S. D. 2011. Oviposition preference of Lycaena salustius for, and larval performance on, a novel host plant: an example of ecological ﬁtting. Ecological Entomology 36(5):616–624.

Gratton, C. & Welter, S. 1999. Does "enemy-free space" exist? Experimental host shifts of an herbivorous ﬂy. Ecology 80(3):773–785.

Groman, J. & Pellmyr, O. 2000. Rapid evolution and specialization following host colonization in a yucca moth. Journal of Evolutionary Biology 13(2):223–236.

Hanski, I. 1991. Single-species metapopulation dynamics - concepts, models and observations. Biological Journal of the Linnean Society 42(1-2):17–38.

Heidel-Fischer, H., Freitak, D., Janz, N., Soderlind, L., Vogel, H., & Nylin, S. 2009. Phylogenetic re- latedness and host plant growth form inﬂuence gene expression of the polyphagous comma butterﬂy (Polygonia c-album). BMC Genomics 10:506.

Hodkinson, I. 1997. Progressive restriction of host plant exploitation along a climatic gradient: The willow psyllid Cacopsylla groenlandica in Greenland. Ecological Entomology 22(1):47–54.

Janz, N. 2011. Ehrlich and Raven revisited: Mechanisms underlying codiversiﬁcation of plants and enemies. Annual Review of Ecology, Evolution and Systematics 42:71–98.

Janz, N., Nyblom, K., & Nylin, S. 2001. Evolutionary dynamics of host-plant specialization: A case study of the tribe Nymphalini. Evolution 55(4):783–796.

Janz, N. & Nylin, S. 1998. Butterﬂies and plants: A phylogenetic study. Evolution 52(2):486–502.

Janz, N. & Nylin, S. 2008. The oscillation hypothesis of host plant-range and speciation. In K. Tilmon (ed.), Specialization, Speciation, and Radiation: the Evolutionary Biology of Herbivorous Insects, pp. 203–215. University of California Press, Berkeley, California.

Janz, N., Nylin, S., & Wahlberg, N. 2006. Diversity begets diversity: host expansions and the diversiﬁcation of plant-feeding insects. BMC Evolutionary Biology 6:4.

Janzen, D. 1988. Ecological characterization of a Costa Rican dry forest caterpillar fauna. Biotropica 20(2):120–135.

Jermy, T. 1984. Evolution of insect/host plant relationships. American Naturalist 124(5):609–630.

Keese, M. 1998. Performance of two monophagous leaf feeding beetles (Coleoptera: Chrysomelidae) on each other’s host plant: Do intrinsic factors determine host plant specialization? Journal of Evolutionary Biology 11(4):403–419.

Kerr, J. 2001. Butterﬂy species richness patterns in Canada: Energy, heterogeneity, and the potential con- sequences of climate change. Conservation Ecology 5(1):10. Kim, K. 1993. Biodiversity, conservation and inventory - why insects matter. Biodiversity and Conservation 2(3):191–214.

Kodandaramaiah, U., Weingartner, E., Janz, N., Dalen, L., & Nylin, S. 2011. Population structure in relation to host-plant ecology and Wolbachia infestation in the comma butterﬂy. Journal of Evolutionary Biology 24(10):2173–2185.

Krasnov, B., Shenbrot, G., Khokhlova, I., Mouillot, D., & Poulin, R. 2008. Latitudinal gradients in niche breadth: empirical evidence from haematophagous ectoparasites. Journal of Biogeography 35(4):592– 601.

Kristensen, N. 1981. Phylogeny of insect orders. Annual Review of Entomology 26:135–157.

Loder, N., Gaston, K., Warren, P., & Arnold, H. 1998. Body size and feeding speciﬁcity: macrolepidoptera in Britain. Biological Journal of the Linnean Society 63(1):121–139.

MacArthur & Levins, R. 1967. Limiting similarity convergence and divergence of coexisting species. American Naturalist 101(921):377–&.

Maes, D. & Van Dyck, H. 2001. Butterﬂy diversity loss in Flanders (north Belgium): Europe’s worst case scenario? Biological Conservation 99(3):263–276.

Mitter, C., Farrell, B., & Wiegmann, B. 1988. The phylogenetic study of adaptive zones - Has phytophagy promoted insect diversiﬁcation? American Naturalist 132(1):107–128.

Müller, F. 1879. Ituna and Thyridia; a remarkable case of mimicry in butterﬂies. Transactions of the Entomological Society of London pp. 22–29.

New, T. 1997. Are Lepidoptera an effective ’umbrella group’ for biodiversity conservation? Journal of Insect Conservation 1:5–12.

Nosil, P. 2002. Transition rates between specialization and generalization in phytophagous insects. Evolu- tion 56(8):1701–1706.

Novotny, V., Drozd, P., Miller, S., Kulfan, M., Janda, M., Basset, Y., & Weiblen, G. 2006. Why are there so many species of herbivorous insects in tropical rainforests? Science 313(5790):1115–1118.

Nylin, S. & Janz, N. 2009. Butterﬂy host plant range: an example of plasticity as a promoter of speciation? Evolutionary Ecology 23(1):137–146.

Nyman, T., Vikberg, V., Smith, D., & Boeve, J. 2010. How common is ecological speciation in plant-feeding insects? A ’Higher’ Nematinae perspective. BMC Evol Biol 10:266.

Päivinen, J., Grapputo, A., Kaitala, V., Komonen, A., Kotiaho, J. S., Kimmo, S., & Wahlberg, N. 2005. Negative density-distribution relationship in butterﬂies. BMC Biology 3:5:1–13.

Peña, C., Nylin, S., & Wahlberg, N. 2011. The radiation of Satyrini butterﬂies (Nymphalidae: Satyrinae): a challenge for phylogenetic methods. Zoological Journal of the Linnean Society 161(1):64–87.

Peña, C. & Wahlberg, N. 2008. Prehistorical climate change increased diversiﬁcation of a group of butter- ﬂies. Biology Letters 4(3):274–278.

Pimm, S., Russell, G., Gittleman, J., & Brooks, T. 1995. The future of biodiversity. Science 269(5222):347– 350.

Quinn, R., Gaston, K., & Roy, D. 1998. Coincidence in the distributions of butterﬂies and their foodplants. Ecography 21(3):279–288.

Robbins, R. & Opler, P. 1997. Butterﬂy diversity and a preliminary comparison with bird and mammal diversity. In M. Reaka-Kudla, D. Wilson, & E. Wilson (eds.), Biodiversity II: Understanding and pro- tecting our biological resources, pp. 69–82. Joseph Henry Press, Washington DC. Schluter, D. 2009. Evidence for Ecological Speciation and Its Alternative. Science 323(5915):737–741.

Schoonhoven, L., van Loon, J., & Dicke, M. 2005. Insect-plant biology. Oxford University Press, Oxford.

Scriber, J. 1973. Latitudinal gradients in larval feeding specialization of the world Papilionidae (Lepi- doptera). Psyche 80(4):355–373.

Scriber, J. & Feeny, P. 1979. Growth of herbivorous caterpillars in relation feeding specialization and to the growth form of their food plants. Ecology 60(4):829–850.

Singer, M., Thomas, C., & Parmesan, C. 1993. Rapid human-induced evolution of insect host associations. Nature 366(6456):681–683.

Stireman, J. 2005. The evolution of generalization? Parasitoid ﬂies and the perils of inferring host range evolution from phylogenies. Journal of Evolutionary Biology 18(2):325–336.

Strong, D., Lawton, J., & Southwood, T. 1984. Insects on plants. Community patterns and mechanisms. Blackwell, Oxford.

Thomas, C., Thomas, J., & Warren, M. 1992. Distributions of occupied and vacant butterﬂy habitats in fragmented landscapes. Oecologia 92(4):563–567.

Thomas, J., Telfer, M., Roy, D., Preston, C., Greenwood, J., Asher, J., Fox, R., Clarke, R., & Lawton, J. 2004. Comparative losses of British butterﬂies, birds, and plants and the global extinction crisis. Science 303(5665):1879–1881.

Thompson, J. 1994. The coevolutionary process. University of Chicago Press, Chicago.

Vázquez, D. & Stevens, R. 2004. The latitudinal gradient in niche breadth: Concepts and evidence. Ameri- can Naturalist 164(1):E1–E19.

Weingartner, E., Wahlberg, N., & Nylin, S. 2006. Dynamics of host plant use and species diversity in Polygonia butterﬂies (Nymphlidae). Journal of Evolutionary Biology 19(2):483–491.

West-Eberhard, M. 2003. Developmental plasticity and evolution. Oxford University Press, Oxford.

Wheat, C., Vogel, H., Wittstock, U., Braby, M., Underwood, D., & Mitchell-Olds, T. 2007. The genetic basis of a plant-insect coevolutionary key inovation. Proceedings of the National Academy of Sciences of the United States of America 104:20427–20431.

Wiklund, C. 1975. Evolutionary relationship between adult oviposition preferences and larval host plant range in Papilio machaon l. Oecologia 18(3):185–197.

Winkler, I. & Mitter, C. 2008. The phylogenetic dimension of insect-plant interactions: A review of recent evidence. In K. Tilmon (ed.), Specialization, Speciation and Radiation: The Evolutionary Biology of Herbivorous Insects, pp. 240–263. University of California Press, Berkeley, California.