And Food-Resource-Dependent Courtship Behaviour in Poecilobothrus Nobilitatus 123

Density- and Food-Resource-Dependent Courtship Behaviour in Poecilobothrus nobilitatus 123

Entomologie heute 18 (2006): 123-132

Density- and Food-Resource-Dependent Courtship Behaviour in the Fly Poecilobothrus nobilitatus L. (Diptera, Dolichopodidae)

Dichte- und ressourcenabhängiges Balzverhalten bei der Langbeinfliege Poecilobothrus nobilitatus L. (Diptera, Dolichopodidae)

KLAUS LUNAU, ANDREA M IDDELMANN & MARION PIANKA

Summary: Males of the dolichopodid fly species Poecilobothrus nobilitatus display conspicuous wings with apical white and subapical dark areas when courting a female. In this study, we analyse how the presence of prey objects influences the aggregation of males and females, and how the performance of courtship is correlated with the density of males and females. Within few minutes, the exposure of prey led to an increased number of both males and females in experimental areas. Males were more likely to detect the prey items before the females did; females were more likely to start feeding on the prey items before the males did. When large numbers of males and females have aggregated in suitable areas, courting males are frequently interrupted by male competitors. Males courted females longer if the females were feeding on prey. The length of male courtship display decreased with increasing density of conspecifics, caused by shorter individual courtship phases, less repetitions of courtship phases, and more frequent interruptions of courtship by male competitors.

Keywords: Poecilobothrus nobilitatus, Dolichopodidae, courtship, mating

Zusammenfassung: Männchen der Dolichopodidenart Poecilobothrus nobilitatus präsentieren ihre auffälligen Flügel mit apikalen weißen und subapikalen, schwarzen Bereichen während der Balz dem Weibchen. In dieser Studie analysieren wir, wie das Vorkommen von Beuteobjekten die Aggregation von Männchen und Weibchen beeinflusst und wie sich das Balzverhalten mit der Dichte von Männchen und Weibchen ändert. Innerhalb von wenigen Minuten nach der Exposition von Beuteobjekten stieg die Anzahl von Männchen und Weibchen in den Versuchsarealen. Männ- chen fanden die Beuteobjekte häufiger als Weibchen, während Weibchen häufiger als Männchen mit dem Fressen begannen. Wenn Männchen und Weibchen in geeigneten Habitaten in großer Anzahl aggregieren, unterbrechen Störungen von Männchen häufiger die Balz. Männchen balzten Weibchen länger an, wenn diese an Beutetieren fraßen. Die Dauer des Balzverhaltens der Männ- chen sank mit steigender Dichte von Artgenossen, verursacht durch kürzere Balzphasen, weniger Wiederholungen einzelner Balzphasen und häufigere Unterbrechungen der Balz durch männliche Konkurrenten.

Schlüsselwörter: Poecilobothrus nobilitatus, Dolichopodidae, Balz, Paarung

1. Introduction al. 2003) and spectacular action on the wing (LAND 1993a,b). Various aspects of the court- The courtship behaviour of male dolicho- ship behaviour of the common species Poeci- podid flies (Diptera, Dolichopodidae) is out- lobothrus nobilitatus L. have been extensively standing, because of the males’ display of studied, namely male-male-interactions (LAND signalling structures (LUNAU 1992; ZIMMER et 1993b), aerial male display (LAND 1993a), and

Entomologie heute 18 (2006) 124 KLAUS LUNAU, ANDREA MIDDELMANN & MARION PLANKA body size-dependent mating success (LUNAU berances of the abdomen. Closely related spe- 1992). Males and females of P. nobilitatus are cies often possess analogous signalling struc- frequently found ashore of lakes, ponds, tures on homologous organs, e.g. middle legs puddles and rivers. However, areas of low in Dolichopus plumipes with a modified tarsal and high density are found. In these areas, segment 1, in D. pennatus with ornamented males and females can be seen feeding on tarsal segments 2-5, and in D. popularis with prey and courting. In this study, we tested modified tarsal segments 3-5. Some species whether males and females aggregate in areas even have a double set of male signalling with available food and the dependence of structures, as for example Nodicornis nodicor- male courtship behaviour on the density of nis possessing black and white signalling struc- conspecifics. tures on the elongated antennae and on the middle legs. The signalling structures are very 1.1. Ecological background uniform with the apical ends of elongated organs bearing black and/or white signalling The two most species-rich families of the areas (LUNAU 1996). A rare exception is the Empidoidea, Empididae and Dolichopod- genus Eucoryphus, in which the males display idae, show marked peculiarities in their court- an orange crown-like signalling structure on ship behaviour. The Empididae are outstand- the head. It has been hypothesised that in ing, because the males’ courtship is associ- dolichopodid flies there is a shift from court- ated with the transfer of a nuptial gift to the ship on the wing to courtship on the ground female. Several authors have stated an evolu- associated with a shift from wings as signal- tionary shift from the transfer of a prey ob- ling structures towards other organs bearing ject as a nuptial gift, which females feed on signalling devices mimicking the wings’ sig- during copulation, to the display of an empty nal (LUNAU 1996, 2002; ZIMMER et al. 2003). It gift without any nutritional value (CUMMING is still unknown whether specific adaptations 1994; SADOWSKI et al. 1999). In some species in the dolichopodid eyes are related to court- the great male investment in reproduction is ship. Many Dolichopodidae exhibit metallic associated with the procurement of the nup- green reflections of the ommatidial cornea tial gift and has led to male choice and sex caused by the wavelength-selective spectral role reversal (FUNK & TALLAMY 2000). Like reflectance of the cornea which is built like a the Empididae, dolichopodid flies are pre- multilayer mirror (BERNARD & MILLER 1968; dators preying on small crustaceans, insects, LAND 1993a) and reduces the transmission and enchytraeid worms (SMITH & EMPSON of green light to the photoreceptors by that 1955; ULRICH 2004). It has never been tested, amount of light that is reflected from the whether the availability of prey plays a role in coloured cornea (KNÜTTEL & LUNAU 1997). mating of Dolichopodidae. The reduction of light transmission caused Many species of the Dolichopodidae show by reflection from the cornea can amount up sexual dimorphism. The males display orna- to 50 % in distinct wavelength ranges (LUNAU mental structures during courtship. Among & KNÜTTEL 1995). the Dolichopodidae there is an enormous diversity of organs bearing the male signal- 1.2. Previous studies of the courtship of ling structures and a surprisingly high ho- Poecilobothrus nobilitatus mogeneity of signal structures. The diversity of organs bearing the male signalling struc- The spectacular courtship dances of the com- tures includes signalling structures on the mon dolichopodid fly P. nobilitatus have been antennae, forelegs, middle legs, hind legs, studied in some detail (SMITH & EMPSON 1955; wings, cerci, and those with special protu- LUNAU 1992; LAND 1993a,b). Only males have Density- and Food-Resource-Dependent Courtship Behaviour in Poecilobothrus nobilitatus 125 conspicuous wings comprising an apical white intraabdominal joint associated with a tip and a subapical dark area. The wing length complete 180° inversion and forward-bending of males is about 5.7±0.4 mm and that of of the abdomen (ULRICH 1974). females 5.2±0.3 mm. The wing spread of males is about 1 mm larger that that of equally- 2. Material and methods sized females (sized determined by thorax width). Females preferably mate with large The study areas were the natural habitats of males: Copulating males have a larger wing P. nobilitatus in the surroundings of Düssel- length of 6.0±0.3 mm as compared to ran- dorf in the summer of 2002. The bounda- domly caught males with 5.7±0.4 mm long ries of the specific study sites were marked wings. Do features of the courtship display for identification in the video material. All allow for an assessment of a male’s size by a experiments were filmed with a video camera female? The courtship of males consists of (Digital Handycam Sony). Studying the several parts: (1) the courting male positions video tapes was possible in a frame-by-frame himself exactly in front of the courted female analysis with 0.04 s intervals between frames. at a distance of about 3 cm; (2) the wing-fan- Experiment 1: Two flat dishes (24 cm in di- ning display consists of several wing-fanning ameter) completely filled with sterilised soil were actions in the head-to-head position with the exposed close to each other. The surface of female; (3) the flight display is a series of rapid one of the two dishes was supplied with 3 g flights from one side of the female to the other. of chironomid larvae. In the video analysis it The male turns 180° when flying over the was registered how many males and females female and always lands in a face-to-body of P. nobilitatus were present on the dishes for position to the courted female. The aerial turn 1 min beginning 5 min after exposure. At this on the wing is the fastest known rotation time interval, usually some flies had detected around the yaw axis known in the animal king- the prey, but none had left the dish. The ex- dom (LAND 1993a). The courting male can re- periment was repeated ten times by the ex- peat one or several phases, before he flies be- posure of fresh dishes in the same area. hind the courted female and attempts to Experiment 2: To study the courtship in areas copulate. However, successful copulation re- with and without food in more detail, single quires co-operation by the courted female as dishes (24 cm in diameter) either filled with ster- she has to spread her wings slightly. As in other ilised soil without food or filled with sterilised dolichopodid flies, the hypopygium of the soil with food (3 g chironomid larvae and half males is very prominent and movable by an a teaspoon of honey) were filmed. In the video

Table 1: Categories of density of conspecifics (DOC) and density of male competitors (DOM) in experiment 3. Tab. 1: Kategorien der Dichte von Artgenossen (DOC) und der Dichte von Männchen (DOM) in Versuch 3.

Ryegistrated density Categor 1s-2 individuals in a 225 cm² area low density of conspecific 2s.5-3.5 individuals in a 225 cm² area middle density of conspecific 4s-7 individuals in a 225 cm² area high density of conspecific 0s-1 male conspecifics in a 225 cm² area low density of male competitor 1.5-2.5 male conspecifics in a 225 cm² area middle density of male competitors 3s.0-4.5 male conspecifics in a 225 cm² area high density of male competitor

Entomologie heute 18 (2006) 126 KLAUS LUNAU, ANDREA MIDDELMANN & MARION PLANKA analysis the courtship behaviour in dishes with a male fly settled on the dish before a female, food was compared to the control. but in 8 of 10 cases a female started feeding Experiment 3: In the natural habitat of P. before a male did. Altogether 363 males in- nobilitatus, plots of 225 cm² were marked and cluding 85 territorial males, and 96 females filmed for 10 min. If possible, three court- were observed. Males that patrolled within ships from each film, selected by chronologi- the dish area were considered as territorial cal order, were analysed in detail. The num- males. Territorial males frequently left dishes ber of males and females was registered at for fighting against intruders; during male- the beginning and at the end of each court- male-interactions the territorial male was ship sequence in order to calculate the density likely to leave the area which was registered by of conspecifics (DOC) and the density of the video, and possibly was registered as a male competitors (DOM) (tab. 1). new male if coming back to his territory. That is probably one of the reasons why the num- 3. Results ber of registered males surpasses that of females. Experiment 1: In the dishes without food To test the influence of food on the court- 0.4±0.7 females and 0.8±1.2 males were ship behaviour only courtships that were not registered 5 min after the exposure of the disturbed by conspecifics were analysed, in- dishes in the natural habitat for one minute. cluding 12 courtships in dishes without and In the dishes with food 1.4±0.8 females and 40 courtships in dishes with food. The total 2.9±1.7 males were observed. For both duration of courtships was significantly lon- sexes the number of conspecifics in dishes ger in dishes with food than in dishes with- with food significantly surpassed the num- out food (fig. 2). The total courtship had se- ber of conspecifics without food (fig. 1). veral components: Males in dishes with Experiment 2: Following exposure of ex- food took more time to position themselves perimental dishes with food, in 7 of 10 cases opposite to the females, exhibited longer

Fig. 1: Mean frequency of male and female Poecilobothrus nobilitatus in dishes with and without food in the 6th minute after exposition of dishes. The columns give the mean frequency of males and females out of ten trials; the bars indicate the positive standard deviation. Unpaired p-values are given according to the t-test with comparison of the indicated means. Abb. 1: Mittlere Häufigkeit von Männchen und Weibchen von Poecilobothrus nobilitatus in Schalen mit und ohne Futter in der 6. Minute nach Exposition der Schalen. Die Säulen geben die mittlere Häufigkeit von Männchen und Weibchen aus zehn Versuchen an; die Balken geben die positive Standardabweichung an. Die angegebenen p-Werte wurden mit einem ungepaarten t-Test zum Vergleich der angegebenen Mittelwerte berechnet. Density- and Food-Resource-Dependent Courtship Behaviour in Poecilobothrus nobilitatus 127

Fig. 2: Mean duration of courtship phases of Poecilobothrus nobilitatus males in areas with (n = 40) and without food (n = 12): positioning in front of female (black), wing-fanning display (dark grey), flight display (light grey), and copulation attempt (white). The duration of the four courtship phases are not significantly different in areas with and without food, the total courtship duration is (unpaired t-test). Abb. 2: Mittlere Dauer der Balzphasen von Poecilobothrus nobilitatus-Männchen in Bereichen mit (n = 40) und ohne (n = 12) Futter: Positionierung gegenüber dem Weibchen (schwarz), Flügelpräsen- tation (dunkelgrau), Sprungflug (hellgrau) und Kopulationsversuch (weiß). Die Dauer der einzel- nen Balzphasen unterscheidet sich nicht signifikant voneinander in Bereichen mit und ohne Nah- rung, jedoch die Gesamtdauer der Balz (ungepaarter t-Test).

Fig. 3: Mean duration of courtship phases of Poecilobothrus nobilitatus males with low density of conspecifics (DOC) (n = 59), middle DOC (n = 51), and high DOC (n = 25); positioning in front of female (black), wing-fanning display (dark grey), flight display (light grey), and copulation attempt (white). Repetitions of courtship phases were not combined. Abb. 3: Mittlere Dauer der Balzphasen von Poecilobothrus nobilitatus-Männchen in Bereichen geringer Dichte von Artgenossen (DOC) (n = 59), mittlerer DOC (n = 51) und hoher DOC (n = 25); Positionierung gegenüber dem Weibchen (schwarz), Flügelpräsentation (dunkelgrau), Sprung- flug (hellgrau) und Kopulationsversuch (weiß). Wiederholungen von Balzphasen wurden nicht zusammengefasst. wing-fanning display and longer flight dis- or DOM (see tab. 1), was low (figs. 3 and 4). play; however, the duration of these court- Particularly, the males exhibited a second flight ship phases dependent to the presence or display only rarely when density was high. Sta- absence of food differed not significantly. tistical analysis by linear regression was done Experiment 3: The total duration of court- with the raw data; we found a negative corre- ships (n = 135) was longer when density, DOC lation between the total duration of courtship

Entomologie heute 18 (2006) 128 KLAUS LUNAU, ANDREA MIDDELMANN & MARION PLANKA

Fig. 4: Mean duration of courtship phases of Poecilobothrus nobilitatus males with low density of male competirors (DOM) (n = 59), middle DOM (n = 51), and high DOM (n = 25); positioning in front of female (black), wing-fanning display (dark grey), flight display (light grey), and copulation attempt (white). Repetitions of courtship phases were not combined. Abb. 4: Mittlere Dauer der Balzphasen von Poecilobothrus nobilitatus-Männchen in Bereichen geringer Dichte von Männchen (DOM) (n = 59), mittlerer DOM (n = 51) und hoher DOM (n = 25); Positionierung gegenüber dem Weibchen (schwarz), Flügelschlagen (dunkelgrau), Flugbalz (hellgrau) und Kopulationsversuch (weiß). Wiederholungen von Balzphasen werden nicht zusammengefasst.

Fig. 5: Number of Poecilobothrus nobilitatus males that exhibited one courtship sequence including wing-fanning display and flight display (grey), or two courtship sequences (black) plotted against the density of conspecifics (DOC). Chi-square-test: df = 2, χ2 = 2.194, p = 0.334, n = 109. Abb. 5: Anzahl von Poecilobothrus nobilitatus-Männchen, die eine Balzsequenz (Flügelpräsentation und Sprungflug) zeigten (grau) oder zwei Balzsequenzen (schwarz) in Abhängigkeit von der Dichte der Artgenossen (DOC). Chiquadrattest: df = 2, χ2 = 2,194, p = 0,334, n = 109. and both DOC (R2 = 0.042, p = 0.018) and remaining 134 courtship sequences were in- DOM (R2 = 0.061, p = 0.004). terrupted, either by the courted female (51 Among 135 courtships analysed, 109 included %), by a male competitor (43 %) or by the at least one wing-fanning display or one flight courting male (6 %). The interruption of display. Among these, more males exhibited courtship was dependent of DOC. Generally, only one wing-fanning display or flight display the frequency of interruption of courtship than two such displays (fig. 5), which was, how- increased with DOC. In areas with low den- ever, not significantly dependent of DOC. sity, females were more likely to interrupt the Altogether 135 courtship sequences of P. no- courtship, whereas in areas with middle and bilitatus have been analysed from video data. high density, male competitors were more Only a single copulation was observed. The likely to interrupt the courtship (fig. 6). Density- and Food-Resource-Dependent Courtship Behaviour in Poecilobothrus nobilitatus 129

Fig. 6: Frequency of interrupted courtships by females (black), male competitors (dark grey), and courting males (light grey) plotted against the density of conspecifics (DOC), with n = 58 for low DOC, n = 51 for middle DOC, and n = 25 for high DOC. Chi-square-test: df = 4, χ2 = 22.523, p = 0.0002, n = 134. Abb. 6: Häufigkeit des Balzabbruchs durch Weibchen (schwarz), konkurrierende Männchen (dunkelgrau) und balzende Männchen (hellgrau) in Abhängigkeit von der Dichte der Artgenossen (DOC), mit n = 58 für geringe DOC, n = 51 für mittlere DOC und n = 25 für hohe DOC. Chiquadrattest: df = 4, χ2 = 22,523, p = 0,0002, n = 134.

4. Discussion Feeding as well as mating behaviour can easi- ly be observed. The relationship between The courtship of male P. nobilitatus is fo- food density, feeding and mating behaviour cussed on a single female. However, the has not yet been studied, although it is ob- presence of other males can strongly de- vious that many students of the courtship termine female choice enabling simultaneous and mating behaviour of P. nobilitatus took choice instead of successive choice behaviour, advantage of the fact that sexes aggregate in and the presence of many females and males large numbers at feeding sites (LUNAU 1992; may stimulate mating activities as well as LAND 1993a,b). hamper courtship and mating due to time The trade-off between time for feeding and consuming male-male interactions. When the time for courtship seems to differ between probability of meeting conspecifics of the males and females: most of the time males are opposite sex is low, the aggregation of both engaged in male-male interactions and court- sexes at rendezvous sites facilitates encoun- ship, whereas females are feeding most of the ters between males and females, e.g. many time even if they are courted by males. Males dipteran and hymenopteran males swarm defend small territories of about 100 cm2 in above species-specific landmarks such as hill- size against male intruders and court females tops or single trees (ALCOCK 1998). Many entering the territory (LUNAU 1992). In a dense insects combine feeding and mating activi- aggregation of P. nobilitatus, territorial males ties, e.g. many oligolectic bees mate on the have 13 antagonistic interactions with other flowers of their pollen food-plants (WES- males per minute, initiate courtship displays 6 TRICH 1990), tephritid gall-flies mate close to times per minute, and start feeding only less the oviposition sites of the females which than once per minute on average, which is a are the larval food habitats (ZWÖLFER 1974). new action every 4 seconds. The dolichopodid fly P. nobilitatus is very Both experiments in which the flies’ behav- common and frequently found in the direct iour in experimental areas with and without vicinity of water in various numbers, i.e. prey items was compared provide evidence single individuals, small or large groups. that the flies aggregate in areas with food. In

Entomologie heute 18 (2006) 130 KLAUS LUNAU, ANDREA MIDDELMANN & MARION PLANKA areas with food, females were feeding on prey wingspread in holometabolous insects is fixed most of the time, which obviously had im- when the imagines harden following hatching pact on the courtship duration of the males. from the pupa. Size is an index of larval growth This is probably related to females staying and does not change during imaginal life, i.e. longer; thus, a male with a territory that is size is not an index of bad or good condition. rich in prey has a prolonged chance to court a Distinct features of a flight display are likely female. Courting males displayed longer dependent of actual condition and indices of when the courted female was feeding, and nutrition and parasitism. shorter when the courted female was not feed- In many species of the Dolichopodidae the ing. However, we were not able to show any males display very similar apical black-and- relationship to mating success, because white signalling structures which in some among hundreds of observed courtships cases are born on different organs such as only a single courtship ended up with a wings, antennae, forelegs, middle legs, hind copulation. The analysis of the video data legs, cerci, and specific protuberances (LUNAU showed that there are three different causes 1996). The key feature explaining both for a premature end of courtship: (1) the court- homogeneity of signals and convergence of ing male stops courting; (2) the courted fe- signalling organs likely is an original innate male flies off; and (3) the courting male inter- female preference. From a female’s perspective, acts with another male. Obviously, courtships the male’s wing size is not easy to determine are more frequently interrupted by male-male due to the rapid movement of the wings interactions when the density of individuals during flight courtship (ZIMMER et al. 2003). is increasing. In addition, females fly off rare- The amount of wing movement is largest ly when feeding. No indication was found on the tip of the wings which will appear that females actively search in areas of high bright as opposed to the base of the wings density of males for mating opportunities, which will appear dark. White wing tips and and prefer low or high density of males for subapial dark areas thus amplify the wing mating, mostly because the great majority of signal. Additional similar signals from other courtships do not end up with a copulation, organs spread like the wings may further and only a single copulation was observed. It amplify the signal. In this interpretation the is unknown whether females of P. nobilitatus black-and-white signalling structures on the mate several times or only once. wings are amplifications of natural signals, It remains thus an unanswered question why the black-and-white signalling structures on males of P. nobilitatus engage in such com- other organs are automimetical signal copies plex courtship behaviour. There is good evi- (LUNAU 2002), and the females’ use of these dence that male size plays a role in female black-and-white signals for the estimation of choice, and in the outcome of male-male in- male size is caused by an ancestral preferential teractions (LUNAU 1992). Most likely males behaviour. demonstrate size by wingspread during the DARWIN (1871) first recognised that many wing-fanning display. The way how males conspicuous signalling traits that males use carefully position themselves in a distinct dis- in courtship display probably confer a sur- tance exactly in a head-to-head position in vival disadvantage to those males that bear front of the female before starting courtship them. Therefore, explaining the existence of indicates the male’s position during the wing- these traits poses a difficult problem. DAR- fanning display is decisive for how optimal WIN proposed a solution with the theory of the wingspread is presented. It is not known sexual selection. If males that exhibit these whether the male’s flight display also deter- conspicuous traits are more successful in ob- mines female choice. Body size including taining a mate, then these traits might evolve Density- and Food-Resource-Dependent Courtship Behaviour in Poecilobothrus nobilitatus 131 through what he termed sexual selection in unknown. The handicap associated with the spite of the fact that they result in a survival possession of male traits for male survival disadvantage. DARWIN claimed an aesthetic or courtship could be related to the preda- sense of females as an explanation for the ex- tion risk caused by the conspicuousness of istence of many conspicuous male traits. male traits, and to the flight performance It may be interesting to interpret the con- caused by larger wing load of large-winged spicuous traits of so many male dolichopodid individuals. The indication hypothesis is flies such as the black and/or white coloured, plausible, because wingspread is a good indi- exaggerated morphological characters, and cator of larval growth and flight display is a complex display behaviours in the light of good indicator of actual condition both of modern theories of sexual selection and which are parameters known to play a role in female choice (DAY 2000; SMITH & HARPER female choice. 2003): FISHER’s runaway process (FISHER 1958) postulates that a positive genetic correlation Acknowledgements between the females’ preference and the males’ traits. The runaway process requires We thank JULIA M UMME (Düsseldorf) for as- an initial female preference for a male’s trait. sistance in the field, HARTMUT GREVEN and As a consequence, females choosing con- MARCEL BRENNER (Düsseldorf) for their sup- spicuous males are incidentally also choosing port with the video analysis. males that carry genes for the female preference. The handicap theory of ZAHAVI (1975) References assumes that certain exaggerated male structures and conspicuous forms of male be- ALCOCK, J. (1998): Animal behavior. 6th edition. haviour have evolved because they apparently Sinauer Associates; Sunderland. BERNARD, G.D., & MILLER, W.H. (1968): Inter- act to reduce the chances of individual sur- ference filters in the corneas of Diptera. In- vival of the animal exhibiting the behaviour. vestigative Ophthalmology 7: 416–434. He argued that females which select males CUMMING, J.M. (1994): Sexual selection and the with the strongest handicaps can be sure that evolution of dance fly mating systems (Di- they have selected from among those males ptera: Empididae; Empidinae). The Canadian which have successfully passed a survival test Entomologist 126: 907-920. largely dependent on good genes for survival. DARWIN, C. (1871): The descent of man, and selec- The indicator hypothesis (SMITH & HARPER tion in relation to sex. John Murray; London. 2003) claims that female preferences evolve DAY, T. (2000): Sexual selection and the evolution of costly female preferences: spatial to exploit the condition-dependence or ‘in- effects. Evolution 54: 715-730. dicator value’ of male traits, which in turn FISHER, R.A. (1958): The genetical theory of nat- may cause these traits to evolve to elaborate ural selection. 2. Auflage. Dover; New York. extremes. Condition of males is determined FUNK, D.H., & TALLAMY, D.W. (2000): Courtship by resistance against parasites, uptake and role reversal and deceptive signals in the long- utilisation of food, and many other param- tailed dance fly, Rhamphomyia longicauda. Ani- eters. minal Behaviour 59: 411-421. These theories of female choice are not LAND, M.F. (1993a): The visual control of court- mutually exclusive. Nothing is known about ship behaviour in the fly Poecilobothrus nobilitatus. Journal of Comparative Physiolology A how these theories can explain the courtship 173: 595-603. and mating behaviour in Dolichopodidae. LAND, M.F. (1993b): Chasing and pursuit in the The genetic linkage between genes deter- dolichopodid fly Poecilobothrus nobilitatus. mining male traits and female preference for Journal of Comparative Physiolology A 173: these traits postulated by FISHER’s model is 605-613.

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Prof. Dr. Klaus Lunau Marion Pianka Andrea Middelmann AG Sinnesökologie Institut für Neurobiologie Heinrich Heine University Düsseldorf Universitätsstr. 1 D-40225 Düsseldorf E-Mail: [email protected]