Response to chemical cues from conspecifics reflectsmale mating preference for large females and

avoidance of large competitors in the European pondturtle, Emys orbicularis

Jens R. Poschadel1,2), Yvonne Meyer-Lucht1) & Martin Plath3,4)

(1 Biozentrum Grindel, University of Hamburg, Martin-Luther-King-Platz 3, 20146Hamburg, Germany; 3 Unit of Evolutionary Biology and Systematic Zoology, Department of

Biochemistry and Biology, University of Potsdam, Karl-Liebknecht Str. 24-25, 14476Potsdam, Germany; 4 Department of Zoology, University of Oklahoma, 730 Van Vleet Oval,

Norman, OK 73019, USA)

(Accepted: 3 February 2006)

Summary

We examined chemical communication in male and female European pond turtles (Emysorbicularis). In simultaneous binary choice tests, a focal animal was given a choice betweenpheromones from a conspecific and a choice chamber containing untreated water. Femalesdid not show a preference, both when male and when female stimuli were presented. On thecontrary, males preferred the odor of a female over untreated water, suggesting that malesactively search for females. The strength of preference was positively correlated with thebody size difference between the female and the focal male, indicating that males prefer tomate with larger females. Female fecundity is positively correlated with female size in E.orbicularis, which may account for male choosiness. No overall preference for the stimulusanimal was observed when males were presented cues from another male. However, thestrength of preference was negatively correlated with the difference in body size. Malesavoided large males, but oriented towards smaller stimulus males. This reflects that malesform dominance hierarchies, where large males aggressively attack smaller ones. Far-rangechemical communication probably enables males to minimize the risk of costly aggressiveinteractions. This is, to our knowledge, the first study on the role of chemical cues for inter-and intrasexual communication in the European pond turtle.

Keywords: Chelonia, chemical communication, male mate choice, pheromones, sexual selec-tion.

2) Corresponding author’s e-mail address: jposchadel@web.de

© Koninklijke Brill NV, Leiden, 2006 Behaviour 143, 569-587Also available online - www.brill.nl

570 Poschadel, Meyer-Lucht & Plath

Introduction

Chemical communication is probably one of the most basic forms of com-munication and is found in numerous taxa throughout the animal kingdom(Doty & Müller-Schwarze, 1992; Bradbury & Vehrencamp, 1998; Gosling &Roberts, 2001; Wyatt, 2003). A multitude of studies illustrate the importanceof chemical communication for reptilian social behavior (e.g., Mason, 1992;Alberts, 1993; Cooper, 1994; Cooper, 1995; Greene et al., 2001; LeMaster etal., 2001; Cooper & Perez-Mellado, 2002), for example, for marking a ter-ritory or basking site (Bull et al., 1999; Wyatt, 2003 for a review). In manyreptiles, odors play an important role also in non-social contexts like foodselection (Burghardt, 1969; Mason, 1992; Cooper, 1994; Cooper & Hartde-gen, 1999; Cooper et al., 2000) or predator detection (e.g., Dial et al., 1989;Cooper, 1990; Head et al., 2002). Several authors have documented the rel-evance of species-specific odors for species recognition, mate searching andmate choice – i.e. mate quality recognition – in reptiles (Cooper & Vitt, 1984,1986; Mason, 1992, 1993; Martin & Lopez, 2000; Cooper & Perez-Mellado,2002; Shine et al., 2004; Quinn & Hews, 2005). For example, female lizardschoose males based on odors emitted by their femoral glands, which mayconvey specific information about the male (López et al., 2003; Olsson et al.,2003; López & Martin, in press).

So far, the role of chemical communication in the behavior of chelonians,however, has been given comparatively little attention, although the functionof the olfactory and vomero-nasal systems in this group have been intenselystudied (Halpern, 1992; Manteifel et al., 1992; Fadool et al., 2001; Murphyet al., 2001). For example, turtles have been shown to be able to discriminatebetween water from domestic and unknown ponds (Quinn & Graves, 1998;Muñoz, 2004). Several authors have assumed that chemical cues play animportant role for the behavior of turtles also in social (namely aggressiveand sexual) contexts (Rose, 1970; Eisner et al., 1977; Mason, 1992). For theEuropean pond turtle Emys orbicularis, Manteifel et al. (1992) reported on ahigh sensitivity to dissolved amino-acids, but experimental data on the roleof far-range chemical communication for mate finding in turtles are scarce(Mauremys leprosa: Muñoz, 2004); mate choice or avoidance of competitorsby using chemical cues is as yet unknown for turtles.

In the present study we examined chemical communication in E. orbicu-laris. In our first experiment, we asked whether chemical cues are being used

Chemical communication in turtles 571

by males to localize females. Home ranges of E. orbicularis males are con-siderably larger than those of females and encompass several female homeranges (Paul, 2004). During the mating season, directly after hibernation,males show high locomotory activity and search for females (Lebboroni &Chelazzi, 1991, 2000). We asked whether males can use chemical cues totrace females.

In a second experiment we asked whether males respond to chemical cuesfrom another male. Encounters of two males regularly end up in agonis-tic interactions (Lebboroni & Chelazzi, 1991, 2000). These findings are inagreement with the results of studies on other turtles, such as Gopherusagassizii (McCrae et al., 1981) and Chelydra serpentina (Galbraith et al.,1993). Large Clemmys insculpta males usually dominate smaller ones. In thisspecies males form dominance hierarchies, and large males achieve a highernumber of matings than smaller, subdominant males (Kaufmann, 1992). Pa-ternity analyses by Galbraith (1991) showed a higher rate of paternity fordominant males in this species. Severe aggressive behavior between malescan be found also in other turtles (Chinemys reevesii: M.P., pers. obs.; seealso Auffenberg, 1977 for tortoises). Investigations using molecular pater-nity analysis suggest that large males father more offspring than small malesalso in E. orbicularis (Roques, unpubl. data). Strong aggression betweenmales suggests that small males might try to avoid the odor of a larger males,whereas large males should try to attack smaller males, hence, large malesmight be attracted by the odor of a smaller male. We asked whether maleswould also use chemical cues to trance competitors. We predicted males toavoid the odor of a larger, physically stronger male, but to show a positiveresponse to chemical cues from a smaller, inferior male.

The mating system of E. orbicularis suggests that male-male competi-tion is an important predictor of male mating success. Nevertheless, femalesmight have mating preferences. Therefore, in another part of this study, wetested whether females respond to chemical cues from males and whetherthey prefer chemical cues from large males. Female choice relative to malesize has been found in numerous species (Andersson, 1994 for a review).Size-dependent mate choice has been shown to be mediated by chemical cuesin many cases (e.g., plethodontid salamanders: Marco et al., 1998; skinks:Cooper & Vitt, 1993).

Finally, female E. orbicularis are much less aggressive than males, and au-thentic reports of fighting females are scarce (Fritz & Günther, 1996). Home

572 Poschadel, Meyer-Lucht & Plath

ranges of females frequently overlap (Paul, 2004), and in dense populations(e.g., in southern Europe), basking sites are sometimes shared by numer-ous females (J.P., pers. obs.). Thus, we asked whether females respond tochemical cues from other females. This part of our study also sheds light onthe question whether females actively aggregate with other females by us-ing chemical cues to localize them, or whether the occasional aggregationsobserved in nature are solely due to specific habitat properties like optimalbasking sites.

Specifically, we conducted 4 experiments, presenting single male or fe-male European pond turtles with chemical cues from another male or a fe-male. Stimulus animals were of different sizes, allowing us to determine theeffect of the body size of the stimulus animals on the focus animals’ associ-ation preferences.

Materials and methods

Study organism

E. orbicularis is distributed from Northern Africa to Asia Minor. In Europe,it occurs from the Mediterranean Sea northwards to the Baltic Sea (Fritz,2001). Its distribution depends mainly on the occurrence of calm vegetation-rich lakes, ponds or anabranches of rivers combined with nearby warm andsandy terrestrial microhabitats for egg deposition. Since this habitat combi-nation has become extraordinarily scarce in Central Europe, E. orbicularis isthreatened by extinction or de facto extinct throughout most parts of CentralEurope (Fritz, 2001). It is listed as threatened species by the IUCN (2004)and is protected by national and international law throughout Europe. Be-side the loss of suitable habitats (Schneeweiß, 1998), cold winters and rainysummers may have a severe effect on Central European populations, becauseeggs do not develop under those conditions (Schneeweiß et al., 1998). A suc-ceeding problem for E. orbicularis in Central Europe are extremely smallpopulations that may suffer the negative effects of inbreeding (Poschadel &Parzefall, 2003). Additionally, sex ratios in some Central European popula-tions appear to be strongly female-biased (Paul, 2004). Given that males areextremely rare in many German populations, the question how males findfemales is also relevant for conservation purposes. Therefore, this study con-tributes to the conservation biology of this species.

Chemical communication in turtles 573

Our study was carried out in Brandenburg, Germany. However, for thechoice tests we did not use specimens from the autochthonous populationof the local sub-species (E. o. orbicularis). Rather, we used animals fromprivate stocks. Additionally, we had access to several specimens of the intro-duced sub-species E. o. hellenica, naturally occurring in the eastern Mediter-ranean, which had been caught in the study area and were subsequently main-tained in semi-natural enclosures. Molecular studies have revealed that theEuropean subspecies of E. orbicularis show extremely low genetic diver-gence (Lenk et al., 1999). Caged Emys of different subspecies readily matewith any other subspecies, even when both sexes of each of two or more sub-species are kept together, suggesting that mate choice relative to subspeciesstatus does not occur (Ballasina, pers. comm.). Furthermore, several naturalhybrid zones between subspecies are described (Fritz, 2001). We thereforecombined our test animals regardless of subspecies status in this study.

In total, we used 8 specimens of E. o. orbicularis (3 females and 5 males)and 12 E. o. hellenica (4 females and 8 males). The size (carapax length)of the female turtles available for this study ranged from 125 to 191 mm(mean ± SD: 143 ± 23 mm), their weight was between 420 and 1,500 g(mean ± SD: 666 ± 389 g). Males ranged from 98 to 159 mm in length(mean ± SD: 140 ± 24 mm), and weighed between 190 and 590 g (mean ±SD: 413 ± 147 g).

Maintenance of the turtles

Choice experiments were carried out in a greenhouse of the Landesumwelt-amt Brandenburg after hibernation of the turtles in early April of 2000, 2001and 2002. Due to the limited number of animals available for the tests, somefocal animals were tested in more than one experiment, but never in the sameyear. In the northern part of the distribution area, mating typically occursat this time of the year (Fritz, 2001 and references therein). Prior to theexperiments, all specimens were kept in separate aquaria (148 × 63 × 44cm), which were filled with water to 12-14 cm height. Additional to naturaldaylight, illumination was provided by UV-neon tubes at a 10:14 h light:darkrhythm. Thermal lamps were installed app. 20 cm above natural baskingfacilities like roots and stones, simulating sunshine for 6 h per day. Watertemperature varied between 10 and 16◦C (mean ± SD: 12.4 ± 1.8◦C), roomtemperature ranged between 8◦C and 23◦C (mean ± SD: 15.6 ± 4.3◦C). All

574 Poschadel, Meyer-Lucht & Plath

Figure 1. Experimental set-up. For details see main text.

temperature measurements were conducted daily at 1:00 pm. Turtles werefed daily ad libitum a diet of specially prepared turtle pate (Schneeweiß,pers. comm.) and dehydrated cat food.

Experimental design

For the choice experiments we used a transparent 150 × 60 × 30 cm Plexi-glas aquarium (Figure 1). The water level was adjusted at 14 cm. The meanwater temperature (±SD) during the tests was 16.7 ± 1.1◦C. One third (50cm) of the test aquarium was separated into two equal choice compartments(‘preference zones’) by a transparent Plexiglas plate (Figure 1). The remain-der (two thirds of the tank) was defined as ‘neutral zone’. The test tank wasshielded by dark curtains in order to prevent any influence by the observer.A small hole in the curtain at the outflow end of the test aquarium, 15 cmin length, allowed us to observe the focus animal. E. orbicularis is a diurnalspecies, hence all experiments were conducted during the daytime. Diffuseillumination was provided by daylight passing through the rooftop of thegreenhouse.

We used two Braun Intrafix® Air medical infusion tubes for a definedinflow of stimulus water into both choice compartments. The inflow tubeswere fixed at the front walls of the choice compartments by transparentadhesive tape. We used new tubes for each trial. This method guaranteedan identical inflow of stimulus water into both compartments. Using new

Chemical communication in turtles 575

tubes between trials made time-consuming and possibly ineffective cleaningsuperfluous. Two outflow tubes were situated at the opposite wall of theexperimental tank, ensuring a continuous flow of stimulus water through thetank. The inflow rate was 0.16 l/min, coming to a total inflow of 9.6 l for anobservation time of 1 h.

Control water without chemical cues was taken from a nearby well, whichalso provided the water for the holding tanks. Control water was stored in a60×40×30 cm tank, filled to 21 cm, for 20 hours prior to the tests. Likewise,to generate water containing pheromones, a stimulus animal was placed inanother, identical tank for 20 h. Stimulus animals were not fed for 48 hoursbefore a trial to avoid any influence of chemical cues by feces. Turtles wereremoved from the tank one hour before a test. The stimulus tanks wereinstalled above the level of the test tank. The infusion tubes were pluggedto the stimulus tanks using rubber corks, which were stuck into openingsabout 10 cm above the base. The two stimulus tanks were thoroughly rinsedwith water after each trial. Trials were conducted between 9:00 a.m. and 4:00p.m.

To initiate a trial, the focus animal was gently introduced centrally intothe test aquarium, heading towards the choice compartments. During an ac-climation period of 30 minutes, an opaque but water permeable (perforated)PE-plate prevented the turtle from entering the choice compartments. Then,the PE-plate was carefully removed, the inflow tubes were opened and thetime spent in either of the choice compartments was recorded for 1 hour. Af-ter the first test period, the focus animal was removed from the test aquariumand placed in its holding tank for some minutes. Meanwhile, the inflow tubeswere interchanged from left to right and vice versa. After another acclima-tion phase of 30 minutes (with the PE-plate installed), a second measure-ment was conducted accordingly. This procedure was carried out to preventstimuli-independent side biases. We ensured that no chemical cues from thefirst part of the trial would be present during part two of a trial by carefullycleaning the test tank after the first part of the trial.

Statistical analyses

Times spent in either preference zones from both parts of a trial weresummed up. We decided a priori to exclude individual trials: The combinedarea of both choice compartments was one third of the test aquarium; hence,

576 Poschadel, Meyer-Lucht & Plath

trials in which the focal turtles spent less than 33% of their time inside thepreference zones were discarded due to low response. These animals wereconsidered not to be motivated to choose. Furthermore, we excluded trialsdue to side bias if the test animal spent more than 90% of the time inside thechoice compartments in only one choice compartment during both parts of atrial. Three out of 36 trials had to be discarded, two due to low response, onedue to side bias.

Since our data were not normally distributed, only non-parametric testswere employed. To test for a preference of the focal animal for chemicalcues from a conspecific, we compared the time spent in the ‘stimulus com-partment’ with the time spent in the ‘control compartment’ using Wilcoxonsigned-rank tests. To test for an influence of the body size of the stimulusanimal on the strength of the focal animals’ preferences, we calculated thestrength of preference as: (timestimulus chamber−timecontrol chamber)/(timestimulus+timecontrol), whereby +1 would indicate maximum preference to the stimu-lus, −1 would indicate avoidance of the stimulus and 0 would indicate nopreference. We used Spearman rank correlations to test for an influence ofthe size difference between the stimulus and the focal animal (difference incarapax lengths) on the strength of preference.

Results

When comparing the time spent in the choice compartment containing chem-ical cues of a conspecific stimulus animal with the time spent in the op-posite (control) chamber, males significantly preferred the odor of females(Wilcoxon signed-rank test: T = 0, N = 7, p = 0.016; Figure 2). No sig-nificant differences were found in the other experiments (males with malestimulus: T = 27, N = 12, p = 0.38; females with female stimulus:T = 10, N = 6, p = 1.0; with male stimulus: T = 16, N = 8, p = 0.84).

In the experiments with focal males, the strength of preference was pos-itively correlated with the difference in body size (stimulus – focal animal)when chemical cues from females were presented (Spearman rank correla-tion: rs = +0.82, N = 7, p = 0.015; Figure 3). Hence, males preferredthe odor of larger females. When chemical cues from male stimulus animalswere provided, the strength of preference was negatively correlated with thesize difference (rs = −0.66, N = 12, p = 0.019). Males were attracted by

Chemical communication in turtles 577

Figure 2. Boxplots showing the time the focal males (left) and females (right) spent inthe choice compartment containing pheromones from a conspecific stimulus animal (graybars) and in a control compartment without pheromones (open bars). Median (middle line),

quartiles (box) and 5th and 95th percentile.

the odor of smaller males, but avoided the odor of larger males (Figure 3).During the experiments with focal females, no significant correlations werefound in both experiments (with female stimuli: rs = −0.60, N = 6, p =0.24; with male stimuli: rs = −0.071, N = 8, p = 0.84).

Discussion

Individual European pond turtles (Emys orbicularis) were given an oppor-tunity to choose between water containing pheromones of a conspecific andcontrol water without pheromones. We found males to show an overall pref-erence for the odor of a female, and association preferences were strongerthe larger the stimulus female was. When odors from another male were pre-sented, the focal males showed no overall preference: they avoided the odorof a larger male, but were attracted by the odor of a smaller male. Femalesshowed no preference both for male and for female stimuli.

578 Poschadel, Meyer-Lucht & Plath

Figure 3. Response to chemical cues in E. orbicularis. A test animal (male, above orfemale, below) was given a choice between control water and water containing specificcues from a stimulus female (left) or a stimulus male (right). The strength of preferencein relation to the difference in carapax length (size difference) is presented. Positive valuesindicate preference for the stimulus, negative values indicate avoidance of the stimulus. rs is

calculated from Spearman-rank correlations.

All males tested in the experiment using stimulus females invariably pre-ferred the side of the test tank containing pheromones over control water.A prerequisite for this behavior is that females release pheromones into thewater. Since the response of male turtles towards chemical cues from a fe-male differed from the response to the odor of another male, sex-specificpheromones are likely to exist. Externally secreting glands are known to belocated in the skin of most freshwater and sea turtles (Ehrenfeld & Ehren-feld, 1973; Solomon, 1984), whereas special ‘inframarginal musk glands’,as known from Australian chelid turtles (e.g., Chelodina longicollis: Eisneret al., 1978), are not found in E. orbicularis. Upon finding a female, malesof many turtle species, including E. orbicularis, sniff at the female cloacalregion, suggesting that pheromones from the cloacal glands play an impor-tant role (Graptemys pseudogeographica and Chinemys reevesii: M.P., pers.obs.; see also Auffenberg, 1965 for tortoises).

Chemical communication in turtles 579

Male green sea turtles (Chelonia mydas) appear to be able to discriminatebetween reproducing and non-reproducing females, which implies that fe-males produce some kind of sex pheromones (Crowell-Comuzzie & Owens,1990). A response to sex-specific pheromones has also been described foranother turtle species, Mauremys leprosa (Muñoz, 2004) and many otherreptiles (green iguanas: Alberts et al., 1994; skinks: Cooper, 1995; browntree snakes: Greene et al., 2001; garter snakes: LeMaster & Mason, 2002;lacertid lizards: Martin & Lopez, 2000; Cooper & Perez-Mellado, 2002;but see Shine, 2005 for sea snakes), and also for several other aquatic ver-tebrates, such as newts and salamanders (Parzefall, 1976; Parzefall et al.,1980; Aragón et al., 2000; Iwata et al., 2000; Park & Propper, 2001; Wirsig-Wiechmann et al., 2002; Thompson & Moore, 2003; Toyoda et al., 2004) andfishes (Liley, 1982; Sorensen et al., 1992, 2005; Olsen et al., 2001; Stacey etal., 2003). This study, however, is the first to demonstrate chemical commu-nication in a sexual context – i.e. mate finding and mate quality assessment– in E. orbicularis.

In our experiments, female turtles did not respond to cues from a stimu-lus male. Sample sizes are small in this study due to the endangered statusof the species, which made it impossible to obtain more specimens. Hence,negative results are discussed with caution. Likely, male E. orbicularis ac-tively search for females during the mating period, but females do not searchfor males. Far-range chemical communication via water-borne pheromonesenables males to find mating partners even over long distances, or in veryturbid water, as is often the case in E. orbicularis habitats (Fritz & Gün-ther, 1996). This is also relevant for the general conservation biology of thisrare and endangered species: For example, many German populations havebecome extremely small and therefore vulnerable. Far-range chemical com-munication explains how males find females under these conditions. Futurestudies will have to reveal the maximum distance over which males can tracefemales by using chemical information.

We found males to prefer the odor of larger females. This likely reflects amale mating preference for large female body size. Male mate choice is pre-dicted if females differ in fecundity (Andersson, 1994; Berglund & Rosen-quist, 2001), if mating or sperm production is costly for males and thus amale cannot mate with all females present (Nakatsuru & Kramer, 1982; Ver-rell, 1982), and if the sex ratio is female-biased (van den Berghe & Warner,1989). Male mate choice for large females has been found in several species

580 Poschadel, Meyer-Lucht & Plath

(e.g., fishes: Ptacek & Travis, 1997; Ojanguren & Magurran, 2004; Plath etal., in press; newts: Verrell, 1982, 1985; Marco et al., 1998; lizards: Ols-son, 1993; Whiting & Bateman, 1999; snakes: LeMaster & Mason, 2002;but see Shine et al., 2001 for size-assortative mating in a snake). Like inother reptiles (snakes: Seigel & Ford, 1987; lizards: Olsson et al., 2002), thenumber of eggs increases with increasing female body size in E. orbicularis(Zuffi et al., 1999). Hence, larger females are more fecund than smaller ones.Secondly, given that females may be dispersed over a large area and maleshave to search for them, mating probably imposes high energetic costs tomales – at least in some populations. Upon finding a female, males courtfemales which inflicts further costs to the male. Third, sex ratios can be ex-tremely female-biased in Germany (Paul, 2004). Altogether, these factorsmay account for male choosiness. Far-range chemical cues provide an op-portunity for a male to estimate female fecundity (in terms of a female’s size)well before he approaches the female, so that a male can adjust his invest-ment in time-consuming near-field localization of the female and subsequentcourtship.

It has been shown for garter snakes (Thamnophis sirtalis) that smalland large females may differ in the composition of skin lipids (LeMaster& Mason, 2002), providing a potential mechanism for pheromone-basedmale mate choice relative to female size also in E. orbicularis. An alter-native explanation would be that males alter their response in relation to theconcentration of female pheromones in the water, whereby the amount ofpheromones produced would increase with increasing female body size. Itremains unsolved which mechanism allows E. orbicularis to estimate thesize of conspecifics. Dilution experiments by Kamio et al. (2005) revealeda stronger response of female helmet crabs to higher concentrations of malesex pheromones. Similar experiments with E. orbicularis would offer an el-egant approach to the question whether differences in the chemical structureof the pheromone(s) or different concentrations are responsible for the de-scribed size discrimination in this species. We propose a future experimentin which ‘stimulus water’ from large females is diluted, and the responseof males towards chemical cues from a small vs. diluted water from a largefemale is examined (e.g., in a simultaneous choice situation).

We found no evidence that females would prefer larger males. However,the lack of a pheromone-based preference in our experiments does not ex-clude the possibility that females of this species have mating preferences. For

Chemical communication in turtles 581

example, females may not express an existing preference based on chemicalcues alone. Multiple mating is frequently observed in E. orbicularis females(Fritz & Günther, 1996) and sperm storage is likely since it was found inrelated species (Ewing, 1943; Gist & Jones, 1989). This mechanism wouldinclude the possibility for cryptic female choice (Evans et al., 2003) as wasfound in other reptiles (e.g., Vipera berus: Madsen et al., 1992; side-blotchedlizards: Calsbeek & Sinervo, 2004; sand lizards: Olsson et al., 2004). SinceEuropean pond turtles do not show any pair-bonding, and maternal care is re-stricted to egg deposition, females might benefit from mating multiply, withdifferent males (Shine, 1988 for snakes; see Pearse & Avise, 2001 for a dis-cussion). This would increase the possibility for cryptic female choice, butalso the possibility for sperm competition, which would be another mecha-nism to obtain ‘high quality sperm’.

Also during the male-male tests, focal males showed a significant re-sponse: they oriented towards the smaller stimulus male, but strongly avoidedthe larger male. We conclude that the production of pheromones is notrestricted to the female sex. Apparently, males also release water-solublepheromones, and like female pheromones, male pheromones seem to con-vey size-specific information (for snakes, Thamnophis sirtalis see LeMaster& Mason, 2002). Our results suggest that smaller males attempt to reducethe risk of direct combat while avoiding the odor of large males. In contrast,larger males apparently try to attack approaching smaller males to preventthem from mating. In both cases, chemical communication allows males toindividually adjust their behavior to the specific characteristics of conspecificmales well before they actually encounter them. Chemical cues are known toplay an important role during aggressive encounters of lizards (e.g., Cooper& Vitt, 1987; Alberts et al., 1994), are presumed to have a function for themaintenance of dominance relationships (Alberts et al., 1992) and may helpto keep actual combat at a minimum in these species (Lopez et al., 2001;Lopez & Martin, 2002).

In summary, we provide evidence for inter- and intrasexual communica-tion via water soluble pheromones in the European pond turtle. Males re-sponded to chemical cues from females and from other males, and their be-havioral responses suggest a function for mate searching/mate choice, as wellas in the context of aggressive male-male competition.

582 Poschadel, Meyer-Lucht & Plath

Acknowledgements

This study was supported by a PhD grant of the Deutsche Bundesstiftung Umwelt DBU(AZ 6000/668) to J.R.P. and by the Landesumweltamt Brandenburg. Norbert Schneeweißand Richard Podloucky kindly provided animals. We are indebted to Jakob Parzefall, DeliaRamcke, Hans Loberenz and Regina Paul for logistical support as well as for valuable com-ments and discussions. Claudia Keller and Rüdiger Riesch kindly read an earlier version ofthe manuscript. The experiments reported in this paper comply with the current laws in Ger-many.

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