Acta Herpetologica 12(1): 109-112, 2017 ISSN 1827-9635 (print) © Firenze University Press ISSN 1827-9643 (online) www.fupress.com/ah DOI: 10.13128/Acta_Herpetol-19155 Where is my place? Quick chorus structure assembly in the European tree frog Michal Berec Faculty of Agriculture, University of South Bohemia, Studentská 13, 370 05 České Budějovice, Czech Republic. E-mail: michal.berec@ seznam.cz Submitted on 2016, 4th October; revised on 2016, 24th November; accepted on 2017, 3rd April Editor: Giovanni Scillitani Abstract. Lek mating systems are characteristic of anurans that use oviposition sites that cannot be easily monopo- lized by individual males. The dynamics of the chorus structure in leks is not well known. Here, we examine the rela- tionship between the movement activity of individual males during the breeding season and their size. According to our observations, the site fidelity of males is not completely random, with the larger males moving significantly short- er distances than smaller males. However, this difference applies only to the distance between the first and second captures. Whether higher site fidelity contributes to higher mating success needs further investigation. Keywords. Vocalization, chorus, movement, size, tree frog. Individuals of the majority of amphibian species live their own solitary lives throughout the year except dur- ing the reproductive period, when they gather in defined spaces to find appropriate sexual partners. Males of some of these species do not occupy territories during the reproductive period but rely on physical characteristics during short and intensive bouts (scramble competition) to overpower mating competitors (Duellman and Trueb, 1994). Males of the other species divide the space into defended segments and lure individual females by acous- tic or visual stimuli (Wells, 2007). In lek mating systems, males typically occupy and defend small areas in which they vocalize (Höglund and Alatalo, 1995). Whenever intruders of the same sex approach too closely, they fight against them. Females choose their mates by moving both within and between several aggregations of males (Höglund and Alatalo, 1995). Surprisingly, there are only a handful of stud- ies describing lek structure and dynamics in anurans (Emlen, 1976, Tárano, 2009), although many species of frogs and toads form typical lek aggregations (Wells, 2007). This lack of research is surprising, as the positions of individual males within the lek can strongly influence their mating success (Arita and Kaneshiro, 1985; Kokko et al. 1998; Howard et al. 2011; but see Sæther et al. 2005 for the opposite results). At the same time, the size of individual males is the most important determinant of attractiveness in many anurans (Wells, 2007 and refer- ences therein). Here, we report the results of our survey of move- ment dynamics within a lek system of European tree frog (Hyla arborea). We specifically focused on the relation- ship between the movement of males during the repro- ductive season and their size (as a proxy for age). Our goal was to examine whether leks in this tree frog species show spatiotemporal structure. Despite its possible rel- evance to complex frog reproductive behaviour, this sub- ject has not previously been analysed in detail. We investigated a population of European tree frog (Hyla arborea) in Velký Vávrovský pond (1.5 ha, 390 m a.s.l., average depth 40 cm, maximum depth 120 cm, 48°59’25.18”N, 14°25’55.24”E) at the outskirts of České 110 M. Berec Budějovice in South Bohemia, Czech Republic. This pond is used for carp production and is also a breeding site used by other anurans (Bombina bombina, Bufo bufo, Rana dalmatina, Pelophylax kl. esculentus). This pond is nearly square in shape. Three of its four sides are over- grown by willow shrubs (Salix sp.), and the fourth side is paved. The littoral vegetation consists of sparse clumps (less than 3% of water area) of Carex sp., Typha angustifo- lia, and Alisma plantago-aquatica. The frogs were there- fore easily observed and caught. Tree frog males were collected during the breeding season, beginning at the onset of calling activity every day from April 13 to June 17, 2005, excluding the days with unsuitable conditions (pouring rain, storms). Each night, all males in the chorus were captured and meas- ured. As all males called within four metres from the shore, we walked slowly around the pond and entered the water only to catch males to reduce disturbance to the chorus. All males were caught by hand and indi- vidually marked by toe-clipping, and the snout-urostyle length (SUL) was measured to the nearest millimetre using a vernier calliper. Only one digit per limb was toe- clipped, with a maximum of three digits per individual. For toe-clipping, we used scissors disinfected in alcohol. No analgesic was used. We did not observe any signs of pain or distress in the frogs when handled. Addition- ally, we did not observe any negative effect on survival (we have used this method repeatedly in previous stud- ies). Some males resumed calling a few minutes after toe clipping (see Funk et al., 2005 for comments on the toe- clipping method). The position of each male was determined using coloured tags with numerical codes positioned along the breeding-site shoreline at 2 m intervals. When an individual frog was recaptured on a subsequent night or nights, we measured its position to the nearest centime- tre from the previous position, using a measuring tape in cases of distances within a radius of five metres. For greater distances, we measured the distance covered by using the marks on the map and rounded the value to the nearest ten centimetres. We did not use GPS or similar system because the measurement error with such devices is at least as large as that with our approach. All statistical tests were performed using the software package Statistica 10.0 (StatSoft, 2012). All distances were log-transformed before analysis. In total, 188 males were captured and individually marked. During the season, 44% of males were captured only once, 22% were captured twice, 15% were captured three times, 13% were captured four times, 3% were captured five times, and 3% were captured six times. The number of captures of the same individual was not dependent on the SUL of males (Kruskal-Wallis ANO- VA by ranks: H (5, n = 188) = 0.581, P = 0.988). Mean- while, the SUL of males captured did not depend on the day of the season (R = 0.082; R2 = 0.007; F1,186 = 1.266; P = 0.262). In contrast, the SUL of tree frog males partially determined the movement pattern during the breeding season. Our analysis revealed significant relationships between SUL and distances between subsequent captures (R = -0.382; R2 = 0.146; F1,222 = 37.848; P < 0.001; Fig. 1). However, only the distance between the 1st and 2nd cap- ture was clearly associated with the above mentioned relationship. Here, smaller males covered longer dis- tances between the first and the second capture than did Fig. 2. Relationship between the SUL of males and the distance between the first and second captures. Fig. 1. Relationship between the SUL of males and the average dis- tance between all pairs of subsequent captures. 111Movement dynamics of tree frogs larger males (Fig. 2). None of the subsequent movements showed a significant association with SUL (Table 1). Although the distance covered by males stead- ily decreased between subsequent captures (Table I), this effect was not statistically significant (Kruskal-Wallis ANOVA by ranks: H (4 n = 171) = 0.127, P = 0.998). In general, larger males usually spend more nights in a lek, which is related to their mating success in lek- breeding anurans (Pröhl, 2003; Friedl and Klump, 2005; Castellano et al. 2009; Botto and Castellano, 2016). Con- trary to this, our data did not support this pattern, as the number of captures (i.e., nights when the male attended the lek) was not dependent on the SUL of males. Here, the data suggest another scenario, in which males of dif- ferent sizes spend similar amounts of time (numbers of nights) in a lek. However, the size of males determined their movement behaviour. Male size is generally the most important determi- nant of mating success in explosive competitors (Hol- liday and Tejedo, 1995), whereas the situation is much more complex in lek-breeding anurans (Höglund and Alatalo, 1995). Studies of lekking non-anuran vertebrates suggest that individual position in the lek can be very important (Kokko et al., 1998; Howard et al., 2011). Sur- prisingly, despite the large number of lek-breeding anu- rans, hardly any studies linking mating success of males and their individual positions within a lek have been published. As many lek-breeding anurans establish non- random spacing patterns during reproduction events (Whitney and Krebs, 1975; Brenowitz et al., 1984; Tára- no, 2009), different outcomes from different positions in the lek could be predicted. The lek is re-established every night in lek-breeding anurans, including European tree frog (Grosse, 2009). According to our data, the site fidelity of males is not completely random and is deter- mined by their size during part of the breeding season. In fact, the larger males (i.e., older sensu Kyriakopoulou- Sklavounou and Grumiro, 2002) moved significantly shorter distances than smaller (younger) males. How- ever, this difference applies only to the distance between the first and second captures. After that, no differences were observed in movement activity between subse- quent captures. Emlen (1976) f ound a different pattern of chorus formation in bullfrogs (Lithobates catesbe- ianus). He described leks in bullfrogs as “both spatially and temporally ephemeral” but subsequently found that larger (older) males occupied more centrally located ter- ritories. On the other hand, the locations of individual males changed rapidly, and they moved from one aggre- gation to another during the breeding season. The fact that larger males occupied much “stable” area implies question of the advantage of this behaviour. This can be the result of their previous experience as larger males are presumed to be older ones (Friedl and Klump, 1997). Thus, larger males have better knowledge about the locality from previous reproductive seasons and should improve their position according to their previous mat- ing success. Simultaneously, experienced males can also recognize better mating positions (e.g., determined by abundance and structure of vegetation cover, distance from the shore, or oviposition site, etc.) in shorter time than smaller ones. Moreover, physical superiority of larger males enables the territories to be hold for long- er period. More intensive movement activity of smaller males can therefore be only the consequence of their effort to find better mating opportunities. Site fidelity has been documented in several anu- ran species. Various authors explain this behaviour as advantageous for male-male competition (Davis, 1987; Brenowitz and Rose, 1994; Marshall et al., 2003), search strategies of females (Fellers, 1979; Murphy and Ger- hardt, 2002), female attraction or choice (Bradbury and Gibson, 1983; Grafe, 1997), female paths (Grafe, 1997), or sound transmission (Narins and Hurley, 1982; Wells and Schwartz, 1982; Marshall et al., 2003). Using dynamic programming, the theoretical model by Switzer (1993) of sequential settlement decisions predicted site fidelity to be positively correlated to age. Unfortunately, previous studies did not relate the observed behaviour directly to the size of males. The reason why larger tree frog males chose and returned to the same positions more pre- cisely than smaller males is not obvious at this time and deserves further investigation. Table 1. Mean distances ± standard deviation between two subsequent captures, as well as results of regression analyses between the SUL of males and distances between subsequent captures. Capture Mean distance ± SD (cm) Range (cm) R R2 F d.f. p 1st -2nd 801 ± 870 0-4660 -0.533 0.284 45.311 1,104 <0.001 2nd -3rd 614 ± 494 0-2450 -0.182 0.033 2.163 1,63 0.143 3rd -4th 541 ± 498 0-2020 -0.237 0.056 2.016 1,34 0.165 4th -5th 414 ± 294 52-840 -0.311 0.097 0.966 1,9 0.351 112 M. Berec ACKNOWLEDGEMENTS Permission for conducting the study was issued by the Ministry of Environment of the Czech Republic (per- mission number 1211/32/SOP/E/05/456/Cho). I would like to thank Irena Šetlíková, Luděk Berec, and two anon- ymous reviewers for valuable comments on the earlier versions of the manuscript. Research was financially sup- ported by the GAJU 081/2016/Z. REFERENCES Botto, V., Castellano, S. (2016): Attendance, but not per- formance, predicts good genes in a lek-breeding treefrog. Behav. 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