Sexual dimorphism, reproduction and diet of the casque-headed treefrog Itapotihyla langsdorffii (Hylidae: Lophiohylini)

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Sexual dimorphism, reproduction anddiet of the casque-headed treefrogItapotihyla langsdorffii (Hylidae:Lophiohylini)Davor Vrcibradic a , Rogério L. Teixeira b & Vitor N.T. Borges-Júnior aa Departamento de Ecologia, Universidade do Estado do Rio deJaneiro, Rio de Janeiro, Brazilb Museu de Biologia Prof. Mello Leitão, Santa Teresa, Brazil

Version of record first published: 02 Sep 2009.

To cite this article: Davor Vrcibradic, Rogério L. Teixeira & Vitor N.T. Borges-Júnior (2009): Sexualdimorphism, reproduction and diet of the casque-headed treefrog Itapotihyla langsdorffii (Hylidae:Lophiohylini), Journal of Natural History, 43:35-36, 2245-2256

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Journal of Natural HistoryVol. 43, Nos. 35–36, September 2009, 2245–2256

ISSN 0022-2933 print/ISSN 1464-5262 online© 2009 Taylor & FrancisDOI: 10.1080/00222930903015824http://www.informaworld.com

TNAH0022-29331464-5262Journal of Natural History, Vol. 1, No. 1, May 2009: pp. 0–0Journal of Natural HistorySexual dimorphism, reproduction and diet of the casque-headed treefrog Itapotihyla langsdorffii (Hylidae: Lophiohylini)Journal of Natural HistoryD. Vrcibradic et al.Davor Vrcibradica*, Rogério L. Teixeirab and Vitor N.T. Borges-Júniora

aDepartamento de Ecologia, Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brazil; bMuseu de Biologia Prof. Mello Leitão, Santa Teresa, Brazil

(Received 12 November 2008; final version received 4 May 2009)

Itapotihyla langsdorffii is a large “casque-headed” treefrog (Hylidae: Lophio-hylini) found along most of the Brazilian Atlantic Forest biome. We studiedsome aspects of the ecology of a population of I. langsdorffii from the EstaçãoBiológica de Santa Lúcia, in Espírito Santo State, southeastern Brazil. Itapoti-hyla langsdorffii shows considerable sexual size dimorphism, with females (meansnout-vent length 103 mm) being significantly larger than males (mean snout-vent length 81 mm). This species is an explosive breeder with a generalized repro-ductive mode and has a mean brood size of over 6000 eggs. It feeds on few, largeprey, with orthopterans being the dominant items in the diet, though even smallerfrogs may occasionally be preyed upon. We discuss our data, making compari-sons with other Neotropical hylids, with emphasis on other species in the TribeLophiohylini.

Keywords: Lophiohylini; reproductive ecology; Atlantic Forest; feeding habits;sexual dimorphism

Introduction

The great species diversity of anuran amphibians is paralleled by their diversity ofecological characteristics such as reproductive and feeding strategies, most nota-bly in tropical areas (Duellman and Trueb 1994; Haddad and Prado 2005). Thereproductive and trophic biology of anuran amphibians tend to have a strongphylogenetic component (Parmelee 1999; Haddad and Prado 2005), but are alsoinfluenced to a large extent by other factors. For example, fecundity (Prado andHaddad 2005) and diet composition (Parmelee 1999) are strongly affected bybody size among anurans in general, independent of phylogeny. Autoecologicalstudies, when placed in a phylogenetic context, can aid in the understanding ofhow much of a given species’ ecology is related to phylogeny and how much isindependent of it.

Hylid frogs, with few exceptions, are primarily arboreal anurans (Faivovich et al.2005) and because of this are collectively known as treefrogs. Hylids are among themost speciose and geographically widespread of anuran lineages (Frost 2008), thoughtheir diversity is greatest by far in the Neotropics (Wiens et al. 2006), and they have arelatively wide range of body sizes (Duellman and Trueb 1994; Moen and Wiens2009). Within many Neotropical forest frog assemblages, hylids practically represent

*Corresponding author. Email: [email protected]

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a guild in themselves, as few members of other families (e.g. Centrolenidae, Hemi-phractidae) occupy the arboreal niche (Parmelee 1999).

Recent studies on phylogenetic relationships among hylid frogs using moleculardata (Faivovich et al. 2005; Wiens et al. 2005, 2006) have consistently recovered amonophyletic group of South American/West Indian “casque-headed” treefrogs andtheir allies (comprising mainly medium to large-sized taxa) plus the genus Phyllodytes(containing mainly small-sized species). This clade was recognized as the tribeLophiohylini by Faivovich et al. (2005) and currently contains 10 genera. Amongthose is the monotypic Itapotihyla, erected by Faivovich et al. (2005) to accommodatethe large-sized Osteocephalus langsdorffii, as their molecular analyses indicated that itwas not closely related to other species of Osteocephalus (later confirmed by Moenand Wiens 2009). Itapotihyla langsdorffii is a large treefrog found along most of theAtlantic Forest biome of eastern Brazil, ranging from the states of Sergipe to RioGrande do Sul, and also occurring in Paraguay and northeastern Argentina (Arzabeand Loebmann 2006; Lingnau et al. 2006; Frost 2008). Little has been published onthe biology and ecology of I. langsdorffii, with only a few data on reproductive activ-ity, habitat and microhabitat utilization (Toledo et al. 2003; Pombal and Gordo2004), and basking behaviour (Thomé et al. 2007) available in the literature. There iscurrently no information available on some aspects of the ecology of this species,such as diet composition, fecundity and degree of sexual dimorphism. In the presentstudy we assess some aspects of the ecology of I. langsdorffii, such as microhabitatuse, sexual size dimorphism, breeding ecology, and feeding habits, making compari-sons with other Neotropical hylids, with emphasis on other species in the tribeLophiohylini.

Material and methods

Fieldwork was carried out by one of us (R.L.T.) at the Estação Biológica de SantaLúcia (EBSL) (19°58′ S, 40°32′ W), in the Municipality of Santa Teresa, State ofEspírito Santo, southeastern Brazil. The EBSL comprises a fragment of montaneAtlantic Rainforest of approximately 440 ha, with altitudes varying from 550 to950 m (Mendes and Padovan 2000). Mean annual rainfall in the area is 1868 mm,with November being the rainiest month and June the driest (Mendes and Padovan2000). Mean annual temperature is 19.9°C, with the warmest period being January–February and the coolest being June–July (Thomaz and Monteiro 1997).

Data were gathered during monthly nocturnal visits to the study area (usuallythree nights per month, each visit lasting approximately 5 hours) from August 2002to July 2004. The study site was a semi-permanent pond located at the border of atrail inside the forest, surrounded by trees and bamboo. Thirty-seven individuals ofI. langsdorffii encountered during visits were collected.

Shortly after capture, the frogs were killed in a 50% alcohol solution and laterfixed in 10% formalin solution. All of them had their snout-vent length (SVL) meas-ured with digital callipers before being dissected for examination of their gonads andstomachs. Stomachs were removed and their contents were individually identifiedand their mass was measured on an electronic balance (precision of 0.001 g). Forreproductive females, ovaries were removed and the eggs were counted individually.

Differences between males and females in mean SVL were tested using one-wayanalyses of variance (ANOVA; Zar 1999). We tested the relationship between number

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of mature oocytes and female SVL using simple regression analysis, after testing bothvariables for homocedasticity of distribution (Zar 1999). Basic statistics given in thetext represent arithmetic means ± SD. Throughout the text, we follow the taxonomyof Faivovich et al. (2005) for hylid frogs.

Results

In total, 41 specimens of I. langsdorffii were recorded during fieldwork, of which 37were collected (the remaining four were measured in the field and released). Most ofthe animals were recorded between September and December 2002 (27) and betweenSeptember 2003 and January 2004 (13). Except for a single immature individual(38 mm SVL; not collected) from May 2003, no specimens of I. langsdorfii wererecorded in August 2002, nor between January and August 2003, nor from Februaryto July of 2004. Of 40 animals for which microhabitats were recorded, 36 (90%) wereon bamboo stems, two (5%) were on shrubs and two (5%) were on a tree trunk (thelatter being an amplectant pair). Mean height above ground was 1.97 ± 0.61 m (range0.5–3.2 m).

On 17 November 2003 an explosive aggregation of I. langsdorffii was witnessedby RLT during the morning (c. 1000 h) on a sunny day (no frogs were collected dur-ing this event). A total of 117 individuals (98 males and 19 females) was counted, butthis can be considered an approximation (there was constant movement amongmales, which made counting difficult). There was intense calling activity by themales, which could be heard about 50 m away. Several amplectant pairs were seen,and on five occasions females were being grasped by two males simultaneously.Some males were seen grabbing and pushing at each other, an apparent demonstra-tion of intrasexual aggression. Numerous eggs were seen in the water, with some ofthem lying exposed to the air, on the aquatic vegetation. This explosive aggregationlasted until the next day, as the intense vocalization could still be heard the follow-ing morning.

Among collected individuals of I. langsdorffii, males averaged 81.3 ± 5.1 mm (range71.4–92.1 mm; n = 26) and females averaged 102.7 ± 5.3 mm (range 92.0–112.1 mm; n =14) in SVL, with the size difference between sexes being highly significant (ANOVA:F1.38 = 152.64, p < 0.001). Eight females (98.1–110.4 mm SVL), collected inSeptember 2002 (three) and in September (one) and November (four) 2003, contained6607.6 ± 987.7 (range 5347–7953) mature oocytes in their ovaries. Mean clutch sizewas positively and significantly related to female SVL (r2 = 0.596; p < 0.05; n = 8).

Of 37 examined stomachs, 12 (32.4%) were empty. For stomachs containing iden-tifiable prey, mass of the largest prey item varied from 0.03 to 3.41 g (mean 0.449 ±0.785 g). Number of prey per stomach varied from 1 to 3 (mean 1.3 ± 0.6), with moststomachs (52%) containing a single prey item. Representatives of seven differentarthropod orders were found with grasshoppers and crickets (Orthoptera) being thedominant prey items in the diet (Table 1). The occurrence of vertebrates in the diet ofI. langsdorffii was recorded, with three anurans and the tail feathers of an unidenti-fied bird being found in stomachs. The anurans were one Physalaemus crombiei(Leiuperidae), one Scinax argyreornatus (Hylidae) and one unidentified hylid (theformer two were nearly intact, whereas the latter was much digested). Plant materialwas recorded in three stomachs and comprised about 9% of the total volume ingested(Table 1).

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Discussion

There is considerable sexual size dimorphism in I. langsdorffii (Figure 1). The female-to-male size ratio (FMR, being the female SVL divided by the male SVL; sensu Fitch,1981) in our sample, based on the mean and maximum sizes for each sex, was 1.26and 1.22, respectively. Values for other genera within Lophiohylini (based on litera-ture data) are usually above 1.10 and range up to 1.44 (considering the mean values)and to 1.60 (considering the maximum values), though for small species such as Oste-opilus wilderi and Phyllodytes spp. and one population of the large-sized Trachyceph-alus venulosus, values are close to one (Table 2). It therefore seems that lophiohylines,in general, tend to show strong sexual size dimorphism with females growing largerthan males. This characteristic may be plesiomorphic for anurans, with the derivedcondition (males larger than females) occurring mainly in taxa that have male–malecombat (Shine 1979). Nevertheless, the observation of fights among maleI. langsdorffii and other large-bodied lophiohylines such as Osteopilus septentrionalis(Vargas-Salinas 2006) indicates that the presence of male–male combat is not neces-sarily indicative of large male size in anurans (see Halliday and Verrell 1986).

Our results confirm that I. langsdorffii is an explosive breeder (sensu Wells 1977),with a generalized reproductive mode (mode 1 in Haddad and Prado 2005), and thatits reproductive period is concentrated between September and November. In otherareas where this species was studied in the State of São Paulo, calling activity wasrecorded only in the months of September–October (Pombal and Gordo 2004) andOctober–November (Toledo et al. 2003). Toledo et al. (2003) observed explosivereproduction in I. langsdorffii, with calling activity concentrated on one or a fewnights. In the present study, an explosive aggregation was observed in the month ofNovember, with calling and reproductive activity lasting for at least 24 hours.

Table 1. Number of items (N), total wet mass (M, in mg) and frequency ofoccurrence (F), with respective percentage values, for each food category in thediet of Itapotihyla langsdorffii (n = 37) at the Santa Lúcia Biological Reserve,southeastern Brazil.

Food categories N (%) M (%) F (%)

ArachnidsAraneae 5 (20.0) 847 (6.8) 5 (13.5)

InsectsBlattodea 3 (12.0) 302 (2.4) 3 (8.1)Coleoptera 1 (4.0) 315 (2.5) 1 (2.7)Homoptera 1 (4.0) 58 (0.5) 1 (2.7)Isoptera 2 (8.0) 40 (0.3) 1 (2.7)Lepidoptera (larva) 2 (4.0) 328 (2.6) 2 (5.4)Orthoptera 8 (32.0) 5437 (43.8) 8 (21.6)

VertebratesFrogs 3 (12.0) 2133 (17.2) 3 (8.1)Bird feathers – 416 (3.3) 1 (2.7)

Plant material – 1083 (8.7) 3 (8.1)Miscellaneous – 1441 (11.6) –

Total 25 12,400

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Figure 1. Amplectant pair of Itapotihyla langsdorffii at the Estação Biológica de Santa Lúcia,in the State of Espírito Santo, southeastern Brazil. Note the size difference between the maleand the female. Photo taken by W. Pertel.

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Explosive reproduction and a short breeding season are common traits among pond-breeding lophiohylines (Argenteohyla siemersii – Céspedez 2000; Osteocephalus lep-rieurii – Jungfer and Hödl 2002; O. taurinus – Duellman 2005; Trachycephalus meso-phaeus – Prado et al. 2003; T. coriaceus – Duellman 2005; T. venulosus, – Duellman2005; Rodrigues et al. 2005; Osteopilus septentrionalis – Vargas-Salinas 2006;I. langsdorffii – this study), but not among phytotelmonous-breeding taxa, whichtend to have prolonged/continuous reproduction (Nyctimantis rugiceps – Crump1974; Phyllodytes luteolus – Teixeira et al. 1997; Trachycephalus resinifictrix – Schiesariet al. 2003).

With a mean brood size of over 6000 eggs and a maximum of about 8000 eggs,I. langsdorffii appears to be generally more prolific than other lophiohylines of similarsize. Crump (1974) and Duellman (2005) give maximum clutch sizes of less than 2000eggs for some species of Amazonian Osteocephalus and Trachycephalus (= Phrynohyas).During a study on the Jamaican phytotelmonous-breeding species Osteopilus brun-neus, Lannoo et al. (1987) found a mean of only 276 (range 20–622) eggs per plant in18 examined bromeliads. Prado et al. (2003) reported clutches of 1831–3180 eggs forthe Atlantic forest species Trachycephalus mesophaeus and Schiesari et al. (2003)reported a mean clutch size of 436 eggs (range 106–1540) for Amazonian Trachyceph-alus resinifictrix based on six clutches laid in tree holes. All those values are low incomparison to the clutch size of I. langsdorffii. However, T. resinifictrix is known tolay as many as 4336 eggs in terraria (Jungfer and Proy 1998), and maximum clutchsizes of 4310 eggs (Prado and Haddad 2005) and 9794 eggs (Rodrigues et al. 2005)have been reported for T. venulosus in central Brazil. The Cuban treefrog Osteopilusseptentrionalis may be even more prolific, having been reported to lay up to 16,000eggs (Meshaka 2001). Hence, more data on fecundity of large-sized lophiohylines areneeded to assess whether the clutch size of I. langsdorffii reported in the present studyis exceptional or if it represents the norm.

The proportion of empty stomachs (32%) observed for I. langsdorffii in thepresent study was relatively low compared to those reported for some other hylidtaxa: e.g. 76% for Hypsiboas albopunctatus (Vaz-Silva et al. 2004a); 36–48% for Den-dropsophus nanus (Menin et al. 2005); 48–72% for D. sanborni (Menin et al. 2005);65% for Trachycephalus venulosus (Duré and Kehr 2006); 57% for Xenohyla truncata(Silva and Britto-Pereira 2006); > 50% for Hypsiboas faber, Dendropsophus nanus,Scinax granulatus and S. perereca (Solé and Pelz 2007). Hence, it seems that foodavailability for I. langsdorffii may not be limited at the study area. Nevertheless, thestomachs of this species usually contained a few (usually one) large prey. In a studyon the trophic ecology of an anuran assemblage from the Peruvian Amazon, Parme-lee (1999) observed that hylids tended to have a higher percentage of empty stomachsand to consume fewer and proportionally larger prey when compared to frogs ofother families. It is also noteworthy that I. langsdorffii does not seem to stop feedingduring the reproductive season, as do many anuran species (Woolbright and Stewart1987; Parmelee 1999; Solé and Pelz 2007).

Orthopterans were the most important items in the diet of I. langsdorffii at SantaLúcia. Data from Duellman (1978) and Parmelee (1999) also indicate that orthop-terans tend to constitute the primary prey item in the diets of medium and largeAmazonian hylids (particularly those in the genera Hypsiboas, Osteocephalus, Tra-chycephalus and Phyllomedusa). Because orthopterans tend to be relatively abun-dant and may attain relatively large sizes, they probably represent an energetically

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rewarding food source for most large hylids (Parmelee 1999). Large treefrogs suchas I. langsdorffii may feed selectively on large prey, which tend to be less abundantthan smaller prey. This may explain the low number of food items per stomach, aswell as the apparent absence of ants in its diet. Although ants are frequently (andoften substantially) consumed by many Neotropical taxa of terrestrial frogs of vari-ous sizes and from different families (see Duellman 1978; Strüssmann et al. 1984;Caldwell 1996; Howard et al. 1997; Parmelee 1999; Van Sluys et al. 2001; Marra etal. 2004; Santos et al. 2004; Siqueira et al. 2006; Berazategui et al. 2007), they seemto be unimportant in the diets of treefrogs in general (see Duellman 1978; Meshaka1996; Van Sluys and Rocha 1998; Parmelee 1999; Rosa et al. 2002; Maneyro andRosa 2004; Santos et al. 2004; Teixeira and Vrcibradic 2004; Vaz-Silva et al.2004a,b,c,d,e; Menin et al. 2005), with few exceptions: Sphaenorhynchus spp. (seeDuellman 1978; Parmelee 1999); Dendropsophus nanus (see Peltzer and Lajmanovich2000); Aparasphenodon brunoi (see Teixeira et al. 2002; Mesquita et al. 2004). Antsmay represent an abundant and clumped (when taken in their nests) food source forinsectivorous vertebrates (Pianka 1986). Parmelee (1999) suggested that hylids ingeneral may avoid ants for some reason, as those insects are not usually favoured asfood by those frogs, despite being available as prey at all levels of the forest, fromleaf-litter to canopy.

The occurrence of smaller anurans and bird feathers in the stomachs of I.langsdorffii indicates that this large treefrog occasionally preys on vertebrates.This is not surprising because it exceeds most sympatric anurans (see Rödder et al.2006 for a list of anuran species for the area) and a number of other small verte-brates in size. Large neotropical hylids may be “convenience predators” (sensuToledo et al. 2007) on smaller vertebrates: anurans have been recorded as prey ofHypsiboas faber (Solé et al. 2004) and Trachycephalus venulosus (Dundee andLiner 1985); Osteopilus septentrionalis has been recorded as a predator of frogs,lizards and small snakes (Meshaka 1996, 2001; Maskell and Waddle 2003;Campbell 2007); and predation upon bats has been reported for Trachycephalusvenulosus (as Phrynohyas hebes; Strüssman and Sazima 1991) and Hypsiboas boans(Arrington and Arrington 2000). Nevertheless, the proportion of vertebrate preyin the diet of I. langsdorffii was not substantial, as the four stomachs that con-tained vertebrate remains represent 11% of all stomachs examined and 16% ofstomachs with identifiable items (though the presence of bird feathers in the stom-ach of one individual is puzzling because no bone or skin remains were present).Although I. langsdorffii is an arboreal species, the presence of a terrestrial frog(Physalaemus crombiei) in one stomach indicates that it may sometimes descend tothe ground to feed.

Data from the present study elucidate some aspects of the ecology of I. langsdorf-fii, such as the occurrence of aggressive behaviour among males, the presence anddegree of sexual size dimorphism, the feeding habits, and the fecundity of females,that were previously unreported for this species. Itapotihyla langsdorffii is a sexuallydimorphic, large-clutched, explosively breeding species, as are many or most of theirclosest relatives among Hylidae. It also normally feeds on few prey of relatively largesize, as is common among treefrogs in general. Though the ecology of I. langsdorffiican be partly related to its phylogenetic relationships, much of it is simply a reflectionof the species’ large body size, which enables it to be both highly prolific and possiblya top predator within the local amphibian assemblage.

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Acknowledgements

A licence to collect the frogs was granted by the IBAMA (Process # 02009-000252/03) toR.L.T. We thank B.V.S. Pimenta for identifying the anurans found in the stomachs. J.J. Wiensand L.F. Toledo contributed valuable suggestions to this paper.

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