Small Tree Frog Research Articles

LACK OF SIZE-ASSORTATIVE MATING IN A WIDESPREAD TREEFROG: PSEUDACRIS CRUCIFER IN IOWA

The Spring Peeper (Pseudacris crucifer) is a small treefrog native to much of the Central and Eastern USA. Here, we tested if Spring Peepers exhibit size-assortative mating—non-random mate pairings based on body size—from a population in eastern Iowa. We captured 75 amplecting pairs of Spring Peepers during the 2021 breeding season, measured their body sizes, and marked them for future recognition. We found that while sexual-size dimorphism exists between males and females, there was no evidence for size-assortative mating among amplectant pairs. Our study contributes to other recent work indicating that size-assortative mating is rare among most anurans, and that previous findings of this phenomenon in frogs should be interpreted with caution.

Five new species of the pelodryadid genus Litoria Tschudi from the southern versant of Papua New Guinea’s Central Cordillera, with observations on the diversification of reproductive strategies in Melanesian treefrogs

New Guinea has the most diverse insular frog fauna in the world, and rates of species discovery and description have increased rapidly in the last two decades. Pelodryadid treefrogs are the second most diverse family of anurans on the island but their taxonomy, relationships, and especially ecology remain poorly documented. Based on differences in morphology, advertisement calls (where available) and phylogenetic analyses of a 787 base pair alignment from the mitochondrial ND4 gene and flanking tRNA, we describe five new species of small treefrogs from hill and lower montane forests in the high rainfall belt that straddles the southern versant of Papua New Guinea's Central Cordillera. Three of these species are known only from forest growing on karst substrates, adding to the growing number of herpetofauna species currently known only from the extensive karst habitats of Papua New Guinea's South-fold Mountains. We also describe the arboreal breeding strategies of two of the new species, and report obligate treehole (phytotelm) breeding in New Guinean frogs for the first time. The new phytotelm-breeding species has juveniles with colour and patterning that closely resemble bird droppings, suggesting defensive mimicry or masquerade. A preliminary phylogeny suggests that arboreal-breeding frogs do not form a monophyletic group and that arboreal breeding has evolved multiple times within the New Guinean pelodryadid radiation. A further striking feature of the phylogeny is poor support for most basal nodes in the most diverse radiation of Melanesian Pelodryadidae, suggesting rapid ecological diversification and speciation, potentially following colonisation from Australia and/or mountain uplift. These new taxa and observations highlight previously unrecognised ecological and reproductive diversity in the Melanesian Pelodryadidae.

A new species of Gracixalus (Anura, Rhacophoridae) from northwestern Vietnam.

A new species of small tree frog is described from northwestern Vietnam based on morphological differences and molecular divergence. Gracixalustruongisp. nov. is distinguishable from its congeners and other small rhacophorid species on the basis of a combination of the following characters: size relatively small, SVL 32.2-33.1 mm in males, 37.6-39.3 mm in females; head slightly wider than long; vomerine teeth absent; snout round and long RL/SVL 0.17-0.19 in males, 0.16-0.17 in females; spines on upper eyelid absent; supratympanic fold distinct; tympanum distinct; dorsal skin smooth; throat smooth and venter granular; tibiotarsal projection absent; webbing of fingers rudimentary, toes with moderately developed webbing; dorsum moss-green, with an inverse Y-shaped dark green marking extended from interorbital region to posterior region of dorsum; external vocal sac absent in males; males with a nuptial pad on finger I. In the molecular analyses, the new species has no clear sister taxon and is at least 4.5% divergent from other congeners based on a fragment of the mitochondrial 16S rRNA gene.

Network analysis reveals context-dependent structural complexity of social calls in serrate-legged small treefrogs.

Vocal communication plays an important role in survival, reproduction, and animal social association. Birds and mammals produce complex vocal sequence to convey context-dependent information. Vocalizations are conspicuous features of the behavior of most anuran species (frogs and toads), and males usually alter their calling strategies according to ecological context to improve the attractiveness/competitiveness. However, very few studies have focused on the variation of vocal sequence in anurans. In the present study, we used both conventional method and network analysis to investigate the context-dependent vocal repertoire, vocal sequence, and call network structure in serrate-legged small treefrogs Kurixalus odontotarsus. We found that male K. odontotarsus modified their vocal sequence by switching to different call types and increasing repertoire size in the presence of a competitive rival. Specifically, compared with before and after the playback of advertisement calls, males emitted fewer advertisement calls, but more aggressive calls, encounter calls, and compound calls during the playback period. Network analysis revealed that the mean degree, mean closeness, and mean betweenness of the call networks significantly decreased during the playback period, which resulted in lower connectivity. In addition, the increased proportion of one-way motifs and average path length also indicated that the connectivity of the call network decreased in competitive context. However, the vocal sequence of K. odontotarsus did not display a clear small-world network structure, regardless of context. Our study presents a paradigm to apply network analysis to vocal sequence in anurans and has important implications for understanding the evolution and function of sequence patterns.

Heterospecific eavesdropping on disturbance cues of a treefrog.

Alarm signals and cues are crucial to animal survival and vary greatly across species. Eavesdropping on heterospecific alarm signals and cues can provide eavesdroppers with information about potential threats. In addition to acoustic alarm signals, evidence has accumulated that chemical alarm cues and disturbance cues can also play a role in alerting conspecifics to potential danger in adult anurans (frogs and toads). However, there is very little known about whether disturbance cues are exploited by heterospecifics. In the present study, we conducted a binary choice experiment and a prey chemical discrimination experiment, respectively, to test the responses of a sympatric anuran species (red webbed treefrogs, Rhacophorus rhodopus) and a sympatric predator species (Chinese green tree vipers, Trimeresurus stejnegeri) to disturbance odors emitted by serrate-legged small treefrogs (Kurixalus odontotarsus). In the binary choice experiment, we found that the presence of disturbance odors did not significantly trigger the avoidance behavior of R. rhodopus. In the prey chemical discrimination experiment, compared with odors from undisturbed K. odontotarsus (control odors) and odorless control, T. stejnegeri showed a significantly higher tongue-flick rate in response to disturbance odors. This result implies that disturbance odor cues of K. odontotarsus can be exploited by eavesdropping predators to detect prey. Our study provides partial evidence for heterospecific eavesdropping on disturbance cues and has an important implication for understanding heterospecific eavesdropping on chemical cues of adult anurans.

Conspecific disturbance odors act as alarm cues to affect female mate choice in a treefrog

Mate choice in frogs depends heavily on acoustic communication, and females in many species possess an inherent preference for longer and/or more complex calls. Recently, it has become clear that conspecific chemical cues can also be useful in attracting potential mates in anuran species. However, how conspecific chemical cues influence mate choice decisions when paired with acoustic signals remains less clear. In the present study, we conducted three experiments to investigate whether and how male odor cues affect female choice decisions in the absence or presence of acoustic signals in serrate-legged small treefrogs (Kurixalus odontotarsus). We found that disturbance odors alone can trigger avoidance behavior of females, suggesting that the odors of disturbed K. odontotarsus can act as an alarm cue for conspecifics. Females also avoided disturbance odors in the presence of advertisement calls, except for calls with five notes. In addition, females preferred calls with two notes to calls with four notes when the latter was paired with disturbance odors. In contrast, female choice decisions were not affected by the odors of undisturbed males, either in the absence or the presence of advertisement calls. Our results indicate that disturbance odors can influence, or even reverse, mate choice by females for acoustic signals. In addition to acoustic signals, chemical cues can also be used in close-range communication in some anuran species. In the present study, we investigated how female Kurixalus odontotarsus use male chemical cues and/or acoustic signals during the mate choice process. We demonstrate that male disturbance odors can act as an alarm cue to trigger the avoidance behavior of females. Furthermore, this alarm cue can even reverse mate choice by females for acoustic signals. Our study highlights the importance of integrating multisensory signals and cues in mate choice decisions and has important implications for understanding chemical communication in anurans.

New distributional records of the Baibung Small Treefrog, Theloderma baibungense (Jiang, Fei, and Huang 2009) (Anura: Rhacophoridae), from Mizoram, India with comments on taxonomy, natural history and conservation status.

New distributional records of the Baibung Small Treefrog, Theloderma baibungense (Jiang, Fei, and Huang 2009) (Anura: Rhacophoridae), from Mizoram, India with comments on taxonomy, natural history and conservation status.

Rich but random: parasite communities of snouted treefrog, Scinax fuscovarius (Anura: Hylidae), in Bodoquena Mountains, western Brazil.

Hosts represent discrete habitats that contain finite parasite communities, and individual hosts can be used as replicates in parasitism studies, such as investigations of the processes that mediate the formation of parasite communities. However, within a single host population, there may be singularities among individuals that affect parasite contact rates. Accordingly, the goals of the present study were to document the parasites associated with the small treefrog Scinax fuscovarius, to verify possible variation and co-occurrences in parasite infracommunities, and to assess the effects of host characteristics (size and sex) on infracommunity structure. Treefrog specimens (n = 75) were collected from the Bodoquena Mountains in Mato Grosso do Sul, Brazil. After collection, the specimens were transported to the laboratory, and examined for parasitic. The parasites found were removed, fixed, and identified. Patterns in parasite infracommunity organization were analyzed using the checkerboard score index, which was calculated using a presence-absence matrix. The matrix was randomized under the null hypothesis that the infracommunities independently represent the component community. Forty-two (56%) of the individuals harbored at least one parasite, and a total of 500 metazoan parasites were recovered, with a particularly rich composite community of 18 taxa, including 13 nematodes, two trematodes, one cestode, one oligochaete, and one mite larvae. The parasite species were randomly distributed among the infracommunities, with no evidence of co-occurrence, segregation, or aggregation. However, both body size and sex influenced infection, with larger hosts harboring more parasites and parasites were more abundant in male specimens and more species rich in female specimens. These results suggest that the parasite infracommunities of S. fuscovarius are shaped by both random factors and individual host characteristics.

Conspecific odor cues induce different vocal responses in serrate-legged small treefrogs, but only in the absence of acoustic signals

BackgroundSignal detection is crucial to survival and successful reproduction, and animals often modify behavioral decisions based on information they obtained from the social context. Undeniably, the decision-making in male-male competition and female choice of anurans (frogs and toads) depends heavily on acoustic signals. However, increasing empirical evidence suggests that additional or alternative types of cue (e.g., visual, chemical, and vibratory) can be used to detect, discriminate and locate conspecifics in many anuran species. Nevertheless, few studies have investigated whether conspecific odor cues affect male’s calling behavior. In this study, we conducted an experiment to investigate whether and how different chemical cues (male odors, female odors, and stress odors) from conspecifics affect male’s calling strategies in serrate-legged small treefrogs (Kurixalus odontotarsus), and whether the combined chemical and acoustic stimuli have additive effects on calling behavior or not.ResultsWe found that compared with female odors, male K. odontotarsus reduced calling investment in response to male odors or stress odors, in the absence of rival’s advertisement calls. When odor stimuli and advertisement calls were presented simultaneously, however, there were no differences in the vocal response of focal males among odor groups.ConclusionsThese results provide evidence that male treefrogs switch calling investment according to different odor cues from conspecifics, and further demonstrate that calling behavior can be affected by chemical cues in anuran species. Our study highlights the potential role of airborne chemical cues in sex identification and contributes to increase our understanding of anuran communication.

Females and males respond differently to calls impaired by noise in a tree frog.

Both human and nonhuman animals communicating acoustically face the problem of noise interference, especially anurans during mating activities. Previous studies concentrated on the effect of continuous noise on signal recognition, but it is still unknown whether different notes in advertisement calls impaired by noise affect female choice and male–male competition or not. In this study, we tested female preferences and male‐evoked vocal responses in serrate‐legged small tree frog (Kurixalus odontotarsus), by broadcasting the five‐note advertisement call and the advertisement call with the second, third, or fourth note replaced by noise, respectively. In phonotaxis experiments, females significantly discriminated against the advertisement call with the fourth note impaired by noise, although they did not discriminate against other two calls impaired by noise, which indicates that the negative effect of noise on female preference is related to the order of impaired notes in the advertisement call. In playback experiments, males increased the total number of notes in response to noise‐impaired calls compared with spontaneous calls. More interestingly, the vocal responses evoked by noise‐impaired calls were generally similar to those evoked by complete advertisement calls, suggesting that males may recognize the noise‐impaired calls as complete advertisement calls. Taken together, our study shows that different notes in advertisement calls replaced by noise have distinct effects on female choice and male–male competition.

Buccopharyngeal morphology of the tadpoles of Scinax v-signatus/, with comments on larval characters of the S. perpusillus/ species group(Amphibia: Anura: Hylidae).

The Neotropical genus Scinax Wagler currently comprises 127 species of small treefrogs distributed from southern Mexico to Argentina and Uruguay, including some islands such as Trinidad and Tobago, and St. Lucia (Frost 2020). Two major clades are recognized within Scinax, the S. catharinae and the S. ruber clades. The former is composed of two species groups, the S. catharinae and the S. perpusillus groups (Faivovich 2002; Faivovich et al. 2005). The S. perpusillus species group currently comprises 13 species: S. alcatraz (Lutz); S. arduous Peixoto; S. atratus (Peixoto); S. belloni Faivovich, Gasparini Haddad; S. cosenzai Lacerda, Peixoto Feio; S. faivovichi Brasileiro, Oyamaguchi Haddad; S. insperatus Silva Alves-Silva; S. littoreus (Peixoto); S. melloi (Peixoto), S. peixotoi Brasileiro, Haddad, Sawaya Martins; S. perpusillus (Lutz Lutz); S. tupinamba Silva Alves-Silva; and S. v-signatus (Lutz). These species are endemic of the Brazilian Atlantic Forest and are recognized by their intimate association with bromeliads (Fig. 1), in which adults breed and lay their eggs, and tadpoles develop (Peixoto 1987, 1995; Alves-Silva Silva 2009).

Multisensory modalities increase working memory for mating signals in a treefrog.

Animal choruses, such as those found in insects and frogs, are often intermittent. Thus, females sampling males in the chorus might have to remember the location of the potential mates' calls during periods of silence. Although a number of studies have shown that frogs use and prefer multimodal mating signals, usually acoustic plus visual, it is not clear why they do so. Here we tested the hypothesis that preference for multimodal signals over unimodal signals might be due to multimodal signals instantiating longer memories than unimodal signals, particularly during the inter-chorus intervals. We tested this hypothesis in serrate-legged small treefrogs Kurixalus odontotarsus whose males produce advertisement calls accompanied by conspicuous vocal sac inflation. Females were tested with acoustic and acoustic+visual (video of inflating-deflating vocal sac) mating calls. We found that females prefer multimodal calls over unimodal, audio-only calls. Furthermore, multimodal calls are still preferred after a silent period of up to 30s, a time that spans the average silent period of the chorus. This was not true of unimodal calls. Our results demonstrate that a multimodal signal can engage longer working memory than a unimodal signal, and thus female memory might favour the evolution of multimodal signals in males through sexual selection. Selection might also favour female preference for multimodal signals if longer memory facilitates mate searching and assessment. Our study does not allow us to elucidate the sequence of evolution of this trait and preference.

From mainland to islands: colonization history in the tree frog Kurixalus (Anura: Rhacophoridae).

The origin and colonization history of Kurixalus, a genus of small arboreal tree frogs breeding exclusively in shallow swamps, is under disputed. On the basis of comprehensive sampling program, the evolutionary history of Kurixalus is investigated based on 3 mitochondrial genes. Our results indicate that the genus Kurixalus originated in the Asian mainland and subsequently arrived at its current distribution in Borneo, Taiwan, Ryukyu, and Hainan islands by a series of dispersal events. Moreover, the colonization of Taiwan from mainland Asia has occurred 2 times. The initial colonization of Taiwan occurred at 3.46–8.68 Mya (95% highest posterior density), which rejects the hypothesis that Kurixalus probably originated from Taiwan during the early Oligocene and favors the model of Neogene-origin rather than the model of Quaternary-origin for Taiwanese Kurixalus. Kurixalus eiffingeri has dispersed from Taiwan to the Ryukyus once or 2 times pending more data. Both transoceanic dispersal and landbridge dispersal have played a role in the colonization process; the former resulted in the colonization of Taiwan and the Ryukyus and the latter led to the colonization of Borneo and Hainan.

New records of the Near Threatened species <i>Ololygon trapicheiroi</i> (Anura: Hylidae)

Ololygon trapicheiroi is a small tree frog of the O. catharinae group which inhabits mountainous areas in the Atlantic Rainforest region of Southeastern Brazil. On 30 April 2017, in the area rural of the Municipality of Passa Vinte, State of Minas Gerais, Brazil, we observed several specimens of O. trapicheiroi. Here we report new records of O. trapicheiroi throughout Minas Gerais, Rio de Janeiro and São Paulo states, Brazil and provide a distribution map of the species.

Male serrate-legged treefrogs adjust competition strategies according to visual or chemical cues from females.

There is increasing evidence that many anurans use multimodal cues to detect, discriminate and/or locate conspecifics and thus modify their behaviors. To date, however, most studies have focused on the roles of multimodal cues in female choice or male-male interactions. In the present study, we conducted an experiment to investigate whether male serrate-legged small treefrogs (Kurixalus odontotarsus) used visual or chemical cues to detect females and thus altered their competition strategies in different calling contexts. Three acoustic stimuli (advertisement calls, aggressive calls and compound calls) were broadcast in a randomized order after a spontaneous period to focal males in one of four treatment groups: combined visual and chemical cues of a female, only chemical cues, only visual cues and a control (with no females). We recorded the vocal responses of the focal males during each 3 min period. Our results demonstrate that males reduce the total number of calls in response to the presence of females, regardless of how they perceived the females. In response to advertisement calls and compound calls, males that perceived females through chemical cues produced relatively fewer advertisement calls but more aggressive calls. In addition, they produced relatively more aggressive calls during the playback of aggressive calls. Taken together, our study suggests that male Kodontotarsus adjust their competition strategies according to the visual or chemical cues of potential mates and highlights the important role of multisensory cues in male frogs' perception of females.

Mate choice decisions of female serrate-legged small treefrogs are affected by ambient light under natural, but not enhanced artificial nocturnal light conditions

Artificial light at night (ALAN) is a widespread anthropogenic stimulus that can significantly alter nocturnal animals’ behavior, from migration to foraging to vocal communication. In the present study, we tested the hypothesis that the mate choice decisions of female serrate-legged small treefrogs (Kurixalus odontotarsus) were influenced by ambient light intensity. Standard two-speaker phonotaxis tests were conducted in a sound attenuating chamber. We set four light treatments (I-IV, from low to high) based on a range of light intensities from the maximum natural light at night (i.e., full moon) to that of the actual calling sites, which had artificial light. Contrary to our prediction, female frogs showed a preference for calls on the bright side in treatment I when they were exposed to identical stimuli. However, females preferred longer calls on the dim side to shorter calls on the bright side in this treatment. In addition, there were no significant effects of choice side, light treatment or their interaction on leave time or choice time. Our results suggest that females are more attracted to mates in bright light under natural nocturnal light conditions, but the preference for longer calls is not altered in serrate-legged small treefrogs.

Dwarf vs giant: An unexpected interaction between a small treefrog and a large nematode

Parasitism is one of the most common strategies of resource exploitation in the planet, and the body size of the interacting species is a key factor to understanding the ecology and evolution of this trophic strategy. Here we report for the first time an unexpected interaction between a large nematode species of Eustrongylides (162 mm) and an adult female of the dwarf treefrog Dendropsophus nanus (28 mm). Species of Eustrongylides have complex life cycles, and their transmission occurs through a series of trophic interactions. The first intermediate hosts are oligochaetes, which can be ingested by several species of fish and, occasionally, by amphibians and reptiles. The parasite cycle is completed when these hosts are preyed on by birds. Anurans fill an important trophic position in terrestrial and aquatic ecosystems, acting as prey and predators for a wide variety of invertebrates and vertebrates. In this sense, parasites are good indicators of food web links, and the occurrence of a parasite in a host may reflect interactions between the host and its prey and predators. One intriguing fact we observed is the large size achieved by the parasite in a such a small host, since larger parasites tend to be associated with larger hosts that provide more relaxed niche constraints. Our finding raises many questions on the frequency and outcomes of such interactions, pointing to the critical influence of parasite transmission in food webs.

First Record of Liuixalus feii Yang, Rao et Wang, 2015 (Anura: Rhacophoridae) from Vietnam and Taxonomic Assignment of L. jinxiuensis Li, Mo, Xie et Jiang, 2015

Liuixalus feii Yang, Rao et Wang, 2015, a small tree frog species recently described from Heishiding Nature Reserve, Fengkai County, Guangdong Province, Southern China, is recorded for the first time from Vietnam based on two specimens from Bac Giang Province. The newly collected specimens from Vietnam slightly differ from the type series from China in dorsal color pattern as well as by a low genetic divergence of 0.1% (16S rRNA fragment). In addition, our molecular analyses revealed L. jinxiuensis Li, Mo, Xie et Jiang, 2015 from Jinxiu, China to represent a junior synonym of L. feii .

A new species of the genus Theloderma Tschudi, 1838 (Amphibia: Anura: Rhacophoridae) from Tay Nguyen Plateau, central Vietnam.

A new species of small tree frog from a primary montane tropical forest of central Vietnam, Tay Nguyen Plateau, is described based on morphological, molecular, and acoustic evidence. The Golden Bug-Eyed Frog, Theloderma auratum sp. nov., is distinguishable from its congeners and other small rhacophorid species based on a combination of the following morphological attributes: (1) bony ridges on head absent; (2) smooth skin completely lacking calcified warts or asperities; (3) pointed elongated tapering snout; (4) vocal opening in males absent; (5) vomerine teeth absent; (6) males of small body size (SVL 21.8–26.4 mm); (7) head longer than wide; ED/SVL ratio 13%–15%; ESL/SVL ratio 16%–20%; (8) small tympanum (TD/EL ratio 50%–60%) with few tiny tubercles; (9) supratympanic fold absent; (10) ventral surfaces completely smooth; (11) webbing between fingers absent; (12) outer and inner metacarpal tubercles present, supernumerary metacarpal tubercle single, medial, oval in shape; (13) toes half-webbed: I 2–2¼ II 1½–2¾ III 2–3¼ IV 3–1½ V; (14) inner metatarsal tubercle present, oval; outer metatarsal tubercle absent; (15) iris bicolored; (16) dorsal surfaces golden-yellow with sparse golden-orange speckling or reticulations and few small dark-brown spots; (17) lateral sides of head and body with wide dark reddish-brown to black lateral stripes, clearly separated from lighter dorsal coloration by straight contrasting edge; (18) ventral surfaces of body, throat, and chest greyish-blue with indistinct brown confluent blotches; (19) upper eyelids with few (3–5) very small flat reddish superciliary tubercles; (20) limbs dorsally reddish-brown, ventrally brown with small bluish-white speckles. The new species is also distinct from all congeners in 12S rRNA to 16S rRNA mitochondrial DNA fragment sequences (uncorrected genetic distance P>8.9%). Advertisement call and tadpole morphology of the new species are described. Our molecular data showed Theloderma auratum sp. nov. to be a sister species of Th. palliatum from Langbian Plateau in southern Vietnam.

Male-male competition and female choice are differentially affected by male call acoustics in the serrate-legged small treefrog, Kurixalus odontotarsus.

BackgroundThe evolution of exaggerated vocal signals in anuran species is an important topic. Males and females have both evolved the ability to discriminate communication sounds. However, the nature of sexual dimorphism in cognition and sensory discrimination and in the evolution and limitation of sexual signal exaggeration remain relatively unexplored.MethodsIn the present study, we used male calls of varied complexity in the serrate-legged small treefrog, Kurixalus odontotarsus, as probes to investigate how both sexes respond to variations in call complexity and how sex differences in signal discrimination play a role in the evolution of sexual signal exaggeration. The compound calls of male K. odontotarsus consist of a series of one or more harmonic notes (A notes) which may be followed by one or more short broadband notes (B notes).ResultsMale playback experiments and female phonotaxis tests showed that increasing the number of A notes in stimulus calls elicits increased numbers of response calls by males and increases the attractiveness of the stimulus calls to females. The addition of B notes, however, reduces male calling responses. Moreover, call stimuli which contain only B notes suppress spontaneous male calling responses. Phonotaxis experiments show that females prefer calls with greater numbers of A notes and calls containing both A notes and B notes, but do not prefer calls with only B notes.DiscussionMale-male competition and female choice appear to have played different roles in the evolution and limitation of signal complexity in K. odontotarsus. These results provide new insights into how exaggerated compound signals evolve and how signal complexity may be limited in anurans.