Genomic adaptations for arboreal locomotion in Asian flying treefrogs.

SignificanceTo adapt to arboreal lifestyles, treefrogs have evolved a suite of complex traits that support vertical movement and gliding, thus presenting a unique case for studying the genetic basis for traits causally linked to vertical niche expansion. Here, based on two de novo-assembled Asian treefrog genomes, we determined that genes involved in limb development and keratin cytoskeleton likely played a role in the evolution of their climbing systems. Behavioral and morphological evaluation and time-ordered gene coexpression network analysis revealed the developmental patterns and regulatory pathways of the webbed feet used for gliding in Rhacophorus kio.

Experimental evaluation of how biological invasions and climate change interact to alter the vertical assembly of an amphibian community.

While biotic-abiotic interactions are increasingly documented in nature, a process-based understanding of how such interactions influence community assembly is lacking in the ecological literature. Perhaps the most emblematic and pervasive example of such interactions is the synergistic threat to biodiversity posed by climate change and invasive species. Invasive species often out-compete or prey on native species. Despite this long-standing and widespread issue, little is known about how abiotic conditions, such as climate change, will influence the frequency and severity of negative biotic interactions that threaten the persistence of native fauna. Treefrogs are a globally diverse group of amphibians that climb to complete life-cycle processes, such as foraging and reproduction, as well as to evade predators and competitors, resulting in frog communities that are vertically partitioned. Furthermore, treefrogs adjust their vertical position to maintain optimal body temperature and hydration in response to environmental change. Here, utilizing this model group, we designed a novel experiment to determine how extrinsic abiotic and biotic factors (changes to water availability and an introduced predator, respectively) interact with intrinsic biological traits, such as individual physiology and behaviour, to influence treefrogs' vertical niche. Our study found that treefrogs adjusted their vertical niche through displacement behaviours in accordance with abiotic resources. However, biotic interactions resulted in native treefrogs distancing themselves from abiotic resources to avoid the non-native species. Importantly, under altered abiotic conditions, both native species avoided the non-native species 33 %- 70 % more than they avoided their native counterpart. Additionally, exposure to the non-native species resulted in native species altering their tree climbing behaviours by 56 % - 78 % and becoming more vertically dynamic to avoid the non-native antagonist. Our experiment determined that vertical niche selection and community interactions were most accurately represented by a biotic-abiotic interaction model, rather than a model that considers these factors to operate in an isolated (singular) or even additive manner. Our study provides evidence that native species may be resilient to interacting disturbances via physiological adaptations to local climate and plasticity in space-use behaviours that mediate the impact of the introduced predator.

Genetic and phenotypic evidence of a contact zone between divergent colour morphs of the iconic red-eyed treefrog.

Hybrid zones act as natural laboratories where divergent genomes interact, providing powerful systems for examining the evolutionary processes underlying biological diversity. In this study, we characterized patterns of genomic and phenotypic variation resulting from hybridization between divergent intraspecific lineages of the Neotropical red-eyed treefrog (Agalychnis callidryas). We found genetic evidence of a newly discovered contact zone and phenotypic novelty in leg colour-a trait suspected to play a role in mediating assortative mating in this species. Analysis of hybrid ancestry revealed an abundance of later-generation Fn individuals, suggesting persistence of hybrids in the contact zone. Hybrids are predominantly of southern ancestry but are phenotypically more similar to northern populations. Genome-wide association mapping revealed QTL with measurable effects on leg-colour variation, but further work is required to dissect the architecture of this trait and establish causal links. Further, genomic cline analyses indicated substantial variation in patterns of introgression across the genome. Directional introgression of loci associated with different aspects of leg colour are inherited from each parental lineage, creating a distinct hybrid colour pattern. We show that hybridization can generate new phenotypes, revealing the evolutionary processes that potentially underlie patterns of phenotypic diversity in this iconic polytypic frog. Our study is consistent with a role of hybridization and sexual selection in lineage diversification, evolutionary processes that have been implicated in accelerating divergence in the most phenotypically diverse species.

Revisiting the evolution of the North American tetraploid treefrog (Hyla versicolor).

Hyla chrysoscelis and H. versicolor are common treefrogs in eastern North America and are a cryptic diploid-tetraploid species pair. They are morphologically identical but H. versicolor is a tetraploid. They can be identified acoustically by the male's advertisement mating call, which has a pulse repetition rate that has twice as many pulses per second in the diploid species, H. chrysoscelis. We used isozymes, microsatellite DNA alleles, and mitochondrial cytochrome b sequences to test the hypothesis that gene exchange occurs between the diploid and tetraploid species in sympatric populations. Each method provided results that are best explained by occasional hybridization of female H. versicolor and male H. chrysoscelis. We propose that H. versicolor first arose from an autotriploid H. chrysoscelis female that produced unreduced triploid eggs. After H. versicolor became established, genes could be passed from H. chrysoscelis to H. versicolor in sympatric populations when these species hybridize. Their F1 female progeny produce unreduced triploid eggs that are fertilized by haploid H. chrysoscelis sperm to reconstitute H. versicolor. Genes can be passed from diploid H. chrysoscelis to tetraploid H. versicolor in sympatric populations.

Collateral damage or a shadow of safety? The effects of signalling heterospecific neighbours on the risks of parasitism and predation.

Although males often display from mixed-species aggregations, the influence of nearby heterospecifics on risks associated with sexual signalling has not been previously examined. We tested whether predation and parasitism risks depend on proximity to heterospecific signallers. Using field playback experiments with calls of two species that often display from the same ponds, túngara frogs and hourglass treefrogs, we tested two hypotheses: (1) calling near heterospecific signallers attractive to eavesdroppers results in increased attention from predatory bats and parasitic midges (collateral damage hypothesis) or (2) calling near heterospecific signallers reduces an individual's predation and parasitism risks, as eavesdroppers are drawn to the heterospecifics (shadow of safety hypothesis). Bat visitation was not affected by calling neighbours. The number of frog-biting midges attracted to hourglass treefrog calls, however, rose threefold when played near túngara calls, supporting the collateral damage hypothesis. We thus show that proximity to heterospecific signallers can drastically alter both the absolute risks of signalling and the relative strengths of pressures from predation and parasitism. Through these mechanisms, interactions between heterospecific guild members are likely to influence the evolution of signalling strategies and the distribution of species at both local and larger scales.

Not so cryptic-differences between mating calls of Hyla arborea and Hyla orientalis from Bulgaria.

Anurans are among the most vocally active vertebrate animals and emit calls with different functions. In order to attract a mate, during the breeding season male frogs produce mating calls which have species-specific structure and parameters, and have been successfully used to resolve issues in taxonomy and phylogenetic relations. This is particularly useful when closely related taxa are concerned, as many species are morphologically almost identical, but still their status is well-supported by molecular and genetic data, suggesting the existence of mechanisms for reproductive isolation. Such is the case for treefrogs from the Hyla arborea group, which are now recognized as several distinct species. The present study aims to establish differences in call parameters between the European tree frog, Hyla arborea, and the Eastern tree frog, Hyla orientalis, which both occur on the territory of Bulgaria. Using autonomous audio loggers, calls from six sites (three in the range of H. arborea and three in the range of H. orientalis) were recorded between 7 p.m. and 12 a.m. during the breeding season in 2020-2023. The following parameters in a total of 390 mating calls were analyzed: call count, pulse count, call series duration, call period, peak (dominant) frequency, entropy. Results indicated that sites formed two distinct groups, which corresponded to the known distribution ranges of H. arborea and H. orientalis. The first two components of the PCA explained 71% of the total variance, with variables call count, call series duration, peak frequency and entropy being most important for differentiation between the sites. This study presents the first attempt to differentiate between the calls of these two sister taxa, which both fall within the "short-call treefrogs" group, and results are discussed in terms of known data for mating calls in Hyla sp., as well as limitations and future perspectives.

Genetic and morphometric analyses of historical type specimens clarify the taxonomy of the Ethiopian Leptopelisgramineus species complex (Anura, Arthroleptidae).

Frogs of the genus Leptopelis have diversified in the Ethiopian Highlands to occupy forests and montane grasslands both east and west of the Great Rift Valley. Genetic studies revealed that the endemic species Leptopelisgramineus (Boulenger, 1898) comprises multiple unnamed taxa. A careful examination of historical type specimens is, however, needed to fully resolve the taxonomy of the group. Here we use mitochondrial DNA and morphological analyses on a large sample of recently-collected Ethiopian Leptopelis, as well as century-old type specimens to demonstrate that the recently resurrected L.montanus Tiutenko & Zinenko, 2021 (previously Pseudocassinaocellata Ahl, 1924) is a junior synonym of L.rugosus (Ahl, 1924) and corresponds to the taxon found west of the Great Rift Valley, not east as previously thought. Our results show that populations inhabiting the mountains and plateaus east of the Rift constitute a distinct and undescribed species. We provide a re-description of L.rugosus and describe two new species inhabiting the Highlands east of the Great Rift Valley. We provide an identification key, as well as a description of the calls of the members of the Leptopelisgramineus species complex.

A rare new treefrog of the genus Sarcohyla (Anura: Hylidae) from Guerrero, Mexico.

Based on morphological data collected from treefrogs related to Sarcohyla hazelae, we describe a new species of the genus Sarcohyla from the cloud forest of the Sierra Madre del Sur of Guerrero, Mexico. We compare physical charactersitics of this new species to its closest relatives within the genus Sarcohyla, including dorsal and ventral coloration, head shape, tympanum distinctiveness, morphometrics and the condition of the tubercles on hands and feet. We analyze accoustic data from the advertisement call of males of the new species. We discuss the relationship of the species described herein with several of its cogeners, plus we resurrect the Sarcohyla hazelae group for these frogs. We describe habitat and distribution species related to Sarcohyla hazelae and also comment on the conservation priorities of these frogs.