Natural History of Model Organisms: The big potential of the small frog Eleutherodactylus coqui

The Puerto Rican coquí frog Eleutherodactylus coqui (E. coqui) is both a cultural icon and a species with an unusual natural history that has attracted attention from researchers in a number of different fields within biology. Unlike most frogs, the coquí frog skips the tadpole stage, which makes it of interest to developmental biologists. The frog is best known in Puerto Rico for its notoriously loud mating call, which has allowed researchers to study aspects of social behavior such as vocal communication and courtship, while the ability of coquí to colonize new habitats has been used to explore the biology of invasive species. This article reviews research on the natural history of E. coqui and opportunities for future research.

Seen only once: an evolutionarily distinct species of Toadlet (Uperoleia: Myobatrachidae) from the Wessel Islands of northern Australia

There is a high rate of recent species discovery in remote regions of northern Australia, especially for amphibians and reptiles. The Wessel Islands, located in the northeastern corner of the Northern Territory, has recently been identified as a region of high species and phylogenetic endemism based on samples collected during the sole reptile and amphibian survey there in 1993. Using a phylogenetic approach, we describe a new, evolutionarily distinct species of Uperoleia endemic to the Wessel Islands. This description is based on three specimens, one female and two juveniles, which represent the only confirmed vouchers of the species. Due to the low number of specimens, this new species cannot be diagnosed morphologically from other closely related Uperoleia, and nothing is currently known about the mating call or basic biology. The discovery of this species provides further evidence for the islands’ importance as an area of endemism and identifies an urgent need for further surveys to document the unique biological diversity of the Wessel Islands.

Not only a listener: female frog-biting midges (Corethrellidae) also distinguish the shape of frogs

It is well known that female adults of frog-biting midges (Corethrellidae) are attracted by anuran mating calls. However, the role of host-emitted cues other than mating calls in determining the level of attraction remains poorly understood. Here, we performed field playback experiments to test how the host-seeking behaviour of Corethrella Coquillett is influenced by different sound stimuli: mating call of a tree frog, cricket call, and no sound. Then, after long-distance host detection, we evaluated if Corethrella can distinguish landing sites by using at short distance the colour and/or shape of anurans. For that, we placed artificial models of frogs with different colours (light green and dark brown) and an artificial caterpillar model (light green colour) on the top of speakers. We found that only frog mating calls presented with the visual cue of an artificial frog were attacked by Corethrella, suggesting that frog shape, regardless of colour, is an important cue for the identification of its hosts. This is the first study providing evidence that after flying long distances guided by frog calls, Corethrella can identify their hosts using visual cues at short distances.

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.

Effect of temperature on life-history traits and mating calls of a field cricket, Acanthogryllus asiaticus

Ectotherms are sensitive to the changes in ambient temperature with respect to their physiology and development. To compensate for the effects of variation in temperature, ectotherms exhibit physiological plasticity which can be for short or long term. An extensive body of literature exists towards understanding these effects and the solutions ectotherms have evolved. However, to what extent rearing temperature during early life stages impacts the behaviour expressed in adulthood is less clearly understood. In the present study, we aimed to examine the effect of developmental temperature on life-history traits and mating call features in a tropical field cricket, Acanthogryllus asiaticus. We raised A. asiaticus at two different developmental conditions: 25°C and 30°C. We found developmental time and adult lifespan of individuals reared at 30°C to be shorter than those at 25°C. Increased developmental temperature influenced various body size parameters differentially. Males raised at 30°C were found to be larger and heavier than those raised at 25°C, making A. asiaticus an exception to the temperature-size rule. We found a significant effect of the change in immediate ambient temperature on different call features of both field-caught and lab-bred individuals. In addition, developmental temperature also affected mating call features as individuals raised at higher temperature produced faster calls with a higher peak frequency compared to those raised at lower temperature. However, the interaction of both developmental and immediate temperature on mating calls showed differential effects. Our study highlights the importance of understanding how environmental temperature shapes life-history and sexual communication in crickets.

High and dry: Trade-off in arboreal calling in a treefrog mediated by local environment

Trade-offs shaping behavioral variation are often influenced by the environment. We investigated the role that the environment plays in mediating trade-offs using a widespread frog with a conspicuous mating display, Pseudacris crucifer. We first demonstrated, using playback and desiccation experiments, that calling site selection involves a trade-off between sound transmission and desiccation. We then determined the influence of local environmental conditions on the intensity of the trade-off by examining range-wide behavioral and environmental data. We showed that the benefit of improved call transmission is positively influenced by vegetation density and ground cover. Behavioral data are consistent with this relationship: sites with a greater transmission benefit have increased prevalence of arboreally calling males. We also found that the prevalence of arboreal calling behavior increases with relative humidity and air temperature, suggesting an influence of these environmental variables on the desiccation cost of arboreal calling. This study provides a clear example of the role of the environment in mediating trade-off intensities and shaping critical behavioral traits. Local environment mediates the intensity of a trade-off associated with arboreal calling behavior in a treefrog. Combining observational and experimental approaches, we show that arboreal calling behavior increases the transmission of a mating call while potentially subjecting individuals to a rate of desiccation six times greater than terrestrial calling. Local environmental conditions influence both the benefit and the cost of this trade-off, subjecting different populations to varying trade-off intensities and shaping arboreal calling behavior.

The Mating Call of the Terrestrial Toad, Rhinella arenarum, as a Cue for Spatial Orientation and Its Associated Brain Activity

Acoustic communication is essential for reproduction and predator avoidance in many anuran species. For example, mating calls are generally produced by males and represent a conspicuous communication signal employed during the breeding season. Although anuran mating calls have been largely studied to analyze content and phonotaxis toward choruses, they are rarely discussed as sources of information guiding spatial behavior in broader contexts. This is striking if we consider that previous studies have shown anurans to be impressive navigators. In the current study, we investigated whether terrestrial toad (Rhinella arenarum) males can use a mating call as a spatial cue to locate a water reward in a laboratory maze. Male toads could indeed learn the location of a reward guided by a mating call. This navigational ability, as indicated by c-Fos, was associated with greater neuronal activity in the telencephalic hippocampal formation (HF; also referred to in amphibians as medial pallium), the medial septum (MS), and the central amygdala (CeA). HF and MS are telencephalic structures associated with spatial navigation in mammals and other vertebrates. The CeA, by contrast, has been studied in the context of acoustic processing and communication in other amphibian species. The results are discussed in the framework of an evolutionary conserved, HF-septal spatial-cognitive network shared by amphibians and mammals.

Redescription, distribution and mating call of Pristimantis colomai (Lynch and Duellman, 1997) (Anura, Craugastoridae)

We redescribe Pristimantis colomai (Lynch & Duellman, 1997) on the basis of new specimens from Colombia and Ecuador. Also provide a new diagnosis, reassess its distribution, and describe the mating call for the first time. Besides the data in the original description, only is available for this species: (i) new records from Ecuador (Yánez-Muñoz et al. 2011) and (ii) molecular phylogenetic inferences that place this species in the Pristimantis ridens series (Hedges et al. 2008; Padial et al. 2014). Pristimantis colomai is currently classified as endangered due to its restrict distribution and habitat quality (Castro et al. 2004).