Hyla Chrysoscelis Research Articles

Partitioning variance in a signaling trade-off under sexual selection reveals among-individual covariance in trait allocation.

Understanding the evolution of traits subject to trade-offs is challenging because phenotypes can (co)vary at both the among- and within-individual levels. Among-individual covariation indicates consistent, possibly genetic, differences in how individuals resolve the trade-off, while within-individual covariation indicates trait plasticity. There is also the potential for consistent among-individual differences in behavioral plasticity, although this has rarely been investigated. We studied the sources of (co)variance in two characteristics of an acoustic advertisement signal that trade-off with one another and are under sexual selection in the gray treefrog, Hyla chrysoscelis: call duration and call rate. We recorded males on multiple nights calling spontaneously and in response to playbacks simulating different competition levels. Call duration, call rate, and their product, call effort, were all repeatable both within and across social contexts. Call duration and call rate covaried negatively, and the largest covariance was at the among-individual level. There was extensive plasticity in calling with changes in social competition, and we found some evidence for among-individual variance in call rate plasticity. The significant negative among-individual covariance in trait values is perpendicular to the primary direction of sexual selection in this species, indicating potential limits on the response to selection.

In your CORT: Corticosterone and its receptors in the brain underlie mate choosiness in female Cope's gray treefrogs (Hyla chrysoscelis)

Selecting an attractive mate can involve trade-offs related to investment in sampling effort. Glucocorticoids like corticosterone (CORT) are involved in resolving energetic trade-offs. However, CORT is rarely studied in the context of mate choice, despite its elevated levels during reproductive readiness and the energetic transitions that characterize reproduction. Few systems are as well suited as anuran amphibians to evaluate how females resolve energetic trade-offs during mate choice. Phonotaxis tests provide a robust bioassay of mate choice that permit the precise measurement of inter-individual variation in traits such as choosiness–the willingness to pursue the most attractive mate despite costs. In Cope's gray treefrogs (Hyla chrysoscelis), females exhibit remarkable variation in circulating CORT as well as choosiness during mate choice, and a moderate dose of exogenous CORT rapidly (<1 h) and reliably induce large increases in choosiness. Here we measured the expression of glucocorticoid (GR) and mineralocorticoid (MR) receptors in the brains of females previously treated with exogenous CORT and tested for mate choosiness. We report a large decrease in GR expression in the hindbrain and midbrain of females that were treated with the moderate dosage of CORT–the same treatment group that exhibited a dramatic increase in choosiness following CORT treatment. This association, however, does not appear to be causal, as only forebrain GR levels, which are not affected by CORT injection, are positively associated with variation in choosiness. No strong effects were found for MR. We discuss these findings and suggest future studies to test the influence of glucocorticoids on mate choice.

The effect of biofluorescence on predation upon Cope’s gray treefrog: A clay model experiment

Biofluorescence, the ability to absorb light and reemit it at a longer wavelength, is present in many taxa but has been examined only recently in amphibians. Over half of the studies documenting biofluorescence in the last century suggest this fluorescent signal may affect predation; however, to date, only one other experimental study has tested this hypothesis. To address this question, we experimentally tested the effect of biofluorescence on predation through the study of the Cope’s Gray Treefrog, Hyla chrysoscelis. First, we quantified the spectral characteristics of a novel biofluorescence pattern in H. chrysoscelis. In both sexes of this species, the fluorescent signal is concentrated in an area that contains a proposed aposematic pattern to warn predators of the frog’s toxic secretions. We hypothesized that the biofluorescent trait may increase the conspicuousness of this pattern and enable the frogs to deter predators more effectively. Second, we tested this prediction by conducting a clay model field experiment to assess differences in predation attempts on fluorescent versus non-fluorescent H. chrysoscelis models by various predator types. We found no effect of biofluorescence on the overall presence, type, or location of predation, suggesting that biofluorescence alone does not act as an antipredator signal of H. chrysoscelis. This study represents one of the first attempts to experimentally test the effect of biofluorescence on predation in any organism and the first to do so in amphibians. Further work is needed to explore the role of this trait in predation in other systems and to investigate alternative functions for the biofluorescent signal in H. chrysoscelis.

Image Processing of Thigh Color Pattern Is an Effective Method for Identifying Individual Cope's Gray Treefrogs, Hyla chrysoscelis

Image Processing of Thigh Color Pattern Is an Effective Method for Identifying Individual Cope's Gray Treefrogs, Hyla chrysoscelis

Male Cope’s gray treefrogs (Hyla chrysoscelis) in amplexus have elevated and correlated steroid hormones compared to solitary males

Gonadal steroid hormones are typically elevated during the breeding season—a finding known as an associated reproductive pattern. Though less studied, there is also evidence, in both sexes, for elevated adrenal/interrenal steroids, including acute elevations on the day of mating. I investigated gonadal and interrenal steroids in wild male Cope’s gray treefrogs at breeding aggregations. I collected blood from males found in amplexus with female mates (amplexed males) and males sampled at the same time and location that were actively advertising vocally and without a mate (solo males). Concentrations of plasma corticosterone, testosterone, and 17β-estradiol (CORT, T and E2, respectively) were validated and measured. These two categories of males differed in four ways: (1) amplexed males exhibited significantly elevated concentrations of all three steroids compared to solo males (CORT: +347 %; T: +60 %; and E2: +43 %); (2) these hormone profiles alone accurately predicted male mating category with ca. 83 % accuracy using a discriminant function analysis; (3) amplexed males exhibited significant between-hormone correlations (T and E2 were positively correlated and CORT and E2 were negatively correlated) whereas no correlations were found in solo males; (4) amplexed males showed a negative correlation with CORT concentration and the time of night, whereas no such pattern was present in solo males. These findings suggest an acute and strong coactivation of the interrenal and gonadal axes that could drive phenotypic integration during this fitness-determining moment. I discuss these findings and suggest experiments to determine causation, including the role of motor behavior driving endocrine states and the role of female selection on endocrine profiles.

Biogeography and the evolution of acoustic communication in the polyploid North American grey treefrog complex.

After polyploid species are formed, interactions between diploid and polyploid lineages may generate additional diversity in novel cytotypes and phenotypes. In anurans, mate choice by acoustic communication is the primary method by which individuals identify their own species and assess suitable mates. As such, the evolution of acoustic signals is an important mechanism for contributing to reproductive isolation and diversification in this group. Here, we estimate the biogeographical history of the North American grey treefrog complex, consisting of the diploid Hyla chrysoscelis and the tetraploid Hyla versicolor, focusing specifically on the geographical origin of whole genome duplication and the expansion of lineages out of glacial refugia. We then test for lineage-specific differences in mating signals by applying comparative methods to a large acoustic data set collected over 52 years that includes >1500 individual frogs. Along with describing the overall biogeographical history and call diversity, we found evidence that the geographical origin of H. versicolor and the formation of the midwestern polyploid lineage are both associated with glacial limits, and that the southwestern polyploid lineage is associated with a shift in acoustic phenotype relative to the diploid lineage with which they share a mitochondrial lineage. In H. chrysoscelis, we see that acoustic signals are largely split by Eastern and Western lineages, but that northward expansion along either side of the Appalachian Mountains is associated with further acoustic diversification. Overall, results of this study provide substantial clarity on the evolution of grey treefrogs as it relates to their biogeography and acoustic communication.

Responses to saltwater exposure vary across species, populations and life stages in anuran amphibians.

To predict the impacts of environmental change on species, we must first understand the factors that limit the present-day ranges of species. Most anuran amphibians cannot survive at elevated salinities, which may drive their distribution in coastal locations. Previous research showed that coastal Hyla cinerea are locally adapted to brackish habitats in North Carolina, USA. Although Hyla squirella and Hyla chrysoscelis both inhabit coastal wetlands nearby, they have not been observed in saline habitats. We take advantage of naturally occurring microgeographic variation in coastal wetland occupancy exhibited by these congeneric tree frog species to explore how salt exposure affects oviposition site choice, hatching success, early tadpole survival, plasma osmolality and tadpole body condition across coastal and inland locations. We observed higher survival among coastal H. cinerea tadpoles than inland H. cinerea, which corroborates previous findings. But contrary to expectations, coastal H. cinerea had lower survival than H. squirella and H. chrysoscelis, indicating that all three species may be able to persist in saline wetlands. We also observed differences in tadpole plasma osmolality across species, locations and salinities, but these differences were not associated with survival rates in salt water. Instead, coastal occupancy may be affected by stage-specific processes like higher probability of total clutch loss as shown by inland H. chrysoscelis or maladaptive egg deposition patterns as shown by inland H. squirella. Although we expected salt water to be the primary filter driving species distributions along a coastal salinity gradient, it is likely that the factors dictating anuran ranges along the coast involve stage-, species- and location-specific processes that are mediated by ecological processes and life history traits.

Delayed Effects of Nutrients in the Larval Environment on Cope's Gray Treefrogs (Hyla chrysoscelis) Exposed to Batrachochytrium dendrobatidis

Excess nutrient runoff can profoundly alter aquatic habitats and has been associated with changes in host–pathogen interactions. Floating macrophyte mats have been suggested as a management strategy to improve water quality for aquatic communities and, thus, may have the potential to protect hosts from some disease outbreaks. We assessed the impact of ammonium nitrate and sodium phosphate addition in the presence or absence of floating macrophyte mats (blue flag iris [Iris versicolor] and ice dance sedge [Carex morrowii]) on Cope's Gray Treefrog (Hyla chrysoscelis) metamorphosis to examine whether macrophyte management treatments improve outcomes for amphibians. At metamorphosis, we infected individuals with the amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd), to assess whether larval treatments resulted in differential susceptibility to this pathogen. We found that nutrient addition significantly increased time to metamorphosis without affecting mass at metamorphosis or survival. Additionally, Bd exposure decreased mass of juvenile treefrogs, regardless of earlier larval environment or condition at metamorphosis. Macrophyte addition had no direct impact on larval anurans, but the aquatic community was altered via fluctuations in aquatic nutrient concentrations. Overall, our study suggests that nutrient exposure and Bd infection individually affect anurans, and larval exposure to nutrients may have latent effects on metamorphosed anurans that could affect future fitness.

Assessing the Impact of Chemical Algae Management Strategies on Anurans and Aquatic Communities.

Pond management with chemical and biological agents that reduce overgrowth of algae is an important means of maintaining water quality in residential ponds, yet the effects on nontarget species are not fully understood. We assessed the impact of Aquashade (a common nontoxic pond dye) and copper sulfate (a toxic algaecide) on American toad (Anaxyrus americanus), northern leopard frog (Lithobates pipiens), and Cope's gray treefrog (Hyla chrysoscelis) metamorphosis in outdoor mesocosm experiments. We also evaluated the relative impact of tadpole grazing versus chemical treatment on phytoplankton and periphyton abundance. We found no significant effects of pond management treatment on anuran metamorphosis, suggesting that addition of Aquashade and copper sulfate at tested concentrations does not significantly impact anurans under these experimental conditions. Interestingly, we found that the presence of tadpoles more strongly reduced algal abundance than Aquashade or copper sulfate by significantly decreasing phytoplankton and periphyton abundance over time. The present study suggests that anuran tadpoles may be effective at maintaining water quality, and that Aquashade and copper sulfate may have minimal effects on amphibian metamorphosis. Environ Toxicol Chem 2023;42:213-224. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Effects of Leaf Litter Species on Cope's Gray Treefrog Oviposition Site Selection

Leaf litter is an important input to a variety of freshwater ecosystems. The species of leaf litter affects water chemistry, ecosystem processes, and the survival and growth of aquatic organisms. Given the potential fitness consequences, it is likely that aquatic organisms have preferences for aquatic habitats with particular species of leaf litter input. To investigate this, we placed shallow experimental pools at a field-forest edge in northern Louisiana, USA as potential sites for Cope's Gray Treefrog (Hyla chrysoscelis) oviposition with leaf litter from one of 14 different tree species in each pool. Tree species included 13 native trees and one invasive species, Bradford Pear (Pyrus calleryana). We measured the concentrations of tannins and 12 elements in leaf tissue, along with water quality and water depth in the pools. We used an information-theoretic approach and created different models to determine what variables best predict the number of treefrog eggs laid in each pool and thus may serve as a cue for female treefrogs during oviposition site selection. We found that tree species treatment was by far the best predictor of the number of eggs Cope's Gray Treefrogs laid in the pools. Treefrogs laid more eggs in pools with Post Oak and Sweetgum leaves and fewer eggs in pools with Southern Red Oak and Southern Magnolia leaves. It is unclear how female treefrogs are able to differentiate among these tree species or what cue they are using to make their choices. Our results highlight the importance of tree species to aquatic community assembly.

Female preferences for the spectral content of advertisement calls in Cope's gray treefrog (Hyla chrysoscelis).

Amphibians have inner ears with two sensory papillae tuned to different frequency ranges of airborne sounds. In frogs, male advertisement calls possess distinct spectral components that match the tuning of one or both sensory papillae. Female preferences for the spectral content of advertisement calls can depend on signal amplitude and can vary among closely related lineages. In this study of Cope's gray tree frog (Hyla chrysoscelis), we investigated the amplitude dependence of female preferences for the spectral content of male advertisement calls, which have a "bimodal" spectrum with separate low-frequency (1.25kHz) and high-frequency (2.5kHz) components. In two-alternative choice tests, females generally preferred synthetic calls with bimodal spectra over "unimodal" calls having only one of the two spectral components. They also preferred unimodal calls with a high-frequency component over one with the low-frequency component. With few exceptions, preferences were largely independent of amplitude across both a 30dB range of overall signal amplitude and an 11dB range in the relative amplitudes of the two spectral components. We discuss these results in the context of evolutionary lability in female preferences for the spectral content of advertisement calls in North American tree frogs in the genus Hyla.

Sensory biases in response to novel complex acoustic signals in male and female grey treefrogs, Hyla chrysoscelis.

The sensory bias hypothesis proposes that female preferences for male sexual signalling traits evolved in contexts other than mating. Individuals of both sexes may experience similar selection pressures in these contexts; thus males may have similar biases to females for variation in signal traits. We tested this prediction in the grey treefrog, Hyla chrysoscelis, in which males produce simple advertisement calls, but females are more attracted to certain novel complex stimuli. We recorded males' responses to playbacks of both simple advertisement calls and complex calls consisting of the advertisement call with an acoustic appendage (filtered noise, or heterospecific call pulses) either leading or following the call. We tested females' preferences for the same stimuli in phonotaxis tests. We found evidence for a sensory bias in both sexes: males gave more aggressive calls in response to complex stimuli and females sometimes preferred complex over simple calls. These biases were not universal and depended on both temporal order and appendage characteristics, but how these effects manifested differed between the sexes. Ultimately, our approach of studying biases of both sexes in response to novel mating signals will shed light on the origin of mating preferences, and the mechanisms by which sensory biases operate.

Vocal sacs do not function in multimodal mate attraction under nocturnal illumination in Cope's grey treefrog

Multimodal communication signals consist of two or more distinct components produced in different sensory modalities and transduced by receivers using multiple sensory systems. One evolutionary trajectory by which incipient multimodal signals may arise is when receivers are selected to attend both to a well-established signal and a cue in a different sensory modality associated with that signal's production. Previous studies of frogs suggest movement of the male's vocal sac, which is inextricably tied to vocal production in most species, functions as the dynamic visual component of a multimodal mate attraction signal that modulates female responses to sexually advertising males. Most of this work, however, has presented multimodal stimuli using video playbacks or artificially illuminated robots in laboratory settings, which leaves open the question of whether the vocal sac functions in multimodal signalling under more natural nocturnal illumination. In this study of Cope's grey treefrog, Hyla chrysoscelis , a nocturnally breeding species, we tested the hypothesis that vocal sacs are a dynamic visual component of a multimodal mate attraction signal that influences female responses to sexually advertising males. Using robotic frogs as stimuli, we performed multimodal playback experiments outdoors under nocturnal illumination. We found no evidence that vocal sacs were attractive to females or that they influenced the responses of females when acoustic information was rendered less certain due to a degraded signal structure or background noise. While these negative results may reflect genuine species differences, they also corroborate a negative result from one of the only previous studies conducted under natural nocturnal illumination to investigate frog vocal sacs as the visual component of a putative multimodal mate attraction signal (Taylor et al., 2007, Animal Behaviour, 74 , 1753–1763). We consider possible proximate and ultimate explanations for our results and critically review previous research on multimodal mate attraction in nocturnal frogs. • Multimodal signals stimulate multiple receiver sensory organs. • Diverse animals use multimodal signals in many contexts, including mate choice. • Frog vocal sacs previously implicated as components of multimodal sexual signals. • Robotic playbacks under natural, nocturnal illumination suggest otherwise. • Current methods may mismeasure multimodal mate choice in nocturnal animals.

A wolf in sheep's clothing: Predatory fish have convergent consumptive effects but divergent predation‐risk effects

AbstractAlthough consumptive effects of predators have long been central to ecology, predation‐risk effects have emerged as major components of predator–prey interactions. Both consumptive and predation‐risk effects should vary with predator functional traits (e.g., hunting mode, gape size), where consumption rates and induction of morphological and behavioral defenses correlate with prey‐specific predator threat. Ambush predators, in contrast with active predators, may face selection pressure to be cryptic to avoid detection by prey. Thus, ambush predators may change prey density through consumptive effects but have reduced or absent predation‐risk effects. We performed two mesocosm experiments with free‐roaming and caged predators to explore post‐colonization interactions of the chemically camouflaged, large‐gaped, ambush predator, pirate perch (Aphredoderus sayanus), active, large‐gaped green sunfish (Lepomis cyanellus), and active, small‐gaped golden topminnow (Fundulus chrysotus), with larval gray treefrogs (Hyla chrysoscelis) and mole salamanders (Ambystoma talpoideum). We examined the consumptive and predation‐risk effects of each predator on amphibian mortality, growth rates, tail morphology, and polyphenisms. Large‐gaped pirate perch and green sunfish had strong, equivalent consumptive effects, but only the free‐roaming active predator, green sunfish, suppressed the growth of survivors through risk‐induced trait responses. Caged green sunfish induced much stronger non‐consumptive mortality than pirate perch in gray treefrogs, an effect that was absent for mole salamanders; golden topminnows had intermediate effects. Tail defenses were a function of prey mortality and only manifested in free‐roaming predator treatments, suggesting the necessity of predator attacks or conspecific alarm signals. Likewise, mole salamander polyphenism was unaffected by caged predators, whereas free‐roaming green sunfish prevented all metamorphosis. Free‐roaming golden topminnows increased the proportion of individuals remaining as larvae, and pirate perch increased the proportion of paedomorphs and metamorphs. Overall, the prey had positively correlated anti‐predator responses across life stages, suggesting multicomponent defenses. Predator effects varied with functional traits with large‐gaped predators having strong consumptive effects, but active predators causing stronger risk‐induced changes in growth compared to cryptic ambush predators, which provides more evidence for chemical camouflage. Our results emphasize the role of hunting mode and gape size in determining consumptive and predation‐risk effects, and that predation‐risk effects cannot be reliably predicted from consumptive effects.

Interval-counting neurons allow gray treefrogs to make the right choice

At the right time of year across the eastern USA, from Texas to Maine, wetlands come alive with the sound of trilling eastern gray treefrogs (Hyla versicolor), each hoping to attract the attention of a nearby female. However, male eastern gray treefrogs are not the only vociferous suitors in the neighbourhood; they share their wetland breeding grounds with another close relative, Cope's gray treefrogs (Hyla chrysoscelis). ‘The two species are visually indistinguishable’, says Saumya Gupta from the University of Minnesota, USA. Yet, the consequences of a Cope's gray treefrog inadvertently selecting an eastern gray treefrog partner would be disastrous; their offspring rarely survive and, if they do, they are infertile. Fortunately, eastern and Cope's gray treefrogs barely make this rookie mistake, thanks to their trilling croaks. Even though the trill structures of their amorous calls are similar, they are sufficiently different – eastern gray treefrogs trill a little more slowly than their Cope's cousins – for females to avoid selecting the wrong mate. Yet, no one was sure exactly how these closely related species distinguish between each other's trills. However, Gupta and Mark Bee (University of Minnesota) had a hunch. They knew that a unique set of neurons in frog brains – called interval-counting neurons – are often tuned to the trill rate of their own species’ calls. Could these neurons hold the key to female eastern gray treefrogs rebuffing Cope's gray treefrog serenades and vice versa?Collecting female gray treefrogs in amorous embraces with their male partners from the Tamarack Nature Center in Minnesota, USA, Gupta first had to identify which species each frog belonged to. ‘I played mating calls of the eastern and Cope's gray treefrogs from two separate loudspeakers and identified the species based on which speaker it approached’, she says. Next, Gupta simulated a series of gray treefrog trills composed of individual pulses – 10 ms pulses, 20 ms apart for the Cope's gray treefrogs and 30 ms pulses separated by 60 ms for the eastern gray treefrogs. After recreating the distinctive pulse signatures of both species, she played a range of trills to the females, from a single pulse up to 16 repetitions, recording the number of pulses when the female's attention switched from indifference to attraction as she hopped toward the loudspeaker.Comparing the females’ reactions, it was clear that the Cope's gray treefrogs tended to become interested in trills composed of ∼8, 10 ms pulses when the calls were softer (65 dB SPL) while trills of ∼7.5 pulses became attractive when louder (85 dB SPL). In contrast, the eastern gray treefrog females only required ∼5, 30 ms pulses to get their attention, falling to 3.5 pulses when the volume was higher. But how would the interval-counting neurons in the treefrog brain respond to each species-specific serenade?This time, Rishi Alluri and Gary Rose from the University of Utah, USA, played simulated trills with increasing numbers of pulses to the frogs while painstakingly recording when interval-counting neurons in the frog brain began sending electrical nerve signals. Eventually, the duo identified a subset of neurons in the Cope's gray treefrog brain tuned to fire when they heard trills of at least 6–8, 10 ms pulses. Meanwhile, the eastern gray treefrogs’ interval-counting neurons responded strongly when the frogs heard trills containing at least 3–5, 30 ms pulses.‘Interval-counting neurons play key roles in decoding information about species identity in frogs’, says Gupta, placing the neurons at the hub of the mechanism protecting eastern and Cope's gray treefrogs from interbreeding, keeping them faithful to their own species’ serenades.

Neural basis of acoustic species recognition in a cryptic species complex.

Sexual traits that promote species recognition are important drivers of reproductive isolation, especially among closely related species. Identifying neural processes that shape species differences in recognition is crucial for understanding the causal mechanisms of reproductive isolation. Temporal patterns are salient features of sexual signals that are widely used in species recognition by several taxa, including anurans. Recent advances in our understanding of temporal processing by the anuran auditory system provide an opportunity to investigate the neural basis of species-specific recognition. The anuran inferior colliculus consists of neurons that are selective for temporal features of calls. Of potential relevance are auditory neurons known as interval-counting neurons (ICNs) that are often selective for the pulse rate of conspecific advertisement calls. Here, we tested the hypothesis that ICNs mediate acoustic species recognition by exploiting the known differences in temporal selectivity in two cryptic species of gray treefrog (Hyla chrysoscelis and Hyla versicolor). We examined the extent to which the threshold number of pulses required to elicit behavioral responses from females and neural responses from ICNs was similar within each species but potentially different between the two species. In support of our hypothesis, we found that a species difference in behavioral pulse number thresholds closely matched the species difference in neural pulse number thresholds. However, this relationship held only for ICNs that exhibited band-pass tuning for conspecific pulse rates. Together, these findings suggest that differences in temporal processing of a subset of ICNs provide a mechanistic explanation for reproductive isolation between two cryptic treefrog species.

Anuran Vocal Communication: Effects of Genome Size, Cell Number and Cell Size

Significant variation in genome size occurs among anuran amphibians and can affect cell size and number. In the gray treefrog complex in North America, increases in cell size in autotriploids of the diploid (Hyla chrysoscelis) altered the temporal structure of mate-attracting vocalizations and auditory selectivity for these properties. Here, we show that the tetraploid species (Hyla versicolor) also has significantly fewer brain neurons than H. chrysoscelis. With regard to cell size in tissues involved in vocal communication, spinal motor neurons were larger in tetraploids than in diploids and comparable to differences in erythrocyte size; smaller increases were found in one of the three auditory centers in the torus semicircularis. Future studies should address questions about how environmental conditions during development affect cell numbers and size and the causal relationships between these cellular changes and the vocal communication system.

Patch size drives colonization by aquatic insects, with minor priority effects of a cohabitant.

Patch size is one of the most important factors affecting the distribution and abundance of species, and recent research has shown that patch size is an important niche dimension affecting community structure in aquatic insects. Building on this result, we examined the impact of patch size in conjunction with presence of larval anurans on colonization by aquatic insects. Hyla chrysoscelis (Cope's gray treefrog) larvae are abundant and early colonists in fishless lentic habitats, and these larvae can fill multiple ecological roles. By establishing larvae in mesocosms prior to colonization, we were able to assess whether H. chrysoscelis larvae have priority effects on aquatic insect assemblages. We conducted a series of three experiments in naturally colonized experimental landscapes to test whether (1) H. chrysoscelis larval density affects insect colonization, (2) variation in patch size affects insect colonization, and (3) the presence and larval density of H. chrysoscelis shift colonization of insects between patches of different size. Larval density independently had almost no effect on colonization, while patch size had species‐specific effects consistent with prior work. When larvae and patch size were tested in conjunction, patch size had numerous, often strong, species‐specific effects on colonization; larval density had effects largely limited to the assemblages of colonizing beetles and water bugs, with few effects on individual species. Higher larval densities in large mesocosms shifted some insect colonization to smaller patches, resulting in higher beta diversity among small patches in proximity to high density large mesocosms. This indicates establishing H. chrysoscelis larvae prior to insect colonization can likely create priority effects that slightly shape insect communities. Our results support the importance of patch size in studying species abundances and distributions and also indicate that colonization order plays an important role in determining the communities found within habitat patches.

The Complex History of Genome Duplication and Hybridization in North American Gray Treefrogs.

Polyploid speciation has played an important role in evolutionary history across the tree of life, yet there remain large gaps in our understanding of how polyploid species form and persist. Although systematic studies have been conducted in numerous polyploid complexes, recent advances in sequencing technology have demonstrated that conclusions from data-limited studies may be spurious and misleading. The North American gray treefrog complex, consisting of the diploid Hyla chrysoscelis and the tetraploid H. versicolor, has long been used as a model system in a variety of biological fields, yet all taxonomic studies to date were conducted with only a few loci from nuclear and mitochondrial genomes. Here, we utilized anchored hybrid enrichment and high-throughput sequencing to capture hundreds of loci along with whole mitochondrial genomes to investigate the evolutionary history of this complex. We used several phylogenetic and population genetic methods, including coalescent simulations and testing of polyploid speciation models with approximate Bayesian computation, to determine that H. versicolor was most likely formed via autopolyploidization from a now extinct lineage of H. chrysoscelis. We also uncovered evidence of significant hybridization between diploids and tetraploids where they co-occur, and show that historical hybridization between these groups led to the re-formation of distinct polyploid lineages following the initial whole-genome duplication event. Our study indicates that a wide variety of methods and explicit model testing of polyploid histories can greatly facilitate efforts to uncover the evolutionary history of polyploid complexes.

Arginine vasotocin affects motivation to call, but not calling plasticity, in Cope's gray treefrog Hyla chrysoscelis.

The ability to respond to competition is critical for social behaviors involved in mating, territoriality and foraging. Physiological mechanisms of competitive social behaviors may determine not only baseline behavior, but possibly also the plasticity of the response to competition. We examined the effects of the neuropeptide arginine vasotocin (AVT), which is implicated in social behavior in non-mammalian vertebrates, on both spontaneous acoustic advertisement calling behavior and the plastic response to a simulated competitive challenge in Cope's gray treefrogs, Hyla chrysoscelis. We injected males either with AVT or a saline control and then analyzed recordings of spontaneous calling prior to playback, playback of average advertisement calls, playback of highly competitive advertisement calls, and spontaneous calling after playback. We found a tendency for AVT-treated males to be more likely to resume calling, and AVT males had higher call rates than control males, although they did not differ in pulse number or call effort. There were no differences between the AVT and control treatments in the plasticity of calling behavior in response to simulated competitors. Our results generally align with other studies on how AVT affects anuran vocalizations, and suggest that its primary effect is on motivation to call, with less of an effect on plasticity in response to competition. Nevertheless, these effects on call motivation are significant, because mating success is often determined more by participation in the chorus than by the values of specific call characteristics.