Dendropsophus Ebraccatus Research Articles

Correction to: Effects of multiple-speaker playbacks on aggressive calling behavior in the treefrog Dendropsophus ebraccatus

Correction to: Effects of multiple-speaker playbacks on aggressive calling behavior in the treefrog Dendropsophus ebraccatus

Flexible oviposition behavior enabled the evolution of terrestrial reproduction

Among vertebrates, nearly all oviparous animals are considered to have either obligate aquatic or terrestrial oviposition, with eggs that are specialized for developing in those environments. The terrestrial environment has considerably more oxygen but is dry and thus presents both opportunities and challenges for developing embryos, particularly those adapted for aquatic development. Here, we present evidence from field experiments examining egg-laying behavior, egg size, and egg jelly function of 13 species of Central and South American treefrogs in the genus Dendropsophus, which demonstrates that flexible oviposition (individuals laying eggs both in and out of water) and eggs capable of both aquatic and terrestrial development are the likely factors which enable the transition from aquatic to terrestrial reproduction. Nearly half of the species we studied had previously undescribed degrees of flexible oviposition. Species with obligate terrestrial reproduction have larger eggs than species with aquatic reproduction, and species with flexible reproduction have eggs of intermediate sizes. Obligate terrestrial breeding frogs also have egg masses that absorb water more quickly than those with flexible oviposition. We also examined eight populations of a single species, Dendropsophus ebraccatus, and document substantial intraspecific variation in terrestrial oviposition; populations in rainy, stable climates lay fewer eggs in water than those in drier areas. However, no differences in egg size were found, supporting the idea that the behavioral component of oviposition evolves before other adaptations associated with obligate terrestrial reproduction. Collectively, these data demonstrate the key role that behavior can have in facilitating major evolutionary transitions.

One of these things is not like the other: Mixed predator cues result in lopsided phenotypic responses in a Neotropical tadpole.

Many organisms have evolved to produce different phenotypes in response to environmental variation. Dendropsophus ebraccatus tadpoles develop opposing shifts in morphology and coloration when they are exposed to invertebrate vs vertebrate predators. Each of these alternate phenotypes are adaptive, conferring a survival advantage against the predator with which tadpoles were reared but imposing a survival cost with the mismatched predator. Here, we measured the phenotypic response of tadpoles to graded cues and mixed cues of both fish and dragonfly nymphs. Prey species like D. ebraccatus commonly co-occur with both of these types of predators, amongst many others as well. In our first experiment, tadpoles increased investment in defensive phenotypes in response to increasing concentrations of predator cues. Whereas morphology only differed in the strongest predation cue, tail spot coloration differed even at the lowest cue concentration. In our second experiment, tadpoles reared with cues from both predators developed an intermediate yet skewed phenotype that was most similar to the fish-induced phenotype. Previous studies have shown that fish are more lethal than dragonfly larvae; thus tadpoles responded most strongly to the more dangerous predator, even though the number of prey consumed by each predator was the same. This may be due to D. ebraccatus having evolved a stronger response to fish or because fish produce more kairomones than do dragonflies for a given amount of food. We demonstrate that not only do tadpoles assess predation risk via the concentration of predation cues in the water, they produce a stronger response to a more lethal predator even when the strength of cues is presumed to be identical.

Colonization order of bacterial isolates on treefrog embryos impacts microbiome structure in tadpoles.

Priority effects, or impacts of colonization order, may have lasting influence on ecological community composition. The embryonic microbiome is subject to stochasticity in colonization order of bacteria. Stochasticity may be especially impactful for embryos developing in bacteria-rich environments, such as the embryos of many amphibians. To determine if priority effects experienced as embryos impacted bacterial community composition in newly hatched tadpoles, we selectively inoculated the embryos of laboratory-raised hourglass treefrogs, Dendropsophus ebraccatus, with bacteria initially isolated from the skin of wild D. ebraccatus adults over 2 days. First, embryos were inoculated with two bacteria in alternating sequences. Next, we evaluated the outcomes of priority effects in an in vitro co-culture assay absent of host factors. We then performed a second embryo experiment, inoculating embryos with one of three bacteria on the first day and a community of five target bacteria on the second. Through 16S rRNA gene amplicon sequencing, we observed relative abundance shifts in tadpole bacteria communities due to priority effects. Our results suggest that the initial bacterial source pools of embryos shape bacterial communities at later life stages; however, the magnitude of those changes is dependent on the host environment and the identity of bacterial colonists.

An experimental test of disease resistance function in the skin-associated bacterial communities of three tropical amphibian species.

Variation in the structure of host-associated microbial communities has been correlated with the occurrence and severity of disease in diverse host taxa, suggesting a key role of the microbiome in pathogen defense. However, whether these correlations are typically a cause or consequence of pathogen exposure remains an open question, and requires experimental approaches to disentangle. In amphibians, infection by the fungal pathogen Batrachochytrium dendrobatidis (Bd) alters the skin microbial community in some host species, whereas in other species, the skin microbial community appears to mediate infection dynamics. In this study, we completed experimental Bd exposures in three species of tropical frogs (Agalychnis callidryas, Dendropsophus ebraccatus,andCraugastor fitzingeri) that were sympatric with Bd at the time of the study. For all three species, we identified key taxa within the skin bacterial communities that were linked to Bd infection dynamics. We also measured higher Bd infection intensities in D. ebraccatus and C. fitzingeri that were associated with higher mortality in C. fitzingeri. Our findings indicate that microbially mediated pathogen resistance is a complex trait that can vary within and across host species, and suggest that symbiont communities that have experienced prior selection for defensive microbes may be less likely to be disturbed by pathogen exposure.

Calling phenology of four anurans in tropical Mexico

Anuran vocalizations transmit relevant information that aids in individual recognition and sexual selection by females. When studied over time, vocalizations can help us to understand reproductive phenology. Here, we used an automated recording system to obtain calls of 4 anurans in southeastern Mexico, described the calling phenology of the species and tested its relationship with environmental variables. We performed Generalized Linear Mixed Effects Models (GLMM’s) to explore possible relationships between calling and environmental variables. The hylid species ( Agalychnis callidryas, A. moreletii and Dendropsophus ebraccatus ) showed a clear calling pattern; they began calling in April/May and increased in their intensity during the rainy season, from June to September. Craugastor loki showed, contrarily, no clear patterns of calling, preferring to call almost continuously throughout the year. Among the environmental factors tested, only minimum temperature and the amount of days without rain had an effect (positive and negative, respectively) on calling activity of the hylids, but we found that calling from other species had greater positive effects within the group. There was a strong phenological overlap in the calling behavior of these species, which may suggest that competition for site of calling or acoustic niche partitioning can be present in the community.

Right phenotype, wrong place: predator-induced plasticity is costly in a mismatched environment.

Like many animals, tadpoles often produce different, predator-specific phenotypes when exposed to risk of predation. It is generally assumed that such plasticity enhances survival in the presence of the predator and is costly elsewhere, but evidence remains surprisingly scarce. We measured (1) the survival trade-off of opposing phenotypes developed by Dendropsophus ebraccatus tadpoles when exposed to different predators and (2) which specific aspects of morphology drive any potential survival benefit or cost. Tadpoles developed predator-specific phenotypes after being reared with caged fish or dragonfly predators for two weeks. In 24 h predation trials with either a fish or a dragonfly, survival was highest in the groups with their matched predator, and lowest among with those the mismatched predator, with predator-naive controls being relatively intermediate. Then, using a large group of phenotypically variable predator-naive tadpoles, we found that increased survival rates are directly related to the morphological changes that are induced by each predator. This demonstrates that induced phenotypes are indeed adaptive and the product of natural selection. Furthermore, our data provide clear evidence of an environmental cost for phenotypic plasticity in a heterogeneous environment. Such costs are fundamental for understanding the evolution and maintenance of inducible phenotypes.

Skin bacterial communities of neotropical treefrogs vary with local environmental conditions at the time of sampling.

The amphibian skin microbiome has been the focus of recent studies aiming to better understand the role of these microbial symbionts in host defense against disease. However, host-associated microbial communities are complex and dynamic, and changes in their composition and structure can influence their function. Understanding temporal variation of bacterial communities on amphibian skin is critical for establishing baselines from which to improve the development of mitigation techniques based on probiotic therapy and provides long-term host protection in a changing environment. Here, we investigated whether microbial communities on amphibian skin change over time at a single site. To examine this, we collected skin swabs from two pond-breeding species of treefrogs, Agalychnis callidryas and Dendropsophus ebraccatus, over 4 years at a single lowland tropical pond in Panamá. Relative abundance of operational taxonomic units (OTUs) based on 16S rRNA gene amplicon sequencing was used to determine bacterial community diversity on the skin of both treefrog species. We found significant variation in bacterial community structure across long and short-term time scales. Skin bacterial communities differed across years on both species and between seasons and sampling days only in D. ebraccatus. Importantly, bacterial community structures across days were as variable as year level comparisons. The differences in bacterial community were driven primarily by differences in relative abundance of key OTUs and explained by rainfall at the time of sampling. These findings suggest that skin-associated microbiomes are highly variable across time, and that for tropical lowland sites, rainfall is a good predictor of variability. However, more research is necessary to elucidate the significance of temporal variation in bacterial skin communities and their maintenance for amphibian conservation efforts.

You cannot have it all: Heritability and constraints of predator-induced developmental plasticity in a Neotropical treefrog.

Many organisms have evolved phenotypic plasticity but examples of a heritable genetic basis or genetic constraints for plasticity across environments remain scarce. Tadpoles of the Neotropical treefrog Dendropsophus ebraccatus alter tail coloration and shape differently in response to fish or aquatic insect predators. To assess the genetic basis of plasticity we raised 1020 tadpoles from 17 maternal half-sib pairs (34 unique families) individually with chemical cues of fish or aquatic insects, or with cue-free control water. We used Bayesian animal models to estimate narrow sense heritability of morphology and cross-trait genetic correlations in all three treatments, heritability of plasticity in response to each predator, and genetic correlations between responses to fish and insects. Families showed remarkably different responses to predators and heritability was often high (0.45-0.75), as was heritability of plasticity itself (0.42-0.62). We detected strong negative genetic correlations for responses to each predator (-0.45 and -0.59), providing clear evidence of a limit to plasticity. Most importantly, we show that prey genotypes are constrained in their capacity to respond to different types of predators, which likely maintains genetic variation for plasticity in a temporally and spatially dynamic landscape where there is no single adaptive peak.

Phenotypic integration and the evolution of signal repertoires: A case study of treefrog acoustic communication.

Animal signals are inherently complex phenotypes with many interacting parts combining to elicit responses from receivers. The pattern of interrelationships between signal components reflects the extent to which each component is expressed, and responds to selection, either in concert with or independently of others. Furthermore, many species have complex repertoires consisting of multiple signal types used in different contexts, and common morphological and physiological constraints may result in interrelationships extending across the multiple signals in species’ repertoires. The evolutionary significance of interrelationships between signal traits can be explored within the framework of phenotypic integration, which offers a suite of quantitative techniques to characterize complex phenotypes. In particular, these techniques allow for the assessment of modularity and integration, which describe, respectively, the extent to which sets of traits covary either independently or jointly. Although signal and repertoire complexity are thought to be major drivers of diversification and social evolution, few studies have explicitly measured the phenotypic integration of signals to investigate the evolution of diverse communication systems. We applied methods from phenotypic integration studies to quantify integration in the two primary vocalization types (advertisement and aggressive calls) in the treefrogs Hyla versicolor, Hyla cinerea, and Dendropsophus ebraccatus. We recorded male calls and calculated standardized phenotypic variance–covariance (P) matrices for characteristics within and across call types. We found significant integration across call types, but the strength of integration varied by species and corresponded with the acoustic similarity of the call types within each species. H. versicolor had the most modular advertisement and aggressive calls and the least acoustically similar call types. Additionally, P was robust to changing social competition levels in H. versicolor. Our findings suggest new directions in animal communication research in which the complex relationships among the traits of multiple signals are a key consideration for understanding signal evolution.

The hatching process and mechanisms of adaptive hatching acceleration in hourglass treefrogs, Dendropsophus ebraccatus

Environmentally cued hatching is well documented in anurans, enabling embryos to escape diverse threats. However, knowledge of anuran hatching mechanisms is limited and based largely on aquatic-breeding species without known plasticity in hatching timing. Generally, hatching gland cells produce a hatching enzyme that degrades the vitelline membrane. We investigated hatching and its regulation in terrestrial embryos of hourglass treefrogs, Dendropsophus ebraccatus, which accelerate hatching to escape dehydration. We specifically tested if changes in hatching gland cell development or hatching enzyme gene expression are associated with accelerated hatching. We measured perivitelline chamber size of well-hydrated eggs over development as an indicator of breakdown of the vitelline membrane and found that the size of the perivitelline chamber increased steadily until hatching, suggesting gradual hatching enzyme release and vitelline membrane degradation. Hatching gland cells peaked in abundance and began regression substantially prior to hatching, but we found no developmental differences in the abundance or surface area of hatching gland cells between dry and well-hydrated embryos. Hatching enzyme gene expression also peaked early in development then declined, with no difference between hydration treatments. In D. ebraccatus breakdown of the vitelline membrane appears gradual, mediated by hatching enzyme release starting long before hatching. However, hatching acceleration is not associated with ontogenetic changes in hatching gland cell development or hatching enzyme gene expression. This hatching process contrasts with that of red-eyed treefrogs, Agalychnis callidryas, which appear to release enzyme acutely at hatching, yet both species are capable of hatching to escape acute threats.

Variation in Abundance and Efficacy of Tadpole Predators in a Neotropical Pond Community

Abstract Variation in predation risk plays an important role in shaping prey behavior, morphology, life history, population dynamics, and community structure in freshwater systems. Anuran larvae are important prey in freshwater communities and spatiotemporal variation in risk can arise from changes in the number and identity of predators; however, our understanding of variation in abundance, identity, and foraging rates for natural predator assemblages in tropical pond communities is limited. We surveyed ponds near Gamboa, Panama in 2004 and 2010 to estimate variation in predator communities of tadpoles over space and time. We also conducted short-term predation trials with the 10 most common predators using hatchling tadpoles of two widespread Neotropical frog species, Red-Eyed Treefrogs (Agalychnis callidryas) and Pantless Treefrogs (Dendropsophus ebraccatus). Predator abundance varied nearly threefold across ponds within a single year and as much as 19-fold within a pond across years. Dominant taxa als...

Multimodal cues improve prey localization under complex environmental conditions.

Predators often eavesdrop on sexual displays of their prey. These displays can provide multimodal cues that aid predators, but the benefits in attending to them should depend on the environmental sensory conditions under which they forage. We assessed whether bats hunting for frogs use multimodal cues to locate their prey and whether their use varies with ambient conditions. We used a robotic set-up mimicking the sexual display of a male túngara frog (Physalaemus pustulosus) to test prey assessment by fringe-lipped bats (Trachops cirrhosus). These predatory bats primarily use sound of the frog's call to find their prey, but the bats also use echolocation cues returning from the frog's dynamically moving vocal sac. In the first experiment, we show that multimodal cues affect attack behaviour: bats made narrower flank attack angles on multimodal trials compared with unimodal trials during which they could only rely on the sound of the frog. In the second experiment, we explored the bat's use of prey cues in an acoustically more complex environment. Túngara frogs often form mixed-species choruses with other frogs, including the hourglass frog (Dendropsophus ebraccatus). Using a multi-speaker set-up, we tested bat approaches and attacks on the robofrog under three different levels of acoustic complexity: no calling D. ebraccatus males, two calling D. ebraccatus males and five D. ebraccatus males. We found that bats are more directional in their approach to the robofrog when more D. ebraccatus males were calling. Thus, bats seemed to benefit more from multimodal cues when confronted with increased levels of acoustic complexity in their foraging environments. Our data have important consequences for our understanding of the evolution of multimodal sexual displays as they reveal how environmental conditions can alter the natural selection pressures acting on them.

Oviposition site choice under conflicting risks demonstrates that aquatic predators drive terrestrial egg-laying.

Laying eggs out of water was crucial to the transition to land and has evolved repeatedly in multiple animal phyla. However, testing hypotheses about this transition has been difficult because extant species only breed in one environment. The pantless treefrog, Dendropsophus ebraccatus, makes such tests possible because they lay both aquatic and arboreal eggs. Here, we test the oviposition site choices of D. ebraccatus under conflicting risks of arboreal egg desiccation and aquatic egg predation, thereby estimating the relative importance of each selective agent on reproduction. We also measured discrimination between habitats with and without predators and development of naturally laid aquatic and arboreal eggs. Aquatic embryos in nature developed faster than arboreal embryos, implying no cost to aquatic egg laying. In choice tests, D. ebraccatus avoided habitats with fish, showing that they can detect aquatic egg predators. Most importantly, D. ebraccatus laid most eggs in the water when faced with only desiccation risk, but switched to laying eggs arboreally when desiccation risk and aquatic predators were both present. This provides the first experimental evidence to our knowledge that aquatic predation risk influences non-aquatic oviposition and strongly supports the hypothesis that it was a driver of the evolution of terrestrial reproduction.

Feeding Site Selection by Frog-Biting Midges (Diptera: Corethrellidae) on Anuran Hosts

A critical challenge of obtaining a blood meal resides in selecting a feeding site at the host. We investigate the feeding sites of species of frog-biting midges (Corethrella spp) on tungara frogs, Engystomops pustulosus (Cope), and two species of treefrogs, Dendropsophus ebraccatus (Cope) and Dendropsophus microcephalus (Cope). To investigate the differences in midge feeding sites, we performed field observations, histological sections of the frogs and examined the mouthparts of the midges. Feeding sites are predicted by the vascular properties of the skin in different body areas of the frogs. According to optimal foraging theory, the midges should feed on host body areas that maximize blood intake. Contrary to optimal foraging theory predictions, however, their feeding sites correspond to body areas with high intensity host defensive behavior.

Patterns of variability are consistent across signal types in the treefrogDendropsophus ebraccatus

Animal signal characteristics vary at multiple levels, and this variation can be related to the selective forces acting on signal structure. However, the effectiveness of selection acting on any one signal type may depend on selective forces acting on the same characteristics in other signal types, particularly if the signals share a common physical production mechanism. In anurans, signal variability has been related to the potential for various forms of selection by female choice on the characteristics of male advertisement calls. The significance of variability in the characteristics of another vocalization type, the aggressive call, is less well understood. In the present stiudy, within- and between-male variability was measured in several characteristics of both advertisement and aggressive calls in the treefrog Dendropsophus ebraccatus. Many characteristics of both call types were repeatable within males. Fine-temporal and spectral characteristics generally had low variation within males, whereas gross-temporal characteristics were more variable. Unexpectedly, there were strong correlations between both measures of variability and mean values of the call characteristics of advertisement and aggressive calls. Thus, despite potentially conflicting selection pressures acting on advertisement and aggressive calls, the characteristics of individuals' calls were consistent across these two signal types. The potential forces responsible for consistency across call types are discussed, including morphological constraints and behavioural syndromes that act across different signalling contexts. In general, it is argued that measurements of variability made across multiple signal types, as in the present study, can provide important insights into the evolution of signal structure in organisms with complex signal repertoires. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109, 131–145.

Uso de recursos alimentares e espaciais por dois anuros do gênero Dendropsophus (Anura: Hylidae) de La Selva, Costa Rica.

Use of food and spatial resources by two frogs of the genus Dendropsophus (Anura: Hylidae) from La Selva, Costa Rica. Differences in the use of resources by similar species have been related to a reduction in the interspecific competition that allows coexistence. Also, other factors, such as high availability of resources in the environment, vegetation structure, environmental heterogeneity, reproductive modes, and predation, can influence the use of resources and favor coexistence. We studied the use of space and food resources by males of two species of hylid frogs, Dendropsophus ebraccatus and D. phlebodes, in two swamps in the Neotropical lowland forest at La Selva Biological Station, Costa Rica. We determined space and food use by characterizing calling sites and the diet of the frogs by stomach flushing. Males call from different substrates, and use different sizes of leaves and perch heights. Both species seem to be feeding generalists. Their diets are similar and indicate a moderate trophic niche overlap based on the type of prey consumed. Many males of both species had empty stomachs, suggesting that food resources are not an important factor affecting the coexistence of these species. Our study also indicates a lack of competitive interactions for space and food resources, and suggests that the abundant and structurally diverse vegetation provides many different vocalization sites for the male frogs and fosters coexistence of these species during the breeding season at La Selva.

A Treefrog with Reproductive Mode Plasticity Reveals a Changing Balance of Selection for Nonaquatic Egg Laying

Nonaquatic reproduction has evolved repeatedly, but the factors that select for laying eggs on land are not well understood. The treefrog Dendropsophus ebraccatus has plasticity in its reproductive mode, laying eggs that successfully develop in or out of water. This permits the first experimental comparison of the selective agents that shape adult oviposition behavior and embryo developmental capacity. I quantified the sources and strengths of arboreal and aquatic egg mortality and how mortality varies with weather patterns, and I assessed 39 years of daily rainfall patterns to infer historic levels of egg mortality and effects of climate change on the selective balance between aquatic and nonaquatic egg deposition. Aquatic predators and desiccation were the strongest selective agents in water and air, respectively. Egg mortality varied with weather such that aquatic oviposition was advantageous when rainfall was low but laying eggs out of water increased survival when rainfall was high. Additionally, I found that since 1972 there have been significant changes in the rainfall patterns in central Panama, and this has altered the selective landscape acting on egg-laying behavior. This work provides insight into the evolution and maintenance of adaptive phenotypic plasticity as well as historic and current selection on reproduction.

Call timing is determined by response call type, but not by stimulus properties, in the treefrog Dendropsophus ebraccatus

A common form of signal competition in acoustically chorusing animals involves the precise timing of calls relative to those of other nearby individuals. In this study, I present a detailed description of nonrandom timing of both advertisement and aggressive calls in males of the Neotropical treefrog Dendropsophus ebraccatus. I used playback tests to measure call delays for both advertisement and aggressive calls given in response to synthetic advertisement and aggressive call stimuli presented with either a fixed or random timing arrangement. Call delays for a given response call type were nonrandomly distributed and did not differ depending on the fixed or random periodicity of stimulus presentation or on the stimulus call type. In general, advertisement call responses overlapped the playback stimuli, while aggressive calls were given with a much longer delay and did not overlap the playback stimuli. A second test involved the presentation of low pulse number advertisement and aggressive call stimuli to determine if males were capable of nonrandom timing to truncated stimuli. These playbacks also assessed whether they responded more aggressively to truncated aggressive call stimuli. Males usually showed synchrony in response to truncated calls of both types, more commonly in response to truncated advertisement calls. There were no differences in aggressive responses to truncated advertisement or aggressive calls. Call delays appear to be a property solely of the type of call that the male produces, regardless of the kind of stimulus. Thus, there may be a conflict between the ability to discriminate between signals and the ability to rapidly respond to these signals with an appropriate call delay.

Effects of multiple-speaker playbacks on aggressive calling behavior in the treefrog Dendropsophus ebraccatus

In addition to producing signals, males of chorusing species also act as receivers by adjusting properties of their vocalizations in response to those of other nearby individuals. Although it is likely that males are responsive to more than one other individual, most playback studies investigating male response have involved dyads in which vocal responses are measured to stimuli presented from a single speaker. In this study, I explored changes in both the propensity to give aggressive calls and the temporal properties of those calls in response to the playback of multiple aggressive call stimuli in the treefrog Dendropsophus ebraccatus. I found that males were sensitive to both the number of simulated aggressive callers and their specific call characteristics. Males generally gave a highly aggressive response to the first stimulus presented, but their response to the modification of this stimulus by the addition or subtraction of a simulated competitor depended on the degree of aggressiveness of the stimuli. Males tended to decrease their aggressive responses when either a more aggressive call was silenced or a less aggressive call was added and to increase their aggressive responses in the opposite situation. Aggressive calling in this species is clearly affected by complex changes in the social environment and I suggest that future studies explore these issues in other species to improve the understanding of communication interactions.