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“Good genes” models of sexual selection predict that male courtship displays can advertise genetic quality and that, by mating with males with extreme displays, females can obtain genetic benefits for their offspring. However, because the relative performance of different genotypes can vary across environments, these genetic benefits may depend on the environmental context; in which case, static mating preferences may not be adaptive. To better understand how selection acts on the preference that female gray tree frogs (Hyla versicolor) express for long advertisement calls, I tested for genetic benefits in two realistic natural environments, by comparing the performance of half‐sibling offspring sired by males with long versus short calls. Tadpoles from twelve such maternal half‐sibships were raised in enclosures in their natal pond at two densities. In the low‐density treatment, offspring of long‐call males were larger at metamorphosis than were offspring of short‐call males, whereas in the high‐density treatment, offspring of males with long calls tended to metamorphose later than offspring of males with short calls. Thus, although the genes indicated by long calls were advantageous under low‐density conditions, they were not beneficial under all conditions, suggesting that a static preference for long calls may not be adaptive in all environments. Such a genotype‐by‐environment interaction in the genetic consequences of mate choice predicts that when the environment is variable, selection may favor plasticity in female preferences or female selectivity among environments to control the conditions experienced by the offspring.

To forecast biological responses to changing environments, we need to understand how a species's physiology varies through space and time and assess how changes in physiological function due to environmental changes may interact with phenotypic changes caused by other types of environmental variation. Amphibian larvae are well known for expressing environmentally induced phenotypes, but relatively little is known about how these responses might interact with changing temperatures and their thermal physiology. To address this question, we studied the thermal physiology of grey treefrog tadpoles (Hyla versicolor) by determining whether exposures to predator cues and an herbicide (Roundup) can alter their critical maximum temperature (CTmax) and their swimming speed across a range of temperatures, which provides estimates of optimal temperature (Topt) for swimming speed and the shape of the thermal performance curve (TPC). We discovered that predator cues induced a 0.4 degree C higher CTmax value, whereas the herbicide had no effect. Tadpoles exposed to predator cues or the herbicide swam faster than control tadpoles and the increase in burst speed was higher near Topt. In regard to the shape of the TPC, exposure to predator cues increased Topt by 1.5 degree C, while exposure to the herbicide marginally lowered Topt by 0.4 degree C. Combining predator cues and the herbicide produced an intermediate Topt that was 0.5 degree C higher than the control. To our knowledge this is the first study to demonstrate a predator altering the thermal physiology of amphibian larvae (prey) by increasing CTmax, increasing the optimum temperature, and producing changes in the thermal performance curves. Furthermore, these plastic responses of CTmax and TPC to different inducing environments should be considered when forecasting biological responses to global warming.

1. Coinfections are increasingly recognized as important drivers of disease dynamics. Consequently, greater emphasis has been placed on integrating principles from community ecology with disease ecology to understand within-host interactions among parasites. Using larval amphibians and two amphibian parasites (ranaviruses and the trematode Echinoparyphium sp.), we examined the influence of coinfection on disease outcomes. 2. Our first objective was to examine how priority effects (the timing and sequence of parasite exposure) influence infection and disease outcomes in the laboratory. We found that interactions between the parasites were asymmetric; prior infection with Echinoparyphium reduced ranaviral loads by 9% but there was no reciprocal effect of prior ranavirus infection on Echinoparyphium load. Additionally, survival rates of hosts (larval gray treefrogs; Hyla versicolor) infected with Echinoparyphium 10 days prior to virus exposure were 25% greater compared to hosts only exposed to virus. 3. Our second objective was to determine whether these patterns were generalizable to multiple amphibian species under more natural conditions. We conducted a semi-natural mesocosm experiment consisting of four larval amphibian hosts [gray treefrogs, American toads (Anaxyrus americanus), leopard frogs (Lithobates pipiens) and spring peepers {Pseudacris crucifer)] to examine how prior Echinoparyphium infection influenced ranavirus transmission within the community, using ranavirus-infected larval wood frogs (Lithobates sylvaticus) as source of ranavirus. Consistent with the laboratory experiment, we found that prior Echinoparyphium infection reduced ranaviral loads by 19 to 28% in three of the four species. 4. Collectively, these results suggest that macroparasite infection can reduce microparasite replication rates across multiple amphibian species, possibly through cross-reactive immunity. Although the immunological mechanisms driving this outcome are in need of further study, trematode infections appear to benefit hosts that are exposed to ranaviruses. Additionally, these results suggest that consideration of priority effects and timing of exposure are vital for understanding parasite interactions within hosts and disease outcomes.

Freshwater salinization is an emerging environmental filter in urban aquatic ecosystems that receive chloride road salt runoff from vast expanses of impervious surface cover. Our study was designed to evaluate the effects of chloride contamination on urban stormwater pond food webs through changes in zooplankton community composition as well as density and biomass of primary producers and consumers. From May - July 2009, we employed a 222 full-factorial design to manipulate chloride concentration (low = 177 mg L-1 Cl-/high = 1067 mg L-1 Cl-), gray treefrog (Hyla versicolor) tadpoles (presence/absence) and source of stormwater pond algae and zooplankton inoculum (low conductance/high conductance urban ponds) in 40, 600-L mesocosms. Road salt did serve as a constraint on zooplankton community structure, driving community divergence between the low and high chloride treatments. Phytoplankton biomass (chlorophyll [a] mu g L-1) in the mesocosms was significantly greater for the high conductance inoculum (P<0.001) and in the high chloride treatment (P = 0.046), whereas periphyton biomass was significantly lower in the high chloride treatment (P = 0.049). Gray treefrog tadpole time to metamorphosis did not vary significantly between treatments. However, mass at metamorphosis was greater among tadpoles that experienced a faster than average time to metamorphosis and exposure to high chloride concentrations (P = 0.039). Our results indicate differential susceptibility to chloride salts among algal resources and zooplankton taxa, and further suggest that road salts can act as a significant environmental constraint on urban stormwater pond communities.

Auditory streaming underlies a receiver’s ability to organize complex mixtures of auditory input into distinct perceptual “streams” that represent different sound sources in the environment. During auditory streaming, sounds produced by the same source are integrated through time into a single, coherent auditory stream that is perceptually segregated from other concurrent sounds. Based on human psychoacoustic studies, one hypothesis regarding auditory streaming is that any sufficiently salient perceptual difference may lead to stream segregation. Here, we used the eastern grey treefrog, Hyla versicolor, to test this hypothesis in the context of vocal communication in a non-human animal. In this system, females choose their mate based on perceiving species-specific features of a male’s pulsatile advertisement calls in social environments (choruses) characterized by mixtures of overlapping vocalizations. We employed an experimental paradigm from human psychoacoustics to design interleaved pulsatile sequences (ABAB…) that mimicked key features of the species’ advertisement call, and in which alternating pulses differed in pulse rise time, which is a robust species recognition cue in eastern grey treefrogs. Using phonotaxis assays, we found no evidence that perceptually salient differences in pulse rise time promoted the segregation of interleaved pulse sequences into distinct auditory streams. These results do not support the hypothesis that any perceptually salient acoustic difference can be exploited as a cue for stream segregation in all species. We discuss these findings in the context of cues used for species recognition and auditory streaming.

The global decline in amphibian diversity has become an international environmental problem with a multitude of possible causes. There is evidence that pesticides may play a role, yet few pesticides have been tested on amphibians. For example, Roundup is a globally common herbicide that is conventionally thought to be nonlethal to amphibians. However, Roundup has been tested on few amphibian species, with existing tests conducted mostly under laboratory conditions and on larval amphibians. Recent laboratory studies have indicated that Roundup may be highly lethal to North American tadpoles, but we need to determine whether this effect occurs under more natural conditions and in post-metamorphic amphibians. I assembled communities of three species of North American tadpoles in outdoor pond mesocosms that contained different types of soil (which can absorb the pesticide) and applied Roundup as a direct overspray. After three weeks, Roundup killed 96-100% of larval amphibians (regardless of soil presence). I then exposed three species of juvenile (post-metamorphic) anurans to a direct overspray of Roundup in laboratory containers. After one day, Roundup killed 68-86% of juvenile amphibians. These results suggest that Roundup, a compound designed to kill plants, can cause extremely high rates of mortality to amphibians that could lead to population declines.

Pesticides constitute a major anthropogenic addition to natural communities. In aquatic communities, a great majority of pesticide impacts are determined from single-species experiments conducted under laboratory conditions. Although this is an essential protocol to rapidly identify the direct impacts of pesticides on organisms, it prevents an assessment of direct and indirect pesticide effects on organisms embedded in their natural ecological contexts. In this study, I examined the impact of four globally common pesticides (two insecticides, carbaryl [Sevin] and malathion; two herbicides, glyphosate [Roundup] and 2,4-D) on the biodiversity of aquatic communities containing algae and 25 species of animals. Species richness was reduced by 15% with Sevin, 30% with malathion, and 22% with Roundup, whereas 2,4-D had no effect. Both insecticides reduced zooplankton diversity by eliminating cladocerans but not copepods (the latter increased in abundance). The insecticides also reduced the diversity and biomass of predatory insects and had an apparent indirect positive effect on several species of tadpoles, but had no effect on snails. The two herbicides had no effects on zooplankton, insect predators, or snails. Moreover, the herbicide 2,4-D had no effect on tadpoles. However, Roundup completely eliminated two species of tadpoles and nearly exterminated a third species, resulting in a 70% decline in the species richness of tadpoles. This study represents one of the most extensive experimental investigations of pesticide effects on aquatic communities and offers a comprehensive perspective on the impacts of pesticides when nontarget organisms are examined under ecologically relevant conditions.

Abstract In anuran amphibians, as well as many other animals, it is common for males to form breeding aggregations where they advertise to females of the same species. For female gray treefrogs (Hyla versicolor), the characteristics of male calls are integral to their preferences while the distance to the males represents a key feature of the required investment. Therefore, the spatial arrangement of males and the quality of their advertisement calls can influence sexual selection processes. We recorded the calls of male gray treefrogs, as well as the spatial position of individuals in the chorus, for aggregations in northern Michigan over three breeding seasons. Males were not randomly distributed across the chorus but showed both clustered patterns and dispersed patterns, depending on the scale of analysis. On active chorus nights, we identified clusters of males and individual males closest to the centers of those clusters (“medoids”) using a novel analytical approach. Medoids displayed some call characteristics that are preferred by females significantly more often than the other members of their clusters and thus may represent “hotshot” males. Non-medoid males in the clusters displayed less preferred call features. Irrespective of overall cluster membership, the size of the chorus (number of males calling per night) and nearest neighbor distances were also correlated with specific call features. We suggest that the smaller clusters within choruses that we identified may represent the spatial scale over which female gray treefrogs sample and choose male mates.Significance statementAggregations of animals for the sole purpose of mating are common and conspicuous occurrences. However, such aggregations provide both costs and benefits to participants. For males, the quality of their displays and spatial location in the aggregation can determine whether they mate at all. Females also face constraints as their preferred mates may represent costly choices. Using an objective point pattern analysis technique, we demonstrated that the male advertisement choruses of the gray treefrog can be subdivided into smaller local groups that contain higher quality males at the center. These local groups display some features of classic “hotshot” style leks and may represent the units females consider for choice of male mates.

Female mate choice is remarkably complex and has wide-ranging implications for the strength and direction of male trait evolution. Yet mating decisions can be fickle and inconsistent. Here, we explored predation risk as a source of variation in the effort a female is willing to invest in acquiring a preferred mate type (“choosiness”). We did so by comparing phonotaxis behaviors of female eastern gray treefrogs (Hyla versicolor) across trials with and without simulated predators. We tested the behavioral adjustment hypothesis (mate choice is unchanged under predation threat, but mate searching behaviors are modified to reduce conspicuousness) against the mate choice flexibility hypothesis (mate choice becomes indiscriminate under predation threat). Additionally, effectiveness of evasive behaviors may depend on predator attack strategy, so we incorporated two simulated predator cues (bird model vs predatory ranid call). We found support for the behavioral adjustment hypothesis: choosiness was maintained in the presence of predators, but females reduced conspicuousness of mate searching locomotion. Females approached the conspecific male stimuli slower and more cautiously in both predator treatments. In the ranid frog call treatment (stationary cue), females adjusted movements away from predator location. Females also attempted escape more frequently when predator cues were present. We suggest that focusing exclusively on the final mate decision may overlook nuances in mating decisions and hamper our understanding of the remarkable complexity of mate choice.

Hyla chrysoscelis (Cope's Gray Treefrog) and H. versicolor (Gray Treefrog) are common and important species in woodland ecosystems throughout Appalachia, including southeastern Ohio. While the monitoring of treefrogs is comparatively easy in their aquatic breeding habitat, accurately measuring relative abundance in their terrestrial dwelling is more difficult, and biologists must balance search effort with data quality and effectiveness. In this study, we used PVC pipe refugia of differing colors (gray and white) to monitor the treefrog population in a mixed deciduous forest, conducting 30 surveys (5 per year, spanning April–October) over a 6-year period (2018–2023). Treefrog abundances were largest in the first (April) and last (October) yearly surveys, suggesting that early and late-season surveys are sufficient for accurately assessing population trends and dynamics. We also detected a strong preference among treefrogs to utilize west-facing refugia stations, and a slight preference for white PVC refugia. In addition, we observed many non-target species in PVC pipe refugia, which may deter usage by treefrogs as they never co-occurred with other species.