A total of 35 adult Eastern gray treefrogs, Hyla versicolor LeConte, 1825, was collected in May 2015 from 1 pond in the Kellogg Biological Station Lux Arbor Reserve in the lower Peninsula of southwestern Michigan, U. S. A., and examined for helminths. Three helminth species (1 Monogenea, Polystoma nearcticum; 1 Digenea, Clinostomum sp.; and 1 Nematoda, Cosmocercoides variabilis) were found in adult treefrogs. Polystoma nearcticum is reported for the first time in Michigan and had the highest prevalence (54%), with a mean intensity of 2.4. Cosmocercoides variabilis had the highest mean intensity (52.6) and the second highest prevalence (40%). Clinostomum sp. infected only 1 frog. Twenty-nine tadpoles of gray treefrogs were collected in June 2015 from the same pond that adults were collected from and examined for helminths. One branchial form of P. nearcticum was found on the gill of 1 tadpole. The nematode Gyrinicola batrachiensis infected 55% of the tadpoles with a mean intensity of 2.8. This study is the first survey of the parasites of Eastern gray treefrogs in Michigan.

For many species sexual signaling is a very costly activity, both in terms of energetic expenditure and increased conspicuousness to predators. One potential strategy to limit the costs of signaling is to only signal at maximum effort in contexts when signaling is expected to be most effective. Multiple studies have documented extensive plasticity in sexual signaling within a variety of contexts, however fewer experiments have examined individual-level variation in the extent of signaling plasticity and the causes of this variation. In this study we examined the influence of size and physical condition on the magnitude of signaling plasticity using a gray treefrog (Hyla versicolor) study system. We quantified signaling plasticity by recording male calling behavior first in the absence and then in the presence of a sexually receptive female. For one call property, call length, we found that both weight and condition had a significant influence on the magnitude of plasticity. Smaller males, and males in higher condition exhibited the greatest degree of plasticity. We discuss several possible explanations for this pattern and provide suggestions for future work to examine the consequences of this plasticity and the potential interactive effects of multiple biotic and abiotic contexts on signaling plasticity.

Current models indicate that an organism’s sensitivity to risk may be heavily influenced by the trade-off between current and future reproduction. Individuals that have fewer future reproductive opportunities are expected to show more risky behavior as they have less to lose if captured by a predator (the asset protection principle). In this study, we examined the effects of age and physical condition on risk taking behavior during sexual signaling in the gray treefrog (Hyla versicolor) to test the prediction that older and poor condition males will take greater risks than their younger or higher-condition counterparts. In accordance with these predictions, we found that males in low physical condition resumed signaling activity more rapidly following a simulated predator attack than their higher-condition counterparts, although this effect was only apparent in one of two study years. Further, males that resumed calling early did not offset their risk of detection by predators via reduced calling effort. Contrary to our predictions, we did not find age to be a significant predictor of risk taking in male signaling behavior. We conclude with a discussion of possible explanations for the discrepancy observed between years and highlight the potential reproductive consequences of variation in risk taking behavior.

Individual variation in female mate choice has important implications for sexual trait evolution and the maintenance of phenotypic diversity. In this study we examined several potential drivers of individual variation in female choosiness for the well-studied, energetically expensive courtship signal of male gray treefrogs, Hyla versicolor. Specifically, we investigated the relationship between female choosiness and other female traits (female body size, physical condition, and age) using a costly choice playback experiment where females traveled different simulated distances to reach attractive mates. We found that larger females maintained their preferences for attractive male calls over greater simulated distances (i.e. were choosier) than smaller females. We discuss possible explanations for why larger females may be choosier and suggest several potential avenues of future research.

Current models indicate that life history trade-offs between current and future reproduction can have a major influence on sexual signaling. Individuals with fewer future reproductive opportunities—regardless of current effort—are expected to allocate greater resources to current reproductive effort (terminal investment) because of the low marginal survival cost to signaling. In this study we examined the effect of age and physical condition on the calling behavior of the Gray Treefrog (Hyla versicolor) to test the prediction that older males should exhibit greater signaling efforts compared to younger males of similar condition. Contrary to our predictions, calling males showed no significant effect of age or condition on any of the three call properties measured (call length, call rate, call effort). We offer possible explanations for the apparent discrepancy between theoretical predictions and our observations from the field.

SUMMARY Acoustic communication signals degrade as they propagate between signalers and receivers. While we generally understand the degrading effects of sound propagation on the structure of acoustic signals, we know considerably less about how receivers make behavioral decisions based on the perception of degraded signals in sonically and structurally complex habitats where communication occurs. In this study of acoustic mate recognition in Cope's gray treefrog, Hyla chrysoscelis (Cope 1880), we investigated how the temporal structure of male advertisement calls was compromised by propagation in a natural habitat and how females responded to stimuli mimicking various levels of temporal degradation. In a sound transmission experiment, we quantified changes in the pulsed structure of signals by broadcasting synthetic calls during active choruses from positions where we typically encountered signalers, and re-recording the signals from positions where we typically encountered potential receivers. Our main finding was that the silent gaps between pulses become increasingly ‘filled in’ by background noise and reverberations as a function of increasing propagation distance. We also conducted female phonotaxis experiments to determine the threshold modulation depth required to elicit recognition of the pulsatile structure of the call. Females were surprisingly tolerant of degraded temporal structure, and there was a tendency for greater permissiveness at lower playback levels. We discuss these results in terms of presumed mechanisms of call recognition in complex environments and the acoustic adaptation hypothesis.