Divergence in heritable life history traits suggests potential for local adaptation and trade-offs associated with a coal ash disposal site.

Globally, human activities have resulted in rapid environmental changes that present unique challenges for wildlife. However, investigations of local adaptation in response to simultaneous exposure to multiple anthropogenic selection pressures are rare and often generate conflicting results. We used an in situ reciprocal transplant design within a quantitative genetic framework to examine how adaptive evolution and phenotypic plasticity contribute to the persistence of an amphibian population inhabiting an environment characterized by high levels of multiple toxic trace elements. We found evidence of phenotypic divergence that is largely consistent with local adaptation to an environment contaminated with multiple chemical stressors, tied to potential trade-offs in the absence of contaminants. Specifically, the population derived from the contaminated environment had a reduced risk of mortality and greater larval growth and in the contaminated environment, relative to offspring from the naïve population. Further, while survival in the uncontaminated environment was not compromised in offspring from the contaminant-exposed population, they did show delayed development and reduced growth rates over larval development, relative to the naïve population. We found no evidence of reduced additive genetic variation in the contaminant-exposed population, suggesting long-term selection in a novel environment has not reduced the evolutionary potential of that population. We also saw little evidence that past selection in the ASH environment had reduced trait plasticity in the resident population. Maternal effects were prominent in early development, but we did not detect any trends suggesting these effects were associated with the maternal transfer of toxic trace elements. Our results demonstrate the potential for adaptation to multiple contaminants in a wild amphibian population, which may have facilitated long-term persistence in a heavily impacted environment.

Naproxen and Its Phototransformation Products: Persistence and Ecotoxicity to Toad Tadpoles (Anaxyrus terrestris), Individually and in Mixtures.

Although pharmaceutical pollution is a global environmental concern, much remains unknown about the transformation of pharmaceuticals in the wild and their effects on wildlife. In the environment, pharmaceuticals typically transform to some extent into different, structurally related compounds. Pharmaceutical transformation products resulting from exposure to sunlight (i.e., ultraviolet radiation) in surface waters are of particular concern; these products can be more hydrophobic, persistent, and toxic than their parent compounds. In the present study, naproxen, a widely used nonsteroidal anti-inflammatory drug, and its phototransformation products were studied to assess the overall persistence and photochemical fate of naproxen. Southern toad (Anaxyrus terrestris) larvae were used as model aquatic vertebrates to evaluate the acute toxicity of naproxen and its phototransformation products singly and in mixtures. The phototransformation products were observed to be more persistent and more toxic than naproxen itself. The slower phototransformation of the phototransformation products relative to naproxen suggests a greater potential to accumulate in the environment, particularly when naproxen is continually released. Mixtures of naproxen and its phototransformation products, in ratios observed during phototransformation, were more toxic than naproxen alone, as predicted by the model of concentration addition and the greater toxicity of the phototransformation products. Together, these results indicate that the ecological risk of naproxen may be underestimated by considering environmental levels of naproxen alone. Environ Toxicol Chem 2019;38:2008-2019. © 2019 SETAC.

Developmental Stage Affects the Consequences of Transient Salinity Exposure in Toad Tadpoles.

Development can play a critical role in how organisms respond to changes in the environment. Tolerance to environmental challenges can vary during ontogeny, with individual- and population-level impacts that are associated with the timing of exposure relative to the timing of vulnerability. In addition, the life history consequences of different stressors can vary with the timing of exposure to stress. Salinization of freshwater ecosystems is an emerging environmental concern, and habitat salinity can change rapidly due, for example, to storm surge, runoff of road deicing salts, and rainfall. Elevated salinity can increase the demands of osmoregulation in freshwater organisms, and amphibians are particularly at risk due to their permeable skin and, in many species, semi-aquatic life cycle. In three experiments, we manipulated timing and duration of exposure to elevated salinity during larval development of southern toad (Anaxyrus terrestris) tadpoles and examined effects on survival, larval growth, and timing of and size at metamorphosis. Survival was reduced only for tadpoles exposed to elevated salinity early in development, suggesting an increase in tolerance as development proceeds; however, we found no evidence of acclimation to elevated salinity. Two forms of developmental plasticity may help to ameliorate costs of transient salinity exposure. With early salinity exposure, the return to freshwater was accompanied by a period of rapid compensatory growth, and metamorphosis ultimately occurred at a similar age and size as freshwater controls. By contrast, salinity exposure later in development led to earlier metamorphosis at reduced size, indicating an acceleration of metamorphosis as a mechanism to escape salinity stress. Thus, the consequences of transient salinity exposure were complex and were mediated by developmental state. Salinity stress experienced early in development resulted in acute costs but little long-lasting effect on survivors, while exposures later in development resulted in sublethal effects that could influence success in subsequent life stages. Overall, our results suggest that elevated salinity is more likely to affect southern toad larvae when experienced early during larval development, but even brief sublethal exposure later in development can alter life history in ways that may impact fitness.

Assessment of interactive effects of elevated salinity and three pesticides on life history and behavior of southern toad (Anaxyrus terrestris) tadpoles.

Because habitats are increasingly exposed to multiple stressors simultaneously, assessing the interactive effects of stressors is crucial for understanding how populations respond to human-altered habitats. Salinization of freshwater habitats is increasing and has the potential to interact with other stressors. Chemical pollutants also contribute to habitat degradation in freshwater environments, and both salinity and various pesticides can harm amphibians. The present study used a factorial experiment to investigate the effect of elevated salinity alone and in combination with each of 3 pesticides-atrazine, carbaryl, and glyphosate-on life history and behavior of southern toad larvae (Anaxyrus terrestris). Tadpoles were negatively affected by elevated salinity and by exposure to the insecticide carbaryl, with the most deleterious outcomes associated with both stressors combined. Carbaryl exposure led to reduced survival as well as sublethal effects on growth, activity and feeding behavior, escape response swimming, and time to metamorphosis. Tadpoles reared at elevated salinity were also smaller and less active, and ultimately metamorphosed later and at smaller size. Together, carbaryl and elevated salinity had a synergistic effect, resulting in particularly poor growth, depressed activity and feeding, and sluggish escape swimming among tadpoles exposed to both stressors simultaneously. These results suggest that both elevated salinity and carbaryl represent threats for amphibian populations and that pesticide exposure in salinized habitats may pose a particularly high risk.

A multivariate analysis of genetic variation in the advertisement call of the gray treefrog, Hyla versicolor.

Genetic variation in sexual displays is crucial for an evolutionary response to sexual selection, but can be eroded by strong selection. Identifying the magnitude and sources of additive genetic variance underlying sexually selected traits is thus an important issue in evolutionary biology. We conducted a quantitative genetics experiment with gray treefrogs (Hyla versicolor) to investigate genetic variances and covariances among features of the male advertisement call. Two energetically expensive traits showed significant genetic variation: call duration, expressed as number of pulses per call, and call rate, represented by its inverse, call period. These two properties also showed significant genetic covariance, consistent with an energetic constraint to call production. Combining the genetic variance-covariance matrix with previous estimates of directional sexual selection imposed by female preferences predicts a limited increase in call duration but no change in call rate despite significant selection on both traits. In addition to constraints imposed by the genetic covariance structure, an evolutionary response to sexual selection may also be limited by high energetic costs of long-duration calls and by preferences that act most strongly against very short-duration calls. Meanwhile, the persistence of these preferences could be explained by costs of mating with males with especially unattractive calls.

Prevalence of Batrachochytrium dendrobatidis in Agalychnis moreletii (Hylidae) of El Salvador and association with larval jaw sheath depigmentation.

Amphibian populations around the world have been declining at an alarming rate due to factors such as habitat destruction, pollution, and infectious diseases. Between May and July 2008, we investigated a fungal pathogen in the critically endangered Morelet's treefrog (Agalychnis moreletii) at sites in El Salvador. Larvae were screened with a hand lens for indications of infection with Batrachochytrium dendrobatidis (Bd), a fungus that can cause lethal chytridiomycosis in amphibians. Subsets of inspected tadpoles were preserved for analysis by polymerase chain reaction to determine the effectiveness of hand lens screening for presence of Bd and to estimate infection prevalence at various sites. Because individuals with signs of infection were preferentially included, we used a novel method to generate unbiased estimates of infection prevalence from these biased samples. External mouthpart deformities, identified with a hand lens, successfully predicted Bd infection across a large spatial scale. Two of 13 sites sampled had high (≥ 89%) estimated prevalence, whereas little or no Bd was detected at the remaining sites. Although it appears that A. moreletii populations in this region are not suffering rapid declines due to Bd, further monitoring is required to determine the extent to which these populations are stably coexisting with the pathogen.

Genetic benefits of a female mating preference in gray tree frogs are context-dependent.

"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.

The cost of mutualism in a fly-fungus interaction.

Botanophila flies act as "pollinating" parasites of the ascomycetous fungus, Epichloë elymi. Flies transfer fungal spermatia (gametes) among fungi as they visit their hosts for oviposition. Fly larvae consume the products of cross-fertilization (ascospores). We tested whether the cost to the fungus of engaging in the obligate mutualism rises as fly visitation increases and whether mechanisms operate to prevent excessive exploitation of the fungus. Fungi and flies were monitored over 3 years. We recorded the reproductive output of fungi, the amount of feeding by fly larvae on host reproductive tissues, and the mortality of fly eggs and larvae. In two of three years, fly eggs were randomly dispersed; eggs were clumped in the remaining year. The reproductive output of fungi did not decrease with increasing egg load; rather, fungal reproductive output tended to increase as more eggs were laid on fungi. Larval feeding was only weakly associated with the number of eggs on fungi. The lack of over-exploitation of the fungus by the fly shows that the interaction was stable during the period of time we conducted our study. Our data suggest the stability was primarily due to high fly egg/larval mortal-ity that increased as egg load increased.