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Emerging infectious diseases are increasing globally and are an additional challenge to species dealing with native parasites and pathogens. Therefore, understanding the combined effects of infectious agents on hosts is important for species’ conservation and population management. Amphibians are hosts to many parasites and pathogens, including endemic trematode flatworms (e.g., Echinostoma spp.) and the novel pathogenic amphibian chytrid fungus ( Batrachochytrium dendrobatidis [ Bd ]). Our study examined how exposure to trematodes during larval development influenced the consequences of Bd pathogen exposure through critical life events. We found that prior exposure to trematode parasites negatively impacted metamorphosis but did not influence the effect of Bd infection on terrestrial growth and survival. Bd infection alone, however, resulted in significant mortality during overwintering—an annual occurrence for most temperate amphibians. The results of our study indicated overwintering mortality from Bd could provide an explanation for enigmatic declines and highlights the importance of examining the long-term consequences of novel parasite exposure.

The destruction of freshwater habitat is a major contributor to biodiversity loss in aquatic ecosystems. However, created or restored wetlands could partially mitigate aquatic biodiversity loss by increasing the amount of available habitat across a landscape. We investigated the impact of surrounding terrestrial habitat and water quality variables on suitability for two species of pond-breeding amphibians (bullfrogs [ Lithobates catesbeianus ] and Blanchard’s cricket frogs [ Acris blanchardi ]) in created permanent wetlands located on an agricultural landscape. We examined tadpole growth and survival in field enclosures placed in ponds surrounded by agricultural, forested, or grassland habitats. We also evaluated the potential for carryover effects of the aquatic environment on terrestrial growth and overwinter survival of cricket frog metamorphs. We found that habitat adjacent to ponds did not predict tadpole growth or survival. Rather, phytoplankton abundance, which showed high variability among ponds within habitat type, was the only predictor of tadpole growth. Cricket frogs emerged larger and earlier from ponds with higher phytoplankton abundance; bullfrogs were also larger and at a more advanced developmental stage in ponds with higher levels of phytoplankton. Overwinter survival of cricket frogs was explained by size at metamorphosis and there were no apparent carryover effects of land use or pond-of-origin on overwinter growth and survival. Our results demonstrate that created ponds in human-dominated landscapes can provide suitable habitat for some anurans, independent of the adjacent terrestrial habitat.

Animal movement is a key process that connects and maintains populations on the landscape, yet for most species, we do not understand how intrinsic and extrinsic factors interact to influence individual movement behavior. Land‐use/land‐cover changes highlight that connectivity among populations will depend upon an individual's ability to traverse habitats, which may vary as a result of habitat permeability, individual condition, or a combination of these factors. We examined the effects of intrinsic (body size) and extrinsic (habitat type) factors on desiccation tolerance, movement, and orientation in three anuran species (American toads, Anaxyrus americanus; northern leopard frogs, Lithobates pipiens; and Blanchard's cricket frogs, Acris blanchardi) using laboratory and field studies to connect the effects of susceptibility to desiccation, size, and movement behavior in single‐habitat types and at habitat edges. Smaller anurans were more vulnerable to desiccation, particularly for species that metamorphose at relatively small sizes. Habitat type had the strongest effect on movement, while body size had more situational and species‐specific effects on movement. We found that individuals moved the farthest in habitat types that, when given the choice, they oriented away from, suggesting that these habitats are less favorable and could represent barriers to movement. Overall, our work demonstrated that differences in habitat type had strong impacts on individual movement behavior and influenced choices at habitat edges. By integrating intrinsic and extrinsic factors into our study, we provided evidence that population connectivity may be influenced not only by the habitat matrix but also by the condition of the individuals leaving the habitat patch. We examined the effects of intrinsic (body size) and extrinsic (habitat type) factors on desiccation tolerance, movement, and orientation in three anuran species using a combination of laboratory desiccation trials and field studies to disentangle the individual and combined effects of these factors on movement. Habitat type had the strongest effect on movement, while body size had more situational and species‐specific effects on movement. We found that the habitats that most individuals oriented away from were the ones in which that same species moved the farthest, suggesting that this habitat is less favorable and could represent a barrier for movement.

ContextThe current biodiversity crisis has intensified the need to predict species responses to landscape modification and has renewed attention on the fundamental question of what influences the dynamics of species distributions. Landscape composition can affect two main components that dictate distributions: habitat suitability and habitat connectivity. Elucidating the relative importance of these factors and associated landscape features can help prioritize management action for species conservation.ObjectivesOur objective was to use species distribution models and network-based landscape connectivity models to understand which landscape factors were most predictive of the distribution of an anuran, Blanchard’s cricket frog (Acris blanchardi), in an agriculturally-dominated landscape.MethodsWe conducted our study in Ohio, USA, near the edge of the cricket frog’s contracting range. To obtain a current assessment of cricket frog distribution, we surveyed 367 pond and stream locations across three North–South transects. We then tested seven regression models, combining habitat suitability and landscape connectivity metrics, to determine which factors best predicted cricket frog presence.ResultsWe detected cricket frogs in 24% of surveyed locations and they were more likely to occupy pond sites than stream sites. Cricket frog presence was best predicted by models with habitat suitability and the number of interconnected habitat patches. We found that, while there was high variation in habitat suitability across the study area, landscape connectivity was relatively uniform where we surveyed.ConclusionsAgricultural landscapes around the world are often mosaics of land cover types, which may functionally provide connectivity for some species. In such areas, conservation management should focus on preserving and restoring regions of highly suitable habitat. This focus may be particularly relevant for species that do not appear to be dispersal limited and, therefore, able to maintain metapopulation dynamics.

The role of parasites can change depending on the food web community. Predators, for instance, can amplify or dilute parasite effects on their hosts. Likewise, exposure to parasites or predators at one life stage can have long‐term consequences on individual performance and survival, which can influence population and disease dynamics. To understand how predators affect amphibian parasite infections across life stages, we manipulated exposure of northern leopard frog (Rana pipiens) tadpoles to three predators (crayfish [Orconectes rusticus], bluegill [Lepomis macrochirus], or mosquitofish [Gambusia affinis]) and to trematode parasites (Echinostoma spp.) in mesocosms and followed juveniles in outdoor terrestrial enclosures through overwintering. Parasites and predators both had strong impacts on metamorphosis with bluegill and parasites individually reducing metamorph survival. However, when fish were present, the negative effects of parasites on survival was not apparent, likely because fish altered community composition via increased algal food resources. Bluegill also reduced snail abundance, which could explain reduced abundance of parasites in surviving metamorphs. Bluegill and parasite exposure increased mass at metamorphosis, which increased metamorph jumping, swimming, and feeding performance, suggesting that larger frogs would experience better terrestrial survival. Effects on size at metamorphosis persisted in the terrestrial environment but did not influence overwintering survival. Based on our results, we constructed stage‐structured population models to evaluate the lethal and sublethal effects of bluegill and parasites on population dynamics. Our models suggested that positive effects of bluegill and parasites on body size may have greater effects on population growth than the direct effects of mortality. This study illustrates how predators can alter the outcome of parasitic infections and highlights the need for long‐term experiments that investigate how changes in host–parasite systems alter population dynamics. We show that some predators reduce parasite effects and have indirect positive effects on surviving individuals potentially increasing host population persistence. Using an amphibian‐trematode model system, our study demonstrates that predators can alter the outcome of parasitic infections and highlights the need for long‐term experiments that investigate how changes in host‐parasite systems alter population dynamics. Predator identity matters; some predators reduce parasite effects and have indirect positive effects on surviving individuals increasing host population persistence.

Context Land use/land cover change (LULCC) is rapidly altering the quality and quantity of the habitat matrix for many species, potentially reducing the connectivity of species across the landscape. Many measures of connectivity do not directly account for quantitative movement behavior, which can inform the relative influence of specific landscape features on overall connectivity. Objectives We evaluated the population genetics and landscape conductivity in two anuran species, exploring the utility of parameters derived from quantitative movement data and landscape features in models of landscape conductance and connectivity. Methods We utilized a suite of population genetic tools to assess population genetic structure and gene flow between 21 localities of American toads in southwest Ohio, USA ( Anaxyrus americanus ) and Blanchard’s cricket frogs ( Acris blanchardi ) in an agriculturally dominated landscape. We used individual movement behavior data at habitat edges to select landscape variables and used major road and riparian networks to inform models of landscape conductance and functional connectivity. Results Parameters selected based on movement data were informative in landscape-scale models of connectivity; however, landscape features, especially river/riparian habitat had stronger influences on overall functional connectivity. We additionally found species-specific responses in functional connectivity across the same landscape. Conclusions Movement behavior data scale up and can be utilized to inform models of connectivity across the landscape, though the inclusion of established landscape features should continue to be included in models of functional connectivity. Species-specific responses to landscape features can result in alternate patterns of connectivity across the same landscape, highlighting the need for individualized measures of connectivity in the context of rapid LULCC.

Chemical contamination of aquatic environments is widespread, but we have a limited understanding of how contaminants alter critical host–parasite interactions that can influence disease dynamics. We manipulated Northern Leopard Frog (Lithobates pipiens) exposure to pesticides (no pesticides, the insecticide Bacillus thuringiensis israelensis [Bti], or the herbicide atrazine) and trematode-infected (Ribeiroia ondatrae and Echinostoma spp.) snails in outdoor mesocosms. Bti exposure extended host larval period, and atrazine exposure had a nonsignificant trend toward reducing host survival; however, neither pesticide influenced parasite success nor magnified the effects of parasites on their hosts. Parasites negatively influenced tadpole development and, by metamorphosis, parasitized frogs had severe limb deformities and greater mass than unparasitized frogs. The greater mass in parasitized frogs may have resulted from reduced competition between tadpoles and snails for algal resources because parasites decreased snail abundance in mesocosms. Reduced competition between tadpoles and snails may offset the direct negative effects of trematodes on tadpoles, enabling them to survive with high infection intensities. Trematodes may further facilitate their own success by inducing limb deformities that likely increase anuran consumption by definitive hosts. Our results demonstrate how common pesticides and parasites impact amphibians and suggest that, at environmentally relevant concentrations, these pesticides may not dramatically alter host–parasite dynamics.

Context Species distributions are a function of an individual’s ability to disperse to and colonize habitat patches. These processes depend upon landscape configuration and composition. Objectives Using Blanchard’s cricket frogs ( Acris blanchardi ), we assessed which land cover types were predictive of (1) presence at three spatial scales (pond-shed, 500 and 2500 m) and (2) genetic structure. We predicted that forested, urban, and road land covers would negatively affect cricket frogs. We also predicted that agricultural, field, and aquatic land covers would positively affect cricket frogs. Methods We surveyed for cricket frogs at 28 sites in southwestern Ohio, USA to determine presence across different habitats and analyze genetic structure among populations. For our first objective, we examined if land use (crop, field, forest, and urban habitat) and landscape features (ponds, streams, and roads) explained presence; for our second objective, we assessed whether these land cover types explained genetic distance between populations. Results Land cover did not have a strong influence on cricket frog presence. However, multiple competing models suggested effects of roads, streams, and land use. We found genetic structuring: populations were grouped into five major clusters and nine finer-scale clusters. Highways were predictive of increased genetic distance. Conclusions By combining a focal-patch study with landscape genetics, our study suggests that major roads and waterways are key features affecting species distributions in agricultural landscapes. We demonstrate that cricket frogs may respond to landscape features at larger spatial scales, and that presence and movement may be affected by different environmental factors.

To prevent dehydration, terrestrial animals and humans have developed a sensitive and versatile system to maintain their water homeostasis. In states of hypernatremia or hypovolemia, the antidiuretic hormone vasopressin (AVP) is released from the pituitary and binds its type-2 receptor in renal principal cells. This triggers an intracellular cAMP signaling cascade, which phosphorylates aquaporin-2 (AQP2) and targets the channel to the apical plasma membrane. Driven by an osmotic gradient, pro-urinary water then passes the membrane through AQP2 and leaves the cell on the basolateral side via AQP3 and AQP4 water channels. When water homeostasis is restored, AVP levels decline, and AQP2 is internalized from the plasma membrane, leaving the plasma membrane watertight again. The action of AVP is counterbalanced by several hormones like prostaglandin E2, bradykinin, dopamine, endothelin-1, acetylcholine, epidermal growth factor, and purines. Moreover, AQP2 is strongly involved in the pathophysiology of disorders characterized by renal concentrating defects, as well as conditions associated with severe water retention. This review focuses on our recent increase in understanding of the molecular mechanisms underlying AVP-regulated renal water transport in both health and disease.

Although aquatic communities frequently are exposed to a number of pesticides, the effects of chemical mixtures are not well understood. In two separate studies, I examined how insecticide mixtures influenced the likelihood of unpredictable, nonadditive effects on American toad (Bufo americanus) and green frog (Rana clamitans) tadpoles reared in outdoor aquatic communities. I exposed tadpoles to single or multiple insecticides at approximately half the reported median lethal concentrations using insecticides that were either acetylcholinesterase inhibitors (carbaryl or malathion) or a sodium-channel disruptor (permethrin). I found that combinations of insecticides with the same mode of action were more likely to have nonadditive effects on amphibian metamorphosis compared with those having different modes of action. Additionally, in one study, a commercial formulation of permethrin led to near-complete elimination of American toads, suggesting that this formulation could have adverse effects on aquatic communities. Many community studies exploring the ecological effects of expected environmental concentrations of pesticides have suggested that indirect effects in the food web, rather than direct effects on individual physiology, have the largest effect on amphibians. The present study indicates that direct effects of pesticides may become particularly important when insecticides with the same mode of action are present in the environment.