Sun-compass orientation tests were performed on adults and larvae of the spring peeper (Hyla crucifer) and the western chorus frog (Pseudacris triseriata triseriata). All animals were tested outdoors in a circular test pool from which all visible landmarks were obscured. Response on the Y-axis varied with the life history stage, and significant interspecific differences in sun-compass orientation behavior were noted. Statistical analysis was performed with Batschelet's V-test.Adult frogs were captured as they migrated to the breeding pond and tested under sunny skies. Chorus frogs oriented on the deep-water Y-axis of the nearest shoreline (n=30, p <0.005) but spring peepers did not orient (n=42, p >0.10).Frogs were also captured in the breeding pond at weekly intervals throughout the breeding season and tested under sunny skies. Chorus frogs oriented toward shore on the Y-axis (n=45, p <0.005); spring peepers did not orient (n=96, p >0.10). Adult chorus frogs kept in outdoor enclosures for a month after the breeding season were still oriented toward shore on the Y-axis (n=6, p <0.05). Chorus frogs tested under sunny skies after ten days of constant temperature, dim-light conditions in the laboratory did not orient (n=10, p >0.10).Adult chorus frogs captured as they left the breeding pond and tested under sunny skies did not orient on the Y-axis of the nearest shoreline (n=33, p >0.10), and neither did spring peepers (n=38, p >0.10).Larval western chorus frogs raised in outdoor enclosures oriented toward deep water on the Y-axis within five days after hatching (n=29, p< 0.005) and during late premetamorphosis (n=33, p <0.001). Chorus frog larvae did not orient during mid-premetamorphosis (n=32, p >0.10). Newly metamorphosed juveniles oriented on the Y-axis toward shore within a week after emergence (n=25, p< 0.01).Larval spring peepers oriented on the Y-axis toward shore within 18 days after hatching (n=37, p <0.0001) and also late in metamorphosis (n=29, p< 0.0001). Newly metamorphosed juveniles were not tested.

The boreal chorus frog (Pseudacris maculata) is a widespread species but we know little of its ecology. I examined the nature and existence of competitive mechanisms operating between larvae of the boreal chorus frog and wood frog (Lithobates sylvaticus) from field, mesocosm and laboratory venues spanning nutrient concentrations. I assessed larval performance and diet of tadpoles at natural ponds by measuring tadpole growth and size at metamorphosis, and stable isotope ratios for carbon and nitrogen in tadpole tissue to examine if patterns were consistent with the operation of interspecific competition. In mesocosms I measured chorus frog performance in relation to wood frog presence and nutrient enrichment to confirm the occurrence of competition and examine whether nutrient conditions typical of agriculture ponds impact tadpole performance. In the field I compared larval performance and relative abundance between agricultural ponds and those in Elk Island National Park, to examine whether habitat features surrounding ponds in farmlands reduces the abundance of tadpoles and whether tadpole performance results in reduced abundances. Lastly, I examined whether chemical interference by wood frogs occurs by raising chorus frog tadpoles with caged wood frog tadpoles and/or their feces in the laboratory. Chorus frog performance was reduced by presence and abundance of wood frog tadpoles. Resource partitioning in natural ponds and overlap in mesocosms, based on stable isotopic analysis, suggest that resource competition occurs. In mesocosms chorus frog performance was reduced by wood frog tadpoles in fertilized treatments and nutrient conditions at agricultural sites are not in themselves detrimental to these anurans. Performance of chorus frog tadpoles in agricultural ponds was unaffected, whereas wood frogs were larger at metamorphosis in crop ponds. Reduced tadpole abundances of both species at these ponds may be related to habitat features or conditions in croplands. The existence of chemical interference in the absence of physical interaction was confirmed, as chorus frogs exposed to wood frog tadpoles and/or feces had reduced growth and were smaller at metamorphosis which could reduce terrestrial survival and future reproduction. My research contributes to our knowledge on boreal chorus frog ecology and our general understanding of competition between larval anurans. / Ecology

No description available.

Researchers at the GFS, Washington County, Tennessee through the wet screening of nearly 100%of the sediment excavated at the site, recovered an extensive collection of anuran fossil elements. Until recently, these specimens have not been analyzed. The purpose here is the examination, description, and identification of all non-ranid anuran (frogsand toads) material using the following elements: ilium, urostyle, maxilla, frontoparietal, and last sacral vertebra. Anurans identified include Scaphiopus wardorum(extinct spadefoot toad), Bufo terrestris(southern toad), B. cf. B. marinus(giant neotropical toad), three morphotypes of Hyla(tree frogs), and Pseudacris cf. P. brachyphona(mountain chorus frog). Occurrence of these Anura support a paleoecological environment described as warm, moist, and wooded.

This thesis is composed of two chapters. Chapter one reviews what is known about adaptive plasticity in response to predators, describes the physiological systems involved in such plasticity, and outlines the evolutionary consequences of adaptive plasticity. Chapter two describes a scientific experiment that investigates how malathion may impact adaptive plasticity in the Sierran Treefrog, Pseudacris sierra. Anuran tadpoles suffer high mortality rates due to predation. In response to strong selective forces relating to these high predation rates, tadpoles evolved the ability to adaptively respond to predators through morphological and behavioral plasticity. The morphological and behavioral responses are varied and depend on the hunting strategy of the predator, and the adaptive responses may be influenced by other biotic and abiotic factors. Tadpoles detect alarm cues released from tadpoles being eaten and kairomones that are released by predators. Tadpoles respond to these signals by changing tail and body shape along with a reduction of activity level, which enables tadpoles to escape predators more effectively. These changes in morphology can occur within a week, and behavioral changes can occur within 15 minutes. The adaptive responses are critical for increasing survival rates of tadpoles to metamorphosis and may have important evolutionary consequences for anurans. Amphibians are in decline worldwide, and pollutants are considered to be a major contributor to these declines. Every year 5.2 billion pounds of active ingredients of pesticides are applied worldwide, and these application rates have led to ubiquitous low-level contamination of aquatic ecosystems. How low-level contamination of pesticides directly and indirectly affect how tadpoles respond to their predators is poorly understood. One potential indirect effect of pesticides is the inhibition of adaptive plasticity. Pesticides have been shown to modulate corticosterone levels in tadpoles. Corticosterone is the most likely mediator of the physiological response that results in adaptive morphological change. If the physiological system of tadpoles relies on corticosterone as the mediator of adaptive response, and pesticides can modulate corticosteone levels, then pesticides may inhibit or negatively impact adaptive responses to important biotic factors, like predators. Pesticides have been shown to weaken immune systems, affect developmental and physiological pathways that lead to malformations, and cause direct mortality in anurans. Little research has investigated the effect of pesticides on adaptive morphological and behavioral plasticity in response to predators. Adaptive phenotypic responses to predators increase survival rates to metamorphosis and are important in stabilizing amphibian populations through time. If pesticides influence the ecological interactions of tadpoles and their predators, this could play a part in amphibian declines. In the experiment explained in Chapter two, I tested the hypothesis that malathion at a concentration of 0.1 mg/L inhibits anti-predator morphological and behavioral responses of Pseudacris sierra to the predatory dragonfly larvae Anax junius. The results of this experiment show that malathion alone caused the tail muscle depth to increase to the same magnitude as tadpoles that only experienced a predator’s presence. Malathion also caused a significant increase in tail depth, demonstrating that malathion directly causes morphological change. The experiment did not support the hypothesis that malathion inhibits adaptive plasticity, and malathion had no impact on behavioral plasticity. The results from this experiment give evidence that an ecologically relevant concentration of malathion can influence morphological components that are critical in escaping depredation events, which could affect predator-prey interactions.

Communities are a critical link that impact how species-level population dynamics translate into ecosystem functions, and thus, understanding community assembly is an important goal of ecology. Variation in the relative importance of the four processes of drift, selection, speciation, and dispersal likely govern much of the variation that is observed in community structure across landscapes. Microbial communities provide critical functions across an array of environments, but only recently have technological advances in DNA sequencing allowed us to study these communities with higher resolution. My dissertation research has investigated community assembly in host-associated microbial communities, with a focus on understanding how stochasticity in dispersal that leads to priority affects can impact bacterial community assembly in amphibian embryos. In chapter 1, I experimentally show that priority effects resulting from stochastic dispersal can be observed in the microbiome of newly-hatched hourglass treefrog (Dendropsophus ebraccatus) tadpoles. Changes in microbiome composition due to priority effects could be observed in a simple two bacteria system and when the inoculation by the initial bacteria is followed by a more diverse community inoculum. Outcomes of my two taxa system in co-culture do not strictly mirror those observed in treefrog embryos, highlighting that priority effect outcomes are context dependent. Additionally, these results provide support that priority effects do not benefit all bacterial species equally and the magnitude of these effects will be dependent on the traits of individual colonists. In chapter 2 I demonstrate that priority effects are not unique to the hourglass treefrog system but can be observed in spring peeper (Pseudacris crucifer) tadpoles as well. This study demonstrates the applicability of priority effects in increasing the abundance of target probiotic taxa; a benefit to amphibian populations facing threats by a lethal fungal pathogen. By treating embryos with a priority inoculation of Janthinobacterium lividum, a bacterial species known to inhibit fungal pathogen growth, I increased the relative abundance of J. lividum on newly hatched tadpoles. I also provide evidence that closely-related species of bacteria can effectively co-exist regardless of priority inoculation. An understanding of variation in the amphibian microbiome across life stages in the wild is required to better understand the long-term impacts of priority effects in embryos. My final chapter, therefore, examined compositional changes in the microbiomes of locally occurring amphibians in Virginia across the egg, tadpole, and juvenile developmental stages. In this study, I show characterize the initial egg microbiome across amphibian species and demonstrate that egg microbiomes, are distinct between species but are more similar across species than tadpole or juvenile microbiomes. Additionally, I show that minor differences in host environment can lead to differences in the microbiome structure of conspecific tadpoles. Overall, my dissertation empirically demonstrates the role of dispersal, and more specifically priority effects, in the assembly of the vertebrate microbiome. / Doctor of Philosophy / An ecological community is a set of species that occur at a given site. Communities have been a fundamental focus of ecological research, as communities serve to link the population dynamics of individual species to ecosystem level processes provided by species. Microbial communities, in particular, are of interest because of the wide range of important functions they provide across a variety of systems, yet relatively little is known about how these communities initially come together and are maintained. This is particularly true for the microbial communities that live in and on plants and animals, which are called "host-associated" communities. Host-associated microbial communities contribute many important functions to their hosts, including guiding host development, assisting with nutrient assimilation, and providing disease resistance. Four processes are thought to govern how ecological communities assemble across landscapes at local sites or habitat patches: selection, dispersal, speciation, and drift. Variation in the relative importance of these processes is thought to drive the variation in community composition across sites, or in the case of host-associated microbial communities, across hosts. Selection occurs at a local level when environmental variables or the presence of other species impact where a species occurs. Dispersal of individuals among habitat patches can also impact what species occur at a local site, and speciation gives rise to new species in communities over time. Drift is the stochastic, or random, element of species abundance that is driven by variation in the birth and death rates of a population at a site. I have investigated the assembly of host-associated microbial communities using amphibians as a study system. In chapter 1, I experimentally demonstrate that stochasticity in dispersal that impacts which species arrive first to a site (priority effects) can be observed in the host-associated bacterial communities of newly-hatched treefrog (Dendropsophus ebraccatus) tadpoles. This can be observed in a simplified system where only two bacterial species are used, and also when a single bacterial species arrives and is followed by a more diverse community of bacteria. However, not every bacterial species is able to take advantage of priority, and these results seem to be context dependent, as the outcomes in treefrog embryos do not exactly mirror the outcomes when the bacteria are grown in a nutrient broth together. In chapter 2, I show that priority effects are not unique to the hourglass treefrog system; priority effects can also be observed in spring peeper (Pseudacris crucifer) tadpoles. In this study, I also demonstrated that we may be able to apply our knowledge of priority effects to benefit amphibian populations threatened by a potentially lethal fungal pathogen by manipulating the abundances of bacteria on the skin during development. Priority treatment of embryos with Janthinobacterium lividum, a bacterial species known for its ability to inhibit growth of this fungal pathogen, resulted in increased relative abundance of J. lividum in the tadpoles following hatching. Additionally, I found that even closely-related bacterial species can have differing abilities to take advantage of priority effects and can co-exist on tadpoles. To determine long-term impacts of priority effects in embryos requires an understanding of the variation associated with amphibians in the wild across different life stages. My final chapter, therefore, focused on examining changes in the bacterial communities associated with locally occurring amphibians in Virginia across the egg, tadpole, and juvenile stages of development. Specifically, I characterize the initial communities associated with eggs across different species, including predicted associations with algal symbionts, and examine patterns of host-associated communities among species and across development. Overall, my dissertation showcases the role that dispersal, but more specifically priority effects, can play in the development of the vertebrate microbiome.

Many prey species lack innate recognition of their potential predators. Hence, learning is required for them to recognize and respond to predation threats. When wild-caught, these same species may show amazing sophistication in their responses to predator cues. They are able to adjust the intensity of their antipredator responses to a particular predator according to the degree of threat posed by that predator. This ability is therefore acquired through learning. While many studies have shown that prey can learn to respond to predator cues through different learning modes, little is known about what the prey are actually learning. The results presented in this thesis show that learned predator recognition goes beyond the simple labelling of predators as dangerous. Using fathead minnows (Pimephales promelas), woodfrog (Rana sylvatica) tadpoles and boreal chorus frog (Pseudacris maculata) tadpoles, I demonstrated that a one time learning event, either through pairing with alarm cues or through social learning, was enough for prey to learn the level of threat associated with the novel predator cues. I showed that the level of danger associated with the predator cues was determined by the concentration of alarm cues when learning through pairing of alarm cues, or by the intensity of antipredator response displayed by the tutors and by the tutor-to-observer ratio when learning occurred through cultural transmission. Moreover, when subsequently exposed to predator cues, prey adjusted their antipredator responses according to the change in concentration of predator cues between the learning event and the subsequent exposure. Prey displayed stronger antipredator responses when exposed to higher concentrations of predator cues and vice versa. When minnows were provided with conflicting information about the danger level associated with a predator, they displayed a safety strategy and used the most recent information available to respond to predation threats. On a longer time scale, the data also suggest that woodfrog tadpoles are able to learn to respond to predation threats according to the risk posed by the predator at different times of day. Finally, I showed that prey learn to recognize particular characteristics of predators and can generalize their antipredator responses to novel species sharing those characteristics. However, generalization of predator recognition is dependent on the level of risk associated with the predator. Threat-sensitive learning is an extremely complex process shaped by the millions of years of selection imposed by predators on prey.

Many prey species lack innate recognition of their potential predators. Hence, learning is required for them to recognize and respond to predation threats. When wild-caught, these same species may show amazing sophistication in their responses to predator cues. They are able to adjust the intensity of their antipredator responses to a particular predator according to the degree of threat posed by that predator. This ability is therefore acquired through learning. While many studies have shown that prey can learn to respond to predator cues through different learning modes, little is known about what the prey are actually learning. The results presented in this thesis show that learned predator recognition goes beyond the simple labelling of predators as dangerous. Using fathead minnows (Pimephales promelas), woodfrog (Rana sylvatica) tadpoles and boreal chorus frog (Pseudacris maculata) tadpoles, I demonstrated that a one time learning event, either through pairing with alarm cues or through social learning, was enough for prey to learn the level of threat associated with the novel predator cues. I showed that the level of danger associated with the predator cues was determined by the concentration of alarm cues when learning through pairing of alarm cues, or by the intensity of antipredator response displayed by the tutors and by the tutor-to-observer ratio when learning occurred through cultural transmission. Moreover, when subsequently exposed to predator cues, prey adjusted their antipredator responses according to the change in concentration of predator cues between the learning event and the subsequent exposure. Prey displayed stronger antipredator responses when exposed to higher concentrations of predator cues and vice versa. When minnows were provided with conflicting information about the danger level associated with a predator, they displayed a safety strategy and used the most recent information available to respond to predation threats. On a longer time scale, the data also suggest that woodfrog tadpoles are able to learn to respond to predation threats according to the risk posed by the predator at different times of day. Finally, I showed that prey learn to recognize particular characteristics of predators and can generalize their antipredator responses to novel species sharing those characteristics. However, generalization of predator recognition is dependent on the level of risk associated with the predator. Threat-sensitive learning is an extremely complex process shaped by the millions of years of selection imposed by predators on prey.

The conservation of aquatic-breeding amphibian populations and their habitats is increasingly challenged by urban and rural development, which is occurring more intensively and more rapidly than ever before. Some species are now impacted by development throughout their range. This has forced a re-evaluation of the potential of developed landscapes for providing habitat and contributing to regional conservation strategies. For many amphibians, little is known about the criteria necessary for persistence in a developed landscape. Considerable variation in the physiology, habitat requirements, and movement behaviour of amphibians suggests that responses to habitat loss, alteration, and fragmentation are species-specific. In this thesis, I investigate species-habitat relationships for the northern red-legged frog (Rana aurora) and the Pacific chorus frog (Pseudacris regilla) in a mixed urban-rural landscape in southwestern British Columbia to evaluate the potential for species persistence despite urban and rural development throughout their range. I used repeat auditory surveys of the species’ breeding chorus to determine presence or absence at potential breeding wetlands. I then related species occurrence and abundance to characteristics of the aquatic and terrestrial environment measured at multiple spatial scales. Both species were found to use rural and urban wetlands, though R. aurora were rarely detected while P. regilla were common. Occurrence was best explained by characteristics of the terrestrial environment, rather than within-wetland characteristics, though influential terrestrial characteristics and their scale of impact differed between species. Within the context of the developed landscape, I identify species-specific positive and negative habitat associations and suggest the spatial scales at which management of these habitat characteristics will be most effective. These criteria may help to explain the species’ current distribution, prioritize management strategies, predict the effectiveness of habitat conservation and restoration projects, and inform development in municipalities seeking to maintain or enhance amphibian diversity. / Graduate / 2019-09-11

Understanding how migration, genetic drift, and natural selection interact to maintain the genetic and phenotypic variation we observe in natural populations is a central goal of population genetics. Amphibians provide excellent model organisms for investigating the interplay between these evolutionary forces because amphibians are generally characterized by limited dispersal abilities, high philopatry, and are obligately associated with the areas around suitable habitats (e.g. breeding ponds). Thus, on relatively small geographic scales, the relative effects of all of these evolutionary forces can be studied together. Here, we study the interaction of migration, genetic drift, natural selection, and historical process in the ornate chorus frog (Pseudacris ornata). We report the development and characterization of 10 polymorphic microsatellite genetic markers. Number of alleles per locus ranged from 2 to 21 averaging 9.2 and expected heterozygosities ranged from 0.10 to 0.97 averaging 0.52. However, in an analysis of two populations, three locus-by-population comparisons exhibited significant heterozygote deficiencies and indicated that null alleles may be present some loci. Furthermore, we characterized genetic structure and historical biogeographic patterns in P. ornata using these microsatellite markers along with mitochondrial DNA sequence data. Our data indicate that in these frogs, migration may play a large role in determining population structure as pairwise estimates of FST were relatively small ranging from 0.04 to 0.12 (global FST = 0.083). Additionally, we observed an overall pattern of isolation-by-distance in neutral genetic markers across the species range. Moreover, our data suggest that the Apalachicola River basin does not impede gene flow in P. ornata as it does in many vertebrate taxa. Interestingly, we identified significant genetic structure between populations separated by only 6 km. However, this fine scale genetic structure was only present in the more urbanized of two widespread sampling localities. Finally, in this study, we demonstrated that there was a significant correlation between the frequency of green frogs and latitude. There was a higher frequency of green frogs in southern samples and a lower frequency of green frogs in northern samples. However, when we interpreted this phenotypic cline in light of the overall pattern of isolation-by-distance, it was apparent that the neutral evolutionary forces of genetic drift and migration could explain the cline, and the invocation of natural selection was not necessary.