Chytridiomycosis is an emerging infectious disease of amphibians caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd). Chytridiomycosis has caused declines and extinctions of amphibian species worldwide. Although the disease can be highly virulent, there are large differences both within and between amphibian species in response to Bd infection. Environmental factors are increasingly shown to be critical in the outcome of Bd-infection and emergence of the disease, although these factors remain poorly defined. Using a series of mesocosm experiments, I examine the influence of different environmental and ecological factors on the outcome of exposure to Bd in red-legged frog (Rana aurora) tadpoles, a species in decline in British Columbia. First, I tested the hypothesis that Daphnia, a keystone genus of zooplankton in shallow freshwater ecosystems, consume Bd zoospores in the water column to decrease the transmission of Bd infection in tadpoles. Although Daphnia are nearly always included in amphibian mesocosm experiments, their effects in these systems are overlooked. As such, I also examined the effect of Daphnia on R. aurora in general. I found that Daphnia had dramatic beneficial effects on tadpoles, that ostensibly herbivorous tadpoles consumed large numbers of Daphnia, and that Daphnia interacted with the presence of Bd to influence tadpole survival, with tadpole survival highest in the absence of Bd and presence of Daphnia. Although Daphnia consumed Bd zoospores in the laboratory, they had no discernible effect on transmission in mesocosms. These results have broad implications for the interpretation of mesocosm studies in general. Climate change has been implicated as a trigger of outbreaks of chytridiomycosis, yet, paradoxically, high temperatures are lethal to Bd. Climate change has also impacted amphibian communities by uncoupling the phenology of interacting species. I manipulated the temperature in mesocosms to test the effects of small temperature changes on the outcome of Bd-exposure in R. aurora. I also tested the effect of the presence of the sympatric Boreal chorus frog (Pseudacris regilla) on R. aurora at different temperatures, and in the presence and absence of Bd. I found that negative effects of Bd on tadpole body condition increased with temperature, although when Bd was absent tadpoles benefitted at higher temperatures. Furthermore, both Bd and temperature increased the development rates of P. regilla but not R. aurora, uncoupling the phenology of the species. Increased temperatures thus favoured P. regilla at the expense of R. aurora. In general, slightly higher and more variable temperatures shifted the host-pathogen balance to the detriment of the R. aurora, helping to explain a mechanism by which increasing temperatures may trigger chytridiomycosis outbreaks in susceptible. Together, these experiments clearly demonstrated the importance of ecological context in the outcome of Bd exposure in tadpoles. / Graduate / 0472

Gyrinicola Yamaguti, 1938 are oxyurid mutualists found within the intestinal tract of numerous larval anuran species in Europe, Asia, South America and North America, with 6 species being currently recognized. The systematic placement and hierarchical treatment of the genus has shifted since its discovery, originally considered as its own family (Gyrinicolidae), then treated as a subfamily (Gyrinicolinae) within Cosmocercidae, then considered a member of the Pharyngodonidae, followed by a transference to the Cosmocercidae, and finally a recent proposal to resurrect Gyrinicolidae. The morphology of the uterine tract is a characteristic often used to diagnose members the genus; yet, species show variability in the morphology of these tracts. Until recently very few DNA sequences were available to aid in the phylogenetic placement of this unique group of worms. Within North America, only Gyrinicola batrachiensis is recognized. This species, however, also has a controversial taxonomic history. Historically, two nematodes infecting larval anurans were once recognized in North America: Pharyngodon batrachiensis and Pharyngodon armatus though these were synonymized due to morphological similarity. To evaluate the potential distribution, taxonomic relation, and possible species diversity of Gyrinicola I used an integrative approach utilizing locality, morphology and genetic information of specimens from a wide range within the United States. Phylogenies of the nuclear ribosomal genes 28S, 18S, ITS1-5.8S-ITS2, and newly sequenced partial mitochondrial genomes suggest at least four species groups exist among the nematodes from North America and that these groups, alongside G. japonica, form a well-supported group within Oxyuroidea. This study represents the first genetic evaluation of the diversity of the genus in North America, and the first comparison of these nematodes collected from such distant localities, and clearly indicates that further investigation of these worms is required to characterize their true diversity. It also suggests further representation of Pharyngodonidae from other vertebrate classes may help clarify the relations of this historical grouping to other members of the Oxyuroidea.

Effective movement is central to survival and it is essential for all animals to react in response to changes around them. In many animals the rhythmic signals that drive locomotion are generated intrinsically by small networks of neurons in the nervous system which can be switched on and off. In this thesis I use a very simple animal, in which the behaviours and neuronal networks have been well characterised experimentally, to explore the salient features of such networks. Two days after hatching, tadpoles of the frog Xenopus laevis respond to a brief touch to the head by starting to swim. The swimming rhythm is driven by a small population of electrically coupled brainstem neurons (called dINs) on each side of the tadpole. These neurons also receive synaptic input following head skin stimulation. I build biophysical computational models of these neurons based on experimental data in order to address questions about the effects of electrical coupling, synaptic feedback excitation and initiation pathways. My aim is better understanding of how swimming activity is initiated and sustained in the tadpole. I find that the electrical coupling between the dINs causes their firing properties to be modulated. This allows two experimental observations to be reconciled: that a dIN only fires a single action potential in response to step current injections but the population fires like pacemakers during swimming. I build on this hypothesis and show that long-lasting, excitatory feedback within the population of dINs allows rhythmic pacemaker activity to be sustained in one side of the nervous system. This activity can be switched on and off at short latency in response to biologically realistic synaptic input. I further investigate models of synaptic input from a defined swim initiation pathway and show that electrical coupling causes a population of dINs to be recruited to fire either as a group or not at all. This allows the animal to convert continuously varying sensory stimuli into a discrete decision. Finally I find that it is difficult to reliably start swimming-like activity in the tadpole model using simple, short-latency, symmetrical initiation pathways but that by using more complex, asymmetrical, neuronal-pathways to each side of the body, consistent with experimental observations, the initiation of swimming is more robust. Throughout this work, I make testable predictions about the population of brainstem neurons and also describe where more experimental data is needed. In order to manage the parameters and simulations, I present prototype libraries to build and manage these biophysical model networks.

No description available.

I studied the ecology and distribution of the Florida bog frog (Rana okaloosae) and flatwoods salamander (Ambystoma cingulatum) on Eglin Air Force Base in northwest Florida. I report data on the breeding ecology, population dynamics, home ranges, microhabitat, and distribution of the endemic bog frog and make comparisons to its closest relative, the bronze frog (Rana clamitans clamitans). Bog and bronze frogs occur in the same habitats and are suspected to hybridize. I investigated the potential for auditory and visual mate recognition errors between R. okaloosae and R. clamitans. I also described the vocal repertoire of the bog frog and observed the response of resident males to the playback of unfamiliar conspecific and heterospecific (R. clamitans) calls. The advertisement calls of bog frogs vary among individuals, and individual voice recognition is possible. I exposed tadpoles of bog frogs, bronze frogs, and leopard frogs (R. sphenocephala) to chemical cues from 2 predators, the banded water snake (Colubridae: Nerodia fasciata) and the red fin pickerel (Esocidae: Esox americanus) to evaluate whether swimming behavior or habitat selection differed among tadpole species. The time spent swimming differed among tadpole species and predator treatments, differences which potentially could affect growth rates, survivorship rates, and distribution patterns. Lastly, I discuss the relationship between fire and the federallyâ threatened flatwoods salamander (Ambystoma cingulatum). I compared 13 breeding wetlands with different fire histories in addition to burned and unburned halves of a partiallyâ burned wetland. In general, areas that burned more recently had more open canopies, higher dissolved oxygen concentrations, higher water temperatures, more understory vegetation, and were shallower than unburned areas. Rangewide surveys indicate that prescribed fires typically are applied in winter and early spring in areas inhabited by flatwoods salamanders. Based on what is known about the natural history of the species, the historical burning regime of the longleaf ecosystem, and the effects of fires on ephemeral wetlands, I suggest that land mangers diversify their fireâ management strategy to increase the likelihood of burning the breeding wetlands of flatwoods salamanders. / Ph. D.

Summary of the thesis This works aims at reporting a novel strategy that combines controlled ring-opening polymerization of lactones initiated by a cyclic tin(IV) dialkoxide and intramolecular cyclization by photo-cross-linking of pendant unsaturations next to the propagating sites. No linear species is ever involved in the polymerization, which allows higher molecular weight macrocycles to be prepared with high efficiency. Moreover, the synthetic route is very flexible to the point where macrocyclic polyesters with more complex although well-defined architectures, such as tadpole-shaped and sun-shaped copolyesters, can be tailored. Synthesis of well-defined star- and eight-shaped polyesters and twin tadpole-shaped amphiphilic copolymers has also been explored by using a spirocyclic tin(IV) alkoxide as initiator.

To test the applicability of anuran tadpole functional ecology with regards to diet as a tool to determine ecosystem function of aquatic habitats, all the presently known as southern Africa anuran species’ tadpoles were assigned to ecomorphological guilds. The data set included 106 anuran tadpole species and 84 variables, which include: 23 habitat; 49 morphological; 9 behavioral; and 3 development (time metamorphosis) related variables. Although the data set for the guild delineation did not include genetic data, a phylogeny (evolutionary approach) was used to obtain a tree where species are grouped together based on shared characteristics, similar to that of a cluster analysis where each cluster or group is a guild. Maximum parsimony was employed with PAUP 4.0b10 to construct consensus trees using heuristic search settings. The phylogenetic/taxonomic affiliation of the species in each ecomorphological guilds’ was also observed by constructing a phylogenetic tree. The 12S and 16S mitochondrial gene sequences were retrieved from Genbank, to represent the major lineages documented in the anurans of southern Africa thus far. The ecomorphological guild delineation was further supported by quantify tadpole gut contents to determine their trophic status. Information on the feeding behavior of four guilds was obtained by analyzing a representative anuran tadpole species from each. The IUCN red list of threatened species was consulted to obtain the conservation status of the 106 anuran species used for this study, which made it possible to determine whether there is a link between species found in the same ecomorphological guilds and those species’ conservation status. Considering the high diversity of anuran species in the Phongolo region (offering access to a variety of tadpole guilds), and the ability to analyse the diatom communities found in the gut contents of tadpoles. A portion of this study supplemented the assessment of ecosystem functioning and management of aquatic resources of the lower Phongolo River and floodplain, by providing information regarding the health. Diatom bioassessment was applied as a tool for inferring water quality. The polygenetic approach proved to be very effective for the guild delineation, permitting the recognition of 10 fully characterized ecomorphological guilds, a number of which corresponded with previously characterized guilds. Terminology had to be produced for three new guilds, based on the guild defining criteria. The polygeny of the anuran species within the guild, although belonging to different genera and families belonged to the same phylogenetic clade. The trophic analysis supports the guild delineation, since a clear distinction could be made between the percentage and combination of materials from each trophic category ingested by tadpoles from different ecomorphological guilds. Even though some similarity can be seen between species, based on the criteria for the endangered status, there was still no true correlation between IUCN status and ecomorphological guild. The fact that the critically endangered, endangered and vulnerable species are distributed over so many guilds further emphasizes the extent of amphibian decline. The majority of the diatom species found in the Phongolo River and floodplain favor brackish water, with a moderate to high electrolyte content. Indicating that the Phongolo River and the section of the floodplain considered for this study had a high salinity. This might be due to the water bodies’ close proximity to the coast. The diatom index scores indicated the presence of organic pollutants and labelled these water bodies as mesotrophic to eutrophic. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2014

To test the applicability of anuran tadpole functional ecology with regards to diet as a tool to determine ecosystem function of aquatic habitats, all the presently known as southern Africa anuran species’ tadpoles were assigned to ecomorphological guilds. The data set included 106 anuran tadpole species and 84 variables, which include: 23 habitat; 49 morphological; 9 behavioral; and 3 development (time metamorphosis) related variables. Although the data set for the guild delineation did not include genetic data, a phylogeny (evolutionary approach) was used to obtain a tree where species are grouped together based on shared characteristics, similar to that of a cluster analysis where each cluster or group is a guild. Maximum parsimony was employed with PAUP 4.0b10 to construct consensus trees using heuristic search settings. The phylogenetic/taxonomic affiliation of the species in each ecomorphological guilds’ was also observed by constructing a phylogenetic tree. The 12S and 16S mitochondrial gene sequences were retrieved from Genbank, to represent the major lineages documented in the anurans of southern Africa thus far. The ecomorphological guild delineation was further supported by quantify tadpole gut contents to determine their trophic status. Information on the feeding behavior of four guilds was obtained by analyzing a representative anuran tadpole species from each. The IUCN red list of threatened species was consulted to obtain the conservation status of the 106 anuran species used for this study, which made it possible to determine whether there is a link between species found in the same ecomorphological guilds and those species’ conservation status. Considering the high diversity of anuran species in the Phongolo region (offering access to a variety of tadpole guilds), and the ability to analyse the diatom communities found in the gut contents of tadpoles. A portion of this study supplemented the assessment of ecosystem functioning and management of aquatic resources of the lower Phongolo River and floodplain, by providing information regarding the health. Diatom bioassessment was applied as a tool for inferring water quality. The polygenetic approach proved to be very effective for the guild delineation, permitting the recognition of 10 fully characterized ecomorphological guilds, a number of which corresponded with previously characterized guilds. Terminology had to be produced for three new guilds, based on the guild defining criteria. The polygeny of the anuran species within the guild, although belonging to different genera and families belonged to the same phylogenetic clade. The trophic analysis supports the guild delineation, since a clear distinction could be made between the percentage and combination of materials from each trophic category ingested by tadpoles from different ecomorphological guilds. Even though some similarity can be seen between species, based on the criteria for the endangered status, there was still no true correlation between IUCN status and ecomorphological guild. The fact that the critically endangered, endangered and vulnerable species are distributed over so many guilds further emphasizes the extent of amphibian decline. The majority of the diatom species found in the Phongolo River and floodplain favor brackish water, with a moderate to high electrolyte content. Indicating that the Phongolo River and the section of the floodplain considered for this study had a high salinity. This might be due to the water bodies’ close proximity to the coast. The diatom index scores indicated the presence of organic pollutants and labelled these water bodies as mesotrophic to eutrophic. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2014

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

In species where males do not provide immediate benefits to females in the form of resources or parental care to offspring, adaptive mate choice may be maintained by selection because preferred males sire offspring that are genetically superior. I test the hypothesis that female mating preferences result in enhanced performance of their larvae, owing to genetic variation among sires in two species of red-eyed treefrogs. This variation in males may be manifested as body size or in advertisement call parameters. I examined natural pairing patterns and found that both species display a size-based mating pattern with substantial seasonal effects. In lean years, females mate with males that are larger on average, yet females also seem to favor a constant size ratio of the male relative to her body size. I documented significant call trait variation both within and among males and have evidence to support size-related call traits as indicators of mating success for some properties. Finally, I provide evidence for a pronounced effect of sire size on offspring traits, most notably upon hatching that may have significant post-metamorphic fitness benefits. My study provides data on the basis of female choice and may provide a link between female preference for male traits and enhanced offspring performance by larvae sired by preferred males in the evolution of anuran mating systems.