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• 1. [Article] The effects of multiple pathogens on amphibians in the Pacific Northwest

  The earth is undergoing a “biodiversity crisis” characterized by loss of populations, species, genetic diversity, and ecosystem services. Part of this crisis consists of population declines, extinctions, ...

  Citation × Citation Citation Abstract Copy Title: The effects of multiple pathogens on amphibians in the Pacific Northwest Author: Romansic, John M. The earth is undergoing a “biodiversity crisis” characterized by loss of populations, species, genetic diversity, and ecosystem services. Part of this crisis consists of population declines, extinctions, and increased incidence of deformities in amphibians. It is unknown whether deformities contribute to these declines. Many cases of population declines in amphibians are associated with infectious disease. Water molds (Oomycota: Oomycetes: Saprolegniales) (e.g. Achlya and Saprolegnia) may contribute to amphibian population declines whereas parasitic flatworms (Ribeiroia) appear to be major causes of amphibian deformities. I found that Saprolegnia can kill larval and newly-metamorphosed juvenile amphibians. In addition, I investigated synergistic effects of Saprolegnia and the environmental contaminant nitrate on survival of amphibian larvae. No synergisms were found. However, there was a less-than-additive interaction affecting one frog species. Saprolegnia killed Rana aurora (red-legged frog) larvae, but only when nitrate was not added, consistent with nitrate preventing Saprolegnia from killing R. aurora. I also tested for possible interactions among the pathogenic water mold A. flagellata, the pathogenic fungus Batrachochytrium dendrobatidis (BD), and the parasitic trematode Ribeiroia. No between-pathogen interactions were found, however, there were main effects of Ribeiroia and BD. Ribeiroia caused mortality and increased frequency of limb deformities. There were differences in the composition of deformity types between my study and previous work, suggesting that the relative frequencies of different deformity types produced by Ribeiroia may be context-dependent. Also, there was an overall effect of delayed development in Ribeiroia-exposed individuals. In addition, individuals that did not die or display limb deformities following Ribeiroia exposure had slower development than controls not exposed to Ribeiroia. Delayed development may contribute to the effects of Ribeiroia on amphibian populations. In contrast, BD sped up development, although there was no evidence of BD infection. These results are consistent with amphibian larvae responding to the presence of BD by increasing the rate of development. Hastened metamorphosis and dispersal from larval habitats may decrease the risk of BD infection or reduce BD infection load. Mortality of post-embryonic life stages from water molds and sublethal effects of Ribeiroia and BD on amphibian development may influence how these pathogens interact with amphibian populations. Title: The effects of multiple pathogens on amphibians in the Pacific Northwest Author: Romansic, John M. The earth is undergoing a “biodiversity crisis” characterized by loss of populations, species, genetic diversity, and ecosystem services. Part of this crisis consists of population declines, extinctions, and increased incidence of deformities in amphibians. It is unknown whether deformities contribute to these declines. Many cases of population declines in amphibians are associated with infectious disease. Water molds (Oomycota: Oomycetes: Saprolegniales) (e.g. Achlya and Saprolegnia) may contribute to amphibian population declines whereas parasitic flatworms (Ribeiroia) appear to be major causes of amphibian deformities. I found that Saprolegnia can kill larval and newly-metamorphosed juvenile amphibians. In addition, I investigated synergistic effects of Saprolegnia and the environmental contaminant nitrate on survival of amphibian larvae. No synergisms were found. However, there was a less-than-additive interaction affecting one frog species. Saprolegnia killed Rana aurora (red-legged frog) larvae, but only when nitrate was not added, consistent with nitrate preventing Saprolegnia from killing R. aurora. I also tested for possible interactions among the pathogenic water mold A. flagellata, the pathogenic fungus Batrachochytrium dendrobatidis (BD), and the parasitic trematode Ribeiroia. No between-pathogen interactions were found, however, there were main effects of Ribeiroia and BD. Ribeiroia caused mortality and increased frequency of limb deformities. There were differences in the composition of deformity types between my study and previous work, suggesting that the relative frequencies of different deformity types produced by Ribeiroia may be context-dependent. Also, there was an overall effect of delayed development in Ribeiroia-exposed individuals. In addition, individuals that did not die or display limb deformities following Ribeiroia exposure had slower development than controls not exposed to Ribeiroia. Delayed development may contribute to the effects of Ribeiroia on amphibian populations. In contrast, BD sped up development, although there was no evidence of BD infection. These results are consistent with amphibian larvae responding to the presence of BD by increasing the rate of development. Hastened metamorphosis and dispersal from larval habitats may decrease the risk of BD infection or reduce BD infection load. Mortality of post-embryonic life stages from water molds and sublethal effects of Ribeiroia and BD on amphibian development may influence how these pathogens interact with amphibian populations. Close

• 2. [Article] Ultraviolet radiation as an environmental stressor of amphibians

  My thesis explored the effects of and potential mediating mechanisms for an important environmental stressor, ultraviolet-B (UVB) radiation. UVB radiation has negative effects on organisms in both terrestrial ...

  Citation × Citation Citation Abstract Copy Title: Ultraviolet radiation as an environmental stressor of amphibians Author: Bancroft, Betsy A. My thesis explored the effects of and potential mediating mechanisms for an important environmental stressor, ultraviolet-B (UVB) radiation. UVB radiation has negative effects on organisms in both terrestrial and aquatic systems. I used meta-analysis to quantify the effects of UVB radiation on a diversity of aquatic organisms (Chapter 2). UVB negatively affects aquatic organisms by reducing both survival and growth. In particular, UVB reduces growth of embryos more than any other life history stage. Some taxonomic groups may be more affected by UVB radiation than others. In our analysis, the growth of members of the kingdom Protozoa was suppressed by UVB radiation to a greater degree than any other kingdom. These analyses suggest that UVB is an important stressor in both freshwater and marine systems. Amphibians are a common component of freshwater systems and are experiencing world-wide population declines. These declines may be due to a number of causes including habitat loss, introduced species, global climate change, disease, toxic chemicals and UVB radiation. I used meta-analytic techniques to quantify the effects of UVB radiation on amphibians. By synthesizing the results of 41 articles on the effects of UVB radiation on amphibians (Chapter 3), I found a nearly 2-fold reduction in survival of amphibians exposed to UVB radiation. Salamanders (caudates) appear to be more susceptible to damage from UVB than frogs or toads (anurans). Moreover, survival of larvae was much lower than survival of embryos or metamorphic individuals under UVB radiation. In addition, I used factorial meta-analytic techniques to explore the interaction between UVB radiation and other stressors in amphibian habitats. UVB radiation acted synergistically with other stressors to reduce survival of amphibians. Behavioral avoidance of UVB radiation may help mediate the negative effects of UVB radiation on amphibians. In aquatic systems, behavioral avoidance usually requires movement out of shallow water, where UVB levels can be high, into deeper waters with lower UVB transmittance. However, these two microhabitats have very different thermal profiles, creating a trade-off between exploiting warm waters with high UVB levels and avoiding UVB by seeking cooler, deeper regions of ponds. I explored the microhabitat use of larvae of four species through a series of laboratory experiments, field experiments, and observational field transects at three different amphibian habitats (Chapter 4). Larvae did not avoid UVB radiation in either the laboratory or field experiments. Larvae in thermal gradients selected relatively high temperatures regardless of the UVB exposure at these temperatures. In field transects, salamander larvae were most common in deeper, cooler waters where UVB levels were lower. In contrast, anuran larvae were frequently observed in the warmer and shallower regions of each habitat. These regions also had the highest UVB levels, suggesting that anuran larvae are exposed to high levels of UVB due to thermoregulatory behavior. Behavioral avoidance of UVB radiation is not the only mechanism amphibians may use to prevent damage from UVB. Pigments such as melanin may allow larvae to exploit warm shallow waters by absorbing harmful UVB radiation before it causes cellular damage. I tested the efficacy of melanin as a photoprotective pigment in the larvae of two species, Rana cascadae and Pseudacris regilla (Chapter 5). I found no evidence of a photoprotective function for melanin in these larvae. In contrast, lighter colored tadpoles grew more under UVB radiation compared to darker colored tadpoles. Overall, exposure to UVB reduced survival of P. regilla larvae and reduced growth of R. cascadae larvae. Larvae of both of these species were frequently observed in very shallow water with intense solar radiation. This thesis emphasizes the importance of UVB radiation as an environmental stressor in aquatic habitats. Many aquatic organisms are negatively affected by UVB exposure. My thesis work quantitatively demonstrated that UVB radiation is one factor that reduces survival of amphibians and suggests that some species are exposed to high levels of UVB radiation in natural habitats. While UVB radiation is not the sole cause of amphibian population declines, my work suggests that UVB radiation is an important stressor for amphibians that should not be overlooked. In addition, UVB radiation is clearly an important stressor for many other aquatic organisms. Future work should consider the effects of UVB in aquatic systems, particularly the effects of UVB radiation on community structure and ecosystem function. Title: Ultraviolet radiation as an environmental stressor of amphibians Author: Bancroft, Betsy A. My thesis explored the effects of and potential mediating mechanisms for an important environmental stressor, ultraviolet-B (UVB) radiation. UVB radiation has negative effects on organisms in both terrestrial and aquatic systems. I used meta-analysis to quantify the effects of UVB radiation on a diversity of aquatic organisms (Chapter 2). UVB negatively affects aquatic organisms by reducing both survival and growth. In particular, UVB reduces growth of embryos more than any other life history stage. Some taxonomic groups may be more affected by UVB radiation than others. In our analysis, the growth of members of the kingdom Protozoa was suppressed by UVB radiation to a greater degree than any other kingdom. These analyses suggest that UVB is an important stressor in both freshwater and marine systems. Amphibians are a common component of freshwater systems and are experiencing world-wide population declines. These declines may be due to a number of causes including habitat loss, introduced species, global climate change, disease, toxic chemicals and UVB radiation. I used meta-analytic techniques to quantify the effects of UVB radiation on amphibians. By synthesizing the results of 41 articles on the effects of UVB radiation on amphibians (Chapter 3), I found a nearly 2-fold reduction in survival of amphibians exposed to UVB radiation. Salamanders (caudates) appear to be more susceptible to damage from UVB than frogs or toads (anurans). Moreover, survival of larvae was much lower than survival of embryos or metamorphic individuals under UVB radiation. In addition, I used factorial meta-analytic techniques to explore the interaction between UVB radiation and other stressors in amphibian habitats. UVB radiation acted synergistically with other stressors to reduce survival of amphibians. Behavioral avoidance of UVB radiation may help mediate the negative effects of UVB radiation on amphibians. In aquatic systems, behavioral avoidance usually requires movement out of shallow water, where UVB levels can be high, into deeper waters with lower UVB transmittance. However, these two microhabitats have very different thermal profiles, creating a trade-off between exploiting warm waters with high UVB levels and avoiding UVB by seeking cooler, deeper regions of ponds. I explored the microhabitat use of larvae of four species through a series of laboratory experiments, field experiments, and observational field transects at three different amphibian habitats (Chapter 4). Larvae did not avoid UVB radiation in either the laboratory or field experiments. Larvae in thermal gradients selected relatively high temperatures regardless of the UVB exposure at these temperatures. In field transects, salamander larvae were most common in deeper, cooler waters where UVB levels were lower. In contrast, anuran larvae were frequently observed in the warmer and shallower regions of each habitat. These regions also had the highest UVB levels, suggesting that anuran larvae are exposed to high levels of UVB due to thermoregulatory behavior. Behavioral avoidance of UVB radiation is not the only mechanism amphibians may use to prevent damage from UVB. Pigments such as melanin may allow larvae to exploit warm shallow waters by absorbing harmful UVB radiation before it causes cellular damage. I tested the efficacy of melanin as a photoprotective pigment in the larvae of two species, Rana cascadae and Pseudacris regilla (Chapter 5). I found no evidence of a photoprotective function for melanin in these larvae. In contrast, lighter colored tadpoles grew more under UVB radiation compared to darker colored tadpoles. Overall, exposure to UVB reduced survival of P. regilla larvae and reduced growth of R. cascadae larvae. Larvae of both of these species were frequently observed in very shallow water with intense solar radiation. This thesis emphasizes the importance of UVB radiation as an environmental stressor in aquatic habitats. Many aquatic organisms are negatively affected by UVB exposure. My thesis work quantitatively demonstrated that UVB radiation is one factor that reduces survival of amphibians and suggests that some species are exposed to high levels of UVB radiation in natural habitats. While UVB radiation is not the sole cause of amphibian population declines, my work suggests that UVB radiation is an important stressor for amphibians that should not be overlooked. In addition, UVB radiation is clearly an important stressor for many other aquatic organisms. Future work should consider the effects of UVB in aquatic systems, particularly the effects of UVB radiation on community structure and ecosystem function. Close