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• 1. [Article] Indirect effects of ultraviolet-B radiation on larval amphibians as mediated by food quality and trophic interactions

  Ultraviolet-B radiation (UVB) is an abiotic stressor in both terrestrial and aquatic systems. The stratospheric ozone layer, depleted due to anthropogenic activities and the cause of elevated UVB at earth's ...

  Citation × Citation Citation Abstract Copy Title: Indirect effects of ultraviolet-B radiation on larval amphibians as mediated by food quality and trophic interactions Author: Scheessele, Erin A. Ultraviolet-B radiation (UVB) is an abiotic stressor in both terrestrial and aquatic systems. The stratospheric ozone layer, depleted due to anthropogenic activities and the cause of elevated UVB at earth's surface over the last four decades, is predicted to recover by 2065. However, UVB levels in aquatic systems may continue to increase as UVB penetration of the water column increases due to acidification, warming and changing precipitation patterns. Subsequent to the 1974 prediction and 1985 discovery of the "ozone hole", much work was done investigating the direct effects of UVB on organisms. Much less work has been done examining the role of UVB as a stressor in the context of communities and food webs. Amphibian population declines are one facet of the current crisis of loss in biodiversity, and some population declines may be linked to exposure to UVB radiation. When some amphibian embryos, larvae and juveniles are exposed to UVB, they can experience increased mortality, slowed growth and development, increased malformations, as well as increased susceptibility to other biotic and abiotic stressors including pathogens and competitors. My research moves beyond direct effects of UVB on amphibians and asks what indirect effects may be transmitted via trophic interactions when examined in the context of aquatic communities and food webs. I first focused on how a UVB-exposed natural diet affects early larval growth and development in two anuran species, Pseudacris regilla and Rana cascadae. Growth and development of R. cascadae did not differ between a UVB-exposed and UVB-shielded diet, but P. regilla grew less on the UVB-exposed diet. Previous work has shown that P. regilla is less vulnerable when exposed directly to UVB. My research emphasizes that the main effect of UVB on an organism may not be a direct effect. I next investigated whether P. regilla and Bufo boreas would distinguish between diets when offered both a UVB-exposed and UVB-shielded diet consisting of natural algal assemblage reared in the field. Bufo boreas demonstrated no selectivity, while P. regilla spent more time near the UVB-shielded algae. An ability to discern UVB-stressed food may allow larvae to avoid indirect UVB effects. Analyses in these two experiments indicate that there were no direct effects of UVB at the producer trophic level. Bioassays, however, did indicate a UVB-induced change in the producer trophic level with implications for growth of consumers. My findings imply that effects of UVB on adjacent trophic levels may not be predicted from analysis at one level. In the final study, I investigated the direct and indirect effects of ambient UVB on salamander larvae and a tritrophic freshwater community. Both UVB and predation were forces that structured the community, and there is potential for a direct effect of UVB on the salamanders to mitigate their role as predator. The field of UVB-research must continue to mature in its investigations of effects, both direct and indirect, in evermore real and complex contexts. Title: Indirect effects of ultraviolet-B radiation on larval amphibians as mediated by food quality and trophic interactions Author: Scheessele, Erin A. Ultraviolet-B radiation (UVB) is an abiotic stressor in both terrestrial and aquatic systems. The stratospheric ozone layer, depleted due to anthropogenic activities and the cause of elevated UVB at earth's surface over the last four decades, is predicted to recover by 2065. However, UVB levels in aquatic systems may continue to increase as UVB penetration of the water column increases due to acidification, warming and changing precipitation patterns. Subsequent to the 1974 prediction and 1985 discovery of the "ozone hole", much work was done investigating the direct effects of UVB on organisms. Much less work has been done examining the role of UVB as a stressor in the context of communities and food webs. Amphibian population declines are one facet of the current crisis of loss in biodiversity, and some population declines may be linked to exposure to UVB radiation. When some amphibian embryos, larvae and juveniles are exposed to UVB, they can experience increased mortality, slowed growth and development, increased malformations, as well as increased susceptibility to other biotic and abiotic stressors including pathogens and competitors. My research moves beyond direct effects of UVB on amphibians and asks what indirect effects may be transmitted via trophic interactions when examined in the context of aquatic communities and food webs. I first focused on how a UVB-exposed natural diet affects early larval growth and development in two anuran species, Pseudacris regilla and Rana cascadae. Growth and development of R. cascadae did not differ between a UVB-exposed and UVB-shielded diet, but P. regilla grew less on the UVB-exposed diet. Previous work has shown that P. regilla is less vulnerable when exposed directly to UVB. My research emphasizes that the main effect of UVB on an organism may not be a direct effect. I next investigated whether P. regilla and Bufo boreas would distinguish between diets when offered both a UVB-exposed and UVB-shielded diet consisting of natural algal assemblage reared in the field. Bufo boreas demonstrated no selectivity, while P. regilla spent more time near the UVB-shielded algae. An ability to discern UVB-stressed food may allow larvae to avoid indirect UVB effects. Analyses in these two experiments indicate that there were no direct effects of UVB at the producer trophic level. Bioassays, however, did indicate a UVB-induced change in the producer trophic level with implications for growth of consumers. My findings imply that effects of UVB on adjacent trophic levels may not be predicted from analysis at one level. In the final study, I investigated the direct and indirect effects of ambient UVB on salamander larvae and a tritrophic freshwater community. Both UVB and predation were forces that structured the community, and there is potential for a direct effect of UVB on the salamanders to mitigate their role as predator. The field of UVB-research must continue to mature in its investigations of effects, both direct and indirect, in evermore real and complex contexts. Close

• 2. [Article] Effects of pesticides on amphibians with special reference to the pyrethroid insecticide, cypermethrin

  Pollution by pesticides is a ubiquitous concern for wildlife. The effects of pesticides are especially concerning in aquatic environments, which are particularly vulnerable as they have several exposure ...

  Citation × Citation Citation Abstract Copy Title: Effects of pesticides on amphibians with special reference to the pyrethroid insecticide, cypermethrin Author: Biga, Lindsay M. Pollution by pesticides is a ubiquitous concern for wildlife. The effects of pesticides are especially concerning in aquatic environments, which are particularly vulnerable as they have several exposure routes for the influx of chemicals. These effects are of particular concern as biodiversity loss reaches unprecedented rates. This includes recent declines of amphibian populations and loss of amphibian species. Pesticide exposure may contribute to some amphibian populations and extinctions. This dissertation explores the effects of pesticides on amphibians, with particular reference to the pyrethroid insecticide cypermethrin. I first synthesized acute toxicity data of pesticides for amphibians from the literature (Chapter 2). Using 96h LC50 values for amphibian larvae exposed to insecticides, herbicides, and fungicides, I determined that amphibian species cannot be systematically classified as sensitive or tolerant to pesticides. Rather, relative acute lethal toxicities varied among species and between chemicals and types of pesticides even within a species, indicating that no amphibian species from this analysis can represent anticipated toxic effects to all amphibians. I next examined the differences in sensitivity to cypermethrin among three developmental stages for three anuran (frog) species (Chapter 3). I experimentally exposed embryos, recently hatched larvae and larvae with limb buds to cypermethrin in the laboratory. Exposure to cypermethrin had lethal and sublethal effects on some species and stages, but not all. The Pacific treefrog (Pseudacris regilla) was the most sensitive species and the early larval stage was the most sensitive for these three species. Additionally, cypermethrin exposure induced abnormal behavior in response to prodding for some species and stages. These results indicate differences in sensitivity to cypermethrin among species of amphibians. To further understand differences in sensitivity to pesticides among amphibians, I compared how three populations of P. regilla responded to cypermethrin exposure (Chapter 4). I performed a time-to-death assay in the laboratory, exposing newly hatched larvae from each population to cypermethrin under identical conditions. All populations had high rates of mortality when exposed to cypermethrin compared to unexposed controls and populations varied in the time to death. Moreover, exposed individuals were smaller than unexposed controls. Interestingly, population sensitivity did not appear to be associated with proximity to agriculture, but rather with elevation gradient, indicating that an evolved tolerance to pesticide exposure is not the mechanism for the differences in sensitivity observed here. To investigate the effects of cypermethrin on amphibians within a community context, I studied exposure in mesocosms (Chapter 5). I set up semi-natural aquatic ponds in enclosures that contained zooplankton, phytoplankton, and periphyton along with amphibian larvae. I experimentally exposed these mesocosms to cypermethrin and measured the effects on the amphibians and the other members of the community. Cypermethrin affected the entire aquatic community, even at the lowest dose, indicating the direct and indirect deleterious effects of cypermethrin on both invertebrate and vertebrate species in an aquatic community. This dissertation provides needed data on the effects of the pyrethroid insecticide cypermethrin on amphibians and their communities. Understanding the toxicity of newer, commonly used pesticides to non-target organisms is important as conservation biologists and managers make efforts to combat future amphibian population declines which may be associated with chemicals in the environment. Title: Effects of pesticides on amphibians with special reference to the pyrethroid insecticide, cypermethrin Author: Biga, Lindsay M. Pollution by pesticides is a ubiquitous concern for wildlife. The effects of pesticides are especially concerning in aquatic environments, which are particularly vulnerable as they have several exposure routes for the influx of chemicals. These effects are of particular concern as biodiversity loss reaches unprecedented rates. This includes recent declines of amphibian populations and loss of amphibian species. Pesticide exposure may contribute to some amphibian populations and extinctions. This dissertation explores the effects of pesticides on amphibians, with particular reference to the pyrethroid insecticide cypermethrin. I first synthesized acute toxicity data of pesticides for amphibians from the literature (Chapter 2). Using 96h LC50 values for amphibian larvae exposed to insecticides, herbicides, and fungicides, I determined that amphibian species cannot be systematically classified as sensitive or tolerant to pesticides. Rather, relative acute lethal toxicities varied among species and between chemicals and types of pesticides even within a species, indicating that no amphibian species from this analysis can represent anticipated toxic effects to all amphibians. I next examined the differences in sensitivity to cypermethrin among three developmental stages for three anuran (frog) species (Chapter 3). I experimentally exposed embryos, recently hatched larvae and larvae with limb buds to cypermethrin in the laboratory. Exposure to cypermethrin had lethal and sublethal effects on some species and stages, but not all. The Pacific treefrog (Pseudacris regilla) was the most sensitive species and the early larval stage was the most sensitive for these three species. Additionally, cypermethrin exposure induced abnormal behavior in response to prodding for some species and stages. These results indicate differences in sensitivity to cypermethrin among species of amphibians. To further understand differences in sensitivity to pesticides among amphibians, I compared how three populations of P. regilla responded to cypermethrin exposure (Chapter 4). I performed a time-to-death assay in the laboratory, exposing newly hatched larvae from each population to cypermethrin under identical conditions. All populations had high rates of mortality when exposed to cypermethrin compared to unexposed controls and populations varied in the time to death. Moreover, exposed individuals were smaller than unexposed controls. Interestingly, population sensitivity did not appear to be associated with proximity to agriculture, but rather with elevation gradient, indicating that an evolved tolerance to pesticide exposure is not the mechanism for the differences in sensitivity observed here. To investigate the effects of cypermethrin on amphibians within a community context, I studied exposure in mesocosms (Chapter 5). I set up semi-natural aquatic ponds in enclosures that contained zooplankton, phytoplankton, and periphyton along with amphibian larvae. I experimentally exposed these mesocosms to cypermethrin and measured the effects on the amphibians and the other members of the community. Cypermethrin affected the entire aquatic community, even at the lowest dose, indicating the direct and indirect deleterious effects of cypermethrin on both invertebrate and vertebrate species in an aquatic community. This dissertation provides needed data on the effects of the pyrethroid insecticide cypermethrin on amphibians and their communities. Understanding the toxicity of newer, commonly used pesticides to non-target organisms is important as conservation biologists and managers make efforts to combat future amphibian population declines which may be associated with chemicals in the environment. Close