Browsing by Author "Willson, John D."

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    Like mother, like offspring: maternal and offspring wound healing correlate in snakes
    Hopkins, Brittney Cole; Chin, Stephanie Y.; Willson, John D.; Hopkins, William A. (Company of Biologists Ltd., 2013-07)
    Immune function early in life can be influenced by parental effects and the environment, but it remains unclear how these two factors may interact to influence immunocompetence. We evaluated maternal and environmental contributions to offspring healing ability in a viviparous reptile, the northern watersnake (Nerodia sipedon). We measured wound healing rates, a highly integrative and biologically relevant measure of innate immunity, of females and their offspring collected from sites contaminated with a toxic heavy metal and compared them with those of individuals from reference sites. We found that female watersnakes that healed the fastest produced offspring that also exhibited faster healing rates. However, we detected no influence of environmental pollution on maternal or offspring healing rates. To our knowledge, our study is the first to correlate maternal and offspring wound healing ability in a wild vertebrate.
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    Making leaps in amphibian ecotoxicology: translating individual-level effects of contaminants to population viability
    Willson, John D.; Hopkins, William A.; Bergeron, Christine M.; Todd, B. D. (Ecological Society of America, 2012-09)
    Concern that environmental contaminants contribute to global amphibian population declines has prompted extensive experimental investigation, but individual-level experimental results have seldom been translated to population-level processes. We used our research on the effects of mercury (He) on American toads (Bufo americanus) as a model for bridging the gap between individual-level contaminant effects and amphibian population viability. We synthesized the results of previous field and laboratory studies examining effects of Hg throughout the life cycle of B. americanus and constructed a comprehensive demographic population model to evaluate the consequences of Hg exposure on population dynamics. Our model explicitly considered density-dependent larval survival, which is known to be an important driver of amphibian population dynamics, and incorporated two important factors that have seldom been considered in previous amphibian modeling studies: environmental stochasticity and sublethal effects. We demonstrated that decreases in embryonic survival and sublethal effects (c.a., reduced body size) that delay maturation have minor effects on population dynamics, whereas contaminant effects that reduce late-larval or post-metamorphic survival have important population-level consequences. We found that excessive Hg exposure through maternal transfer or larval diet, alone, had minor effects on B. americanus populations. Simultaneous maternal and dietary exposure resulted in reduced population size and a dramatic increase in extinction probability, but explicit prediction of population-level effects was dependent on the strength of larval density dependence. Our results suggest that environmental contaminants can influence amphibian population viability, but that highly integrative approaches are needed to translate individual-level effects to populations.
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    Prey morphology constrains the feeding ecology of an aquatic generalist predator
    Willson, John D.; Hopkins, William A. (Ecological Society of America, 2011-03)
    Resource availability and accessibility are primary factors guiding the distribution and abundance of organisms. For generalists, prey availability reflects both prey abundance and differences in quality among prey taxa. Although some aspects of prey quality, such as nutritional composition, are well studied, our understanding of how prey morphology contributes to overall prey quality is limited. Because snakes cannot reduce prey size by mastication, many aspects of their feeding ecology (e.g., maximum prey size, feeding performance, and the degree of postprandial locomotor impairment) may be affected by prey shape. We conducted a uniquely comprehensive comparison of prey quality for a generalist species, the banded watersnake (Nerodia fasciata), using prey that were similar in mass and presumably similar in nutritional composition but different in shape and habitat association. Specifically, we compared nutritional composition and shape of paedomorphic salamanders (Ambystoma talpoideum) and sunfish (Lepomis marginatus) and used a series of repeated-measures experiments to examine feeding performance (number of prey consumed, maximum prey size, and intra-oral transport time), digestive metabolism (specific dynamic action, SDA), and postprandial locomotor performance of snakes fed Ambystoma and Lepomis. Cost of digestion was similar between the prey types, likely reflecting their similar nutritional composition. However, snakes consumed larger Ambystoma than Lepomis and intra-oral transport time was much shorter for Ambystoma. Snakes fed Lepomis also suffered greater reduction in crawling speed than those fed Ambystoma. These differences highlight the need for behaviorally integrated approaches to understanding prey quality and support field observations of the importance of amphibian prey for juvenile watersnakes.