Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item Thermal Physiology in a Widespread Lungless Salamander(2018) Novarro, Alexander Joseph; Bely, Alexandra E; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Understanding species responses to climate change has become a top priority for conservation biologists. Unfortunately, current models often treat species as a single entity, ignoring population-level variation. This approach may result in major oversights when managing widespread species, which generally exhibit physiological variation across their geographic range. The eastern red-backed salamander (Plethodon cinereus) is the most widely distributed Plethodon species, extending farther north than any other lungless salamander. This species’ geographic distribution raises two major questions: How does P. cinereus thrive across a wide range of temperatures, and does it possess thermal adaptations that will buffer the ecological consequences of climate change? To explore these questions, I first examined the effects of elevated temperature on metabolic hormone release rates and physiological performance (i.e., ingestion rate and mass gain) across a latitudinal population gradient. I found that physiological traits and populations differ in their thermal flexibility, and that salamanders from warmer localities are more resilient to elevated temperatures. Second, I performed a study to disentangle the environmental and evolutionary drivers of thermal limits across the geographic range of P. cinereus. I found strong support for evolutionary constraints on lower thermal limits, though there was some degree of plasticity in relation to local environmental temperatures. By contrast, upper thermal limits showed little variation across the species’ geographic range and among clades, and far exceeded survival requirements. Third, I combined laboratory experiments, field observations, and population models to explore the role of behavioral thermoregulation in shaping physiological performance in P. cinereus. I found that individuals are likely to exploit moist conditions at the cost of reduced performance, and that populations living in poor thermal quality habitats have greater thermoregulatory accuracy. Overall, my work demonstrates significant variation in thermal physiology across the geographic range and among lineages of P. cinereus and shows that thermal traits differ in their responsiveness to thermal variability. Together, these results highlight the importance of considering multiple physiological metrics and sampling large geographic areas to understand species’ abundance and distributions, and to assess species’ vulnerability to climate change.Item The effect of relatedness on mating behavior in the satin bowerbird (Ptilonorhynchus violaceus)(2010) Reynolds, Sheila Mayo; Borgia, Gerald; Braun, Michael J.; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Behavior is a main component of sexual selection theory in which male competition and female mate choice influence the evolution of a species. Relatedness commonly affects behavioral interactions, but the potential for relatedness to influence sexual selection is often overlooked. Here I show that relatedness affects mating behaviors in satin bowerbirds. Bowerbirds are a model species for non-resource based mating systems in which males provide only sperm to females, and females are free to mate with their preferred males, typically resulting in high skews in male mating success. Males build stick structures (bowers) on the ground to attract, and copulate with, females. Males compete, in part, by destroying neighboring males' bowers. Females search among multiple adjacent bowers and then select subsets of these males for courtship and then copulation. Automated video monitoring of bowers allows identification of males that destroy bowers and females that visit bowers for courtship or copulation. Using microsatellite genetic markers to estimate relatedness, I show that paternity assignments based on observed copulations match the genetic sires of offspring, supporting the hypotheses that copulations occur only at bowers and that male reproductive success can be reliably estimated from observed copulations. Next, I report that competing males are less aggressive, in the form of bower destructions, towards relatives than non-relatives and that this restraining effect of relatedness on aggression favors the close spatial association of relatives' bowers. These results support the hypothesis that relatedness affects male competition and ability to maintain attractive displays for females. Lastly, I investigate the influence of relatedness on female mate choice. I show that females do not actively prefer or avoid relatives in mate choice. However, females bias the areas in which they search for mates to be inclusive of relatives and then mate randomly with respect to relatedness within their search areas, resulting in tendencies to mate with relatives in some years. This effect of relatedness on female mate searching may be due in part to the spatial association of related males, and highlights the influence of mate searching rather than active mate preferences on overall mate choice patterns.