Graduate Theses & Dissertations

Contemporary adaptive shifts in the physiology and life history of Pumpkinseed (Lepomis gibbosus) introduced into a warm climate
Contemporary evolution has the potential to help limit the biological impact of rapidly changing climates, however it remains unclear whether wild populations can respond quickly enough for such adaptations to be effective. In this thesis, I used the introduction of native North American Pumpkinseed (Lepomis gibbosus) into the milder climate of Europe over 140 years ago, as a 'natural' experiment to test for contemporary evolution to a change in climate in wild populations. In 2008, four outdoor pond colonies were established in central Ontario using adult Pumpkinseed from two native Canadian populations, and two non-native populations from northeastern Spain. By raising native and non-native Pumpkinseed within a common environment, this design minimized the impact of phenotypic plasticity on differential trait expression, and allowed me to interpret differences in the phenotype among pond-reared Pumpkinseed as evidence of genetic differences among populations. I demonstrated that Canadian and Spanish Pumpkinseed have similar thermal physiology except when acclimated to seasonally warm temperatures; trait differences are consistent with Spanish Pumpkinseed being better adapted to a warmer climate. Populations also had similar overwintering ecology, however some differences, such as higher survival under starvation conditions and greater energetic benefits associated with winter feeding, indicated that Canadian populations are better adapted to harsh winter conditions typical of the native range. Finally, I determined that the relatively fast life history expressed in wild European Pumpkinseed is largely driven by plastic responses to the local environment; however, the higher reproductive investment by European populations has a genetic basis. Most climate change research considers taxa that are expected to be negatively impacted by warming: my research demonstrates that even warm-tolerant taxa that are unlikely to experience strong climatic selective forces can respond to a warming environment through evolutionary changes. The potential for adaptive contemporary evolution in warm-tolerant taxa should be taken into account when predicting future ecosystem effects of climate change, and when planning management strategies for species introduced into novel climates. Author Keywords: climate change, contemporary evolution, fish, non-native species, thermal biology, winter ecology
role of corticosterone in breeding effort and reproductive success in tree swallows
Glucocorticoids (e.g., corticosterone (CORT)) are hypothesized to mediate decisions regarding reproductive investment during breeding, but the directionality of the relationship is not clear. The CORT-fitness hypothesis posits that high levels of CORT arise from challenging environmental conditions in which an individual will conserve resources for future reproduction or self-maintenance, and thus result in lower reproductive success (a negative relationship). In contrast, the CORT-adaptation hypothesis suggests that, during energetically demanding periods, CORT will mediate physiological or behavioural changes that result in increased reproductive investment and success (a positive relationship). Inconsistencies arise due to the various species and life-history stages studied, and the complex interactions between fitness and glucocorticoids. Using an experimental approach, I investigated the relationship between CORT and reproductive success by manipulating baseline CORT levels in female tree swallows Tachycineta bicolor prior to laying using silastic implants. Implants failed to raise CORT levels of females during either incubation or the nestling stage, and maternal treatment had no effect on indices of fitness at either stage. Using a correlative approach, partial support for the CORT-adaptation hypothesis was found: There was a positive relationship between CORT and hatching success. This only occurred when CORT was measured during incubation, when baseline CORT levels may stimulate increased reproductive effort and success. In contrast, during the nestling stage baseline CORT levels were not related to reproductive investment or success. Maternal CORT levels during incubation also did not influence nestling phenotype, although nestling stress CORT levels were higher in individuals that survived to fledging. In conclusion, CORT mediates reproductive effort and success during some breeding stages, but it is still unclear why this is the case and whether this same pattern will prevail in other contexts. Author Keywords: corticosterone, HPA axis, maternal effects, reproductive success, tree swallow

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