Electronic Thesis and Dissertation Repository


Doctor of Philosophy




Bryan Neff


Ecosystems are being altered at unprecedented rates with little knowledge of the potential impacts on biodiversity. Two of the most pressing contemporary anthropogenic stressors are pollution and global warming. Species can respond to these stressors via dispersal, phenotypic plasticity, or evolutionary adaptation. Many species, especially aquatic organisms, experience ecological or physical barriers to dispersal and will therefore have to respond via phenotypic plasticity or evolutionary responses. I examined the responses of multiple traits associated with fitness in fish to pollution and increased temperature using a 2 × 2 common garden experimental design. I examined the effects of pollution on behaviour in a natural population of brown bullheads (Ameiurus nebulosus), and increased temperature on population demographics, life history traits, reproductive traits, and the immune response in experimental populations of guppies (Poecilia reticulata). The plastic responses to pollution were increased locomotion and decreased aggression and the plastic responses to increased temperature were decreased age at maturity, sperm length, sperm velocity, and sperm path linearity. These results are indicative of stress responses by the fish and could potentially decrease reproductive success and survival. Next, I measured reproductive output in experimental populations of guppies and found that, after many generations in elevated temperature, females produced fewer, smaller broods than control populations. However, I found no effect of temperature on census population size, survivorship, sex ratio, size-at-age, or the immune response, indicating that, despite the decreased reproductive output, guppies appear to cope with the increased temperature. Additionally, genetic diversity in the elevated temperature populations decreased more rapidly than control populations, and was equivalent to one quarter the effective population size relative to the controls. This latter result shows a clear signature of selection. Indeed, I found that sperm length displayed an evolutionary response in an estimated 2-3 generations. And in a natural population of bullheads, after an estimated 33 generations, I found an evolutionary response in locomotion and aggression. However, the reduced genetic diversity could lower the adaptive potential of populations to future stressors. I discuss these results in the context of the scope of organisms to rapidly respond to anthropogenic stressors.