UC Santa Barbara

Global climate change will likely impose selective pressures on biodiversity to not only increase limits for environmental stress, but the phenotypic plasticity of those limits. While we know a great deal about natural selection on performance traits such as upper thermal tolerance, our knowledge of the evolution of plastic responses to the environment is limited. Whether and when the plasticity of performance traits like thermal tolerance and body size incur fitness costs and benefits is unclear. Opposing theories and a lack of empirical research have resulted in a poor understanding of genetic variation underpinning adaptive phenotypic plasticity. Here I report the results of my dissertation research, which aimed to study ecological and evolutionary processes shaping (i) fitness effects of plasticity in thermal tolerance, (ii) intraspecific variation in plastic and evolved responses to warming, and (iii) the heritability of plastic responses to the environment. Studying populations and families of two coastal marine invertebrates, the intertidal copepod Tigriopus californicus and the purple sea urchin Strongylocentrotus purpuratus, I demonstrated potential for plastic responses to global change to evolve via natural selection evidenced by fitness effects and heritability of phenotypic plasticity. However, this evolution may be constrained by factors including fitness tradeoffs between performance and its plasticity, low genetic variation for maladaptive plasticity, and countergradient variation in performance reducing genetic variation for plasticity.