The ecological and evolutionary effects of environmental perturbations on populations and communities

Environmental perturbations can provide ideal situations to study eco-evolutionary dynamics (feedback loops between ecological and evolutionary interactions) on short timescales. Yet, studies of these dynamics in marine pelagic species, whose populations are not clearly defined, risk obscuring causal relationships. Studies of eco-evolutionary relationships in terrestrial and freshwater systems benefit from utilizing microcosms, which can act as ‘natural laboratories’ to allow better measures of the acting processes. Yet, only recently have marine systems been recognized to have analogous microcosms. I utilized one such marine microcosm – marine lakes – to study a contained population of a pelagic scyphozoan predator, Mastigias papua. Across the Indo-West Pacific, Mastigias spp. occurs in two distinct morphological ecotypes – ocean and lake – that occur locally proximate to one another, yet appear similar within ecotype across the region. I established the evolutionary history, locally and regionally, by reconstructing phylogenetic and intraspecific genetic relationships utilizing two nuclear (H3a, H3b) and three mitochondrial (COI, COIII, 16S) markers. Phylogenetic reconstruction was complemented by morphological characters to reconstruct the macroevolution of ecotypes and test three hypotheses that explain the geographic distribution of ecotypes. Periodic perturbations, consisting at least in part of a highly stratified layer of warmer and more saline water and the disappearance of the medusae stage of Mastigias, occur in the marine lakes. I examined the microevolutionary effects of one such event on the genetics, morphology and behavior in one Palauan lake population. I used the genetic data to exclude one possible hypothesis that explained the difference in morphology and behavior upon medusae return than before the perturbation event. Finally, I examined the associations between environmental factors and Mastigias medusa population size following another such perturbation in a different Palauan marine lake over a decade, as well as examined the associations between medusae and other microplankton population fluctuations. These studies build a foundation for eco-evolutionary work in marine systems. The comparative framework across spatial and temporal scales can elucidate patterns and processes that act in the marine realm. As climatic variability increases, it is increasingly important to understand the eco-evolutionary dynamic of systems and the potential impacts perturbations can have on those systems