RESEARCH
Research in the Walsh Lab has two overarching goals: (1) to further understanding of the ecological mechanisms (i.e., predation, competition, human-induced environmental change) that drive microevolutionary changes in natural populations, and (2) to quantify the importance of evolution as agent of ecological change.
Evolution in LTER experiments
The long-term ecological research (NSF-LTER) program has documented extensive ecological changes in response to such factors as rising temperatures, land-use change, nutrient input, and invasive species. These observed shifts in ecological conditions have the clear potential to exert selection and promote evolutionary change. Yet, the evolutionary consequences of ecological changes in these multi-year programs of research are generally unexplored. Long-term studies provide the unique opportunity to elucidate the tempo and trajectory of evolutionary change. Such information is needed to begin to dissect the reciprocal contributions of evolution to ecological organization.
We were recently funded (NSF DEB 1544356) to exploit long-term ecological data and experiments to ask when, where, and how often changes observed in aquatic organisms represent true evolutionary responses. Research at the Arctic (ARC) LTER and Northern Temperate Lakes (NTL) LTER sites have quantified patterns of ecological change for >30 years in response to such factors as rising temperatures, increased urbanization, eutrophication, and the spread of exotic species. This project is first utilizing data, samples, and experiments from over twenty lakes in Wisconsin and Alaska to test the influence of many common environmental stressors on changes in zooplankton traits. My team and I will then perform experiments to test for genetic changes across these diverse ecosystems. The ultimate goal of research in these systems is to build a research program that utilizes extensive information on observed long-term ecological change to address key unknown questions regarding the interplay between ecological and evolutionary forces in the wild.
We were recently funded (NSF DEB 1544356) to exploit long-term ecological data and experiments to ask when, where, and how often changes observed in aquatic organisms represent true evolutionary responses. Research at the Arctic (ARC) LTER and Northern Temperate Lakes (NTL) LTER sites have quantified patterns of ecological change for >30 years in response to such factors as rising temperatures, increased urbanization, eutrophication, and the spread of exotic species. This project is first utilizing data, samples, and experiments from over twenty lakes in Wisconsin and Alaska to test the influence of many common environmental stressors on changes in zooplankton traits. My team and I will then perform experiments to test for genetic changes across these diverse ecosystems. The ultimate goal of research in these systems is to build a research program that utilizes extensive information on observed long-term ecological change to address key unknown questions regarding the interplay between ecological and evolutionary forces in the wild.
Cascading Evolutionary Change in Lakes
There has been much interest in the potential for evolutionary diversification to impact ecological properties and promote reciprocal interactions between ecological and evolutionary forces, or eco-evolutionary dynamics. It has only recently been shown that intraspecific diversification can impact the properties of populations, communities, and ecosystems. However, this body of research has focused on feedbacks between variation in one organism and the rest of the environment. This is important because natural systems are inherently complex and evolutionary changes in one organism, and associated ecological impacts of these changes, may alter the selective landscape and promote a series of evolutionary changes that propagate throughout the food web. In collaboration with David Post (Yale University), we are exploring the importance of cascading evolution in lakes in Connecticut. In this study system, lakes contain populations of a dominant fish predator, the alewife (Alosa pseudoharengus), that either does (anadromous) or does not (landlocked) migrate between the marine and freshwater environments for the purposes of spawning. Our research has shown that intraspecific variation in alewives has driven evolutionary divergence in their zooplankton prey (Daphnia). This includes significant changes in life history traits as well as divergence in phenotypic plasticity (Daphnia responses to predators). We have also shown that evolution in Daphnia, in turn, has reciprocal impacts on community properties and ecosystem function. Current and future topics of research include: cascading selection on multi-generation plasticity in Daphnia, life history trade-offs in Daphnia, the impact of alewife variation onDaphnia behavior.
Indirect Effects and Evolutionary Change
Much work has shown that predators cause evolution via the consumption of prey. However, the traditional evolutionary perspective is that interactions between predator and prey occur in a vacuum; no consideration is given to feedbacks associated with community- or ecosystem-level processes. This is important because, by reducing prey abundances and increasing food to survivors, predators almost always have indirect effects. Indirect effects are ubiquitous in nature and represent a major focus of ecological research. Moreover, the ecological consequences of indirect effects also provide a link to evolution because it is generally assumed that resource availability influences patterns of evolutionary change. Research in my lab continues to explore links between the indirect effects of predators and life history evolution in a killifish, Rivulus hartii on the island of Trinidad (in collaboration with David Reznick, UC Riverside). This research has focused on a killifish, Rivulus hartii, because they exhibit an enhanced dispersal capability, which allows them to colonize a diversity of aquatic habitats. As a result, Rivulusare located across a series of communities that differ in both the direct and indirect impacts of predators on the ecology of Rivulus. In this system, we utilize a combination of ecological (mark-recapture studies, field surveys) and evolutionary approaches (common garden experiments, introduction experiments) to quantify selection due to indirect effects.