In addition to the mechanisms that presently structure these communities, I am exploring how the abilities of these species to evade predators and acquire and utilize resources have been shaped by evolutionary processes in these two lake types. Phylogenetic studies using morphological characters and mitochondrial DNA data indicate that fish lakes were the ancestral habitat for Enallagma, and at least two separate lineages of Enallagma have invaded dragonfly-dominated lakes. Associated with these habitat shifts into dragonfly lakes, these Enallagma lineages have undergone rapid evolutionary changes in behavioral, morphological and biochemical characters affecting swimming performance to make them better at avoiding dragonfly predators. I have also shown in field experiments that dragonfly predation is still a potent agent of natural selection on these characters. This work represents one of the first studies of adaptation to combine phylogenetic studies with functional studies of performance, ecological studies of selective agents, and measurements of natural selection in the field.
I have extended this work to understand how the more complex network of characters influencing the foraging rate/predation risk trade-off faced by all these species evolves when lineages are shifted between selective environments. This work involves a number of behavioral and physiological studies on 15 species of Enallagma and Ischnura. These studies include behavioral experiments on feeding and activity responses to the presence of predators, biochemical studies of the metabolic pathways involved in influencing burst swimming performance, aerobic respiratory studies, the amounts of energy reserves maintained in glycogen and lipid pools, and analyses of digestive physiological performance for digestive capacity and efficiencies.
One exciting finding was that different species show very different physiological stress responses to the presence of mortality threats. We are currently quantifying the levels of physiological stress induced in various species to explore its evolutionary trajectories within the family, the allocation of ingested food to various molecular pools that fuel metabolic work (i.e., protein, carbohydrates, triglycerides), and the degree of hormonal mediation of these responses. We are also applying genomic methodologies to begin characterizing the molecular basis underlying this difference among species.
McPeek, M. A. 1995. Testing hypotheses about evolutionary change on single branches of a phylogeny using evolutionary contrasts. American Naturalist 145:686-703.
McPeek, M. A. 1995. Morphological evolution mediated by behavior in the damselflies of two communities. Evolution 49:749-769.
McPeek, M. A., A. K. Schrot, and J. M. Brown. 1996. Adaptation to predators in a new community: Swimming performance and predator avoidance in damselflies. Ecology 77:617-629.
McPeek, M. A. 1997. Measuring phenotypic selection on an adaptation: lamellae of damselflies experiencing dragonfly predation. Evolution 51:459-466.
McPeek, M. A. 1999. Biochemical evolution associated with antipredator adaptation in damselflies. Evolution 53:1835-1845.
McPeek, M. A. 2000. Predisposed to adapt? Clade-level differences in characters affecting swimming performance in damselflies. Evolution 54:2072-2080.
Peckarsky, B. L., B. W. Taylor, A. R. McIntosh, M. A. McPeek, and D. A. Lytle. 2001. Variation in mayfly size at metamorphosis as a developmental response to risk of predation. Ecology 82:740-757.
McPeek, M. A., M. Grace, J. M. L. Richardson. 2001. Physiological and behavioral responses to predators shape the growth/predation risk trade-off in damselflies. Ecology 82:1535-1545.
Stoks, R., M. A. McPeek, and J. L. Mitchell. 2003. The evolution of anti-predator behavior as lineages adapt to different habitats: damselflies in fish and dragonfly lakes. Evolution 57:574-585.
Stoks, R., and M. A. McPeek. 2006. A tale of two diversifications: reciprocal habitat shifts to fill ecological space along the pond permanence gradient. American Naturalist 168:S50-S72.