Intellectual merit: Knowledge of geographic patterns in adaptive genetic variation is crucial to species conservation, yet in marine systems our understanding of this phenomenon is virtually nil. Until recently, the belief has been that because most marine species have highly dispersive or mobile life stages, local adaptation could occur only on broad geographic scales. This view is supported by comparatively low levels of genetic variation among populations as indexed by surveys of DNA markers neutral to selection. Phenotypic variation is expected to be largely of environmental origin, especially for physiological traits that are highly sensitive to environmental conditions. Stimulated by studies of the Atlantic silverside (Menidia menidia) and other species, these long-held beliefs are rapidly changing. The silverside shows dramatic evidence of highly structured local adaptation in a suite of coevolving physiological and morphological traits tightly associated with climate change across latitudes along the east coast of North America. Yet preliminary data from molecular genetic surveys suggest extensive gene flow along the entire latitudinal range. This project will address two central problems. The first concerns the micro-geography of local adaptation. How finely scaled is it? How is it influenced by gene flow? Is it closely tied to physical features of the coastline? Do multiple traits co-vary similarly along the same gradient? The second problem focuses on the evolution of growth rate, a trait that strongly displays countergradient latitudinal variation not only in the silverside but also in numerous other taxa. Recent experiments show that growth rate can evolve very rapidly in response to size-selective mortality, including genetic changes caused by fishing. This project will examine the correlates of growth rate evolution. We will study how trade-offs with growth rate influence development, behavior, morphology, and the ability of animals to defend against disease. This research integrates biogeography, physiology, quantitative and molecular genetics, behavior, immunology, and developmental biology. It draws upon natural and experimentally evolved populations, thereby allowing rigorous testing of hypotheses that would be impossible in most other marine species. Broader Implications: This project unites the experience of a senior investigator with the skills of two emerging junior faculty of minority background. Students working on the project will have a unique opportunity to experience both ecological and molecular genetic approaches to marine conservation. Because of the continuous maintenance and availability of captive populations of the silverside at the Flax Pond Marine Laboratory, this project provides excellent opportunities for engaging the public in science through student research projects, class demonstrations, and tours. In addition, the extensive worldwide publicity and interest generated by our recent findings on evolutionary effects of size-selective fishing represent an excellent opportunity to increase public understanding of the principles of evolution and how they affect contemporary societal issues.
