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Sarah Cohen
Ecological and evolutionary genetics; Marine conservation (415) 338-3750 Hensill 545; Romberg Tiburon Center, Bldg 36, by appt. |
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| Research Interests: I am interested in how ecological, behavioral, and environmental features shape evolution and genetic systems in diverse organisms. Most of my work in marine and estuarine settings has asked questions about how life-history, physiological, or behavioral attributes of species affect population structure. Often the results directly address questions about coastal and marine conservation related to our ability to detect and predict anthropogenic effects on natural populations. In addition, I have a particular interest in the ecology and evolution of recognition systems and have been investigating this both in colonial invertebrates and estuarine fishes. Ongoing projects and areas of interest include: Adaptive change in response to environmental stress We are looking at immunogenetic and detoxication genetic variation in natural fish populations subject to varying pollutant and parasite stress. The Major Histocompatibility Complex (MHC) is the extraordinarily variable genetic system that controls the adaptive immune system in vertebrates. This system is under selection related to disease resistance and, in at least some cases, mate choice or reproductive success as well. One part of this system, the Class II antigen-binding receptor, contains the most polymorphic locus found in any organism thus far, and thus presents intriguing population genetic and molecular evolutionary puzzles about the generation and maintenance of very large numbers of alleles within populations and species. Some questions that we are interested in: How fast can adaptation to novel environmental stresses occur? What genetic mechanisms allow this to occur? What types of life histories most favor rapid genetic adaptation to stress rather than acclimation? Do immunogenetic loci show signals of local environmental degradation? This work is funded by the US EPA STAR grants program, the Hudson River Foundation, and includes collaborations with scientists at Woods Hole Oceanographic Institute, the EPA Atlantic Ecology Division, and the University of Rhode Island. Joelle Anderson is a graduate student at SFSU working on MHC and parasite variation in some mid-Atlantic killifish populations as part of this project. Connections between marine populations Current theory suggests that many organisms exist in a patchy network of populations that are loosely linked but may often have independent dynamics. These metapopulations may include both source populations that provide recruits to many other non-reproducing or non-reseeding populations (called sinks). A first step toward identification of source and sink populations is to combine demographic information with genetic markers to identify patterns of connectedness between local populations. Identification of source and sink populations will provide marine managers with the best possible information for designing fisheries regulations and reserves. Ongoing projects related to these issues are studies using microsatellite and Single Nucleotide Polymorphism (SNP) DNA variation in green sea urchins and lobsters in the Northwest Atlantic and Washington state. This collaborative work is funded by Sea Grant and the Marine Ecosystem Health Program at UC Davis. Evolution of recognition systems in colonial invertebrates Invertebrates from sponges to protochordates have the ability to distinguish self from non-self, an ability we more frequently associate with the vertebrate immune system. Invertebrates across the phylogenetic spectrum show a dazzling diversity of mechanisms and uses for such recognition systems from pathogen recognition to competition for space in crowded marine habitats. These systems operate at molecular, cellular, tissue, and whole organism levels and involve specialized morphology and behavior. Studying these intriguing traits in invertebrates gives us an understanding of biological diversity in form and function and also a means to interpret fundamental processes in development and immunity in both invertebrates and vertebrates. The speciose family of botryllid colonial ascidians shows behavioral variation in space competition apparently related to the evolution of their intraspecific highly variable genetic recognition system. Using techniques from molecular phylogenies and ecology to time-lapse video analysis of behavior, we have been studying the role of recognition systems in speciation and invasion success. Identifying populations and species of introduced marine invertebrates Recently, marine species with limited natural dispersal potential have been recognized as an important group of invaders with an added twist. These local dispersers may have an enhanced ability to evolve local adaptions to novel environments, making them a potentially yet more harmful group of invaders. Most phyla of marine invertebrates include short as well as long distance dispersers and many short dispersers, including ascidians, are now recognized as extremely successful global invaders. Many of these species are morphologically cryptic. Our work thus far includes molecular and behavioral characterization of introduced species, in collaboration with scientists in Japan and elsewhere around the world. Much more remains to be done in the lab and field worldwide identifying species and characterizing physiological and ecological tolerances and variability to understand invasion abilities and evolutionary processes in this beautiful and diverse group of invertebrates. Recent Publications & Presentations (** = grad student): Burnett, K., and 25 authors including S. Cohen. In press. Fundulus as the premier teleost model in environmental biology: opportunities for new insights using genomics. Comparative Biochemistry and Physiology. Cohen, S., J. Tirindelli**, M. Gomez-Chiarri, D. Nacci. 2006. Functional implications of Major Histocompatibility (MH) variation using estuarine fish populations. Integrative and Comparative Biology, published online, October 11, 2006, doi: 10.1093/icb/icl044. Cohen, S. 2002. MHC variation in natural populations of an estuarine fish: high levels of variation and relationship to severe environmental stress. Molecular Biology and Evolution 19 (11): 1870-1880. http://mbe.oxfordjournals.org/cgi/content/full/19/11/1870 Cohen, S. and D. Nacci. 2002. Effects of dioxin-like compound (DLC) contamination on an estuarine fish species: adaptive changes at specific loci. Conference proceedings, US/Vietnam Scientific Conference on Agent Orange/Dioxins, March 3-6, 2002, Hanoi, Vietnam. Cohen, S. 2000. Botryllid ascidian invasions: genetic and behavioral evidence for multi-species invasions and character divergence following introductions. In, Proceedings of the First National Conference on Marine Bioinvasions, MIT Sea Grant. Cohen, S., Y. Saito, I. Weissman. 1998. Evolution of allorecognition in botryllid ascidians inferred from a molecular phylogeny. Evolution 52(3):746-756. Cohen, S. 1996. The effects of contrasting modes of fertilization on levels of inbreeding in the marine invertebrate genus Corella., Evolution 50(5): 1896-1907. Cohen, C. S. and R. Strathmann. 1996. Embryos at the edge of tolerance: effects of environment and structure of egg masses on supply of oxygen to embryos. Biol. Bull. 190: 8-15. http://www.biolbull.org/cgi/reprint/190/1/8.pdf |
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