(full paper is archived in the Miller Library)
Title: Thermal adaptations of native and invasive marine mussels (genus Mytilus) evidenced by differing malate dehydrogenase and citrate synthase activities
Student Author(s): Wicklund, Andrew
Faculty Advisor(s): Somero, George
Location: Final Papers Biology 175H
Date: June 2008
Abstract: Previous studies have demonstrated that physiological and biochemical factors, including adaptation to temperature and salinity, may contribute to the success of an invasive species in competition with a native species. Mytilus galloprovincialis, a blue mussel native to the Mediterranean, is a successful invader along the west coast of California, out-competing the native blue mussel, Mytilus trossulus, over much of its range south of the San Francisco Bay. Previous research has studied cardiac function, enzyme biochemistry, and gene expression as factors that have led to M. galloprovincialis’ successful invasion. Enzyme biochemistry, however, has only been studied in the laboratory, using specimens acclimated to common conditions. The objective of my study was to gain an accurate depiction of potential for metabolic function in field-acclimatized congeners of blue mussels collected from a site where both species and their hybrids occur. Estimates of potential metabolic rate were obtained by assaying the activity of two enzymes that are important in ATP production: malate dehydrogenase (MDH) and citrate synthase (CS). Specimens were collected from Bodega Bay harbor, genotyped to their respected species (including hybrids), and enzyme assays were conducted. M. trossulus had a significantly higher activity for both MDH and CS, relative to M. galloprovincialis (one-way ANOVA tests). The hybrids' MDH and CS activities fell between those of M. trossulus and M. galloprovincialis. To determine if size-dependence (“scaling”) of metabolic rate contributed to these differences, I used linear regression analysis to determine the relationship between body size (length of shell) and enzymatic activity. When all genotypes’ MDH and CS activities and mussel size were compared, a significant negative correlation was evident. When the species were analyzed separately, however, the correlations were not significant. The higher activities of MDH and CS in M. trossulus are consistent with this congener being more cold-adapted (able to sustain a high metabolic rate at low temperatures) than the Mediterranean invasive. Furthermore, the hybrids are adapted to both warm and cold water, and can survive in a middle climate range. These data correlate to the mapped distributions of the genotypes along the California coast and to the previous knowledge of the physiological differences between the species.