Spatial and temporal variation in distribution and protein ubiquitination for Mytilus congeners in the California hybrid zone
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Along the west coast of North America, the invasive mussel Mytilus galloprovincialis and a native congener M. trossulus overlap in range and compete for habitat in an extensive hybrid zone along central California. The two species have been shown to exhibit differential abiotic tolerances in laboratory studies, yet little is known about how such tolerances affect spatial and temporal patterns of geographic distribution, particularly in areas of competition. We examined distributions of the two congeners and their hybrids in neighboring intertidal and subtidal habitats in Bodega Bay, CA over 2 years, and compared shell length and seasonal ubiquitin (Ub) conjugates to estimate protein turnover and physiological stress for the species at each site. The two species were spatially segregated, with M. galloprovincialis dominating the subtidal habitat, and M. trossulus constituting a majority of the intertidal mussel population. Hybrid individuals appeared in low numbers at both sites. For each habitat, there was no statistical difference between shell lengths of M. galloprovincialis and hybrids but M. trossulus mussels were statistically smaller than the other two. In regards to physiological performance, ubiquitin conjugate values showed different seasonal cycles for the two species, suggesting different periods of peak environmental stress. The highest levels of Ub-conjugated proteins were observed in winter for M. galloprovincialis and in summer for M. trossulus, consistent with the respective range edges for their distributions since Bodega Bay is near the northern range edge of the invader and the southern edge of the native species. These findings suggest that future assessments of Mytilus populations along the California coast may need to consider vertical distributions and seasonal cycles as part of monitoring and research activities.
KeywordsShell Length Hybrid Zone Intertidal Habitat Mussel Species Subtidal Habitat
The authors would like to thank S. Henkel and L. Hammond for field assistance, and Drs. S. Gaines, B. Kinlan and C. Osovitz for assistance with statistical analyses. This work was partially supported by a Mildred E. Mathias Graduate Research Grant through the University of California Natural Reserve System (awarded to JMD). We also thank the Bodega Marine Reserve for access to facilities and housing. During the preparation of this manuscript, the authors were supported by the NOAA Nancy Foster Scholarship Program (awarded to JMD) and the US National Science Foundation (NSF grant OCE-0425107, awarded to GEH). This is contribution number 293 from PISCO, the Partnership for Interdisciplinary Studies of Coastal Oceans funded primarily by the Gordon and Betty Moore Foundation and David and Lucile Packard Foundation. The experiments contained herein comply with the current laws of the United States, in which they were performed.
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