A Study Of Genetic Variability In Larval And Adult Populations Of Dungeness Crab Cancer Magister

Author : Chris D. Griesemer
Publisher :
ISBN 13 : 9780438627451
Total Pages : pages
Book Rating : 4.6/5 (274 download)

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Download or read book Fine Scale Genetic Structure, Dispersal, and Variable Recruitment in the Flat Porcelain Crab, Petrolisthes Cinctipes, Along the Northern California Coast written by Chris D. Griesemer and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The advent of increasingly affordable next-generation sequencing technologies are key to understanding the role dispersal, drift and selection play in producing signals of population divergence in many marine species. In particular, dispersal has been difficult to track in the oceans, obscuring its contributions to population structure. The dispersing larval phase of the flat porcelain crab, Petrolisthes cinctipes, exhibits behaviors that likely restrict its along-shore displacement despite a rather long development time at sea. In this work, I attempted to resolve previously detected chaotic patterns among P. cinctipes populations with a published Bayesian model showing that a substantial proportion of larvae likely recruit back to their natal populations. I used a large SNP (single nucleotide polymorphism) dataset to (1) analyze 159 adult crabs from 15 populations for patterns of genetic divergence and (2) directly assign 71 returning larvae back to their population of origin. Admixture results and discriminant analysis of principal components showed a strong signal of panmixia across northern California, making larval assignment impractical. Markers putatively under selection revealed the only clear break in the sampling range—between the southernmost population (just south of San Francisco Bay) and the remaining populations to the north. Despite this panmixia, P. cinctipes population genetics is also characterized by weak chaotic patterns, where populations at close proximity may be more diverged than those separated by hundreds of kilometers. Furthermore, we have previous evidence that such patterns change year-to-year. Underlying this phenomenon might be finer-structured processes that produce weak and ephemeral signals of divergence. A handful of recent studies have shown that cohesive dispersal of related individuals may provide a mechanism for generating such signals. I test for the possibility that cohesive dispersal of related larvae may contribute to observed chaotic patterns in Petrolisthes cinctipes because larval crabs exhibit clustered association with conspecifics throughout their dispersal, settling onshore gregariously in age-unified cohorts. These aspects of its life history point to the possibility of long-term kin association. Using a bank of 1,268 SNPs, I characterized the pairwise relatedness between individuals as well as within-group average relatedness of five settling cohorts of post-larvae collected in 2014. No pair exhibited relatedness greater than would be expected among non-relatives, and group relatedness measurements did not differ significantly from zero. It may be that P. cinctipes larvae are unable to maintain cohesion due to the extreme turbulence of the nearshore and surfzone environments. These same barriers to cohesive delivery of siblings may also be key to our understanding of variation in recruitment in this shore crab. In the course of my genetic sampling efforts among 14 sites across three years, I uncovered a pattern of little to no recruitment in a 100 km section of the Sonoma-Mendocino County coastline. This “recruitment gap” persisted for the years 2012 and 2013, disappearing in 2014 and leading me to wonder what might have driven the spatiotemporal variation. I measured a number of potential drivers at each site, obtained regional and basin-scale indices thought to relate to variation in recruitment. All predictor variables were used in a regression tree analysis that indicated local effects of surfzone width and the proportion of each site’s exposure to northwest compass direction. The temporal variation among years was attributed to patterns of relatively high temperature in 2014, though this result is confounded by the limitations of only three years of data. Despite the clear implication of site-level variables as drivers of the recruitment patterns, I discuss the results in the context possible influences across spatial and temporal scales, and highlight the ways in which knowledge of porcelain crab biology enriches our ability to infer a recruitment variability narrative in this system.