Assessment of Population Genetic Differentiation of the Blue Crab (Callinectes sapidus) in the Gulf of Mexico using Next Generation Sequencing Technologies

2014-2016 - $292,874

Dr. Luis Hurtado
Department of Wildlife and Fisheries
Texas A&M University
College Station

Dr. Mariana Mateos
Department of Wildlife and Fisheries
Texas A&M University
College Station

Abstract

The objectives of this research are: (1) To identify the spatial and temporal limits of blue crab populations in the Gulf of Mexico. (2) To obtain estimations of genetic diversity within populations and localities, which will help to assess their genetic health. (3) To identify regions in the genome of the blue crab that can be potentially influenced by selection. (4) To implement methods to assess temporal changes in effective population size.

Identification of the boundaries of genetically differentiated populations of blue crabs can help for their management and conservation. Despite its importance, few studies on population genetics of C. sapidus have been conducted on the US Atlantic coast and the Gulf of Mexico. The few population genetic studies, however, are largely inconclusive, in part, because of inherent limitations of the molecular markers used (i.e., allozymes and mitochondrial markers): they show limited genetic variability or do not represent genetic variation at the whole genome. Nonetheless, according to these studies, some population genetic variation may occur in this species at different geographic and temporal scales in the US Atlantic coast and Gulf of Mexico. Detection of population structure in marine species with historically very large population sizes, such as the blue crab, may be difficult using neutral markers, because little genetic drift occurs. Therefore, it will usually take a long time for recently diverged populations to exhibit detectable differences at neutral markers resulting from genetic drift or accumulation of new mutations (Waples, 1998). In addition, even very low migration rates can eliminate evidence of population genetic differentiation at neutral markers (Allendorf et al., 2010). Markers influenced by selection, on the other hand, could be more sensitive than neutral markers for detecting population structure in marine organisms characterized by extremely large populations, high dispersal potential, and/or with recently diverged populations (Andre et al., 2010). Selection is more efficient in large populations because genetic drift is weaker, and even relatively weak selection may bring about genetic differentiation between populations in species with large population sizes (Allendorf et al., 2010). Loci under differential directional selection can accumulate allelic differences very rapidly among recently diverged populations as a consequence of adaptation to different local conditions; and migration, even extensive, cannot eliminate evidence of population differentiation at locally adaptive loci (Allendorf et al., 2010). Therefore, thorough genomic scans that allow detection of loci under putative directional selection are needed to better understand the spatial and temporal changes in population genetic composition of the blue crab.