Estuary-Level Genomic Variation Confirms Demographic and Life History Differences among Black Drum Populations in Texas

The Black Drum Pogonias cromis is a year-round resident in estuarine and nearshore habitats throughout the Gulf of Mexico and is common in Texas. Multiple studies have highlighted life history and demographic variation in this species among estuaries, and tagging studies conducted in Texas suggest limited migration between adjacent estuaries. While these findings raise the potential for genetic heterogeneity among estuaries via accumulation of genetic drift, such an effect has never been tested. We used 5,340 genomic single nucleotide polymorphisms from a reduced-representation genomic library to assess the magnitude and geographic pattern of genetic heterogeneity in Black Drum sampled from multiple estuaries in Texas. We found significant genetic heterogeneity that could be partitioned into three regional groupings: northern (Sabine Lake to San Antonio Bay), central (upper Laguna Madre and its secondary bays) and southern (lower Laguna Madre). These regional groupings roughly coincide with significant differences in life history strategies noted in previous studies and suggest a regional stock structure that is anchored by two independently collected lines of evidence. There was also evidence for weak but significant genetic structure among adjacent secondary estuaries within the Baffin Bay complex. Finally, outliers from the genomic data set correlated weakly (but significantly) with differences in residual growth among individuals. These findings imply genetic heterogeneity of Black Drum among and within estuaries, correlation of growth phenotypes with a small partition of outlier loci, and correlation between genomic patterns and complex regional differences in life history phenotypes described previously. Stock assessments for this species should carefully consider regional stock definitions and model parameters because such inputs may vary significantly above and below the scale of estuaries.

Automated summary

Studies have shown significant genetic heterogeneity among Black Drum sampled from multiple estuaries in Texas, with regional groupings in the northern, central, and southern areas. Weak but significant genetic structure was also found among adjacent secondary estuaries within the Baffin Bay complex.