Phylogeography, Population Structure, and Historical Demography of Black Drum in North America

Abstract

The Black Drum Pogonias cromis is an abundant estuarine‐dependent fish that supports recreational and commercial fisheries. We examined the phylogeography and historical demography of the Black Drum along the Atlantic and Gulf of Mexico coasts of the United States using mitochondrial DNA sequences and nuclear DNA microsatellites. Black Drum exhibited high haplotype diversity and low nucleotide diversity across its range. We observed 249 haplotypes that resolved into two haplogroups: haplogroup 1 was most abundant along the Texas coast, and haplogroup 2 was more abundant in the Atlantic Ocean and the eastern Gulf of Mexico. Analysis of molecular variance, pairwise estimates of genetic differentiation, assessment of isolation by distance, Bayesian clustering, and multivariate ordination indicated that most population structure within Black Drum was associated with a western Gulf of Mexico versus Atlantic–eastern Gulf of Mexico split. However, analysis of molecular variance, haplotype diversity, and measures of genetic differentiation provided evidence of weak population structure on the Texas coast, perhaps due to a of combination of isolation by distance and limited emigration into and dispersal from the upper and lower Laguna Madre on the lower coast. Mismatch distributions, neutrality tests, and Bayesian skyline plots suggest that haplogroup 1 underwent rapid demographic and range expansion approximately 15,000 years ago, whereas the demographic and range expansion of haplogroup 2 was more gradual and began earlier (circa 25,000–30,000 years ago). Our results suggest that Black Drum may benefit from being managed as two stocks: (1) western Gulf of Mexico and (2) Atlantic Ocean plus eastern Gulf of Mexico. Additionally, weak but significant genetic divergence in the Laguna Madre coincides with known life history divergence in this region. Caution should be used regarding the management of Black Drum in Texas as a single demographic unit.

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

“…Several nongenetic data points exist that imply the potential for population subdivision of Black Drum in Texas beyond the isolation-by-distance pattern described by Karel et al (1996), and consistent with the spatial heterogeneity observed by Williford et al (2021). For instance, in the Baffin Bay complex (BBC) adjacent to the upper Laguna Madre system (ULM), Simmons and Breuer (1962) described divergent morphology of Black Drum adults, which were darker in coloration and often impaired by physical maladies.…”

“…Unfortunately, the gap in sample coverage between SAB and ULM makes it impossible to know the population genomic status of Black Drum in Aransas Bay and Corpus Christi Bay, major estuaries which lie in the sampling gap. Nevertheless, these data have added much-needed resolution to the picture of Black Drum genetic structure in Texas and have elicited genomic patterns of heterogeneity at small spatial scales more prominently than those found in previous studies with more limited genetic loci (Karel et al 1996;Williford et al 2021).…”

“…However, this study did not observe fine-scale genetic differentiation at the estuarine scale, and sampling in Texas was not adequate to cover the broad geographic range and numerous diverse estuaries located therein. A second, more recent study (the companion paper Williford et al 2021, https://doi.org/10.1002/nafm.10608) addressed the western Gulf coverage gap using mtDNA sequences and a larger suite of microsatellite markers distributed across the North American range of Black Drum. This study found a split between Gulf and Atlantic populations similar to what was described by Leidig et al (2014), but evidence from both mtDNA and nuclear genomes seemed to suggest that the split between populations was in the eastern Gulf rather than the Florida peninsula.…”

“…Additionally, this study found significant heterogeneity when comparing samples from within Texas. Williford et al (2021) suggested that increased genomic coverage was necessary to assess estuary-level subdivision that may have been missed with these more traditional, low-coverage genetic data sets.…”

Genetic diversity of the Southern Black Drum Pogonias courbina (Teleostei: Sciaenidae) from Río de la Plata and Atlantic Ocean coasts

“…As well as different life history traits exhibited among P. cromis populations have suggested an adaptation to the high salinity of the environment as occur in the Upper Laguna Madre, a hypersaline estuary in Texas, USA (Bumguardner et al 1996, Olsen et al 2018. Further studies ought to combine information of life history traits of P. courbina in all localities studied which can help to confirm results obtained based on mitochondrial DNA (Williford et al 2021).…”