Contemporary population structure and post‐glacial genetic demography in a migratory marine species, the blacknose shark, Carcharhinus acronotus

Abstract

Patterns of population structure and historical genetic demography of blacknose sharks in the western North Atlantic Ocean were assessed using variation in nuclear-encoded microsatellites and sequences of mitochondrial (mt)DNA. Significant heterogeneity and/or inferred barriers to gene flow, based on microsatellites and/or mtDNA, revealed the occurrence of five genetic populations localized to five geographic regions: the southeastern U.S Atlantic coast, the eastern Gulf of Mexico, the western Gulf of Mexico, Bay of Campeche in the southern Gulf of Mexico and the Bahamas. Pairwise estimates of genetic divergence between sharks in the Bahamas and those in all other localities were more than an order of magnitude higher than between pairwise comparisons involving the other localities. Demographic modelling indicated that sharks in all five regions diverged after the last glacial maximum and, except for the Bahamas, experienced post-glacial, population expansion. The patterns of genetic variation also suggest that the southern Gulf of Mexico may have served as a glacial refuge and source for the expansion. Results of the study demonstrate that barriers to gene flow and historical genetic demography contributed to contemporary patterns of population structure in a coastal migratory species living in an otherwise continuous marine habitat. The results also indicate that for many marine species, failure to properly characterize barriers in terms of levels of contemporary gene flow could in part be due to inferences based solely on equilibrium assumptions. This could lead to erroneous conclusions regarding levels of connectivity in species of conservation concern.

Selection and sex‐biased dispersal in a coastal shark: the influence of philopatry on adaptive variation

“…) including coastal sharks (Portnoy et al . ) and supports results from a recent mtDNA assessment of population structure in the bonnethead (Escatel‐Luna et al . ).…”

“…This pattern is hypothesized to stem from biogeographic processes associated with the Florida Current and/or narrowing of the continental shelf in southeastern Florida (Portnoy et al . ). The absence of significant divergence in N‐SNP loci among the three localities in the Gulf is consistent with gene flow occurring between the Florida Keys (FB) and north‐central Florida (PC).…”

Genetic connectivity and phylogeography of the night shark (Carcharhinus signatus) in the western Atlantic Ocean: Implications for conservation management

“…On the other hand, fluctuations in sea level and temperature during the Pleistocene have been mentioned as factors influencing the phylogeographic pattern of many pelagic marine fishes (e.g. Alvarado Bremer, Viñas, Mejuto, Ely, & Plas, ; Domingues et al, ; Martinez, González, Castilho, & Zardoya, ; Portnoy et al, ). The presence of two sympatric clades composed of representatives’ samples from all populations could be attributed to their recent isolation, which mitochondrial frequencies have not yet homogenized, as has been observed in other shark species (Ashe et al, ; Domingues et al, ; Portnoy et al, ).…”

Echoes of a distant time: effects of historical processes on contemporary genetic patterns in Galaxias platei in Patagonia

“…; Chiucchi & Gibbs ; Graham & Burg ; Portnoy et al . ), the practice is not yet standard. While the absence of geological or glaciological information may sometimes limit the extent to which history can be incorporated in such studies, ABC methods can still be applied as exploratory analyses to examine the relative merits of alternate prior assumptions and can indeed be used to assist in our understanding and predictions of how populations are likely to change under potential future environmental change.…”