Demographic and genetic diversity of the genus Paralichthys in the Buenos Aires Coastal Ecosystem of the southwestern Atlantic

Organisms inhabiting the southwestern Atlantic Ocean shelf have undergone significant population changes as a result of climatic fluctuations during the Pleistocene glaciations. These glaciations led to contractions and expansions in population size. This study investigates three coexisting flatfish species particularly within the Buenos Aires Coastal Ecosystem: Paralichthys orbignyanus, P. patagonicus, and P. isosceles. We analyzed haplotypic and nucleotide diversity, as well as demographic trends, across these species using cytochrome b and mitochondrial control region markers. We hypothesized that habitat loss, sea depth, temperature and salinity variations have differently affected the genetic diversity and demographic histories of these flatfish species. Our results revealed notable differences between species inhabiting shallow and deep waters. Those in shallow and coastal waters, such as P. orbignyanus and P. patagonicus, generally exhibited lower genetic diversity, signs of population expansion and shorter coalescence (i.e. common ancestor) times. In contrast, species from deeper waters, like P. isosceles, displayed higher genetic diversity, population stability, and longer coalescence times. Comparative phylogeographic analyses of these species may offer strong evidence supporting hypotheses about the historical impact of the Last Glacial Maximum on coastal habitats and its effects on the habitat preferences of flatfishes within the Buenos Aires Coastal Ecosystem in the southwestern Atlantic Ocean.