Integrative taxonomy reveals extreme morphological conservatism in sympatric Mugil species from the Tropical Southwestern Atlantic

The biodiversity crisis has had particularly harsh impacts on marine environments. However, there is still considerable uncertainty about how many species have been seriously impacted and the effectiveness of protection measures (e.g., marine protected areas or MPAs) due to high levels of cryptic species in many taxa. Here, we employ an integrative taxonomy approach to mullet species in the genusMugil. In addition to its high economic value, this genus is notable for having diversified similar to 29 million years ago without marked morphological and ecological divergence. We obtained 129 specimens ofMugilfrom the Coral Coast MPA, the largest of its kind in the Tropical Southwestern Atlantic marine province. Although morphometric and meristic traits revealed six taxonomically recognized species, only five mitochondrial lineages were observed. All individuals morphologically identified asM. incilisbelonged to the mitochondrial lineage ofMugil curema, which is consistent with misidentification of morphologically similar species and an overestimation of species diversity. Remarkably,Mugilspecies in our sample that diverged up to similar to 23 million years ago are also the most morphologically similar (M. curemaandM. rubrioculus), suggesting extreme morphological conservatism, possibly driven by similarities in habitat use and life-history traits. This study demonstrates the potential utility of integrative taxonomy (including DNA barcoding) for contributing to the conservation and sustainable use of natural resources.