Nuclear markers reveal a complex introgression pattern among marine turtle species on the Brazilian coast

Surprisingly, a high frequency of interspecific sea turtle hybrids has been previously recorded in a nesting site along a short stretch of the Brazilian coast. Mitochondrial DNA data indicated that as much as 43% of the females identified as Eretmochelys imbricata are hybrids in this area (Bahia State of Brazil). It is a remarkable find, because most of the nesting sites surveyed worldwide, including some in northern Brazil, presents no hybrids, and rare Caribbean sites present no more than 2% of hybrids. Thus, a detailed understanding of the hybridization process is needed to evaluate natural or anthropogenic causes of this regional phenomenon in Brazil, which could be an important factor affecting the conservation of this population. We analysed a set of 12 nuclear markers to investigate the pattern of hybridization involving three species of sea turtles: hawksbill (E. imbricata), loggerhead (Caretta caretta) and olive ridley (Lepidochelys olivacea). Our data indicate that most of the individuals in the crossings L. olivacea x E. imbricata and L. olivacea x C. caretta are F1 hybrids, whereas C. caretta x E. imbricata crossings present F1 and backcrosses with both parental species. In addition, the C. caretta x E. imbricata hybridization seems to be gender and species biased, and we also found one individual with evidence of multispecies hybridization among C. caretta x E. imbricata x Chelonia mydas. The overall results also indicate that hybridization in this area is a recent phenomenon, spanning at least two generations or 40 years.