Extensive hybridization in hawksbill turtles (Eretmochelys imbricata) nesting in Brazil revealed by mtDNA analyses
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Bahia state hosts over 90% of hawksbill (Eretmochelys imbricata) nests registered in the main nesting sites monitored by Projeto Tamar-IBAMA in Brazil. The genetic diversity of this hawksbill population (n=119) was assayed through the analyses of 752 bp of the mitochondrial DNA control region in nesting females. Seven distinct haplotypes, defined by 125 polymorphic sites, were found. Most of the individuals (n=67) display four typical hawksbill haplotypes, 50 individuals display two haplotypes characteristic of the loggerhead turtle (Caretta caretta) and two individuals had a haplotype affiliated with the olive ridley (Lepidochelys olivacea). These results demonstrate hybridization between the hawksbills and two species that nest along the Bahia coast. Of special interest is the high occurrence of loggerhead × hawksbill hybrids (42%), which display loggerhead mtDNA haplotypes but are characterized morphologically as hawksbills. The true hawksbill haplotypes present only three variable sites and low genetic diversity values (h=0.358±0.069; π=0.0005±0.0001). The occurrence of several nesting individuals with identical mtDNA from another species may also suggest a long history of introgression between species producing likely F2 or further generation hybrids. Marine turtle hybrids have been previously reported, but the high frequency observed in Bahia is unprecedented. Such introgression may influence evolutionary pathways for all three species, or may introduce novel morphotypes that develop apart from the parental species. The presence of a unique hybrid swarm has profound conservation implications and will significantly influence the development and implementation of appropriate management strategies for these species.
Key wordshaplotype diversity hawksbill turtles hybridization introgression mitochondrial DNA
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This study was made possible thanks to the support of the Brazilian Environmental Ministry (PROBIO) and to CENPES\PETROBRAS. The Projeto Tamar-Ibama staff collected the samples and provided the necessary field assistance while Libia W. Silva helped with sample processing at the laboratory. Special thanks to Dr F. Alberto Abreu-Grobois (Instituto de Ciencias del Mar y Limnología-Mazatlán) who kindly provided the primers sequences and advised us throughout this research. We also would like to thank Dr Brian Bowen, Dr Julia Horrocks and three anonymous reviewers for their comments on early versions of the manuscript.
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