New Genetic Insights About Hybridization and Population Structure of Hawksbill and Loggerhead Turtles From Brazil

Abstract

An extremely high incidence of hybridization among sea turtles is found along the Brazilian coast. To understand this atypical phenomenon and its impact on sea turtle conservation, research focused in the evolutionary history of sea turtles is fundamental. We assessed high quality multilocus haplotypes of 143 samples of the five species of sea turtles that occur along the Brazilian coast to investigate the hybridization process and the population structure of hawksbill (Eretmochelys imbricata) and loggerhead turtles (Caretta caretta). The multilocus data were initially used to characterize interspecific hybrids. Introgression (F2 hybrids) was only confirmed in hatchlings of F1 hybrid females (hawksbill x loggerhead), indicating that introgression was either previously overestimated and F2 hybrids may not survive to adulthood, or the first-generation hybrid females nesting in Brazil were born as recent as few decades ago. Phylogenetic analyses using nuclear markers recovered the mtDNA-based Indo-Pacific and Atlantic lineages for hawksbill turtles, demonstrating a deep genetic divergence dating from the early Pliocene. In addition, loggerhead turtles that share a common feeding area and belong to distinct Indo-Pacific and Atlantic mtDNA clades present no clear genetic differentiation at the nuclear level. Finally, our results indicate that hawksbill and loggerhead rookeries along the Brazilian coast are likely connected by male-mediated gene flow.

Divergence and hybridization in sea turtles: Inferences from genome data show evidence of ancient gene flow between species

“…Previous investigations of current hybridization patterns from Brazil have failed to detect backcross hybrids beyond F2s between hawksbills, loggerheads, and olive ridleys (Arantes et al, 2020 ; Vilaça et al, 2012 ). Our results show hybridization within Carettini after species divergence, and since these events can still be detected in genome‐wide markers, backcrossing must have happened in the past.…”

“…F1 hybrids can backcross with both parental species and produce viable offspring (Soares et al, 2017 , 2018 ), supporting the idea that the genome mixing that occurs today may have long term consequences. However, later generation hybrids among adult individuals have not been found yet (Arantes et al, 2020 ), and it is not known how frequently hybridization may have occurred in the sea turtles’ evolutionary past.…”

“…However, later generation hybrids among adult individuals have not been found yet (Arantes et al, 2020), and it is not known how frequently hybridization may have occurred in the sea turtles' evolutionary past.…”

Genomic introgression from a distant congener in the Levant fritillary butterfly, Melitaea acentria

“…Closely related species are known to be more prone to hybridization (Abbott et al, 2013), and although introgression between distant taxa has been reported previously (e.g., Arantes et al, 2020; Zhang et al, 2016), it is less common in nature than gene flow between close relatives. Here we examine a case of gene flow between two distantly related species of the genus Melitaea (Lepidoptera, Nymphalidae).…”

Evidence of backcross inviability and mitochondrial DNA paternal leakage in sea turtle hybrids

“…Hybrids were found to migrate to foraging areas typical of both parental species (Marcovaldi et al, 2010(Marcovaldi et al, , 2012. However, the relationship between the hybrids' genetic composition and their migratory pattern is not clear since a combination of mtDNA sequences (Lara-Ruiz et al, 2006) and few nuclear loci identified them as first generation (F1) (Arantes, Vilaça, Mazzoni, & Santos, 2020;Vilaça et al, 2012). The limits of these studies concern both the use of mtDNA and the number of nuclear loci.…”