New genetic insights about hybridization and population structure of hawksbill and loggerhead turtles from Brazil

Abstract

19An extremely high incidence of hybridization among sea turtles is found along the 20 Brazilian coast. To understand this atypical phenomenon and its impact on sea turtle 21 conservation, research focused in the evolutionary history of sea turtles is fundamental. We 22 assessed high quality multilocus haplotypes of 143 samples of the five species of sea turtles 23 that occur along the Brazilian coast to investigate the hybridization process and the population 24 structure of hawksbill (Eretmochelys imbricata) and loggerhead turtles (Caretta caretta). The 25 multilocus data were initially used to characterize interspecific hybrids. Introgression (F2 26 hybrids) was only confirmed in hatchlings of F1 hybrid females (hawksbill x loggerhead), 27 indicating that introgression was either previously overestimated and F2 hybrids may not 28 survive to adulthood, or the first-generation hybrid females nesting in Brazil were born as recent 29 as few decades ago. Phylogenetic analyses using nuclear markers recovered the mtDNA-based 30 Indo-Pacific and Atlantic lineages for hawksbill turtles, demonstrating a deep genetic 31 divergence dating from the early Pliocene. In addition, loggerhead turtles that share a common 32 2 feeding area and belong to distinct Indo-Pacific and Atlantic mtDNA clades present no clear 33 genetic differentiation at the nuclear level. Finally, our results indicate that hawksbill and 34 loggerhead rookeries along the Brazilian coast are likely connected by male-mediated gene 35 flow. 36 37

Genomic evidence of recent hybridization between sea turtles at Abrolhos Archipelago and its association to low reproductive output

“…We extracted genomic DNA from the tissue samples with either a modified phenol-chloroform protocol 33 or the DNeasy Blood and Tissue kit (Qiagen). In order to determine the type of hybrid, we used a multilocus sequencing approach developed by Arantes et al 13, in which 14 loci presenting species-specific diagnostic alleles/haplotypes (i.e. high-quality phased sequences) were selected from double-digest RADseq (ddRADseq) data produced the same way for both loggerhead and hawksbill turtles.…”

“…Since the primers developed were based on data generated for both species, the reproducibility was very high. For the present work, we selected the six nuclear DNA (nDNA) loci (421; 856; 3,061; 64,188; 76,958; and 109,472) presenting the highest species assignment accuracy in the previous study 13 . Based on other cases of hybridization in Brazil, we expected to find hybrids of up to two generations (F1 and backcrossing).…”

“…Hybrid females found nesting in both Brazilian populations are first generation (F1) hybrids, which suggests that the hybridization process is recent and probably associated with environmental changes and global population declines in sea turtles 13 . Backcrossed hatchlings have also been reported, confirming that F1 hybrids are fertile and introgression may be possible 10,13 .…”

“…Hybrid females found nesting in both Brazilian populations are first generation (F1) hybrids, which suggests that the hybridization process is recent and probably associated with environmental changes and global population declines in sea turtles 13 . Backcrossed hatchlings have also been reported, confirming that F1 hybrids are fertile and introgression may be possible 10,13 . Despite the confirmed viability of hybrid F1 females, it has been shown that their nests in northern Bahia have a lower success rate of hatching emergence, whilst other reproductive output parameters, such as hatchling production per clutch, clutch frequency and breeding frequency remained similar to the parental species 14 .…”

“…Furthermore, no negative effect of hybridization was found on hatchling viability 15 . Nonetheless, little is known about sea turtle hybrids in other life stages in terms of survivorship, migratory behavior, feeding preferences, reproductive fitness and mate choice, such that the temporal and spatial extent of hybridization consequences for sea turtle populations remains unclear 13 .…”