Periodic Reporting for period 1 - TurtleHyb (Reconstructing hybridization events between sea turtle species separated by 30 million years: genomic patterns and evolutionary consequences)
Periodo di rendicontazione: 2019-10-01 al 2021-09-30
Sea turtles are truly amazing animals that have been swimming in the oceans since dinosaurs roamed the Earth. These endangered, ancient species have a fascinating hybridization system, as they are one of the oldest lineages known to naturally hybridize and generate viable and fertile offspring. Among all known hybrid combinations, species spanning phylogenetic divergence times from 15 million years (my) up to 48 my can still hybridize. As a comparison, within primates, these divergences are equivalent to the estimated splitting time between humans and gorillas to lemurs.
In a small region of Brazil two sea turtle species frequently hybridize. Previous studies estimated that 32-42% of nesting females morphologically identified as hawksbills (Eretmochelys imbricata) in Praia do Forte, Bahia State in Brazil are hybrids between hawksbills and loggerheads (Caretta caretta). This widespread hybridization process is possibly a consequence of overlapping nesting seasons, which also explained the directionality of the crossings, combined with few available mating partners due to recent population decreases as a consequence of hunting and poaching until the1980s7.
In endangered species, hybridization is often a consequence of declining population numbers. When species that have close or overlapping distribution and can still interbreed – decreases in size and consequently mating partners are rare, species hybridization is a likely outcome. In the project TurtleHyb, we studied the hybridization between sea turtle species in the South Atlantic Ocean. Our goal was 1) To test for putative past hybridization processes between Hawksbills and Loggerheads species; 2) Investigate if past population size changes could have triggered hybridization events; 3) Dissect the current hybridization events occurring in Brazil by identifying genomic regions associated with reproductive isolation by scanning the genomes of non-hybrid individuals for highly divergent regions.
Part of the MSCA results have already been published in scientific journals (Vilaça et al 2021. Molecular Ecology Biology) and presented in conferences (Virtual Evolution 2021, 1st Italian Congress online on Marine Evolution in 2020 and 40th International Symposium of the Sea Turtle Society in 2022). We have also been active at communicating our research to the general public including local newspapers, online magazines, and social media.
Further analyses on all produced genomes are still ongoing and will report this past hybridization process in more details while also investigating the relationships between populations of sea turtle species across the South Atlantic Ocean. A second manuscript will report the findings from all data produced in this study. However, our project was heavily impacted by the pandemic which did not allow us to produce some of the originally planned data.