TurtleHyb · Reconstructing hybridization events between sea turtle species separated by 30 million years: genomic patterns and evolutionary consequences

Reconstructing hybridization events between sea turtle species separated by 30 million years: genomic patterns and evolutionary consequences

Hybridization is a natural experiment of new genomic combinations. The encounter of two genomes that have been evolving separately will bring together untested allelic combinations that are usually unfavorable1 resulting in reduced hybrid viability or fertility. Whole genome studies combined with cutting-edge statistical analysis is increasingly showing that past hybridization events were common, where introgressed loci derived from these ancient events may still be segregating in the genomes of many species. 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.

Текст от CORDIS, на английски · Данни: CORDIS, © Европейски съюз