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

ended

Hawksbills and Loggerheads are two endangered sea turtles species that separated approximately 30 million years ago. Despite this very long divergence time, they are currently hybridizing on the Brazilian coast. Among nesting females morphologically identified as Hawksbills, 42% are F1 hybrids. Hybrids can backcross with both parental species and produce viable offspring. This appears to be a beautiful natural experiment, possibly driven by population decline that favour interspecific mating, to study and understand species hybridization under the extreme conditions of secondary contacts between highly divergent genomes. Here I propose to study causes and consequences of the hybridization in Loggerhead and Hawksbill sea turtles using both whole genomes and RAD sequencing data. I will a) infer timing and intensity of putative ancient hybridization events that may have also occurred in the past, and their relationship with the population size dynamic. Then I will b) dissect the current hybridization event occurring in Brazil, looking for genomic regions associated with reproductive isolation and incompatibilities, and for segregation distortion along the genomes in hybrids parents and hatchlings. The amount of data generated will be unprecedented for sea turtles, will be helpful to identify risks and evolution opportunities of the hybridization process in these turtle species, and will contribute to the general understanding of species hybridization and its genomic aspects. The proposal includes transfer of knowledge to the host institution and the training of the candidate in innovative genomic and statistical techniques. Results will also strengthen the collaborative network of researchers in Europe and the Americas studying sea turtles and their hybridization. This project is in line with current European guidelines to increase knowledge of marine wildlife to protect the environment and adapt to climate change.