Kinship genomics approach to study mating systems in a depleted sea turtle rookery

Abstract

Knowledge of demographic processes and life history strategies is necessary for the conservation and management of endangered sea turtle populations, but it is difficult to ascertain because of the limited accessibility to marine environments that sea turtles use during the different stages of their life cycle. In such cases, molecular genetics and genomic approaches are useful to assess mating systems and operational sex ratios (OSR), which ultimately influence demography. This pilot study used genome-wide single nucleotide polymorphism (SNP) genetic markers for exploring kinship and mating systems in sea turtles where major obstacles prevent a comprehensive assessment in the wild. We sampled 217 young hawksbill turtles (Eretmochelys imbricata) of unknown parentage that had originally been collected locally from seven nests and were being temporarily kept in captivity by Treasure Island Ltd as part of its captive rearing conservation project at Bounty and Treasure Islands, Fiji, in the South Pacific. The raw dataset comprised 13,573 SNPs, of which we retained 639 SNPs for parentage and relatedness analyses. Our findings from seven different pairs of parents suggest a 1:1 male:female OSR and demonstrate that genome-wide SNP genotyping approaches can be used to infer OSR. Knowledge of OSR can help evaluate the magnitude of the impact of warming temperatures and consequent feminisation in sea turtles. Our approach can complement or substitute field observation of breeding males and nesting females when logistical or budgetary constraints prevent observation of OSR in wild sea turtle populations. This approach allows inference of OSR. Protection of beaches with a higher number of pairs of parents should be prioritised to increase genetic resilience. Conservation actions in rookeries with a female-skewed OSR should be prioritised to address population declines in the long run.