Non-random mating between nesting sites of Hawaiian hawksbill turtles: demographic discontinuity within a small isolated population

Abstract

Hawksbill sea turtles (Eretmochelys imbricata) from the Hawaiian archipelago form a small, genetically isolated, population consisting of only a few tens of individuals breeding annually. Most females nest on the island of Hawaii, but little is known about the demographics of this rookery. This study used genetic relatedness, inferred from 135 microhaplotype markers, to determine breeding sex-ratios, estimate female nesting frequency, and assess relationships between individuals nesting on different beaches. Samples were collected during the 2017 nesting season and final data included 13 nesting females and 1,002 unhatched embryos, salvaged from 41 nests, 13 of which had no observed mother. Results show that most females used a single nesting beach laying 1-5 nests each. From female and offspring alleles the paternal genotypes of 12 breeding males were reconstructed and many showed high relatedness to their mates. Pairwise relatedness of offspring revealed one instance of polygyny but otherwise suggest a 1:1 breeding-sex ratio. Relatedness analysis and spatial-autocorrelation of genotypes indicate non-random mating among complexes of nesting beaches, for both sexes, suggesting strong natal philopatry. Nesting complexes also showed unique patterns of inbreeding and outbreeding across loci, further indicating that Hawaiian hawksbill turtles have demographically discontinuous nesting populations at a fine spatial scale.