Non-random mating within an island rookery of Hawaiian hawksbill turtles: demographic discontinuity at a small coastline scale

Hawksbill sea turtles (Eretmochelys imbricata) from the Hawaiian
archipelago form a small and genetically isolated population, consisting
of only a few tens of individuals breeding annually. Most females nest on
the island of Hawai’i, 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, of which 13 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
across loci, further indicating that Hawaiian hawksbill turtles have
demographically discontinuous nesting populations on a fine spatial scale.