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

Abstract

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 1002 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 suggested a 1 : 1 breeding-sex ratio. Relatedness analysis and spatial-autocorrelation of genotypes indicate that turtles from different nesting areas do not regularly interbreed, suggesting that strong natal homing tendencies in both sexes result in non-random mating across the study area. Complexes of nearby nesting beaches also showed unique patterns of inbreeding across loci, further indicating that Hawaiian hawksbill turtles have demographically discontinuous nesting populations separated by only tens of km.

Unraveling fine-scale genetic structure in endangered hawksbill turtle (Eretmochelys imbricata) in Indonesia: implications for management strategies

“…The existence of small islands, particularly those in the Java Sea, has a major impact on preventing the number of hawksbill turtles from declining populations and also maintaining genetic diversity. More importantly, strong nesting site fidelity has been recognized for this species (Horne et al, 2023). Site-specific haplotypes were found on small islands in the Java Sea, highlighting the island's important role in the preservation of the genetic pool.…”

“…While hawksbill turtles are known to have migrated 1,600 km (Nietschmann, 1981;Miller et al, 1998), significant differentiations among nearby nesting sites indicate a high degree of natal philopatry, where turtles return to their birthplace to nest (Gaos et al, 2017). This species has been observed to have extremely strong nesting site fidelity (Horne et al, 2023), which makes it possible to have genetic differentiations occur on a small scale area. In the Java Sea, recaptured records on different places are only between Pesemut Island and Momperang Island (~3.5 km apart), revealed by YPLI and ELNA that conducted tagging programs for nesting females from 1996 to 2024 in 4 sites (Segama Kimar Island and Penambun Island, and Pesemut Island and Momperang Island).…”

A Brief Introduction to Microhaplotypes and their Uses

“…Most of those publications have dealt with applications in humans but some have involved applications in the conservation of various species (e.g., fish . 16 , turtles 17 ). Microhaplotypes of P. falciparum are even used to study the ecology of the parasite .…”