Grant: 22-004R
Project Title: First Characterization of Breeding Sex Ratio for Northern Gulf of Mexico Loggerheads
Project Manager: Mariana Fuentes
Organization: Florida State University (Research and Educational Institute)
Grant Amount: $26,954.00
Completion Date: 2023-07-20
Summary: Effective management of sea turtles requires updated estimates of the abundances of key demographics, particularly mature individuals contributing to the recovery potential of populations. Abundance data for nesting females are globally ubiquitous, but limited information exists on male abundances, as they remain in-water throughout their lives and visual identification of male turtles is only possible once turtles have reached sexual maturity. When mature female abundances are known, knowledge of mature male turtle abundances allows researchers to determine sex ratios and investigate the processes and threats that influence abundance and sex ratios across life-stages, which include climate change and anthropogenic activities. Reconstructing paternity in sea turtle nests is a common technique used to obtain proxy information about breeding male sea turtles. Paternity reconstruction generates a genetic profile of sires of sampled hatchlings, and can be used to generate breeding sex ratios (BSRs) for sampled populations. Representative sampling of nests from individual nesting females should be particularly feasible for small populations with relatively few nesting individuals. This is the case for the Northern Gulf of Mexico Recovery Unit (NGM RU) loggerhead turtles, which is a small, genetically distinct population. The NGM RU has exhibited an estimated two-fold increase in nesting female abundance, but no study has examined male-abundances or BSRs for this population. Our project seeks to address this knowledge gap by using paternity reconstruction to determine a BSR for turtles nesting at St. George Island during the peak of the 2022 nesting season. This BSR will be applicable in future studies examining sex ratios at other high-use areas for NGM RU loggerheads, particularly in the contexts of climate change and sex-dichotomous threat exposure.
Results: We have completed all final deliverables save for publication of our results. 621 hatchlings from 34 nests, and 29 females were genotyped across 16 microsatellite loci. These genotypes were input into COLONY v2.0.6.8 for paternity reconstruction. COLONY was run with inbreeding and polygamy allowed and with no sibship scaling or size priors. COLONY was run for five very long runs using a full-likelihood method of kinship inference. COLONY identified 54 sires in total, making the BSR from this sample of nests at St. George Island about 1.55 M:F. This constitutes a notably low BSR for loggerheads from the northwest Atlantic Ocean, and merits further study. Multiple paternity was only present in 13 nests (about 38%), and only three nests presented with more than two sires. We aim to prepare these results for publication by the end of 2023.