Data from: Potential drivers and implications of a balanced breeding sex ratio in a small population of an imperiled species with environmental sex determination

Small populations of imperiled species are susceptible to the negative
consequences of skewed sex ratios. In imperiled species with environmental
sex determination such as sea turtles, examining sex ratios across a range
of environments and population abundance levels can provide insight into
factors that influence population resilience, which can then be the foci
of management plans for these species. Breeding sex ratios (the ratio of
actively breeding males to females during a reproductive season; BSRs)
extrapolated from genetic parentage analyses are a common approach for
enumerating sex ratios in sea turtles. Such analyses also allow for the
characterization of multiple paternity within sea turtle clutches, which
should reflect BSRs and breeding behaviors. We characterized the first BSR
for a breeding assemblage of loggerhead sea turtles (Caretta caretta)
belonging to the temperate, low-abundance Northern Gulf of Mexico Recovery
Unit using genotypes of 16 microsatellite loci from nesting females and
hatchlings. Unlike prior studies at both more-tropical and more-temperate,
and higher-abundance, Recovery Units in this region, we found a balanced
BSR of 1.3:1 males: female and a low incidence (~17%) of multiple
paternity. This suggests that there are relatively few males breeding at
this assemblage and within this Recovery Unit. Beaches in this region are
expected to produce substantial numbers of male hatchlings based on sand
temperature data. The relative dearth of mature males may then be due to
hydrologic disturbances that disproportionately affect the fitness and
survival of male hatchlings, or due to demographic stochasticity. More
work is needed to study the factors that might influence male hatchling
production and fitness in this region, particularly as climate change is
predicted to lead to feminization in global sea turtle populations. Our
work demonstrates the broad utility of characterizing BSRs and other sex
ratios across a range of populations in imperiled, environmentally
sensitive species.