Deforestation: Risk Of Sex Ratio Distortion In Hawksbill Sea Turtles

Abstract

Phenotypic sex in sea turtles is determined by nest incubation temperatures, with warmer temperatures producing females and cooler temperatures producing males. The common finding of highly skewed female-biased hatchling sex ratios in sea turtle populations could have serious repercussions for the long-term survival of these species and prompted us to examine the thermal profile of a relatively pristine hawksbill nesting beach in Guadeloupe, French West Indies. Data loggers placed at nest depth revealed that temperatures in the forested areas were significantly cooler than temperatures in the more open, deforested areas. Using these temperatures as a predictor of sex ratio, we were able to assess the relative contributions of the different beach zones to the primary sex ratio: significantly more males were likely to be produced in the forested areas. Coastal forests are therefore important male-producing areas for the hawksbill sea turtle, and this has urgent conservation implications. On Guadeloupe, as on many Caribbean islands, deforestation rates are high and show few signs of slowing, as there is continual pressure to develop beachfront areas. The destruction of coastal forest could have serious consequences both in terms of local nesting behavior and of regional demography through the effects on population sex ratios. Human alterations to nesting habitat in other reptile taxa have been shown to modify the thermal properties of nest sites in ways that can disrupt their ecology by allowing parasite transmission, increasing vulnerability to climate change, or rendering existing habitat unsuitable.

Vegetation cover predicts temperature in nests of the hawksbill sea turtle: implications for beach management and offspring sex ratios

“…The significant relationship between vegetation cover and nest temperature indicates that warming of the clutch during development is not sufficient to decouple this correlation. In fact, metabolic heating during the TSP is significantly negatively correlated with vegetation cover, such that nests in the forest experience less warming, despite a similar clutch size to eggs laid in more open areas.The differences in sand temperatures across beach habitats are consistent with previous work documenting broad-scale thermal patterns on this beach (Kamel & Mrosovsky 2006a), whereby temperatures in the forest are often within the male-producing range. In theory, if sand temperatures are close to pivotal then metabolic heating could push nest temperatures over this threshold and feminize potentially male-producing nests.…”

Seleção de locais de nidificação e sucesso de eclosão da tartaruga-de-pente e da tartaruga-cabeçuda (Testudines, Cheloniidae) na Praia de Arembepe, nordeste do Brasil

“…Some environmental variables, like sand temperature (Yntema and Mrosovsky 1982), sand humidity (McGehee 1990) and rate of gas exchange between the nest and the environment (Ackerman 1980) are directly related to embryonic development. These variables differ across available nesting habitats due to such factors as grain size (Mortimer 1990, Foley et al 2006, beach profile Speakman 1993, Kamel andMrosovsky 2006), and presence (or absence) of vegetation (Janzen 1994). Therefore, selection of a nest site by female turtles directly affects hatching success and thereby reproductive success.…”

Climate change and pollution speed declines in zebrafish populations

“…In some reptiles, including tortoises and turtles, warmer temperatures during incubation generally induce female development (15,16). Feminization also occurs in crocodilians at temperatures both above and below temperatures that are optimal for male development (17,18).…”