A review of how the biology of male sea turtles may help mitigate female-biased hatchling sex ratio skews in a warming climate

Abstract

In a warming climate, male sea turtles may become increasingly rare due to temperature-dependent sex determination with females being produced at warmer temperatures. Hence there is widespread concern that a lack of adult males may impact population viability. However, there is controversy over this scenario and here we review aspects of the biology of male sea turtles that will help mitigate female-biased hatchling sex ratios. In particular, there is strong evidence that males generally breed more frequently than females (i.e. have a shorter remigration interval) and that individual breeding males actively search for females and may mate with multiple females from different nesting sites. These aspects of the biology of male turtles will cause female-biased hatchling sex ratios to translate into more balanced adult sex ratios on the breeding grounds (i.e. operational sex ratios). Sexual dimorphism is widespread with adult male turtles generally being smaller than females. In freshwater turtles, this sexual dimorphism is linked to earlier age at maturity for males, although this possibility has not been examined widely in sea turtles. We make a forward-looking horizon-scanning prediction for key changes that might be expected at sea turtle breeding grounds if female-biased sex ratios become so extreme that male turtles start to become limiting and start driving populations to extinction. In particular, as the numbers of adult males on the breeding grounds become limiting there may be changes in egg fertility, multiple paternity and hatching success within clutches.