Different male vs. female breeding periodicity helps mitigate offspring sex ratio skews in sea turtles

Graeme C Hays,Antonios D Mazaris,Gail Schofield

doi:10.3389/fmars.2014.00043

Abstract

The implications of climate change for global biodiversity may be profound with those species with little capacity for adaptation being thought to be particularly vulnerable to warming. A classic case of groups for concern are those animals exhibiting temperature-dependent sex-determination (TSD), such as sea turtles, where climate warming may produce single sex populations and hence extinction. We show that, globally, female biased hatchling sex ratios dominate sea turtle populations (exceeding 3:1 in >50% records), which, at-a-glance, reiterates concerns for extinction. However, we also demonstrate that more frequent breeding by males, empirically shown by satellite tracking 23 individuals and supported by a generalized bio-energetic life history model, generates more balanced operational sex ratios (OSRs). Hence, concerns of increasingly skewed hatchling sex ratios and reduced population viability are less acute than previously thought for sea turtles. In fact, in some scenarios skewed hatchling sex ratios in groups with TSD may be adaptive to ensure optimum OSRs.

Highlights

It is widely acknowledged that climate change is producing profound alterations to ecosystems, including changes in abundance as well as shifts in distribution and phenology, with associated consequences for ecosystem services (Parmesan and Yohe, 2003)
MECHANISTIC MODEL OF BREEDING PERIODICITY To predict the relative breeding periodicities of male and female sea turtles, we developed a model built around the two fundamental differences in their breeding life history: first that females invest energy in clutches of eggs while males do not; second that males have a much shorter period of residence on the breeding grounds than females, so they arrive back at their foraging grounds earlier and, start to re-build their energy reserves sooner than females (Schofield et al, 2013a,b)
We provide comprehensive evidence that male sea turtles breed more frequently than females and, female skewed hatchling sex ratios will translate into more balanced operational sex ratios

Summary

Introduction

It is widely acknowledged that climate change is producing profound alterations to ecosystems, including changes in abundance as well as shifts in distribution and phenology, with associated consequences for ecosystem services (Parmesan and Yohe, 2003). For marine species that have thermally controlled distributions, range changes over recent decades often correspond with the movement of isotherms (local climate velocities), with a general pattern for range expansion by warm water species and vice versa (Pinsky et al, 2013; Hinder et al, 2014) Arising from these studies, one of the concerns is that generally rising temperatures may negatively impact a number of species, with classic examples of species facing an uncertain future being those living at high altitudes (mountain tops) and at high latitudes, since both groups will experience declining (and possibly vanishing) habitat over future decades. Changes in the seasonal timing of peak abundance may disrupt the trophic linkages in food webs and cause new trophic matches and mismatches (Edwards and Richardson, 2004)

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