Abstract
The effect of climate warming on the reproductive success of ectothermic animals is currently a subject of major conservation concern. However, for many threatened species, we still know surprisingly little about the extent of naturally occurring adaptive variation in heat-tolerance. Here, we show that the thermal tolerances of green turtle (Chelonia mydas) embryos in a single, island-breeding population have diverged in response to the contrasting incubation temperatures of nesting beaches just a few kilometres apart. In natural nests and in a common-garden rearing experiment, the offspring of females nesting on a naturally hot (black sand) beach survived better and grew larger at hot incubation temperatures compared with the offspring of females nesting on a cooler (pale sand) beach nearby. These differences were owing to shallower thermal reaction norms in the hot beach population, rather than shifts in thermal optima, and could not be explained by egg-mediated maternal effects. Our results suggest that marine turtle nesting behaviour can drive adaptive differentiation at remarkably fine spatial scales, and have important implications for how we define conservation units for protection. In particular, previous studies may have underestimated the extent of adaptive structuring in marine turtle populations that may significantly affect their capacity to respond to environmental change.
Highlights
In spatially heterogeneous environments, local populations exposed to contrasting selective regimes may diverge for traits that affect survival and reproduction [1]
The proportion of eggs hatching decreased at higher incubation temperatures at both beaches (GLM: temperature, F1,58 1⁄4 56.2, p, 0.001); clutches laid at Northeast Bay (NEB) had higher hatching success at a given temperature compared with Long Beach (LB) clutches, suggesting an increased upper thermal-tolerance limit for the offspring of NEB females
While hatching success was high for eggs from both beaches in the cool incubation treatment (97% of eggs hatched in each case), eggs laid by females nesting on NEB had markedly improved hatching success in the hot treatment compared with those laid by LB females
Summary
Local populations exposed to contrasting selective regimes may diverge for traits that affect survival and reproduction [1]. To date, assessments of nesting population structure and designation of management units in these species have largely been based on molecular genetic approaches [17,18], with almost nothing known about the extent of adaptive phenotypic variation in thermal-tolerance, or any other trait This is surprising, given that temperature has a profound effect on hatching success, embryonic development and sex in marine turtles [19,20], leading to growing concerns regarding the impacts of climate warming on their reproductive success [16,21,22]
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More From: Proceedings of the Royal Society B: Biological Sciences
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