Individual plasticity in response to rising sea temperatures contributes to an advancement in green turtle nesting phenology

Phenological changes – i.e., shifts in the timing of biological events –
are among the most frequently reported population-level responses to
climate change and are often assumed to be adaptive and increase
population viability. These may be driven by both individual-level
phenotypic plasticity and population-level evolutionary and demographic
changes. Yet, few studies have explored how individual-level versus
population-level processes drive phenological trends. Using a 31-year
dataset of over 600 individually marked nesting green turtles (Chelonia
mydas), we quantify the population- and individual-level temporal change
in the first nest date. Of the latter, approximately 30% is attributable
to individual phenological plasticity to a rise in sea surface
temperature, with females advancing their nesting by 6.47 days for every
degree increase in sea surface temperature. The remaining change is almost
entirely explained by individual- and population-level changes in size and
breeding experience (correlates of age), as well as the number of clutches
laid per season. This is the first study of individual-level phenological
change in a marine ectotherm, furthering our understanding of how this and
similar species may respond to rising temperatures.