Limited individual phenotypic plasticity in the timing of and investment into egg laying in southern rockhopper penguins under climate change

Global climate change requires species to adapt to increasing environmental variability, rising air and ocean temperatures and many other effects, including temperature-associated phenological shifts. Species may adapt to such rapid changes by microevolutionary processes and/or phenotypic plasticity. The speed of microevolutionary adaptation may critically be enhanced by between-individual differences in phenotypic plasticity. However, such between-individual differences have rarely been shown, especially for long-lived and migratory species that appear particularly vulnerable to phenological shifts. Southern rockhopper penguins Eudyptes chrysocome chrysocome are migratory, long-lived seabirds with a ‘vulnerable’ conservation status. We studied clutch initiation date (CID) and investment into egg mass in individually marked females in response to broad-scale and local climate variables across 7 yr. We thereby distinguished within-individual and between-individual variation and tested the existence of between-individual differences in the expression of phenotypic plasticity. Because of both within-individual and between-individual variation, CID was significantly advanced under high Southern Annular Mode (SAM), reflecting colder environmental conditions and higher food availability. Total clutch mass increased under low local sea surface temperatures (significant within-individual effect) but was mostly accounted for by female identity. Intra-clutch egg-mass dimorphism was not affected by environmental variables at all. We found no indication of between-individual differences in phenotypic plasticity and overall, the expression of phenotypic plasticity appeared to be limited. This raises the question whether between-individual differences in phenotypic plasticity exist in other long-lived species and whether rockhopper penguins show sufficient phenotypic plasticity to adapt to predicted climate changes