Climate fluctuations and differential survival of bridled and non-bridled Common Guillemots Uria aalge

Abstract

Climate fluctuations and its effects on ecological processes are evident in most areas worldwide but whether such climatic effects are induced phenotypic plasticity or whether animals adapt to the new environment through micro-evolutionary processes is poorly known. In this study we have analyzed long-term data (22 years) on the relationship between climatic fluctuations and the adult survival of two distinct genetic morphs of the Common Guillemot (Uria aalge) breeding in a colony in the southern Barents Sea. In the North Atlantic, the Common Guillemot is a genetic color dimorphic species, with a nonbridled morph, with an entirely black or dark brown head, and a bridled morph having a white eye ring and auricular groove sloping back from the eye. Our results show that the two morphs responded differently to variation in the Barents Sea winter sea-surface temperature (SST). The survival rate of the bridled morph was negatively correlated to the winter SST in the Barents Sea, while that of the non-bridled morph was slightly positively correlated to the same parameter. Over the whole study period, SSTs fluctuated between warm and cold winters and the overall mean survival rates of the two morphs remained similar (96.2% and 95.9% for the bridled and non-bridled morph, respectively). This suggests a balanced selection and a stable dimorphism of the two morphs over this time period. The contrasting trends in the survival of the two morphs with respect to temperature suggest that further warming of the sea may induce directional changes and alter the frequency of the two morphs.