Investigating the evolutionary genetics of plasticity in wild animal populations is of key relevance to advance our understanding on how climate and global change influence the viability of populations in nature. Phenotypic plasticity is defined as the ability of a single genotype to alter its phenotype in response to environmental variability. A vast body of empirical work shows that plasticity is widespread and ubiquitous across natural populations, and that it is an important means by which organisms adapt to spatio-temporal environmental heterogeneity. However, our current understanding of the evolutionary genetics of phenotypic plasticity relies mostly on studies of single traits in short-lived species studied under laboratory conditions. Whether phenotypic plasticity is generally heritable and under selection in the wild therefore remains an open question. In this project, the Researcher investigated how individual and genetic variation in plasticity was shaped by internal factors, such as age, and external factors, such as social environment, temperature, and food availability; and their evolutionary consequences. The data used in PLASTIC TERN came from a long-term study population of common terns (Sterna hirundo) located in the Banter See at Wilhelmshaven on the German North Sea coast (53°36´N, 08°06´E).
The results of PLASTIC TERN provide a fundamental understanding of the evolutionary genetics of plasticity driven by different ecological and intrinsic factors for multiple traits at multiple levels of variation using a unique dataset and advanced statistical tools. These results are of prime importance to better understand how wild populations can adapt to new environments as the ones climate and global change are posing, being of key relevance for the management and conservation of natural populations, and endangered species. For instance, results from PLASTIC TERN showed that common terns are able to adjust their timing of breeding in relation to food availability in the breeding grounds (i.e. there is a direct relationship between the number of offspring produced in the colony and the number of herrings in the North sea). Hence, the findings from PLASTIC TERN have direct societal benefits, as they can be directly used by policy-makers, NGOs and local governments working for the Wadden Sea conservation, and in general, for seabird colony management and conservation, and fisheries.
The overall scientific objectives were two. The first objective (Work Package 1) was to quantify patterns of plasticity in several traits and in response to several environmental gradients, and hence, provide novel insights into the adaptive potential of a wild bird population of common terns. Specifically, findings from PLASTIC TERN showed that 1) telomere length is highly heritable in common terns and shortens with age, although individuals do not differ in the ageing patterns; 2) the breeding timing in female common terns is heritable and partly affected by their male partners; and 3) common terns can plastically adjust their phenology according to sea surface temperature in the wintering grounds, and to fish availability in the breeding grounds. Altogether, Work Package 1 led to three publications (one published, one submitted to a peer-reviewed journal and one in preparation) about patterns of plasticity. The second objective (Work Package 2) was to explore whether the observed phenotypic changes are adaptive. Studying how natural selection acts on plasticity is not only relevant for a better understanding of the evolution of phenotypic plasticity in the wild, but also, for a general better understanding of the evolution and maintenance of phenotypic biodiversity. In Work Package 2, the Researcher investigated whether there was standing additive genetic variation in fitness, as the existence of genetic variation in fitness is a prerequisite for evolution by natural selection. Results demonstrated evidence for genetic variance for fitness in this population, although the evolutionary rate of this population of common terns would be fairly slow. Work Package 2 led to one publication.
