Genetic variance in fitness indicates rapid contemporary adaptive evolution in wild animals

The rate of adaptive evolution, the contribution of selection to genetic changes that increase mean fitness, is determined by the additive genetic variance in individual relative fitness. To date, there are few robust estimates of this parameter for natural populations, and it is therefore unclear whether adaptive evolution can play a meaningful role in short-term population dynamics. We developed and applied quantitative genetic methods to long-term datasets from 19 wild bird and mammal populations and found that, while estimates vary between populations, additive genetic variance in relative fitness is often substantial and, on average, twice that of previous estimates. We show that these rates of contemporary adaptive evolution can affect population dynamics and hence that natural selection has the potential to partly mitigate effects of current environmental change

Selection for foraging efficiency during a population crash in Soay sheep\ud

1. There are surprisingly few examples of the fitness consequences of variation in foraging traits, despite their importance for survival and reproduction. We studied the relationship between traits affecting foraging efficiency and individual fitness in Soay sheep on the island of St Kilda, Scotland.\ud \ud 2. Survival during an over-winter population die-off was related to variation in incisor arcade breadth, a morphometric trait that is known to influence food intake. Other morphometric measures, such as body dimensions and weight, were less well related to survival.\ud \ud 3. Individual survival over winter was also related to gastrointestinal parasite burden, estimated in faecal samples in the previous August. Incisor arcade breadth and parasite burden affect nutrient assimilation rate, energy balance and susceptibility to mortality through starvation. An energetic model developed to predict energy intake and expenditure from incisor arcade structure, body reserves and thermal balance was no better at predicting individual survival than incisor breadth alone.\ud \ud 4. Our results raise questions about stabilizing selection on incisor breadth and the effect of spatial heterogeneity in the vegetation on selection pressure in different home ranges. We discuss the way pleiotropic effects may operate through increased fitness of animals with narrow incisor arcades feeding more selectively when food is plentiful at low population density