Stabilizing selection and adaptive evolution in a combination of two traits in an arctic ungulate

Stabilizing selection is thought to be common in wild populations and act as one of the main evolutionary mechanisms which constrain phenotypic variation. When multiple traits interact to create a combined phenotype, correlational selection may be an important process driving adaptive evolution. Here we report on phenotypic selection and evolutionary changes in two natal traits in a semi-domestic population of reindeer (Rangifer tarandus) in northern Finland. The population has been closely monitored since 1969, and detailed data has been collected on individuals since they were born. Over the length of the study period (1969 - 2015), we found directional and stabilizing selection towards a combination of earlier birth date and heavier birth mass with an intermediate optimum along the major axis of the selection surface. In addition, we demonstrate significant changes in mean traits towards earlier birth date and heavier birth mass, with corresponding genetic changes in breeding values ...