The impact of population bottlenecks on fluctuating asymmetry and morphological variance in two separate populations of reindeer on the island of South Georgia

Abstract

In the early part of the 20th century, whalers on South Georgia in the South Atlantic transported reindeer from Norway to establish a population from which they could cull animals for food. This happened twice, with reindeer obtained from the same source in each case, and with independent founder populations being established on separate parts of the island. As the exact number of founding males and females are known in each case, and as it was possible to obtain materials from the source population, this provided an unusually clear test of expectations about the impact of population bottlenecks on morphological and genetic diversity. In this study, we focus on the impact on morphological variation and on the relationship between genomic stress and indirect measures of fitness. We find that fluctuating asymmetry and morphological variation increased in each bottlenecked population and that the impact was somewhat stronger for the founder group that began with fewer females. Based on several skull measurements, there was also a significant trend for the reindeer in the bottlenecked populations to have smaller skulls. There were consistent correlations between individual genetic diversity and indirect measures of fitness, but these were weak and non-significant after correction for type 1 error. Taken together, these data support the expectation that genomic stress has the potential to impact the expression of morphological phenotype in a large mammal and provide an opportunity to directly compare two parallel events.