As fast as a hare: Did intraspecific morphological change bring the Hallands Väderö Island population of Lepus timidus close to interspecific differences in less than 150 years?

Abstract

The study of insular variation has fascinated generations of biologists and has been central to evolutionary biology at least since the time of Wallace and Darwin. In this context, using 3D geometric morphometrics, I investigate whether the population of mountain hares (Lepus timidus Linnaeus, 1758) introduced in 1857 on the Swedish island of Hallands Väderö shows distinctive traits in cranial size and shape. I find that size divergence follows the island rule, but is very small. In contrast, shape differences, compared to the mainland population, are almost as large as interspecific differences among lineages separated by hundreds of thousands of years of a largely independent evolutionary history. Even if, contrary to what is documented in the scientific literature, mountain hares were present in HV before 1857, the evolutionary history of this population could not have start earlier than the end of the last glaciation (i.e., at least one order of magnitude more recently than the separation of L. timidus from other hare species in this study). My results, thus, suggest that the insular population is a significant evolutionary unit and a potentially important component of the diversity of Swedish mountain hares. This is interesting for evolutionary biologists, but even more relevant for conservationists trying to protect the disappearing population of southern Swedish L. timidus, threatened by changes in climate and the environment, as well as by disease and the introduced European hare (Lepus europaeus Pallas, 1778). Island populations of mountain hares, thus, represent a potential source for future reintroductions on the mainland and, as my research shows, an important component of variability to maximize the preservation of the evolutionary potential in a species facing huge environmental changes.