Line Vej Ugelvig:
Ecological genetics and evolution of the Large Blue butterfly – consequences of an extraordinary lifecycle

Date: 15-08-2010    Supervisor: Jacobus J. Boomsma and David R. Nash

The large blue butterflies (genus Maculinea) have received much attention from both scientists and the general public. The reason for this is their highly specialized life cycle that depends on the dual presence of a species specific larval food-plant and host-ant. The genus consists of at least six species, which are all confined to grasslands. This habitat type has declined rapidly in the last century, and all Maculinea species are locally threatened in large parts of their distribution ranges. Appropriate future conservation of these species requires detailed knowledge on their complex life cycles.


Moreover, this knowledge allows studies of the origin and evolution of specific life history traits, and for this purpose a well resolved phylogeny is essential. The phylogentic relationship between Maculinea and its sister genus Phengaris has been disputed due to conflicting results from molecular and morphological datasets. By including additional taxa and genetic markers to the existing molecular dataset, I improved the molecular phylogeny of the Glaucopsyche section where the two genera are placed, and find high support for Maculinea being a monophyletic clade.

The relationships within Maculinea species have also been unclear. Many subspecies have been described, due to variation in the wing pattern of imagos, but also due to differences in larval food-plant or host-ant. In particular, three species (M. teleius, M. nausithous and M. arion) harbour high genetic variation, suggesting the presence of cryptic species or isolated populations with limited gene flow. I investigated the geographical distribution of evolutionary lineages within M. arion. The distribution range of M. arion covers most of the Palaearctic region, in which three distinct genetic lineages were recovered.

While the distribution of individuals at the continental scale is likely to reflect historical processes, the distribution at the regional and landscape scale also reflects contemporary processes. In a world where natural habitats are rapidly disappearing, a species ability to disperse plays a critical role in population viability – both in terms of colonizing new suitable habitats and by enabling gene flow among neighbouring populations. I estimated the effective dispersal of M. arion, which is considered a sedentary species. Interestingly, gene flow occurs over distances 15 times further than the maximum recorded dispersal distance, however this depends on the presence of interconnected sites. Habitat loss often leads to reductions in population sizes and increasing isolation of populations. Remaining populations will consequently be more vulnerable to stochastic demographic and environmental effects. Furthermore, the lack of gene flow will increase the impact of genetic drift and bottlenecks and can lead to genetically impoverished and inbred populations. We studied an isolated population of M. arion that recently went through a drastic reduction in population size. While the population is genetically less diverse than extant populations that are part of functioning population networks, our time series analysis of natural history collection specimens show that this pattern is due to historical rather than recent influences.