Phylogeography of a ground beetle species in La Gomera (Canary Islands): the effects of landscape topology and population history.

Paraeutrichopus pecoudi (Coleoptera, Carabidae) is a species endemic to the mountain laurel forests of La Gomera in the Canary archipelago. La Gomera is an island of volcanic origin (9.4 mya), where a well-preserved laurel forest is partly fragmented by valleys and ridges. Historically restricted gene flow with isolation by distance are deduced at different clade levels for P. pecoudi populations, an expected scenario arising from landscape discontinuity, which has caused local isolation of these flightless insects. Methodological considerations were investigated for nested clade phylogeographic analysis (NCPA), comparing the results obtained using either (a) pairwise distances between collecting sites measured as surface (route) distances or (b) standard geographical distances calculated from latitude-longitude coordinates. Some differences were found in the NCPA statistics and associated inferences at the higher clade levels in relation to the assumed distance criteria. Coalescent simulations and posterior automated NCPAs assuming different geographical distances were performed to test the robustness of the method when considering the distances used. These analyses showed no significant differences in NCPA conclusions, and the scenario of restricted gene flow was recovered using both distance calculators at the same rate, although the parameter statistics were slightly different. We suggest that in landscapes with extreme topography, geographical distances separating populations are certainly underestimated by standard techniques. More complex and explicit descriptions of the potential dispersal of terrestrial organisms should be explored for implementation in statistical phylogeography in such cases.