What Caused the Disjunct Distributions of the Lachnaia Tristigma Species-Group (coleoptera: Chrysomelidae) on the Iberian Peninsula?

Non-overlapping distributions of closely related species can be explained by two mechanisms, either niche divergence or vicariance in the absence of niche differentiation. We assess which of these mechanisms is the most likely cause of the disjunct distributions of three closely related species of Lachnaia Dejean, 1836 (Coleoptera: Chrysomelidae) on the Iberian Peninsula. We estimated the three species' climatic niches, compared them using multivariate analysis, and projected their potential distributions under climatic conditions during the Last Glacial Maximum (LGM) around 20,000 years ago. Lachnaia tristigma (Lacordaire, 1848) and Lachnaia pseudobarathraea (Daniel and Daniel, 1898) hardly differ in their climatic niches. The temperature ranges are similar among the three species, but Lachnaia gallaeca Baselga and Ruiz-Garcia, 2007 occupies a fraction of the environmental space with higher precipitation. The three climatic niches present a broad overlap, which does not suggest speciation events driven by niche differentiation. In turn, the projection of their climatic envelopes to the LGM conditions shows that their potential distributions are compatible with the existence of different glacial refugia for each species. Therefore, we hypothesize that the contraction of species ranges during LGM and subsequent vicariance could have been a major mechanism behind the disjunct distributions that we observe in the present.