Evaluating species origins within tropical sky-islands arthropod communities

Aim: To (a) evaluate whether colonization of newly emerged high-elevation habitats occurred from neighbouring highlands (allopatric divergence and niche conservatism) or from within the same mountain (peripatric or parapatric divergence and niche shift) and (b) test for the effect of past landscape configurations in geographically structuring biodiversity (a West–East structure spanning the central part of the Transmexican Volcanic Belt). Location: Transmexican Volcanic Belt, Mexico. Taxa: Coleoptera and Araneae. Methods: Coleoptera and Araneae communities were collected in a comparative sampling framework. Seven sky-islands were sampled within two high-elevation habitats separated by altitude. Samples were individually sequenced for a region of the mtDNA COI gene to delimit Operational Taxonomic Units (OTUs) and haplotypes within them. Richness was estimated at the community level, as well as genetic diversity within and among mountains and habitats. The West–East structure was tested with a null model and an analysis of variance with permutations. Results: Few OTUs were shared between the Abies forests and alpine grasslands. High beta diversity was found across mountains. Beta diversity between the West and East grouping is higher than expected by chance. Main conclusions: Our results indicate that colonization from other mountains followed by allopatric divergence dominates as a source of OTU formation, and that despite some probable connectivity during glacial periods existed, ancient communities and genetic structures persist.