Peripatric origin of the only cave-restricted stonefly species known (Insecta: Plecoptera)

Abstract

Cave animals have evolved specialised morphological and behavioural adaptations to a dark and stable environment. When their ancestors were surface species living in continental climates, and thus adapted to annual changes from extreme cold to extreme warm periods; it is highly intriguing how adaptation to cave stable temperature took place. The phylogenetic history of the cave animal can thus help to understand the kind of adaptation process undergone in such a different environment. Here we perform a mitochondrial DNA-based phylogeny for the only Palearctic cave-restricted plecopteran species (Protonemura gevi), whose geographic range is limited to a single cave in the south of the Iberian Peninsula, also including four other Iberian and Moroccan Protonemura species and two other species from different genera as outgroup taxa. Our results indicate that P. gevi shows a genetic distance with P. culmenis being an order of magnitude lower than those with the remaining Protonemura species. Using a relaxed molecular clock, phylogeny dating suggests that their common ancestor probably lived 1.4 million years ago, i.e. during Pleistocene. P. culmenis currently lives in the Pyrenees, so that it is conceivable that this species (or the common ancestor of both) migrated to a southern refuge during one of Pleistocene glaciations, and a few individuals remained isolated within the Siles cave managing to live in such new and different environmental conditions. We thus conclude that the peripatric origin of P. gevi was associated with Pleistocene glaciations, and that its adaptation to cave conditions was quite rapid.