Phylogeography in sexual and parthenogenetic European oribatida

Abstract

Oribatid mites (Acari, Oribatida) are a species rich group which may form the oldest group of Chelicerata, as indicated by fossils from Devonian sediment (~380 million years) and molecular clock data (~570 million years). They are ubiquitous soil living arthropods and important decomposers. In oribatid mites parthenogenesis is common, about 10% of the individuals reproduce parthenogenetically, and they likely radiated while being parthenogenetic. Their high abundance (up to 400.000 individuals per square meter in temperate and boreal forest soils) and their species richness (10.000 described species) render oribatid mites ideal model organisms to answer evolutionary and ecological questions. Using molecular markers I investigated the genetic diversity of two sexual and two parthenogenetic European oribatid mite species. (1) Genetic diversity in soil living microarthropods Pleistocene glaciations shaped the genetic and species diversity of Europe. Using the mitochondrial gene of the cytochrome c oxidase (COI) I investigated the genetic structure of the soil living oribatid mite species Steganacarus magnus. The high intraspecific genetic variance of COI at nucleotide (32% uncorrected p-distance) and protein level (5% uncorrected p-distance) suggests that the climatic change had no strong influence on S. magnus. It survived the last ice ages in cryptic refugia, radiated in the Miocene or earlier and colonized Europe after the last ice age from cryptic refugia. (2) Cryptic species complex in Steganacarus magnus Intraspecific variance of mitochondrial DNA higher than 3% indicates a cryptic species complex. The high intraspecific distance in COI of the oribatid mite species S. magnus (up to 32%) indicates the existence of cryptic species. Using one mitochondrial (COI) and one nuclear marker (elongation factor 1 alpha; ef 1α) I investigated if there is a cryptic species complex in S. magnus. The results suggest that S. magnus does not comprise a cryptic species complex; phylogenetic trees of the genes studied were different indicating recombination between lineages. (3) Post- and pre-glacial colonization of Europe by sexual and parthenogenetic oribatid mite species Belowground organisms could have survived low temperatures undamaged and therefore survived the ice age in cryptic refugia. Using the molecular marker COI I investigated the colonization events of two sexual (Achipteria coleoptrata, S. magnus) and two parthenogenetic (Nothrus silvestris, Platynothrus peltifer) European oribatid mite species. Each oribatid mite species showed a different colonization pattern of Europe. A. coleoptrata, S. magnus and P. peltifer had high nucleotide divergences (19% A. coleoptrata, 31% S. magnus, 20% P. peltifer) but only the two sexual oribatid mite species also had high protein divergences (3% A. coleoptrata, 4% S. magnus). N. silvestris had low nucleotide (2%) and protein (0%) divergences. The results indicate that A. coleoptrata, S. magnus and P. peltifer radiated in the Miocene and survived the Pleistocene ice ages in cryptic refugia. IN contrast, N. silvestris did not survive the ice age in cryptic refugia but colonized Central and Norther! n Europe thereafter and radiated in the Holocene. The high protein variance in sexual and the low variance in parthenogenetic oribatid mites provided hints on mechanisms responsible for the maintenance of sexual reproduction.