Resources and sex: Soil re-colonization by sexual and parthenogenetic oribatid mites

Abstract

Factors responsible for the dominance of sexual reproduction in Metazoa are controversial. Generally, the mode of reproduction is correlated with ecological factors: under resource-limited conditions sexual taxa dominate, whereas theoretically parthenogenetic species prevail in stable habitats. To investigate if sexual or parthenogenetic taxa are more affected by environmental conditions, we analyzed (1) the effect of resource depletion on the density of sexual and parthenogenetic oribatid mite taxa and (2) the re-colonization of defaunated soil and litter by sexual and parthenogenetic taxa. In both experiments, the number of eggs in parthenogenetic and sexual species was counted. For the first experiment, laboratory microcosms were established where resources declined with time; for the second experiment, microcosms were defaunated by heat and inoculated with fresh soil and litter material, respectively, as resource for re-colonization by oribatid mites. We hypothesized that parthenogenetic species will suffer more from resource limitation compared to sexual taxa, and that they will colonize habitable space faster due to their faster mode of reproduction. In agreement with our hypothesis, parthenogenetic taxa suffered more from resource limitation than sexual species. In contrast, in the re-colonization experiment the proportion of parthenogenetic taxa remained constant in the treatment re-colonized from soil as well as from litter, indicating that parthenogenetic species are not faster colonizers. In general, egg numbers were higher in sexual species than in parthenogenetic species.