Sex ratios of oribatid mite assemblages differ among microhabitats

Abstract

This study investigates sex ratios of oribatid mite species and oribatid mite assemblages in different forest microhabitats (dead wood, grass sod, moss, lichen litter, tree bark) to identify possible factors driving sex ratio dynamics. We considered 46,320 individuals belonging to 47 species, and analyzed data on numbers of sexual and parthenogenetic species as well as individuals across microhabitats using paired t-tests and generalized linear mixed effect models. Most species (75 %) were sexual, with females comprising 43 % to 89 % of samples. In twelve out of 35 sexual species sex ratios differed significantly among microhabitats, the sex ratio of most species (23) remained constant. Parthenogenetic species of Enarthronota, Mixonomata, Nothrina and Quadroppia quadricarinata comprised of 100 % females, but in Oppiella nova, and Tectocepheus spp. spanandric males were found (1–3 %). Sex ratios of oribatid mite assemblages were generally female-biased and differed significantly among microhabitats. The highest proportions of females were found on tree bark (~ 72 %) and grass sod (~ 69 %) and the lowest were in lichens (~ 53 %). The mechanism of sex determination in oribatid mites and factors influencing the distortion of primary sex ratios are poorly known, so explanations for the observed patterns remain speculative. Since field observations are mostly infeasible, complex long-term laboratory studies on egg deposition, egg development and development of males and females under different conditions in different species are needed.

Keywords

• sex ratios
• oribatid mites
• microhabitats
• litter
• dead wood
• moss
• grass sod
• lichen
• tree bark