Habitat stratification stratifies a local population: ecomorphological evidence from a bisexual, mobile invertebrate (Carabodes labyrinthicus; Acari)

We present preliminary evidence that local populations may be differentiated among habitat strata also in mobile, sexually reproducing invertebrates. We considered Carabodes labyrinthicus, an oribatid mite species, sampled from the endogeic (below litter layer) and the epigeic stratum in a forest. We found that the endogeion was used by only a few females. Most interestingly, endogeic and epigeic males differed with respect to physiologically relevant traits such as body volume and sensillus shape. Supplementary genetic investigations corroborated this differentiation between strata. Non-parametric tests, jackknife and bootstrap resampling consistently confirmed our findings; indicating that highly robust patterns can be detected even from small samples such as ours. Finally, we found that epigeic males showed a distinctly bimodal distribution of morphology, where one of the two peaks matched the unimodal distribution of endogeic males. We conclude that the population investigated may be gradually differentiated between stratum specialists that are restricted to the epigeion, and stratum generalists.