RESPONSES TO DIRECT AND INDIRECT SELECTION ON AERIAL DISPERSAL BEHAVIOR IN TETRANYCHUS-URTICAE

Dispersal within and between hosts is an important element of arthropod life histories. This study was designed to assess adaptability of traits related to dispersal and colonization in the twospotted spider mite, Tetranychus urticae. Defining the flexibility of mite dispersal and life-history is necessary to understand the response of mites to changes in the spatial and temporal structure of their environment. We found significant direct response to bidirectional selection on aerial dispersal behaviour after eight and five generations of selection. The realized heritability estimated from these lines (h(2)=0.28) was in close agreement with that estimated in a previous sib-analysis on the base population. As predicted from the sib-analysis, there were no correlated responses in fecundity or sex ratio. Crosses between selected lines indicated that the dispersal behaviour was under weak maternal influence and that non-dispersal may be a slightly dominant trait. Mite sensitivity or resistance to starvation or desiccation, the major environmental cues triggering their behaviour, changed in response to selection. Results suggest that variation in aerial dispersal behaviour is largely attributed to different sensitivity or resistance to environmental stress and that genetic variation in this behaviour may be maintained by selection for dispersal when food resources become depleted and against when food is abundant. The dispersal behaviour itself, although not correlated with reproductive traits, may increase mite fitness in temporally and spatially fluctuating environments.