Ambulatory dispersal in Tetranychus urticae: an artificial selection experiment on propensity to disperse yields no response

Dispersal to new hosts is an important process for an invasive herbivore, such
as the two-spotted spider mite. A recent study, using artificial selection experiments, has
suggested that genetic variation and genetic trade-offs are present for propensity to disperse
in this species. However, due to the experimental setup alternative explanations for
the response to selection could not be ruled out. Using an altered setup, we investigated
whether the propensity for ambulatory dispersal differs genetically between individuals
and whether genetic correlations with life-history traits exist. Upward and downward
selection on propensity to leave the colony was performed for seven generations in four
replicate artificial selection experiments and the results were compared to control lines. No
consistent responses to selection were found and no significant effect on life-history traits
(oviposition rate, juvenile survival, development rate and number of adult offspring) or sex
ratio was present across the replicates. The data suggest that our base population of spider
mites harbours at best a low amount of additive genetic variation for this behaviour.