title: 'Vertition' of integumental organs in mites revisited: a case of fluctuating asymmetry.
abstract: Vertition in mites is defined as a meristic variation for a bilateral integumental organ with a separate genetic control for each body side. A prominent hypothesis expressed by Grandjean is the role of vertition in the evolutionary trend towards a reduced number of hair-like organs (mechano- and/or chemo-receptors) known to have occurred in many mite groups. Observations on leg setae in the two-spotted spider mite Tetranychus urticae do not support this hypothesis. Meristic variation for leg setae rather conforms to the notion of fluctuating asymmetry: the difference between the number of leg setae on the right and left sides of the body had a unimodal distribution with a mean of zero. Moreover, lack of heritability for left/right absences of leg setae in an inbred laboratory strain suggests that vertition could be purely environmental. It is therefore argued that meristic variation for hair-like organs in mites is caused by random developmental accidents not corrected by homeostatic mechanisms normally resulting in a perfect bilateral symmetry.
authors: Belgian Royal Institute of Natural Sciences, rue Vautier 29, B-1000 Brussels, Belgium.
authors: M
authors: M
authors: Leponce
authors: M I
authors: MI
authors: Noti
authors: V
authors: V
authors: Bauchau
authors: G
authors: G
authors: Wauthy
mesh_terms: D000818:Animals; D002628:Chemoreceptor Cells; D005121:Extremities / Q000033:anatomy & histology / Q000294:innervation; D008465:Mechanoreceptors; D008925:Mites / Q000033:anatomy & histology*