Links-rechts-asymmetrie in pootverlies en pootletsels van spinnen (Araneae)

Missing legs were recorded from spiders in the field. Small regenerated legs were counted as leg loss preceding the last moult. Catching spiders hidden in the vegetation and in ground litter at haphazard often produced whole or partial leg loss. This was counted in a separate analysis while also including legs with an abnormal orientation and legs that moved less than normal during running, apparently due to a lesion of the coxa-trochanter-joints at the base of the leg. It appeared that legs on the left side were statistically significantly more often lost or hurt than right-side legs in the species Zygiella x-notata (if only specimens missing a single leg were counted: 21 ‘left’ versus 8 ‘right’ specimens). If Zygiella were also counted that missed two or more legs, the difference was not significant (34 specimens with mainly, or only, left-leg loss, versus 23 specimens with mainly, or only, right-leg loss). In Enoplognatha ovata the ratio of left- to right-leg loss and lesions (mainly due to catching the spiders at haphazard in the field) was 79 ‘left’ to 49 ‘right’ specimens (when counting also specimens with two or more severed legs). In general 12 out of 13 spider families showed at least a weak preponderance of species with coxa-trochanter-joints lesions of left-hand legs after catching them at haphazard in the field. When counting the families of spiders for natural leg loss (undisturbed spiders in the field) the left over right preponderance was not significant. Counting natural or catching–produced leg severance of individual spiders instead of counting families only resulted in non-significant preponderances of left- over right-leg severance. When taking into account the front-rear position of the legs on the prosoma, left legs of the second leg pair were significantly more often lost than right legs if only undisturbed spiders missing a single leg were counted in the field. Independently from position on the prosoma, a leg from the longest (first) leg pair was significantly more often lost than a leg from the shortest (third) leg in each of the four species that were most frequently visible in the field (Araneus diadematus, Larinioides sclopetarius, Zygiella x-notata, and Pholcus phalangioides). This supports a study of Bauer (1972) and we also found this in Enoplognatha ovata when caught at haphazard from the vegetation in which it was usually hidden. In a very general way significantly more frequent left-leg than right-leg loss or lesion were found several times, whereas the reverse (significantly more frequent right-leg severance) was never found. Our study and the very few studies undertaken so far (see especially Ades & Ramires, 2002) give support to the general hypothesis that appendages on the left body side are more liable to loss or lesion than those on the right body side in vertebrates and invertebrates. The relative importance of length difference and joint-strength difference between left and right legs deserves to be studied.