Directional asymmetry and correlation of tail injury with left-side dominance occur in Serpentes (Sauropsida)

Abstract

Recent evidence on directional asymmetry (DA) in species of the paraphyletic assemblage "Lacertilia" indicates a possible biological signiWcance of this phenomenon, and we tested its occurrence in Serpentes by examining bilateral morphological characters, such as the numbers of supralabial and infralabial scutes and the diameter of the eyes, on both sides of museum specimens of seven species: Coronella austriaca, Elaphe longissima, Hierophis viridiXavus, Natrix natrix, Natrix tessellata, Platyceps saharicus, and Vipera aspis. SigniWcant DA (not antisymmetry) occurred in at least one sex of four species and in two characters: H. viridiXavus-the number of infralabial scutes in males; N. tessellata-the diameter of the eyes in males; P. saharicus-the number of infralabial scutes in males and the diameter of the eyes in females; and V. aspisthe number of infralabial scutes in the pooled sexes. In N. tessellata and P. saharicus the DA varied geographically. Rank correlation between the DA of diVerent characters, positive or negative, was signiWcant in one character pair in each of three species. In the largest sample (N. tessellata males from the Levant), tail injury correlated with morphological left-dominant asymmetry (a greater number on the left) of infralabial scutes. Four of ten morphologically left-dominant males, but only 1 of 37 symmetrical or right-dominant males, had an injured tail. The syndrome of morphological DA with functional handicap may be genotypical or phenotypical. Our results support three earlier conclusions: bilateral characters should be examined on both sides of an animal; asymmetry should be analyzed separately in each sex; and the accident proneness of left-handed Homo sapiens merits re-evaluation in view of the apparently wide-spread accident proneness in leftbiased Sauropsida (exclusive of Aves).

Morphological, functional and evolutionary aspects of tail autotomy and regeneration in the ‘living fossil’Sphenodon (Reptilia: Rhynchocephalia)

“…The causes for the association of tail loss with left-side dominance are obscure, but the results confirm the existence of this phenomenon in yet another lepidosaurian group (Rhynchocephalia), in addition to the squamate Lacertilia (Seligmann et al, 2003a) and Serpentes (Shacham, 2004(Shacham, , 2005Razzetti, Faiman & Werner, 2007). Conceivably, the assorted responses to suboptimal incubation conditions, known to cause asymmetries and other developmental anomalies in squamates (Osgood, 1978) and to decrease performance in Sphenodon (Nelson et al, 2004(Nelson et al, , 2006, might be pleiotropically associated.…”

“…Although previous analyses of associations of tail state with scale counts in lizards and snakes (Seligmann et al, 2003a, b;Shacham, 2004Shacham, , 2005Razzetti et al, 2007) considered only two tail states, intact and injured, we show here that the extent of original tail retained correlates with DA based on scale counts, an exploration not yet conducted in squamates. In our data, individuals that only lost the tip of the tail relatively resembled intact individuals, whereas those that regenerated the tail from its base were morphologically most different from intact individuals.…”

“…trampling by cows; Jayne & Bennett, 1989). Because, in lizards and snakes, as in man (Seligmann et al, 2003a, b;Shacham, 2004Shacham, , 2005Razzetti et al, 2007), and now in Sphenodon, an elevated injury rate (of the tail or elsewhere) is associated with left-biased asymmetry (Figs 16,19), this hypothesis leads to the further hypothesis that slow escape is associated with left side dominance in lepidosaurians. Although we do not know the cause of this surprisingly general association, presumably it has to be searched in the lateralization of vertebrate brains.…”

Using digital images in the study of fluctuating asymmetry in the spur-thighed tortoise Testudo graeca

“…The femoral and anal scutes' variation was extremely reduced in both males and females. This result indicates a form of directional asymmetry (DA) (Razzetti et al, 2007).…”

Heritabilities of Directional Asymmetry in the Fore- and Hindlimbs of Rabbit Fetuses

“…On the other hand, some have found directional asymmetry in fetal limbs free of mechanic loading (although lateralization in movements also occur in human fetuses; [19]) suggesting a pre-adaptation to handedness during adult life (but results are mixed; see [18]). Although humans have been studied most extensively, correlations between DA and lateralization appear to occur in many vertebrates (e.g., [6], [20]). Nevertheless, most studies cannot reveal a causal link between morphological asymmetry and behavioral lateralization [20].…”