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 significance 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 viridiflavus, Natrix natrix, Natrix tessellata, Platyceps saharicus, and Vipera aspis. Significant DA (not antisymmetry) occurred in at least one sex of four species and in two characters: H. viridiflavus—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. aspis—the number of infralabial scutes in the pooled sexes. In N. tessellata and P. saharicus the DA varied geographically. Rank correlation between the DA of different characters, positive or negative, was significant 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 left-biased Sauropsida (exclusive of Aves).