Coracoid asymmetries in adult Pondsliders,Trachemys scripta (Schoepff 1792), in Spain

Abstract

Morphological variation is the result of interplay among multiple intervening factors. Appendicular bone
morphology in reptiles has been addressed rarely in the literature and, to our knowledge, the girdles of turtles have
never been utilized to address developmental questions of form asymmetry. We quantified left-right symmetry of the
coracoids in 42 (10 male and 32 female) Pondsliders, Trachemys scripta (Schoepff 1792), an exotic emydid in Spain. We
measured form symmetry between the right and left coracoids using geometric morphometric techniques by means of
14 paired landmarks and 66 paired semi-landmarks. Both sexes exhibited fluctuating asymmetry (FA: small and random
deviations in the symmetry, but with a variation normally distributed around a zero mean) and directional asymmetry
(DA: a greater development on one side, with most asymmetry in the same direction). DA has been described
as a product of genotype as well as functional lateralization. The most probable explanation for the detected DA is that
it results from a functional imbalance due to limb lateralization, which results from an unequal pull of paired muscles
on bones. Low levels of FA, apparently the result of subclinical metabolic osteopathies (presumably attributable to
improper diets of most of the animals examined, as they had been kept as pets), are excluded.