Coracoid asymmetries in adult Pondsliders,<i>Trachemys scripta</i> (Schoepff 1792), in Spain

Morphological variation is the result of interplay among multiple intervening factors. Appendicular bonemorphology in reptiles has been addressed rarely in the literature and, to our knowledge, the girdles of turtles havenever been utilized to address developmental questions of form asymmetry. We quantified left-right symmetry of thecoracoids in 42 (10 male and 32 female) Pondsliders, Trachemys scripta (Schoepff 1792), an exotic emydid in Spain. Wemeasured form symmetry between the right and left coracoids using geometric morphometric techniques by means of14 paired landmarks and 66 paired semi-landmarks. Both sexes exhibited fluctuating asymmetry (FA: small and randomdeviations 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 describedas a product of genotype as well as functional lateralization. The most probable explanation for the detected DA is thatit results from a functional imbalance due to limb lateralization, which results from an unequal pull of paired muscleson bones. Low levels of FA, apparently the result of subclinical metabolic osteopathies (presumably attributable toimproper diets of most of the animals examined, as they had been kept as pets), are excluded.