Skull dorsal asymmetries between three different rabbit types signals stress in paedomorpic animals
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Fluctuating asymmetry (FA) is frequently considered a consequence of developmental instability (DI), defined as the inability of an organism to adjust its development to an ideal pattern. The underlying hypothesis is that, under ideal conditions, development should produce nearly symmetric final forms.
DI is not directly observable and that is why one of the main reasons for studying FA relies on the hypothesis that it may reflect DI. Directional asymmetry (DA), on the other side, occurs when one side is more often larger than the other, that is, the consistent difference between a pair of morphological structures. For zootechnical studies, developmental stress can be an important factor for inferring inadequate management or selective conditions. In this regard, cranial asymmetries of domestic rabbit were compared for examining their FA and DA in order to infere aspects of living and selective conditions. In this study, 69 individuals who belong to different types (46 toys, 10 beliers, these both types considered as companion, and 13 meat) were investigated by means of geometric morphometric methods. Digital pictures were obtained for each skull on its dorsal aspects and ten two-dimensional landmarks were then putted on both neurocranium and splachnocranium. Results show that here was statistically significant DA in all three types, but only companion rabbits (toys and beliers) presented significative FA. It is considered that this is a reflect of relatively high developmental stress in the companion animals (toys and beliers), selected for extreme paedomorphic traits, in comparison to meat type, and also a physiological masticatory lateralization in the species, independently of the aptitude. Probably directionalized asymmetry along the left and right side of the skull in mammals may be more prevalent than once believed.