Variation in skull size and shape of the Common wall lizard (Podarcis muralis): allometric and non-allometric shape changes

We analysed patterns of skull size and shape variation among populations of the Common wall lizard (Podarcis muralis) in the Central Balkans, particularly the effecs of insularity and the presence of the ecologically similar lacertid lizard species P. melisellensis. Two components of shape variation were analysed – size dependent (allometric) and size independent shape changes. The observed shape differentiation relating to insularity was greatly size-dependent and concordant to allometric shape changes which explained over 20% of variation in the skull shape in the analysed sample. The explorative analysis of size-independent shape changes revealed that populations of P. muralis which share habitat with P. melisellensis diverge from populations which do not share habitat with potentially competing species. These changes related to the general shortening and widening of the skull and increase of the jaw adductor muscle chambers were more pronounced in males. We suppose that the observed pattern of shape changes is driven by competition among species (character displacement) and, possibly, is further modified by heterospecific aggression and trophic shift.