Cranial Shape and the Modularity of Hybridization in Dingoes and Dogs; Hybridization Does Not Spell the End for Native Morphology

Australia's native wild dog, the dingo (Canis dingo), is threatened by hybridization with feral or domestic dogs. In this study we provide the first comprehensive three dimensional geometric morphometric evaluation of cranial shape for dingoes, dogs and their hybrids. We introduce a novel framework to assess whether modularity facilitates, or constrains, cranial shape change in hybridization. Our results show that hybrid and pure dingo morphology overlaps greatly, meaning that hybrids cannot be reliably distinguished from dingoes on the basis of cranial metrics. We find that dingo morphology is resistant, with observed hybrids exhibiting morphology closer to the dingo than to the parent group dog. We also find that that hybridization with dog breeds does not push the dingo cranial morphology towards the wolf phenotype. Disparity and integration analyses on the ten recovered modules provided empirical support for modularity facilitating shape change over short evolutionary time scales. However, our results show that this is may not be the case in hybridization events, which were not influenced by module integration or disparity levels. We conclude that although hybridization events may introduce breed dog DNA to the dingo population, the native cranial morphology, and therefore likely the feeding eco-niche, of the dingo population is resistant to change. Our results have implications for conservation and management of dingoes and, more broadly, for the influence of integration patterns over ecological time scales in relation to selection pressure.