Hybridization events in Squamata support the viviparity-driven conflict hypothesis.

Hybridization occurs in various groups of vertebrates, although the incidence, frequency and parental divergence times differ. One hypothesis for this difference between taxonomic groups is the so-called viviparity-driven conflict hypothesis, which is built upon the theory that more genetic and immunological mismatches may arise when the zygote spends a longer time within the mother. Accordingly, theory predicts a higher chance of failure of hybridization events between viviparous species compared to oviparous species. In this study, we reviewed hybridization events in both viviparous and oviparous Squamata (lizards, snakes and amphisbaenids) and used the collected data to test the viviparity-driven conflict hypothesis with a phylogenetic generalized linear mixed model. Hybridization was phylogenetically widespread and present among both reproductive modes, although divergence times of parental species were significantly longer in hybridization events between oviparous species. Moreover, the interaction between divergence time and viviparity showed a negative effect on hybridization probability. The results indicate that viviparous species lose the capability of hybridizing more rapidly with increasing divergence time than oviparous species. Hence, our findings provide support for the viviparity-driven conflict hypothesis.