Dobzhansky-Muller model of hybrid dysfunction supported by poor burst-speed performance in hybrid tiger salamanders.

Speciation may result from 'complementary' genetic differences that cause dysfunction when brought together in hybrids despite having no deleterious effects within pure species genomes. The theory of complementary genes, independently proposed by Dobzhansky and Muller, yields specific predictions about the genetics of hybrid fitness. Here, I show how alternative models of hybrid dysfunction can be compared using a simple multivariate analysis of hybrid indices calculated from molecular markers. I use the approach to fit models of hybrid dysfunction to swimming performance in hybrid tiger salamander larvae. Poor burst-speed performance is a dysfunction suggesting low vigour and could translate directly into low survival. My analyses show that the Dobzhansky-Muller model fits these data better than heterozygote disadvantage. The approach demonstrated here can be applied to a broad array of nonmodel species, potentially leading to important generalizations about the genetics of hybrid dysfunction.