High resolution genomes of multipleXiphophorusspecies provide new insights into microevolution, hybrid incompatibility, and epistasis

Abstract

Because of diverged adaptative phenotypes, fish species of the genusXiphophorushave contributed to a wide range of research for a century. ExistingXiphophorusgenome assemblies are not at the chromosomal level and are prone to sequence gaps, thus hindering advancement of the intra- and inter-species differences for evolutionary, comparative, and translational biomedical studies. Herein, we assembled high-quality chromosome-level genome assemblies for three distantly relatedXiphophorusspecies, namely,X. maculatus,X. couchianus, andX. hellerii. Our overall goal is to precisely assess microevolutionary processes in the clade to ascertain molecular events that led to the divergence of theXiphophorusspecies and to progress understanding of genetic incompatibility to disease. In particular, we measured intra- and inter-species divergence and assessed gene expression dysregulation in reciprocal interspecies hybrids among the three species. We found expanded gene families and positively selected genes associated with live bearing, a special mode of reproduction. We also found positively selected gene families are significantly enriched in nonpolymorphic transposable elements, suggesting the dispersal of these nonpolymorphic transposable elements has accompanied the evolution of the genes, possibly by incorporating new regulatory elements in support of the Britten–Davidson hypothesis. We characterized inter-specific polymorphisms, structural variants, and polymorphic transposable element insertions and assessed their association to interspecies hybridization-induced gene expression dysregulation related to specific disease states in humans.