Transcriptomic data support phylogenetic congruence and reveal genomic changes associated with the repeated evolution of annualism in aplocheiloid killifishes (Cyprinodontiformes)

Repeated evolution of novel life histories that are correlated with ecological variables offers opportunities to study convergence in genetic, developmental, and metabolic features. Nearly half of the 800 species of Aplocheiloid killifishes, a clade of teleost fishes with a circumtropical distribution, are "annual" or seasonal species that survive in ephemeral bodies of water that desiccate and are unfeasible for growth, reproduction, or survival for weeks to months every year. But the repeated evolution of adaptations that are key features of the annual life history among these fishes remains poorly known without a robust phylogenetic framework. We present a large-scale phylogenomic reconstruction of aplocheiloid killifishes evolution using newly sequenced transcriptomes obtained from a diversity of killifish lineages representing putative independent origins of annualism. Ancestral state estimation shows that developmental dormancy (diapause), a key trait of the killifish annual life cycle, may have originated up to seven times independently among African and South American lineages. To further explore the genetic basis of this unique trait, we measure changes in evolutionary rates among orthologous genes across the killifish tree of life by quantifying codon evolution using dN/dS ratios. We show that some genes have higher dN/dS ratios in lineages leading to species with annual life history. Many of them constitute key developmental genes or nuclear-encoded metabolic genes that control oxidative phosphorylation. Lastly, we compare these genes with higher ω to genes previously associated to developmental dormancy and metabolic shifts in killifishes and other vertebrates, and thereby identify molecular evolutionary signatures of repeated transitions to extreme environments.