The evolution of diversity and life history traits in annual killifish (Austrolebias) and other Cyprinodontiformes

Abstract

Members of the annual killifish genus Austrolebias live in temporary ponds across South America and possess a remarkable life cycle. These fish live in small ponds that dry out completely; killing the adults but not before they have laid eggs in the substrate of their pond. The desiccation-resistant eggs develop during the dry season, going through multiple stages of diapause until the next wet season rains trigger hatching and the cycle is repeated. There is considerable variation in size in Austrolebias, the largest species can reach up to 150mm in length while the typical size is just 40mm. Phylogenetic trees and species distribution models were built and used together to identify the factors that influence patterns of co-occurrence within this genus. Differences in growth and morphology among Austrolebias species were examined to quantify how differences in growth pattern can lead to the large variation in size and shape seen within the genus. Genomic data was generated for hybrid offspring of two species of Austrolebias using double-digest RAD sequencing. These data were then used to build linkage maps that were in turn used to identify any regions associated with sex determination and potential chromosomal rearrangements. At a broader scale, a generic-level tree for the order Cyprinodontiformes was constructed. Austrolebias is a member of this order, as well as many model fish genera such as Fundulus, Nothobranchius and Poecilia. Two extraordinary reproductive life-history adaptations have evolved in this order; viviparity and annualism. The new tree was used to determine whether the evolution of viviparity or annualism lead to increased rates of diversification. Finally this generic-level tree was used to examine patterns of positive selection in the low-light vision gene, rhodopsin and whether sites under selection were linked to functional changes.