DISSERTATION RESEARCH: The Evolution of Diapause in Aplocheiloid Killifishes (Cyprinodontiformes)

George Washington University, Washington DC

Investigators

Abstract

Diapause, defined as a reversible delay in embryonic development, is often brought on by unfavorable conditions. While common among insects and other invertebrate animals that overwinter in harsh climates, it is rare in vertebrates. One of the most exceptional forms of diapause among vertebrate animals occurs in annual killifishes that complete their life cycle in ephemeral bodies of water subject to seasonal desiccation. Killifish are popular pet fishes around the world that have inspired aquarium organizations such as the American Killifish Association in many countries. Aquarists have long known that killifish can stop cellular growth, delay development, and lower their metabolic rate. This makes them excellent model organisms for studying cancer, storage of embryos, and development in animals, yet the molecular genetic basis and evolution of diapause has not yet been examined. The researchers will participate in Aquarists conventions, sharing information about the importance of these fish for scientific research, highlighting the questions, methods and results of this project. Many annual killifishes are endangered or extinct in the wild and because they occur in isolated pools, which will likely change in geographic range and frequency as a result of climate change, making it important to study these fishes before their biodiversity is lost. The unique diapause of killifish occurs when their ephemeral pool habitat dries up. All the adults die, leaving their eggs behind, buried in the soil. Developing embryos survive until the following wet season by entering unique diapause stages, and the eggs may remain in this dormant state in the soil for over a year if unfavorable conditions persist. Phylogenetic studies suggest that this adaptation to extreme environments;may have evolved at least six times among killifishes. The ultimate goal of this project is to understand the genetic basis of diapause among killifishes focusing on its evolutionary origin. Genes associated with diapause will be identified and the DNA sequence of these diapause genes will be determined and analyzed using mathematical models that estimate the strength of natural selection acting at the molecular level. These data will indicate the evolutionary ancestry of diapause in these fish, how the trait evolved and possibly re-evolved multiple times in these fishes. The project will use comparative transcriptomics to identify, sequence, and characterize candidate genes associated with embryonic diapause. Molecular evolution of diapause-associated genes will be modeled on a phylogeny of annual and non-annual fishes to test hypotheses of the evolutionary origin of diapause and to connect the phylogenetic pattern with signatures of adaptive genetic changes in structural and regulatory genes underpinning the evolution of this complex life history trait.