Molecular Analysis of the Drosophila Hybrid Male Rescue Gene

University Of California-Davis, Davis CA

Investigators

Abstract

Hybrids between different species of animals and plants often suffer from reduced fitness. It is commonly accepted that this fitness reduction results from deleterious interactions between genes that have diverged in each species, but very few examples of such genetic divergence have been reported. Testing this model requires the ability to identify, characterize and manipulate the genes that cause hybrid breakdown. The cross of Drosophila melanogaster females to D. simulans, mauritiana and sechellia males is a well studied example of hybrid breakdown, with the hybrid sons of this cross being fully lethal. The D. melanogaster Hybrid male rescue (Hmr) mutation suppresses this lethality and is therefore a prime candidate for identifying a hybrid lethality gene. The Hmr rescue mutation was recently shown to suppress the lethality of hybrid females that occurs at high temperature, and further genetic analysis has shown that the wild type D. melanogaster Hmr gene does in fact cause hybrid lethality. These findings offer new opportunities for exploring the molecular basis of hybrid lethality. A complete physical map of the Hmr region has been made by deletion mapping and chromosome walking, which will be used for the proposed cloning for Hmr. Once identified, the Hmr locus will be compared in D. melanogaster and its related species to determine whether Hmr has diverged functionally in the melanogaster species complex. The mechanism of hybrid lethality will also be explored by investigating specific eye and wing defects that occur in semi-viable female hybrids. Finally, molecular and genetic screens will be used to search for additional genes that are involved in hybrid lethality. These proposed experiments provide the means to identify and to study the molecular evolution of a network of genes that causes hybrid breakdown in Drosophila. A coherent understanding of the process of species formation has long proven elusive, but progress on numerous fronts suggests that real advances are currently possible. Species are most commonly defined as groups that do not interbreed with other groups. Understanding the genetic basis of reproductive isolation is therefore an essential step towards understanding speciation.