Abstract
BackgroundHybrid male sterility (HMS) is a usual outcome of hybridization between closely related animal species. It arises because interactions between alleles that are functional within one species may be disrupted in hybrids. The identification of genes leading to hybrid sterility is of great interest for understanding the evolutionary process of speciation. In the current work we used marked P-element insertions as dominant markers to efficiently locate one genetic factor causing a severe reduction in fertility in hybrid males of Drosophila simulans and D. mauritiana.ResultsOur mapping effort identified a region of 9 kb on chromosome 3, containing three complete and one partial coding sequences. Within this region, two annotated genes are suggested as candidates for the HMS factor, based on the comparative molecular characterization and public-source information. Gene Taf1 is partially contained in the region, but yet shows high polymorphism with four fixed non-synonymous substitutions between the two species. Its molecular functions involve sequence-specific DNA binding and transcription factor activity. Gene agt is a small, intronless gene, whose molecular function is annotated as methylated-DNA-protein-cysteine S-methyltransferase activity. High polymorphism and one fixed non-synonymous substitution suggest this is a fast evolving gene. The gene trees of both genes perfectly separate D. simulans and D. mauritiana into monophyletic groups. Analysis of gene expression using microarray revealed trends that were similar to those previously found in comparisons between whole-genome hybrids and parental species.ConclusionsThe identification following confirmation of the HMS candidate gene will add another case study leading to understanding the evolutionary process of hybrid incompatibility.
Highlights
Hybrid male sterility (HMS) is a usual outcome of hybridization between closely related animal species
In the current work we focus on locating one hybridmale-sterility (HMS) factor between D. simulans and D. mauritiana and investigating the nature of the disruption behind it
We find that significant variation in fertility is observed when other strains of D. simulans are used
Summary
Hybrid male sterility (HMS) is a usual outcome of hybridization between closely related animal species. When genetically isolated populations have accumulated enough divergence, the hybrid progeny may be sterile due to the disruption of gametogenesis caused by functional incompatibility between factors evolved independently within each population This scenario characterizes post-zygotic isolation, which is frequently found in pairs of species sharing a recent common ancestor. A number of studies have succeeded in identifying, at the molecular level, a few genes that may be involved in speciation (in Drosophila: OdsH [3,4], Nup98 [5], Nup160 [6], Hmr [7], Zhr [8], Ovd [9]; in Mus: Prdm9 [10], in Xiphophorus: Xmrk-2 [11]) These recent data together provide needed insight into the evolution of reproductive isolation, and they largely confirm the traditional view of speciation as an evolutionary process involving multiple genes [12,13]. The existence of multiple reproductive barriers that have accumulated over time is expected [12]
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