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EVOLUTIONARY GENETICS OF TWO SIBLING SPECIES, DROSOPHILA SIMULANS AND D. SECHELLIA.
Jerry A Coyne1, Martin Kreitman2
1Department of Zoology, The University of Maryland, College Park, MD, 20742.
Summary
Genetic analysis reveals multiple genes cause reproductive isolation and morphological differences between Drosophila simulans and D. sechellia. Evolutionary parallels suggest either convergence or common ancestry for island species.
Area of Science:
- Evolutionary genetics
- Speciation biology
- Comparative genomics
Background:
- Drosophila simulans is a cosmopolitan species, while D. sechellia is endemic to the Seychelles Islands.
- Understanding the genetic basis of reproductive isolation and morphological divergence is key to studying speciation.
- Sibling species provide valuable models for investigating evolutionary processes.
Purpose of the Study:
- To quantify the number and effects of genes underlying reproductive isolation and male genital morphology differences between D. simulans and D. sechellia.
- To reconstruct the phylogenetic relationships of D. simulans, D. sechellia, D. mauritiana, and D. melanogaster.
- To investigate the evolutionary history and potential common ancestry of island-endemic Drosophila species.
Main Methods:
- Classical genetic analysis to map genes for hybrid sterility and morphological traits.
- DNA sequencing of the alcohol dehydrogenase (Adh) locus region in D. sechellia.
- Phylogenetic analysis using DNA sequence data and previous studies.
Main Results:
- At least five loci contribute to hybrid male sterility, with two major genes on the X chromosome.
- At least three to four loci influence the size of the posterior process of the male genital arch.
- Phylogenetic analyses indicate D. mauritiana and D. sechellia are closely related to D. simulans, but their exact branching order is ambiguous.
- Intraspecific Adh allele divergence is comparable to interspecific divergence, suggesting ancestral polymorphisms.
Conclusions:
- The genetic architecture and morphological divergence between D. simulans and its island relatives (D. mauritiana, D. sechellia) show striking parallels, possibly due to evolutionary convergence or shared ancestry.
- Accurate phylogenetic reconstruction can be challenging with limited genetic markers due to deep ancestral polymorphisms.
- Further investigation is needed to resolve the evolutionary history of these closely related Drosophila species.
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