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Sequence variation of alcohol dehydrogenase (Adh) paralogs in cactophilic Drosophila
Luciano M Matzkin1, Walter F Eanes
1Department of Ecology and Evolution, State University of New York, Stony Brook, New York 11794-5245, USA. lmatzkin@life.bio.sunysb.edu
Insights
Population genetics reveal distinct alcohol dehydrogenase (Adh) evolution in cactophilic Drosophila. Different Adh gene forms show varied variation patterns, suggesting adaptation to cactus hosts and recent species divergence.
Area of Science:
- Population genetics
- Molecular evolution
- Drosophila speciation
Background:
- Cactophilic Drosophila species, Drosophila mojavensis and D. arizonae, have adapted to hosts with diverse alcohol compounds.
- Two functional alcohol dehydrogenase (Adh) loci exist: Adh-2 (adult) and Adh-1 (larval/ovarian).
Purpose of the Study:
- To investigate the population genetics of alcohol dehydrogenase (Adh) in cactophilic Drosophila.
- To understand the evolutionary patterns and divergence times of Adh paralogs in D. mojavensis and D. arizonae.
Main Methods:
- Analysis of population genetics and molecular variation in Adh loci.
- Estimation of divergence times for species and gene duplication events.
Main Results:
- D. arizonae exhibits greater genetic variation than D. mojavensis, suggesting a larger population size.
- Distinct variation patterns observed between Adh-1 and Adh-2 paralogs.
- Evidence of adaptive protein evolution in D. mojavensis Adh-1, linked to cactus host shifts.
- Recent divergence estimates for D. mojavensis and D. arizonae (2.4 ± 0.7 MY) and Adh duplication (3.95 ± 0.45 MY).
Conclusions:
- Adh gene evolution in cactophilic Drosophila is influenced by host plant chemistry and speciation.
- Gene conversion and selection likely maintain Adh-2 intron structure.
- Host-associated adaptations drive the evolution of larval-expressed Adh paralogs.
Abstract:
This study focuses on the population genetics of alcohol dehydrogenase (Adh) in cactophilic Drosophila. Drosophila mojavensis and D. arizonae utilize cactus hosts, and each host contains a characteristic mixture of alcohol compounds. In these Drosophila species there are two functional Adh loci, an adult form (Adh-2) and a larval and ovarian form (Adh-1). Overall, the greater level of variation segregating in D. arizonae than in D. mojavensis suggests a larger population size for D. arizonae. There are markedly different patterns of variation between the paralogs across both species. A 16-bp intron haplotype segregates in both species at Adh-2, apparently the product of an ancient gene conversion event between the paralogs, which suggests that there is selection for the maintenance of the intron structure possibly for the maintenance of pre-mRNA structure. We observe a pattern of variation consistent with adaptive protein evolution in the D. mojavensis lineage at Adh-1, suggesting that the cactus host shift that occurred in the divergence of D. mojavensis from D. arizonae had an effect on the evolution of the larval expressed paralog. Contrary to previous work we estimate a recent time for both the divergence of D. mojavensis and D. arizonae (2.4 +/- 0.7 MY) and the age of the gene duplication (3.95 +/- 0.45 MY).
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