Species-Wide Genetic Variation and Demographic History of Drosophila sechellia, a Species Lacking Population Structure

Abstract

Long-term persistence of species characterized by a reduced effective population size is still a matter of debate that would benefit from the description of new relevant biological models. The island endemic specialist Drosophila sechellia has received considerable attention in evolutionary genetic studies. On the basis of the analysis of a limited number of strains, a handful of studies have reported a strikingly depleted level of genetic variation but little is known about its demographic history. We extended analyses of nucleotide polymorphism in D. sechellia to a species-wide level using 10 nuclear genes sequenced in 10 populations. We confirmed that D. sechellia exhibits little nucleotide-sequence variation. It is characterized by a low effective population size, .10-fold lower than that of D. simulans, which ranks D. sechellia as the least genetically diverse Drosophila species. No obvious population subdivision was detected despite its fragmented geographic distribution on different islands. We used approximate Bayesian computation (ABC) to test for demographic scenarios compatible with the geological history of the Seychelles and the ecology of D. sechellia. We found that while bottlenecks cannot account for the pattern of molecular evolution observed in this species, scenarios close to the null hypothesis of a constant population size are well supported. We discuss these findings with regard to adaptive features specific to D. sechellia and its lifehistory strategy.

Genome sequencing reveals complex speciation in the Drosophila simulans clade

“…Instead, we find evidence for nontrivial amounts of nuclear gene flow between two of the three species pairs. Finally, we find that the relatively smaller effective population size of D. sechellia Kliman et al 2000;Legrand et al 2009) has entailed a lineage-specific increase in the rate of slightly deleterious substitution and a concomitant decrease in the rate of presumed adaptive substitution.…”

“…Most recent analyses, however, suggest that, first, D. sechellia and, slightly more recently, D. mauritiana were separately derived from a D. simulans ancestor (Kliman et al 2000;McDermott and Kliman 2008). Today, D. simulans occurs on the same islands as D. sechellia (Cariou et al 1990;R'Kha et al 1991;Legrand et al 2009), but not D. mauritiana (David et al 1989;Legrand et al 2011). Additionally, all three species are incompletely isolated by premating (Coyne 1992;Coyne and Charlesworth 1997), postmating-prezygotic (Price et al 2000), and intrinsic postzygotic barriers (F 1 hybrid females are fertile, F 1 hybrid males are sterile) (Lachaise et al 1986).…”

“…D. sechellia may be further isolated by ecological specialization to the toxic fruits of its host plant, Morinda citrifolia, which are lethal to D. simulans and D. mauritiana (Lachaise et al 1988). Notably, D. sechellia has an effective population size roughly an order of magnitude smaller than its two sister species Kliman et al 2000;Legrand et al 2009). Lastly, while the chromosomes of all three species are all homosequential (Lemeunier and Ashburner 1984), small rearrangements do exist .…”

Insulin signalling underlies both plasticity and divergence of a reproductive trait inDrosophila

“…We measured mean ovariole number for multiple isofemale lines from both species, and observed greater betweenpopulation variation for ovariole number in D. melanogaster sechellia is known to be lower than that of other melanogaster group species [52], and it is possible that this contributes to its reduced interpopulational variation in ovariole number. However, we argue that IIS-dependent plasticity provides a proximate molecular mechanism for the evolutionary divergence of ovariole number.…”

Enzymatic characterization of recombinant α-amylase in the <i>Drosophila melanogaster</i> species subgroup: is there an effect of specialization on digestive enzyme?

“…Evidence for adaptive evolution could theoretically be also gained from sequence polymorphism analysis. However, D. sechellia shows little overall genetic diversity (Legrand et al, 2009) and few strains or populations are currently available for D. erecta. To better understand the impact of specialization on the action of a digestive enzyme such as amylase, we should have a clearer picture of the composition of polysaccharides and oligosaccharides of the host plants Morinda citrifolia and Pandanus candelabrum and test characteristics of amylase from other specialist species.…”