A test of the chromosomal theory of ecotypic speciation inAnopheles gambiae

Abstract

The role of chromosomal inversions in speciation has long been of interest to evolutionists. Recent quantitative modeling has stimulated reconsideration of previous conceptual models for chromosomal speciation. Anopheles gambiae, the most important vector of human malaria, carries abundant chromosomal inversion polymorphism nonrandomly associated with ecotypes that mate assortatively. Here, we consider the potential role of paracentric inversions in promoting speciation in A. gambiae via ''ecotypification,'' a term that refers to differentiation arising from local adaptation. In particular, we focus on the Bamako form, an ecotype characterized by low inversion polymorphism and fixation of an inversion, 2Rj, that is very rare or absent in all other forms of A. gambiae. The Bamako form has a restricted distribution by the upper Niger River and its tributaries that is associated with a distinctive type of larval habitat, laterite rock pools, hypothesized to be its optimal breeding site. We first present computer simulations to investigate whether the population dynamics of A. gambiae are consistent with chromosomal speciation by ecotypification. The models are parameterized using field observations on the various forms of A. gambiae that exist in Mali, West Africa. We then report on the distribution of larvae of this species collected from rock pools and more characteristic breeding sites nearby. Both the simulations and field observations support the thesis that speciation by ecotypification is occurring, or has occurred, prompting consideration of Bamako as an independent species. chromosomal inversion ͉ ecological speciation ͉ Bamako chromosomal form ͉ inversion polymorphism ͉ selection

The Population Genomics of Trans-Specific Inversion Polymorphisms in Anopheles gambiae

“…Five of the inversions (2La and 2Rb, -c, -d, and -u) are nonrandomly associated with degree of aridity; each cycles seasonally with rainfall, and all except 2Ru form stable geographic clines in frequency from mesic forest to xeric regions bordering the Sahara (Coluzzi et al 1979;Toure et al 1994Toure et al , 1998Powell et al 1999). Inversion 2Rj is not clinal, but its distribution in Mali is consistent with adaptation to novel rockpool niches (Coluzzi et al 1985;Manoukis et al 2008).…”

Inference of chromosomal inversion dynamics fromPool‐Seq data in natural and laboratory populations ofDrosophila melanogaster

“…They have, for example, been found to be involved in sex chromosome evolution (McAllister 2003; Charlesworth et al 2005) and may be key factors for speciation (Noor et al 2001; Rieseberg 2001; Hey 2003; Manoukis et al 2008; Neafsey et al. 2010).…”

Chromosomal plasticity and evolutionary potential in the malaria vector Anopheles gambiae sensu stricto: insights from three decades of rare paracentric inversions

“…This mechanism is hypothesized to have played a central role in the ecotypic differentiation and speciation events represented by the Anopheles gambiae complex [4,5,11,12], an African group of closely related mosquitoes that contains two of the most significant vectors of human malaria. Although virtually morphologically identical at all developmental stages, most species in the complex are distinguished by at least one fixed inversion difference.…”