Gene expression divergence between malaria vector sibling species Anopheles gambiae and An. coluzzii from rural and urban Yaoundé Cameroon

Abstract

Divergent selection based on aquatic larval ecology is a likely factor in the recent isolation of two broadly sympatric and morphologically identical African mosquito species, the malaria vectors Anopheles gambiae and An. coluzzii. Population-based genome scans have revealed numerous candidate regions of recent positive selection, but have provided few clues as to the genetic mechanisms underlying behavioral and physiological divergence between the two species, phenotypes which themselves remain obscure. To uncover possible genetic mechanisms, we compared global transcriptional profiles of natural and experimental populations using gene-based microarrays. Larvae were sampled as second and fourth instars from natural populations in and around the city of Yaoundé, capital of Cameroon, where the two species segregate along a gradient of urbanization. Functional enrichment analysis of differentially expressed genes revealed that An. coluzzii—the species that breeds in more stable, biotically complex and potentially polluted urban water bodies—over-expresses genes implicated in detoxification and immunity relative to An. gambiae, which breeds in more ephemeral and relatively depauperate pools and puddles in suburbs and rural areas. Moreover, our data suggest that such over-expression by An. coluzzii is not a transient result of induction by xenobiotics in the larval habitat, but an inherent and presumably adaptive response to repeatedly encountered environmental stressors. Finally, we find no significant overlap between the differentially expressed loci and previously identified genomic regions of recent positive selection, suggesting that transcriptome divergence is regulated by trans-acting factors rather than cis-acting elements.

Prominent intraspecific genetic divergence within Anopheles gambiae sibling species triggered by habitat discontinuities across a riverine landscape

“…Noteworthy, this is also in agreement with the more general hypothesis of an ongoing ecological speciation process involving niche expansion of salinity-tolerant coastal populations of An. coluzzii into larval habitats of marginal quality (Cassone et al 2014).…”

Transcriptomic differences between euryhaline and stenohaline malaria vector sibling species in response to salinity stress

“…; Cassone et al . ). Third, a combined list of potential cytoskeleton and cuticle components was made of GO terms including cuticle, microtubule, cytoskeleton, cytoskeletal, chitin and chitinase.…”

“…First, we designated all genes with GO terms of transport, carrier, channel, antiporter, symporter or exchanger as transport genes. Second, a list generated by Rob Waterhouse was used to identify immune-related genes, as in (Waterhouse et al 2013;Cassone et al 2014). Third, a combined list of potential cytoskeleton and cuticle components was made of GO terms including cuticle, microtubule, cytoskeleton, cytoskeletal, chitin and chitinase.…”

“…Only the young 18 h data from 2012 were used for network analysis, to avoid the influence of age on gene expression overwhelming differences from salinity and species identity. Large transcriptomic changes are known to occur during larval development (Koutsos et al 2007;Cassone et al 2014). Prior work has shown that roughly half of An.…”

Habitat segregation and ecological character displacement in cryptic African malaria mosquitoes

“…coluzzii from Central Africa may be more widely applicable geographically and combined with other evidence, prompt a more general working hypothesis: An. coluzzii is adapted to tolerate greater levels of environmental stressors in its larval habitats, not only in sites closely associated with the coast/sea, but also those associated with urban centres containing xenobiotics and ammonia Tene Fossog et al 2013;Cassone et al 2014). Extending bioassays of An.…”