Distinct physiological, biochemical and morphometric adjustments in the malaria vectorsAnopheles gambiaeandAn. coluzziias means to survive to dry season conditions in Burkina Faso

Abstract

Aestivation and dispersive migration are the two strategies evoked in the literature to explain the way in which malaria vectors and survive the harsh climatic conditions of the dry season in sub-Saharan Africa. However, the physiological mechanisms regulating these two strategies are unknown. In the present study, mosquito species were exposed to controlled environmental conditions mimicking the rainy and dry seasons of south western Burkina Faso. Survival strategies were studied through morphometric (wing length), ecophysiological (respiratory gas exchanges), biochemical (cuticular hydrocarbons composition) and molecular (AKH mRNA expression levels) parameters, variations of which are usually considered to be hallmarks of aestivation and dispersion mechanisms in various insects. Our results showed that ecophysiological and morphometric adjustments are made in both species to prevent water losses during the dry season. However, the usual metabolic rate modifications expected as signatures of aestivation and migration were not observed, highlighting specific and original physiological mechanisms sustaining survival in malaria mosquitoes during the dry season. Differences in epicuticular hydrocarbon composition and AKH levels of expression were found between the permanent and temporary populations, illustrating the great phenotypic plasticity of this mosquito species. Altogether, our work underlines the diverse and complex pattern of changes occurring in the two mosquito species and at the population level to cope with the dry season and highlights potential targets of future control tools.

Biological Adaptations Associated with Dehydration in Mosquitoes

“…Cuticular hydrocarbon (CHC) abundance is one major factor in the desiccation tolerance of An. coluzzii [103] and it further supports the suggestion of dry season aestivation by this species [101]. CHC differences were less apparent in An.…”

“…CHC differences were less apparent in An. gambiae , which supports a migratory hypothesis for these mosquitoes [101]. Regardless, the 2La chromosomal inversion in An.…”

Cuticular hydrocarbons are associated with mating success and insecticide resistance in malaria vectors

“…Increased CHC production is likely to impose fitness costs that can only be offset in specific environmental conditions such as insecticide usage or aridity, and indeed there is evidence that CHCs also contribute to desiccation tolerance in An. gambiae [40][41][42] . Fitness costs of CHC production have been reported in Drosophila, where there appears to be a trade-off between CHC abundance and oogenesis, to the point that in the absence of sexual selection total CHC content is reduced in both male and female flies 36,43 .…”

Insects With Survival Kits for Desiccation Tolerance Under Extreme Water Deficits

“…Furthermore, in some insects, restructuring of the cuticle and morphological changes in spiracular features are crucial to minimize water loss. Such restructuring mechanisms are important because water is mainly lost passively and/or actively throughout spiracular respiration and cuticular transpiration (Hadley, 1994; Benoit and Denlinger, 2007; Benoit, 2010; Bazinet et al, 2010; Wadaka et al, 2016; Hidalgo et al, 2018; Ferveur et al, 2018). Other behavioral traits for desiccation protection such as the arrangement of egg laying (layering and density) in the nymphalid butterfly, Chlosyne lacinia (Lepidoptera: Nymphalidae), increases desiccation survival chances of eggs (Clark and Faeth, 1998).…”