# Phenotypic changes in natural populations of Anopheles gambiae s.l. at the onset of the long dry season in tropical savannahs of Burkina Faso, West Africa

## TL;DR

This study examines how different species of malaria mosquitoes adapt physiologically during the dry season in West Africa, revealing species-specific survival strategies.

## Contribution

The study identifies distinct phenotypic changes in Anopheles species under natural field conditions at the onset of the dry season.

## Key findings

- An. coluzzii showed increased gonotrophic dissociation and energy reserves during the dry season transition.
- All three species exhibited increased body size and fat deposits, but with species-specific differences.
- Adaptive responses varied between study sites, indicating the influence of breeding habitat types.

## Abstract

In the tropical savannahs with long dry seasons, malaria mosquito populations virtually disappear after the drying up of breeding sites to reappear in large numbers at the onset of next rainy season. While aestivation and long-distance migration are proposed as key strategies enabling these vectors to persist through the dry-season, the physiological, biochemical, and morphological traits underpinning these mechanisms remain insufficiently explored, particularly under natural field conditions. This study explored seasonal changes in Anopheles coluzzii, An. gambiae, and An. arabiensis at the onset of the dry season in the harsh savannahs of Burkina Faso, West Africa. Late-instar immature specimens were collected from two ecologically distinct sites, one with permanent and the other with only temporary breeding habitats, during the rainy season and the transitional period into the dry season. Larvae were reared to adulthood under natural conditions and several traits were analysed including ovarian development, sub-cuticular fat body hypertrophy, body size, and energy reserves. Gonotrophic dissociation was significantly more frequent in An. coluzzii at the onset of the dry season, indicating a shift toward reproductive arrest. All three species exhibited increased body size and cuticular fat deposits during the transitional period, though with species-specific differences. Notably, only An. coluzzii showed significant increases in energy reserves (proteins, lipids, and carbohydrates) during the transition period. These adaptive responses differed between the study sites, suggesting the influence of breeding habitats. The findings highlight that species within the An. gambiae complex engage in distinct phenotypic trajectories at the onset of the dry season, suggesting divergent adaptations and trade-offs in energy acquisition and allocation to survive during the dry season.