Stage-dependent trade-offs in thermal performance: fluctuating temperatures reverse larval and adult fitness in <i>Anopheles gambiae</i> and <i>An. coluzzii</i>

Temperature is a key environmental factor influencing the development, survival, and transmission potential of malaria vectors. While most laboratory studies use constant temperature (CT) regimes, mosquitoes in natural habitats experience fluctuating temperatures (FTs), which may affect their life-history traits. We investigated the effects of CT (27 °C) and FT (27 ± 3 °C) on larval and adult traits of 2 major malaria vectors, Anopheles gambiae and An. coluzzii, under laboratory conditions. We measured larval survival, development time, adult body size, and adult survival, using survival and mixed-effects models. Species-specific and stage-specific responses to temperature regimes were observed. An. gambiae larvae exhibited higher survival under FT, while An. coluzzii larvae survived better under CTs. However, this pattern reversed in adulthood: An. coluzzii adults showed increased survival and larger body size under FT, whereas An. gambiae adults performed better under CT. Development time was slightly longer under FT for both species, with An. coluzzii pupating faster overall. These opposing patterns suggest that differential larval survival under FTs may influence adult fitness in a species-specific manner. The contrasting and reversed responses of An. gambiae and An. coluzzii across life stages might reflect their ecological adaptations: An. gambiae, found in small and thermally variable habitats, performed better under FT during larval stages, while An. coluzzii, associated with larger, more thermally stable habitats, showed improved adult performance under FT. These findings underscore the importance of incorporating species-specific, stage-dependent thermal responses into models of vector dynamics and control strategies under climate change.