Two novel, tightly linked, and rapidly evolving genes underlie Aedes aegypti mosquito reproductive resilience during drought

Abstract

Female Aedes aegypti mosquitoes impose a severe global public health burden as vectors of multiple viral pathogens. Under optimal environmental conditions, Aedes aegypti females have access to human hosts that provide blood proteins for egg development, conspecific males that provide sperm for fertilization, and freshwater that serves as an egg-laying substrate suitable for offspring survival. As global temperatures rise, Aedes aegypti females are faced with climate challenges like intense droughts and intermittent precipitation, which create unpredictable, suboptimal conditions for egg-laying. Here we show that under drought-like conditions simulated in the laboratory, females retain mature eggs in their ovaries for extended periods, while maintaining the viability of these eggs until they can be laid in freshwater. Using transcriptomic and proteomic profiling of Aedes aegypti ovaries, we identify two previously uncharacterized genes named tweedledee and tweedledum, each encoding a small, secreted protein that both show ovary-enriched, temporally-restricted expression during egg retention. These genes are mosquito-specific, linked within a syntenic locus, and rapidly evolving under positive selection, raising the possibility that they serve an adaptive function. CRISPR-Cas9 deletion of both tweedledee and tweedledum demonstrates that they are specifically required for extended retention of viable eggs. These results highlight an elegant example of taxon-restricted genes at the heart of an important adaptation that equips Aedes aegypti females with 'insurance' to flexibly extend their reproductive schedule without losing reproductive capacity, thus allowing this species to exploit unpredictable habitats in a changing world.

Multiple blood feeding bouts in mosquitoes allow for prolonged survival and are predicted to increase viral transmission during drought

“…Specific genes have been previously linked with egg retention during drought periods in Ae. aegypti (38), which supports these studies that eggs can be retained under suboptimal conditions until a water source can be located to deposit eggs. Our studies suggest that the second bloodmeal is not directly required for oogenesis; instead, the primary role is to ensure hydration and survival until eggs can be deposited.…”

“…2B). This suggests that prolonged retention will allow eggs to remain viable, a finding that has been previously observed when oviposition sites are not available (37). Overall, these studies indicate that dry conditions are likely to result in the ingestion of multiple bloodmeals during each gonotrophic cycle, allowing females to survive for extended dry periods.…”

The Origin and Evolution of Sex Peptide and Sex Peptide Receptor Interactions

“…Overall, signal peptides have a lower sequence constraint, and their substitution rate is three to four times higher than that of mature proteins ( Canale et al 2018 ). Given a timeframe longer than 60 million years, it is feasible for signal peptides to change without becoming recognizable ( Venkataraman et al 2023 ). As for C-terminal sequences, speculation becomes more challenging.…”

Wolbachiastrain wMelM disrupts egg retention byAedes aegyptifemales prevented from ovipositing

“…Methods for forcing egg retention were adapted from a previous study (Venkataraman et al, 2023). Female mosquitoes (5-6 d old) were blood fed on the forearm of a human volunteer (University of Melbourne human ethics approval 0723847) and transferred to BugDorm-1 cages provided with only sugar through a cotton wick (Figure 2).…”

“…aegypti with the flexibility to pause their reproduction for extended periods. This ability to retain eggs can be affected by genetic factors (Venkataraman et al, 2023), but it is unclear whether this variation is driven by ecological differences in conditions experienced by populations. Egg retention could also be affected by other inherited factors, notably maternally inherited endosymbionts including Wolbachia residing naturally or increasingly being introduced deliberately into mosquitoes for disease control (Ant et al, 2023).…”