Student Theses and Dissertations

Date of Award

2022

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Abstract

Female Aedes aegypti mosquitoes impose a severe global public health burden as vectors of viruses that cause dengue, chikungunya, yellow fever, and Zika, and parasites that cause lymphatic filariasis. Under optimal environmental conditions, Aedes aegypti females have access to human hosts that provide blood proteins required for egg development, conspecific males that provide sperm required for fertilization, and freshwater in natural or manmade containers that serves as an egg-laying substrate suitable for offspring survival during larval and pupal stages. As global temperatures rise, Aedes aegypti females are faced with climate challenges like intense droughts and intermittent bouts of precipitation, which create unpredictable, suboptimal conditions for egg-laying. Yet, this species is highly invasive, adeptly domesticated, and continues to expand its stronghold across most continents. How do female Aedes aegypti mosquitoes successfully reproduce when freshwater availability is unpredictable? What behavioral and molecular adaptations have evolved to ensure the reproductive flexibility and resilience of this species when they are faced with intense droughts and changing climates?

Here we show that the reproductive behaviors of adult Aedes aegypti females are tightly interconnected and centered on precise spatiotemporal control of egg-laying in a manner that balances intrinsic physiological needs with extrinsic environmental constraints to ensure maximal fitness. Specifically, in drought-like conditions simulated in the laboratory, females that have mated and blood-fed will 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 that we name 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. A CRISPR-Cas9- mediated mutation that disrupts both tweedledee and tweedledum together 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.

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