Nature Nurtures: How environmental variation influences Anopheles stephensi vectorial capacity
Open Access
- Author:
- Whitehead, Shelley Alexandra
- Graduate Program:
- Entomology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- November 08, 2018
- Committee Members:
- Matthew Brian Thomas, Dissertation Advisor/Co-Advisor
Matthew Brian Thomas, Committee Chair/Co-Chair
Ottar N Bjornstad, Committee Member
Rudolf Johannes Schilder, Committee Member
Stephen Wade Schaeffer, Outside Member
Diana Cox-Foster, Special Member - Keywords:
- mosquito
malaria
climate change
Anopheles
vector ecology
environmental variation
life history
Plasmodium - Abstract:
- Malaria kills approximately 500,000 people each year, leaving a remaining 3.3 billion people at risk. To understand the complexity of its transmission is to understand its vector, the Anopheles mosquito, and its life history, which is sensitive to changes in environmental factors, such as temperature and nutrition. Here, I examine how variations in temperature and diet affect mosquito life history traits and discuss how these dynamics can influence our existing understanding of disease transmission. In Chapter 2, as part of a team, we exposed Anopheles stephensi mosquitoes to Plasmodium falciparum parasites at a range of temperatures to characterize thermal performance curves for this mosquito and parasite species pairing. This experiment did not, however, include additional sources of environmental variation. Therefore, in Chapters 3, 4, and 5, I subjected adult mosquitoes to fluctuating temperatures and various diet regimes to measure how these sources of variation would shift existing predictions. I found that temperature and diet variation resulted in significant changes in adult mosquito life history traits. Temperature fluctuations reduced median mosquito survival by <30% at average temperatures of 27°C and 30°C when females were allowed to sugar feed. This reduction was exacerbated, however, as temperatures fluctuated at 34°C, as median survival was reduced by 35%-55%. When mosquitoes were only allowed to blood feed, temperature fluctuations impacted median survival substantially at 27°C (by 55%), but this impact was not as substantial as temperatures increased (<30%). Absence of sugar in mosquito diets greatly reduced the median survival time; adults with access to blood only (when compared to those fed either blood and sugar or sugar only), experienced an 84% reduction in median survival. These environmental effects also impacted overall mosquito fecundity and blood feeding frequency. I subjected mosquitoes to the same environmental conditions and measured resulting clutches, blood feeding frequencies, and egg viability. Females in no sugar treatments laid larger clutches of eggs and exhibited higher blood feeding rates than those given access to sugar, with no observable effects on egg viability. Temperature fluctuation, as well as nutrition, qualitatively impacted key mosquito reproductive traits, such as eggs per female per day, providing additional evidence that to not include sources of environmental variation in current disease transmission models may lead to over or underestimation of actual transmission dynamics. Finally, to understand dynamics presented in previous experiments, I exposed mosquitoes to either fluctuating temperatures or various diets and measured metabolic rate and overall nutrient composition over mosquito age. Decreases in macronutrients for mosquitoes in sugar absent treatments illustrated possible explanations for decreased survival and increased blood feeding evidenced in Chapters 3 and 4, respectively. Metabolic rates in sugar deprived treatments decreased over two measured points in mosquito age when compared to those allowed to sugar feed. These changes in metabolic rate over fluctuating temperature regimes foster a discussion about our current understanding of insect-rate temperature dynamics and offer explanations for reductions in lifespan observed in Chapters 3 and 4. The results presented in these chapters support the continued investigation of other sources of environmental variation on the shaping of mosquito biology and ecology, as these dynamic changes can influence overall disease transmission. Nutrition is not considered a major factor in many transmission models produced today, yet we have observed how it can affect life history traits not only quantitatively but also qualitatively. Without knowing anything about how often mosquitoes blood or sugar feed, we cannot make accurate predictions about transmission due to temperature. These changes are important when considering how we think about malaria and disease transmission, especially when small changes in temperature, fluctuations in temperature, and changing access to nutrition can significantly affect mosquito life history traits.