Local Adaptation in Aedes aegypti and the implications for Disease Transmission in a Changing Climate
Restricted (Penn State Only)
- Author:
- Dennington, Nina
- Graduate Program:
- Entomology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 03, 2024
- Committee Members:
- Gary Felton, Program Head/Chair
Matthew Thomas, Special Member
Elizabeth Mcgraw, Chair & Dissertation Advisor
Rudolf Schilder, Major Field Member
David Kennedy, Outside Field Member
Joyce Jose, Outside Unit Member - Keywords:
- Vector Biology
Climate Change
Adaptation
Local Thermal Adaptation
Dengue Virus
Ecology
Mosquito-borne Disease - Abstract:
- Vector-borne pathogens transmitted by biting arthropods, create a large portion of infectious disease transmission globally, responsible for 17% of the global infectious disease burden. Dengue virus infects approximately 390 million people annually, with factors such as climate change, globalization, and human population expansion expected to expose 50% of the world population to arbovirus transmission by 2050. Aedes aegypti are one of the primary vectors for dengue virus, along with other arboviruses, and their geographical range expansion is expected to be a major reason for increased vector-borne disease transmission in the future. The ecological relationship between mosquitoes and their environment is complex and often nonlinear. One of the major factors that influence mosquitoes is temperature and changes in temperature. Many studies have documented the effect of temperature on mosquito life history traits including development, survival, biting rates, fecundity, and ability to transmit pathogens. Because each of these traits affects pathogen transmission, we can use mechanistic models, such as temperature-dependent R0, to predict vector-borne disease transmission across temperatures. Previous experiments using temperature-dependent mechanistic models to predict vector-borne disease transmission assume that one species-level, average curve is adequate to represent all populations. But with local adaptation, populations of mosquitoes could be adapted to their local environment to have increased fitness relative to other populations and therefore a single model for a species may be insufficient. Due to the complexity of this issue, understanding the effect of climate change on mosquito-borne disease requires an understanding of the ecology of mosquitoes not only globally but at finer scales. Climate and climate change are expected to impact the dynamics and distribution of mosquito-borne diseases. Our ability to predict how is undermined by a surprising lack of understanding of the ecological and evolutionary responses of mosquitoes to changes in environmental temperature. In particular, despite a large body of literature examining local thermal adaptation in other insects, there has been almost no analogous research in key mosquito vectors. I aim to remedy this knowledge gap by providing an extensive amount of life history data for multiple populations of mosquitoes across their thermal range. I then integrate these data into thermal performance curves and subsequently mechanistic models to better understand the overall effect of temperature on fitness and transmission at a population level. Here, I examine the effect of local adaptation on life history traits of Ae. aegypti mosquitoes across temperature and the implications for vector-borne disease in a changing climate. In Chapter 1, I review the background on the effect of the environment on mosquitoes and vector-borne disease transmission along with local adaptation in mosquitoes. In Chapter 2, I explore whether local adaptation influences thermal tolerance through both common garden experiments using thermal knockdown and evolution experiments. I show evidence of standing variation in life history traits among populations and the effect of adaptation to temperature through experimental evolution on population fitness. In Chapter 3, I expand on our findings in Chapter 2 by taking a deeper look into the influence of local adaptation on fitness and vector-borne disease transmission using mechanistic models derived from our data on thermal performance curves for life history traits across mosquitoes’ biological thermal range. I show that populations have differences across individual traits and these differences culminate to population-level differences in overall fitness and transmission. In Chapter 4, I examine whether locally adapted mosquito populations show differences in vector competence across temperatures and whether they differ from long-standing laboratory lines. These results indicate that at higher temperatures, the effect of local adaptation may be larger. Lastly, in Chapter 5, I review the findings in previous chapters and discuss how they may affect future studies along with where future knowledge gaps. The results of this dissertation are important as they suggest that the short and longer-term responses to climate change are likely to be dynamic and potentially difficult to predict. They also challenge an underlying assumption of most mechanistic models exploring the possible impact of climate on vector-borne diseases, that the relationship between temperature and transmission is fixed for mosquito species and can be readily extrapolated over time and space. Here, I provide compelling evidence for local thermal adaptation in mosquito vectors, suggesting that simplified thermal performance models might be insufficient for predicting the effects of climate on vector-borne disease transmission.