Effect of temperature on mortality, sterility and Wolbachia titre that may cause behavioural changes

Rashid, Amirah (2024) Effect of temperature on mortality, sterility and Wolbachia titre that may cause behavioural changes PhD thesis, University of Liverpool.

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Abstract

Temperature is one of the important factors used to predict the distribution range of insects and observing pathogen-insect relationships. It also affects the fitness of ectotherms such as their adult lifespan, fecundity and biting rate. Taken together, all these factors are crucial for prediction of disease transmission risk and subsequent vector control programmes. Previous study has proven that observing the thermal fertility limit (TFL) of Drosophila flies is better at predicting their distributions as compared to critical thermal limit (CTL) alone. In Chapter 2, I looked at the mortality limit and sterility limit of Aedes aegypti and Culex molestus. Unmated adult mosquitoes were heat and cold shocked for 4 hours and 6 hours respectively to represent day/night extremes. Then, they were allowed to mate for four days before given an egg dish to lay eggs. Sterility was observed based on blood feeding, eggs laying and eggs hatching. To further support the findings, morphology of both the male and female reproductive organs were dissected and observed under microscope to compare between the stressed and normal. We found that Aedes are sterile at 38 °C. We also found that Aedes males are much more sensitive to high temperatures, while female mosquitoes have higher tolerance. On the other hand, both males and females are sterile at -2 °C which is confirmed from the shrunk reproductive organs. Apart from looking at adult mortality and sterility, eggs of Aedes can stand desiccation, hence we also looked at maximum temperature that can cause a detrimental effect on the eggs. Results from this study were then analysed and used for temperature modelling in predicting distributions of Aedes in the current climate and future climate. Wolbachia is a bacterium commonly found in insects. They do not naturally occur in Ae. aegypti. However, Ae. aegypti have been artificially infected with Wolbachia (wAlb) since this bacterium can confer protection against RNA viruses (i.e. dengue and Zika viruses) to their host. Moreover, Wolbachia is also known for their manipulative reproductive phenotypes in mosquitoes by causing cytoplasmic incompatibility. Due to these abilities, Wolbachia are used for vector and arbovirus control. More recently studies have shown that Wolbachia can also change its host behaviour, such as feeding behaviour in older wMelPop-infected female Ae. aegypti. In Chapter 3, I studied the thermal preference of Wolbachia-infected female Ae. aegypti and compared them to the uninfected controls using a thermal gradient setup. Knowing that developmental temperature is crucial for the Wolbachia-conferred antiviral protection, we have compared temperatures where infected and uninfected mosquitoes choose to lay eggs. We observed that Wolbachia alters the mosquito oviposition preference. We have also observed interaction between the presence of Wolbachia, mosquito developmental time, and the temperature where they choose to oviposit. Our results will help us to understand the relationship between Wolbachia, Ae aegypti, and temperature. Such interactions are useful to evaluate the influence of environment on releasing Wolbachia infected mosquitoes and may imposed in future vector control programmes. In Chapter 4, I looked at another endosymbiont, Spiroplasma in infected Drosophila flies. Even though insects choose temperatures optimal for them, presence of parasites force them to change their thermal preference in order to benefit the microbe or minimize the parasite induced harm. Spiroplasma is a bacterium which protects D. melanogaster hosts against parasitoid wasps. It has been shown before that endosymbiont (i.e. Wolbachia) can modulate thermal preference of Drosophila – flies infected with the symbiont seek colder temperatures to minimize Wolbachia replication. In this chapter, I compared the temperature preference of Spiroplasma-infected Drosophila to their non-infected counterparts in the presence of parasitoid wasps. We confirmed that parasitoid reduce the number of eggs laid by D. melanogaster. And that both Spiroplasma and wasps presence increases the D. melanogaster egg laying temperature. Our result will help understand the ecology of these symbiotic interactions. Together, these analyses provide valuable updates to our current understanding on temperature, relationship between host and endosymbiont which will be beneficial for improving preparedness and strategies in vector control programs.

Item Type:	Thesis (PhD)
Divisions:	Faculty of Health & Life Sciences Faculty of Health & Life Sciences > Inst. Infection, Vet & Ecological Sciences
Depositing User:	Symplectic Admin
Date Deposited:	20 Jan 2025 10:50
Last Modified:	08 Feb 2025 03:09
DOI:	10.17638/03187177
Supervisors:	Blagrove, Marcus ORCID: 0000-0002-7510-167X Baylis, Matthew ORCID: 0000-0003-0335-187X Chrostek, Ewa
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3187177
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