Understanding the role of mosquito vectors in food webs of African birds and bats

Overview

Mosquitoes are the deadliest animals on the planet, due to their role as vectors of diseases such as malaria and dengue. These two diseases alone account for approximately 500,000 human deaths every year. In addition to deaths, mosquitoes are important in spreading diseases that can be life altering or cause extensive suffering (e.g. Zika virus and Chikungunya). Mosquitoes also cause diseases in animals (e.g. avian malaria has had a devastating impact on endemic island birds).

While progress has been made in understanding the ecology of the mosquitoes themselves, there are still many gaps to fill. For example, the natural predators of adult mosquitoes are relatively poorly known, as is the role of these predators in controlling mosquito populations. Bats especially are known to be voracious predators, and may be able to consume 600 mosquitoes per hour, however it remains unclear which species they may be consuming (disease vectors or those that are relatively benign). Our DNA sequence data from bird and bat faecal samples collected from Cameroon show that at least 15 species of bats and birds consume mosquitoes from five different genera, including Anopheles, Culex, Coquillettidia, Eretmapodites, and Mansonia, which include important human disease vectors. However, our data remain incomplete, because it is currently very difficult to assign species-level taxonomy to mosquitoes with the traditionally used DNA barcoding approach of sequencing the COI gene. A related key question regards the role of mosquitoes in natural food webs. Some mosquito control strategies (e.g. using genetic modification) aim to produce sterile mosquitoes, which would cause populations to collapse. However, the ecological impact of such an action on food webs remains unclear.

It also remains unclear if wild animals consume a particular subset of mosquitoes at a higher rate. Insecticides are widely used to prevent crop damage and kill harmful pests, including mosquitoes. However, repeated use has led to the evolution of mosquitoes (e.g. in the genus Anopheles) that can survive treatment, making this control measure less effective. Some research suggests that insecticide resistance comes at a cost: alterations during development may make them more vulnerable to predation. Understanding sex bias in consumption of mosquitoes would also be valuable. Male mosquitoes form aerial mating swarms at dusk, which may make them especially vulnerable to predators like bats, but only females take blood meals, thus bats may not control the portion of the mosquito population causing disease. On the other hand, some mosquito control strategies target individuals of one sex (sometimes males and sometimes females), thus understanding if predators preferentially target a specific sex would be important.

Thus, this project aims to:

1) (a) Identify animals consuming mosquito vectors – focusing on birds and bats, but potentially also amphibians – as well as (b) the species of mosquitoes being consumed.
2) Using network and ecological modeling approaches, investigate the food webs that these species participate in, and perform sensitivity analyses to answer questions such as: what would happen if one or more predators were removed (e.g. due to land use or climate change)? What would happen if one or more mosquito species were removed from the system (e.g. due to vector control strategies)?
3) Identify if predators preferentially consume mosquitoes of particular types (i.e. insecticide resistant mosquitoes or a particular sex).

Methodology

The student will leverage an impressive collection of more than 2000 bird, bat, and amphibian samples already in hand from our on-going projects in Cameroon, Ghana and Zambia. They will also potentially have the opportunity to join fieldwork at new sites in Guinea Bissau, Angola, or on São Tomé and Principe Islands with collaborator Dr. Luke Powell.

In the lab, the student will conduct a literature review and employ public databases to assess potential genetic regions to use to identify species-level taxonomy and other characteristics of mosquitoes, build DNA sequence alignments, and design/test candidate PCR primers from these regions. Once a suite of primers has been developed, the student will conduct DNA metabarcoding of bird and bat samples (i.e. simultaneous sequencing of all potential mosquito prey) using advanced DNA sequencing technology. These sequences will then be compared to our reference sequence database to assign taxonomy using sophisticated bioinformatics pipelines. Data will be analysed in ecological community networks as well as in a dynamic ecological modelling framework we are currently developing to link species interactions and abundances.

At the end of the project there will be an opportunity for the student to return to the field to conduct a techniques workshop for local researchers and to disseminate research results to the public.

Project Timeline

Year 1

Potential field work with collaborator Dr Powell; Visit Prof Ferguson at Glasgow University; Literature review and compilation of a database of candidate genetic regions; Building DNA sequence alignments of regions or sequencing reference mosquitoes for these regions; Designing and testing primers suitable for use with faecal samples; Preparation of a technical publication describing these primer sets, which will be a major step forward in the field (Objective 1b).

Year 2

Test primer sets using DNA metabarcoding of ‘mock communities’ composed of mixtures of mosquito DNA; Perform DNA metabarcoding of a range of bird, bat, and amphibian samples from various locations in Africa; visit with Prof Ferguson and our statistical modelling collaborators at University of Glasgow.

Year 3

Attend NERC Environmental Omics Facility workshop on “Metabarcoding for Diet Analysis and Environmental DNA” or similar topic; Food web and statistical modelling of results; preparation of manuscripts for Objectives 1a/2, and Objective 3. Attendance at a national scientific meeting. Potential trip to Africa to lead training workshop and disseminate results.

Year 3.5

Completion/submission of thesis; revision of submitted manuscripts; attendance at an international scientific meeting.

Training
& Skills

This project will build a strong and diverse toolset that can readily be employed by the future ecologist. The IAPETUS2 program itself has been developed to build a strong foundation of transferable skills, and involves an individual postgraduate certification. In addition to this, the student will build deep, specialised understanding of vector ecology, food webs and community ecology, as well as theory and application of molecular ecology. The student will have the opportunity to conduct fieldwork, handle birds and bats, conduct habitat and arthropod abundance surveys, and learn about ethical conduct of research. These skills are widely used for careers in research, environmental surveys and monitoring. In the lab, the student will learn general lab (e.g. preparing solutions, pipetting) and advanced DNA sequencing techniques, which can provide a foundation for further molecular ecological and evolutionary genetics research or be used for careers in environmental testing, molecular biology, and medical testing/research. In addition to this the student will gain a strong foundation in bioinformatics and statistical analyses using sophisticated computational resources, including working at the command line (e.g. computer programming) in R and other programs. Such numerical and computational skills are widely implemented across many career paths. Through writing manuscripts and the thesis, as well as attendance at national and international meetings, the student will develop excellent communication skills.

The student will be primarily based in the Biosciences Department at Durham University under the supervision of Dr. Welch. The department has a strong track record in the fields of ecology and evolution, and a friendly and collegial environment. The Molecular Ecology special interest group is composed of four PIs and involves a large group of postdocs, PhD and MS students that provide a supportive network for journal clubs, student presentations, peer feedback, mentoring for job applications and interview skills. We also host an Ecology Evolution and Environment seminar series with talks from local and international speakers, providing many opportunities for networking. The University offers workshops on transferable skills, such as time management, team working, and leadership skills.

References & further reading

Deiner et al. 2016 Envirnomental DNA metabarcoding: Transforming how we survey animal and plant communities. Molecular Ecology 26:5872-5895

Hammond et al. 2021 Gene-drive suppression of mosquito populations in large cages as a bridge between lab and field. Nature Communications 12:4589

Berticat et al. 2004 Insecticide resistance genes confer a predation cost on mosquitoes, Culex pipiens Genetics Research 83: 189-196

Chandrasegaran et al. 2020 Linking mosquito ecology, traits, behaviour and disease transmission Trends in Parasitology 36:393-403

Further Information

This project is in competition with others for funding, and success will depend on the quality of applicants, relative to those for competing projects. Funding includes tuition fee waiver for Durham University, a competitive stipend, and research support.

To express interest in applying, or for further information, you should contact Dr. Andreanna Welch at a.j.welch@durham.ac.uk by 3 January 2022 at the latest. In your email include: 1) a few sentences detailing your reasons for applying and how your experiences fit with the project, 2) your CV with marks earned for previous degrees and 3) contact information for at least two references.

Only the best applicants will be asked to submit a full application, including two reference letters, by 17:00 on the 7th of January 2022.

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