Reconstructing the Mosquito Family Tree with DNA

Why are there so many different types of mosquitoes? How have they evolved over time and in different parts of the world? And what drives the evolution of various traits, including those which make them vectors of disease? Dr. Brian Wiegmann explored these and other important questions using DNA from mosquitoes collected around the globe, including specimens stored at the NEON Biorepository at Arizona State University (ASU). Wiegmann and his coauthors published their results in Nature Communications, “Phylogenomics reveals the history of host use in mosquitoes.”

What’s All the Buzz About Mosquitoes?

There are more than 3500 species of mosquitoes across the globe, existing on every continent except Antarctica. Nearly 200 species have been identified in North America. Of these, only a small number carry pathogens that cause disease in humans, but they have had an outsized impact on human populations. Mosquito-borne diseases such as malaria, Zika, Dengue fever, West Nile, and yellow fever are responsible for millions of cases of illness every year, with symptoms ranging from mild to severe. In many parts of the world, mosquito-borne diseases are still a significant cause of death, disability, and birth defects.

Mosquitoes, and the pathogens they carry, have also influenced human evolutionary history as populations in endemic areas have developed genetic adaptations to combat these diseases. Malaria, for example, has been a major selective force in human evolution, leading to genetic adaptations such as sickle-cell trait, thalassemia, and glucose-6-phosphate dehydrogenase deficiency, which provide some resistance to malaria but can also cause health issues on their own.

Wiegmann, a professor at North Carolina State University (NCSU) in the Department of Entomology and Plant Pathology, is interested in systematics, a branch of biology that deals with the classification and naming of organisms (taxonomy) and the evolutionary relationships among organisms (phylogenetics). “Systematics is the study of biodiversity: the kinds of organisms that have lived on the planet both in the past and in the present,” he explains. “Systematics looks at patterns of diversity through time and tries to explain how the history and current state of different environments on Earth can help explain the differences that we see in biodiversity in different parts of the world.”

As an entomologist, Wiegmann has focused on flies (order Diptera), one of the most diverse orders of animals on the planet. Mosquitoes are a subset of flies in the family Culicidae. Within this family, mosquitoes can be further divided into several genera, including Aedes, Anopheles, and Culex. “I’m interested in insect diversity and history,” says Wiegmann, “and flies are one of the major insect groups on the planet. And because they play so many different biological roles in the environment, understanding their history ends up being a really important part of studying the impact of climates, environments, and other natural history factors on diversity on the planet.”

Tracing Mosquito Evolutionary History Through Phylogenomic Analysis

One of Wiegmann’s primary goals in the mosquito study was to contribute toward the development of a “mosquito family tree”—also known as a phylogeny. A phylogeny shows the evolutionary relationships among species based on similarities and differences in their physical and genetic characteristics. Essentially, it is a hypothesis about the history of the evolution of a species or group, showing their common ancestry and how they have diverged over time. Each branch in the family tree consists of a clade, or a lineage path showing all the descendants of a common ancestor.

 "It’s like building a roadmap through time of the changes that have occurred for mosquitoes.”

To create the phylogeny, Wiegmann and his co-investigators needed physical samples of mosquitoes from around the world for DNA analysis. Genomic sequencing can be used to infer evolutionary relationships; mosquitoes sharing certain genetic sequences in their genomes can be inferred to come from a common ancestor. Using modern genomic analysis and bioinformatics techniques, it is now possible to sample and compare hundreds or thousands of points on the mosquito genome, enabling rich comparisons between species. Looking at where genomes match or diverge can help to build an evolutionary history of mosquitoes on a global level. Researchers can then explore relationships between genetic markers and climate or environmental factors to make inferences about the drivers of evolutionary change over time and across different climate zones and habitat types.

Wiegmann explains, “It becomes a process of modeling how one can explain how we got to the current diversity of mosquitoes through a pattern of change, adaptation, mutation, and speciation. We are inferring their phylogenetic history. It’s like building a roadmap through time of the changes that have occurred for mosquitoes.”

Mosquitos flying across Alaska's taiga landscape in Domain 19

For this study, Wiegmann was primarily interested in using a new estimate of the mosquito family tree to understand the evolution of host preferences for mosquitoes. He worked with a team of researchers to sequence genomes from hundreds of specimens from bioarchives around the world, including the NEON Biorepository at ASU. Ultimately, they completed phylogenomic analysis of mosquitoes from six continents, encompassing 24 genera and nine tribes (groups of closely related genera). The results provide important clues as to when and where in evolutionary history different groups of mosquitoes diverged—in some cases, as far back as the Jurassic and Cretaceous periods. The study is the largest of its kind for mosquitoes to date.

“Mosquitoes are highly diverse and successful, and they have a complicated evolutionary history,” says Wiegmann. “Genomic research allows us then to ask questions about when major changes occurred that led to different lineages of mosquitoes—what we would call adaptive radiations or diversification events in the mosquito family tree. For example, when did this group emerge that feeds mostly on mammals in Africa? It’s a time-calibrated tree, basically, that gives us not just the pattern of relationships, but their timing.”

In addition to looking at the mosquito genomes, they also looked at what the mosquitoes are feeding on. They did this by mining the published scientific literature for information about the sources of blood extracted from the mosquitoes’ digestive systems. The analysis looked at how genetic markers are correlated with a variety of traits, including habitat preferences, blood feeding and host choice, invasiveness, and their ability to transmit diseases. “For example, why does one species transmit Eastern Equine Encephalitis? And why does this close relative not transmit that disease to humans? Maybe it’s a good vector, but it doesn’t have the same relationship with animals that live in its environment,” Wiegmann says. “This type of study expands our knowledge of mosquito diversity by giving us the framework for asking these kinds of questions and making appropriate comparisons based on accurate evolutionary and ecological context.”

Pinned mosquito sample of Mansonia titillans

Genomic analysis from this study confirms many guesses about how mosquitoes have adapted, evolved, and spread across the globe. Wiegmann says, “Without this kind of genomic analysis, we had guesses about how species were related, but there really was no way to verify our story. What was great and surprising about this research is how it showed that sampling from current environments can reveal interesting things about the past.”

How the NEON Biorepository Supports Phylogenomic Research

A meticulously pinned beetle collection from our HARV site.

The NEON Biorepository archives physical specimens of many types of bugs, including mosquitoes, ticks, ground beetles, and other species collected as “by-catch” in pitfall traps at NEON field sites. Specimens are carefully preserved with state-of-the-art methods and cataloged with rich metadata, including time, location, meteorological data, and information about the habitat in which they were found. Wiegmann says, “It’s really, really high-value material. Their genomes are preserved, along with information about when and where they came from and the conditions under which they were collected. And all these physical samples are being stored and made available within this new sort of open infrastructure that NEON provides.” One of Wiegmann’s colleagues and co-investigators at NCSU, Dr. Michael Reiskind, participated in one of the NEON Technical Working Groups that informed collection and archiving protocols for mosquitoes at NEON field sites.

While many of the North American samples came from the NEON Biorepository, the researchers used physical specimens collected from several organizations including the Smithsonian Institute, the Walter Reed Biodiversity Research Unit, the Natural History Museum in London, the Australian National Insect Collection, and several universities including Wiegmann’s own NCSU. The availability of high-quality and well-preserved specimens has been vital for Wiegmann’s research. He is excited by the potential of next-generation genomics to enable all kinds of research—and the possibilities go far beyond mosquitoes. Systematics can be applied to understand biodiversity and evolutionary history for all kinds of organisms, from viruses to human beings.

For now, Wiegmann and his co-investigators are working to expand and complete the mosquito family tree with more specimens from different environments around the globe, including urban environments. Wiegmann would like to explore how mosquitoes have adapted to niche environments, including where they lay their eggs, what they feed on, and how they compete with other species. “There is so much more left to discover,” he says.

Interested in checking out samples from the NEON Biorepository?

Researchers can request loans for non-destructive use or, in some cases, samples for destructive or consumptive use. Read the Sample Use Policy to learn more, and check out the NEON Biorepository data portal to see what is available.

Contact the NEON Biorepository team at ASU to discuss your sample needs.