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Assignment 1: Publication Review
Mosquito Genomes Galore
Whole-genome sequencing of 16 different mosquito species reveal rapid evolution and could inform malaria research
The phylogenetic tree (1B) generated by Neafsey et al. shows the evolutionary basis (or rather, lack thereof) for malaria vectorial capacity. Squares indicated major vectors, ellipses indicate minor vectors, and triangles indicate non-vectors. As demonstrated above, major and minor vectors did not deviate from non-vectors at any given point; rather, some major vectors are more closely related to non-vectors than they are to other major vectors. This figure suggests that vector status is determined by genes that were exchanged during interspecies mating, rather than inherited from a common ancestry. Published with permission from Neafsey et al.
In two papers published in Science on November 27, 2014, researchers sequenced the genomes of sixteen species of mosquitoes, some of which are known malaria vectors. In investigating the genomic differences between mosquito species, researchers were able to identify what genes dictate vectorial capacity for malaria, a disease that affects millions of people annually. One paper detailed the process of sequencing assorted mosquito species and their closest relatives to create a phylogenetic tree representing the evolution of the mosquito vectors. Interestingly enough, they found that vectorial capacity did not evolve at once; rather, vector species are on distant branches of the evolutionary tree.
Hypothesis or discovery science?
The genomic research performed by the team at University of Notre Dame constitutes discovery science. The team did not propose a hypothesis beyond suggesting that there may be a genomic basis on top of previously known factors that determine mosquitoes’ vectorial capacity. Otherwise, the sequencing, comparative analyses, and creation of phylogenetic trees were purely investigative.
Methods and Genomic Technologies
Researchers assembled the genomes and transcriptomes of sixteen mosquito species (both lab and wild specimens) by using Illumina sequencing technologies on genomic DNA and whole-body RNA from each specimen. Sequences were annotated with MAKER and the resulting gene count was satisfactory, with some variation of total counts due to differing levels of assembly contiguity (Neafsey et al. 2014). Maximum-likelihood phylogenies were constructed with various root species (which did not alter findings) and any discordance between trees was resolved by implementing more in-depth sequence analysis as detailed in the original publication (Fontaine et al. 2014).
Being able to identify the genes responsible for malaria vector status is a big first step in implementing new technologies for malaria control. The computational genome comparisons between the sixteen species identified rapid evolution in mosquitoes, including high rates of gene gain, loss, rearrangement, and interspecies transmission. The evolutionary trees that the research team generated showed that vector species are present on distant branches, and thus, did not evolve separately from non-vector species. This leads researchers to hypothesize that the main factor in vector status is introgression. Understanding this connection between malaria vectors will allow for a strategized disease control that more effectively targets malaria vectors specifically.
While the two publications summarized in this article did not make conclusive statements about a specific gene or set of genes that connect the malaria vector species, they have taken big steps in sequencing such a large number of species and in finding that vector status was not developed by the divergence of two ancestral species but rather by introgression. Their findings, which indicate unusually high rates of gene gain and loss, confirm the researchers' speculations about a genomic factor at play in determining vectorial capacity. Their research was purely investigative, and their findings suggest many more possible directions for research. Since malaria is a disease that affects populations not only in Africa, but in South America and Asia as well, it’s essential that research move beyond studying just the principal vector in Africa. Additionally, taking a multiple species sequencing approach can establish a precedent for future research into other vector-borne (and specifically, mosquito-borne) diseases, such as Dengue fever, Yellow fever, and West Nile virus. It will be interesting to see whether with the interspecies and vector/non-vector comparisons that this research provides, future investigators can pinpoint a particular genomic difference that determines vectorial capacity, and whether that genomic difference can extend to other non-insect vectors. Approaching malaria and other disease control from a genomic approach has potential to be more efficient, cost-effective, healthy, and environmentally friendly than blanket fumigation of at-risk malaria areas.
Fontaine, Michael C. et al. “Extensive Introgression in a Malaria Vector Species Complex Revealed by Phylogenomics.” Science (New York, N.Y.) 347.6217 (2015): 1258524. PMC. Web. 25 Jan. 2016.
E. et al. “Highly
Evolvable Malaria Vectors: The Genomes of 16 Anopheles Mosquitoes."
Science (New York, N.Y.) 347.6217 (2015): 1258522. PMC. Web. 25 Jan.
Ruth. "Mosquito Genomes Galore." The Scientist. 27 Nov. 2014. Retrieved
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