Evolving genome makes malaria mosquito flexible

Anopheles mosquitoes are responsible for transmitting human malaria parasites. To investigate the genetic differences between the deadly parasite-transmitting species and their harmless (but still annoying) cousins, an international team of scientists sequenced the genomes of sixteen Anopheles species from around the globe. Two articles published in Science on 27 November 2014 describe detailed genomic comparisons of these mosquitoes and the deadliest of them all, Anopheles gambiae. Michael C. Fontaine, previously at the University of Notre Dame (IN, USA) and now Assistant Professor at the University of Groningen, is first author of one article and co-author of the other.

Human malaria parasites cause an estimated 200 million cases and more than 600 thousand deaths each year. Of the almost 500 different Anopheles species, only a few dozen can carry the parasite and only a handful of species are responsible for the vast majority of transmissions.

Eliminate diseases

The results published in Science offer new insights into how these species are related to each other and how the dynamic evolution of their genomes may contribute to their flexibility to adapt to new environments and to seek out human blood. These newly sequenced genomes represent a substantial contribution to the scientific resources that will advance our understanding of the diverse biological characteristics of mosquitoes, and help to eliminate diseases that have a major impact on global public health.

Anopheles gambiae

Variation in the ability of different Anopheles species to transmit malaria – known as “vectorial capacity” – is determined by many factors, including feeding and breeding preferences, as well as their immune responses to malaria infections. Much of our understanding of many such processes derives from the sequencing of the Anopheles gambiae genome in 2002.

16 Anopheles genomes

Until now, the lack of such genomic resources for other Anopheles limited comparisons to small-scale studies of individual genes with no genome-wide data to investigate key attributes that impact the mosquito’s ability to transmit parasites. To address these questions, an international team of researchers, led by Professor Nora Besansky from the University of Notre Dame, Indiana (USA), sequenced the genomes of 16 Anopheles species and published their results in Science.

Gene flow

A second paper, led by Prof. Besansky and dr. Michael C Fontaine (Assistant Professor at the University of Groningen formerly at the University of Notre Dame, IN, USA), focalized on the recent evolution and speciation process in the Anopheles gambiae species complex. The question of the true species phylogeny and how new species of mosquitoes diverged in Africa has been a highly contentious issue in the field. The newly available genome sequences provided conclusive evidence of the true relations amongst several species that are very closely related to Anopheles gambiae but nevertheless show quite different traits that affect their vectorial capacity.

The results show that the most efficient vectors are not necessarily the most closely-related species, and that traits enhancing vectorial capacity may be gained by gene flow between species.

Neanderthals

This study substantially improves our understanding how new species diverge from each other and can exchange adaptive mutations through the process of gene flow – a process believed to have occurred from Neanderthals to the ancestors of modern humans. This study highlights how gene flow may affect the evolution of common and distinct biological characteristics of mosquitoes such as ecological flexibility and vectorial capacity. These results are described in a companion paper entitled Extensive introgression in a malaria vector species complex revealed by phylogenomics.

Inherent capacity to evolve

These two very different evolutionary timescales – spanning all the Anopheles or focusing on the subset of very closely-related species – offer distinct insights into the processes that have moulded these mosquito genomes into their present-day forms. Their dynamic evolutionary profiles may represent the genomic signatures of an inherent evolvability that has allowed Anopheles mosquitoes to quickly exploit new human-generated habitats and become the greatest scourge of humankind.

Further information

- Dr. Michael C Fontaine, assistant professor, Centre for Ecological and Evolutionary Studies, University of Groningen, The Netherlands;

Reference:

- Extensive introgression in a malaria vector species complex revealed by phylogenomics .Science 27 November 2014

Fontaine MC*, Pease JB*, Steele A, Waterhouse RM, Neafsey DE, Sharakhov IV, Jiang X, Hall AB, Kakani E, Mitchell SN, Wu YC, Smith HA, Love RR, Lawniczak MKN, Slotman MA, Emrich SJ, Hahn MW, Besansky NJ. (*Contributed equally to this work)

- Highly evolvable malaria vectors: the genomes of 16 Anopheles mosquitoes. Science 27 November 2014