Rapid range shifts in African Anopheles mosquitoes over the last century

Abstract

Facing a warming climate, many tropical species-including the arthropod vectors of several infectious diseases-will be displaced to higher latitudes and elevations. These shifts are frequently projected for the future, but rarely documented in the present day. Here, we use one of the most comprehensive datasets ever compiled by medical entomologists to track the observed range limits of African malaria mosquito vectors (Anopheles spp.) from 1898 to 2016. Using a simple regression approach, we estimate that these species' ranges gained an average of 6.5 m of elevation per year, and the southern limits of their ranges moved polewards 4.7 km per year. These shifts would be consistent with the local velocity of recent climate change, and might help explain the incursion of malaria transmission into new areas over the past few decades. Confirming that climate change underlies these shifts, and applying similar methods to other disease vectors, are important directions for future research.

Keywords: Anopheles; climate change; geographical range shift; malaria.

Figure 1.

(a) The elevational gradient in Africa (averaged to a 10 × 10 fold higher resolution for visual clarity; (b) sites of Anopheles mosquito occurrence in sub-Saharan Africa, where colour represents the maximum temporal span of observations.

Figure 2.

Estimated shifts in Anopheles species’ observed latitudinal and elevational maxima over the twentieth century, where each arrow gives one species’ estimate (see electronic supplementary material, table S1). (a) Species’ estimated southern maxima, where starting points are given at the longitude of the southmost point in the first half of the century (1900–1950), and the arrow shows the estimated latitudinal shift from 1900 to 2000 (chosen as a standardized unit for visualization, rather than the entire observation period, given that some species are sampled over slightly different intervals). (b) Estimated elevational gain, 1900–2000 (y-axis), on a 1:1 elevational ‘gradient' (x-axis gives initial estimated elevational position). Red arrows indicate species for which temporal trends were statistically significant (p < 0.05).