Abstract
BackgroundBefore 1996 the phlebotomine sand fly Lutzomyia neivai was usually treated as a synonym of the morphologically similar Lutzomyia intermedia, which has long been considered a vector of Leishmania braziliensis, the causative agent of much cutaneous leishmaniasis in South America. This report investigates the likely range changes of both sand fly species in response to a stabilisation climate change scenario (RCP4.5) and a high greenhouse gas emissions one (RCP8.5).MethodsEcological niche modelling was used to identify areas of South America with climates currently suitable for each species, and then the future distributions of these climates were predicted based on climate change scenarios. Compared with the previous ecological niche model of L. intermedia (sensu lato) produced using the GARP algorithm in 2003, the current investigation modelled the two species separately, making use of verified presence records and additional records after 2001. Also, the new ensemble approach employed ecological niche modelling algorithms (including Maximum Entropy, Random Forests and Support Vector Machines) that have been widely adopted since 2003 and perform better than GARP, as well as using a more recent climate change model (HadGEM2) considered to have better performance at higher resolution than the earlier one (HadCM2).ResultsLutzomyia intermedia was shown to be the more tropical of the two species, with its climatic niche defined by higher annual mean temperatures and lower temperature seasonality, in contrast to the more subtropical L. neivai. These different latitudinal ranges explain the two species' predicted responses to climate change by 2050, with L. intermedia mostly contracting its range (except perhaps in northeast Brazil) and L. neivai mostly shifting its range southwards in Brazil and Argentina. This contradicts the findings of the 2003 report, which predicted more range expansion. The different findings can be explained by the improved data sets and modelling methods.ConclusionsOur findings indicate that climate change will not always lead to range expansion of disease vectors such as sand flies. Ecological niche models should be species specific, carefully selected and combined in an ensemble approach.
Highlights
Before 1996 the phlebotomine sand fly Lutzomyia neivai was usually treated as a synonym of the morphologically similar Lutzomyia intermedia, which has long been considered a vector of Leishmania braziliensis, the causative agent of much cutaneous leishmaniasis in South America
Our findings indicate that climate change will not always lead to range expansion of disease vectors such as sand flies
The present report uses ecological niche modelling [5] to define the current distributions of two leishmaniasis vectors in South America, Lutzomyia (Nyssomyia) intermedia (Lutz & Neiva, 1912) and the closely-related Lutzomyia (Nyssomyia) neivai (Pinto, 1926), and to predict their geographical ranges in 2050 under two climate change scenarios, Representative Concentration Pathway (RCP) 4.5 and RCP 8.5, both based on the HadGEM2-ES climate model [1]
Summary
Before 1996 the phlebotomine sand fly Lutzomyia neivai was usually treated as a synonym of the morphologically similar Lutzomyia intermedia, which has long been considered a vector of Leishmania braziliensis, the causative agent of much cutaneous leishmaniasis in South America. Before 1996, L. neivai was usually treated as a junior synonym of the morphologically similar L. intermedia [6], which has long been considered an important vector of Leishmania braziliensis, the causative agent of much cutaneous leishmaniasis (CL) in South America [7, 8] Both sand fly species are incriminated vectors of L. braziliensis [4, 9] in different regions, such as L. intermedia in south-east Brazil [10] and L. neivai in south Brazil [11] and Argentina [12]. Distinguishing between L. intermedia and L. neivai is important because any differences in their habitat preferences, adaptations to deforestation and urbanisation, biting preferences and vectorial capacities could influence which areas are at risk of leishmaniasis transmission [13]
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