Larval habitat suitability and landscape genetics of the mosquito Anopheles coluzzii on São Tomé and Príncipe islands

Abstract Context This study was conducted to contribute to the design of a field trial of a novel genetic strategy aimed at the elimination of malaria. The strategy involves the introduction, establishment and spread of a gene construct into natural populations of the malaria vector Anopheles coluzzii on the African islands of São Tomé and Príncipe (STP). The gene construct renders the mosquito incapable of transmitting the parasite. Understanding the ecology of this mosquito is an essential component of the STP trial design. Identifying landscape features that define the target mosquito’s distribution, understanding connectivity among subpopulations and estimating population stability in the face of climate change are critical factors contributing to the field trial. Objectives STP provides an ideal study site to isolate and identify the role of potentially influential environmental factors in mosquito vector distributions across heterogeneous landscapes, critical information for the design of a GEM field trial. In this study we aim to quantify the relative influence of biotic and abiotic environmental factors on Anopheles coluzzii larval habitat suitability and if environmental variables promote or restrict gene flow between local populations. Methods We used an ecological niche modeling (ENM) approach to test the relationship between environmental variables and A. coluzzii larval occurrences within the islands of STP. We implemented high-resolution spatial models of both current and future larval distributions under a range of climate change scenarios. We assessed functional connectivity of A. coluzzii in STP using circuit theory-based approaches to identify environmental variables impeding or promoting gene flow. Results Results from the ENM revealed higher habitat suitability in the northeastern regions of both islands, characterized by higher human population densities and lower elevations. Habitat suitability under future climate projection models predicted minimal range expansions on STP, even under a ‘business-as-usual’ model. There was a signal of isolation-by-resistance on São Tomé, with roads promoting gene flow and higher elevation restricting gene flow. Conclusions This study provides a clearer understanding of the role of climate, topography and human activity on A. coluzzii larval habitat suitability and underscores the importance of considering both current and future climate projections to establish robust baseline data. Additionally, the role of roads in facilitating gene flow of this species will not only be essential to the design of GEM field trials, but will contribute to our understanding of malaria epidemiology in the islands and to improving ongoing vector control programs.