Evaluating evidence for co-geography in the Anopheles Plasmodium host-parasite system.

The often tight association between parasites and their hosts means that under certain scenarios, the evolutionary histories of the two species can become closely coupled. Using spatial genetic inference, we identify a potential signal of correlated dispersal in the Anopheles gambiae and Plasmodium falciparum host-parasite system in Sub-Saharan Africa, as seen through a between-species correlation of the differences between geographic sampling location and geographic location predicted from the genome. An explanation for this correlation is common patterns of dispersal and gene flow between these species, but we also consider possible statistical artifacts due to uneven spatial distribution of sampling locations. Using continuous-space population genetics simulations, we investigate the degree to which uneven distribution of sampling locations leads to bias in prediction of spatial location from genetic data and implement methods to counter this effect. We demonstrate that while algorithmic bias presents a problem in inference from spatiogenetic data, the correlation structure between A. gambiae and P. falciparum predictions cannot be attributed to spatial bias alone, and is thus likely a genetic signal of co-dispersal in a host-parasite system.