Combining landscape genomics and ecological modelling to investigate local adaptation of indigenous Ugandan cattle to East Coast fever

Abstract

AbstractEast Coast fever (ECF) is a fatal sickness affecting cattle populations of eastern, central, and southern Africa. The disease is transmitted by the tickRhipicephalus appendiculatus, and caused by the protozoanTheileria parva parva, which invades host lymphocytes and promotes their clonal expansion. Importantly, indigenous cattle show tolerance to infection in ECF-endemically stable areas. Here, the putative genetic bases underlying ECF-tolerance were investigated using molecular data and epidemiological information from 823 indigenous cattle from Uganda. Vector distribution and host infection risk were estimated over the study area and subsequently tested as triggers of local adaptation by means of landscape genomics analysis. We identified 41 and seven candidate adaptive loci for tick resistance and infection tolerance, respectively. Among the genes associated with the candidate adaptive loci arePRKG1andSLA2.PRKG1was already described as associated with tick resistance in indigenous South African cattle, due to its role into inflammatory response.SLA2 is part of the regulatory pathways involved into lymphocytes’ proliferation. Additionally, local ancestry analysis suggested the zebuine origin of the genomic region candidate for tick resistance.Author summaryThe tick-borne parasiteTheileria parva parvainfects cattle populations of eastern, central and southern Africa, by causing a highly fatal pathology called “East Coast fever”. The disease is especially severe for the exotic breeds imported to Africa, as well as outside the endemic areas of East Africa. In these regions, indigenous cattle populations can survive to infection, and this tolerance might result from unique adaptations evolved to fight the disease. We investigated this hypothesis by using a method named “landscape genomics”, with which we compared the genetic characteristics of indigenous Ugandan cattle coming from areas at different infection risk, and located genomic sites potentially attributable to tolerance. In particular, the method pinpointed two genes, one (PRKG1) involved into inflammatory response and potentially affecting East Coast fever vector attachment, the other (SLA2) involved into lymphocytes proliferation, a process activated byT. parva parvainfection. Our findings can orientate future research on the genetic basis of East Coast fever-tolerance, and derive from a general method that can be applied to investigate adaptation in analogous host-vector-parasite systems. Characterization of the genetic factors underlying East Coast-fever-tolerance represents an essential step towards enhancing sustainability and productivity of local agroecosystems.