Search for Selection Signatures Related to Trypanosomosis Tolerance in African Goats.

Bruno Serranito,Badr Benjelloun,Sahraoui Harkat,Johannes A Lenstra,Sophie Thevenon,François Pompanon,Anne Da Silva,Giuliano Cecchi,Nadjet-Amina Ouchene-Khelifi,Dominique Taurisson-Mouret,Abbas Laoun

doi:10.3389/fgene.2021.715732

Abstract

Livestock is heavily affected by trypanosomosis in Africa. Through strong selective pressure, several African indigenous breeds of cattle and small ruminants have acquired varying degrees of tolerance against this disease. In this study, we combined LFMM and PCAdapt for analyzing two datasets of goats from West-Central Africa and East Africa, respectively, both comprising breeds with different assumed levels of trypanotolerance. The objectives were (i) to identify molecular signatures of selection related to trypanotolerance; and (ii) to guide an optimal sampling for subsequent studies. From 33 identified signatures, 18 had been detected previously in the literature as being mainly associated with climatic adaptations. The most plausible signatures of trypanotolerance indicate the genes DIS3L2, COPS7B, PD5A, UBE2K, and UBR1. The last gene is of particular interest since previous literature has already identified E3-ubiquitin ligases as playing a decisive role in the immune response. For following-up on these findings, the West-Central African area appears particularly relevant because of (i) a clear parasitic load gradient related to a humidity gradient, and (ii) still restricted admixture levels between goat breeds. This study illustrates the importance of protecting local breeds, which have retained unique allelic combinations conferring their remarkable adaptations.

Highlights

The productivity of the livestock sector in Africa is heavily affected by trypanosomosis, via morbidity, mortality, impact on growth and reproduction (Budd, 1999; Kristjanson et al, 1999; Swallow, 2000; Shaw et al, 2017)
West-Central African Goats In the West-Central area we observe three zones with clearly different tsetse infestation patterns: (i) in the north, the arid zones of the Sahel are not suitable for tsetse flies, so that the Sudanese (SDN) and Sahelian (SHL) distribution areas are almost free of tsetse flies. (ii) The Red Sokoto (RSK) and the Cameroonian (CAM) inhabit areas with intermediate levels of infestations (27 and 45%, respectively). (iii) Naine (NAI), Djallonke (DJA), and West African Dwarf of Cameroon (WAD) breeds from Nigeria and Cameroon inhabit areas with high levels of infestation
We observed a number of selection signatures that could be potentially related to trypanosomosis tolerance in goats

Summary

Introduction

The productivity of the livestock sector in Africa is heavily affected by trypanosomosis, via morbidity, mortality, impact on growth and reproduction (Budd, 1999; Kristjanson et al, 1999; Swallow, 2000; Shaw et al, 2017). This vector-borne parasitic infection, called “Nagana” in domestic animals, is caused by extracellular protozoa that are mainly cyclically transmitted by several species of tsetse flies (Glossina spp.). In addition to the economic consequences of trypanosomosis on caprine production (Kanyari et al, 1986), goats could act as a reservoir of trypanosomes for other species, including humans (Informal Expert Group on Gambiense HAT Reservoirs et al, 2018)

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Conclusion