Demographic history was a formative mechanism of the genetic structure for the taste receptor TAS2R16 in human populations inhabiting Africa's Sahel/Savannah Belt

Abstract

Objectives: Mode of subsistence is an important factor influencing dietary habits and the genetic structure of various populations through differential intensity of gene flow and selection pressures. Previous studies suggest that in Africa Taste 2 Receptor Member 16 (TAS2R16), which encodes the 7-transmembrane receptor protein for bitterness, might also be under positive selection pressure.Methods: However, since sampling coverage of populations was limited, we created a new TAS2R16 population dataset from across the African Sahel/Savannah belt representing various local populations of differing subsistence modes, linguistic affiliations, and geographic provenience. We sequenced the TAS2R16 exon gene and analyzed 2250 haplotypes among 19 populations.Results: We found no evidence for selection as a driving force of genetic variation at this locus; instead, we discovered a highly significant correlation between TAS2R16 genetic and geographical distances based on provenience of the sampled populations, strongly suggesting that genetic drift most likely prevailed over positive selection at this specific locus. We also found significant correlations with other independent loci, mainly in sedentary farmers.Discussion: Our results do not support the notion that the genetic diversity of TAS2R16 in Sahelian populations was shaped by selective pressures. This could result from several alternative and not mutually exclusive mechanisms, of which the possibility that, due to the pleiotropic nature of TAS2R16, selective pressures on other traits could counterbalance those acting on bitter taste perception, or that the change of diet in the Neolithic generally relaxed selective pressure on this gene.

Demographic and Selection Histories of Populations Across the Sahel/Savannah Belt

“…Despite low levels of genetic differentiation, certain genetic variants, such as variants associated with lactase persistence (LP), show large frequency differences between Sahelian populations of different linguistic affiliations or different subsistence forms ( Priehodová et al 2017 , 2020 ; Hollfelder et al 2021 ). On the other hand, other genes analyzed in populations from the Sahel/Savannah belt (such as NAT2 or TAS2R16 ) do not show such a clear differentiation ( Podgorná et al 2015 ; Kulichová et al 2021 ). Genome-wide signals of selection and population structure were previously described in a study focused on a limited number of Sahelian populations ( Triska et al 2015 ).…”

“…The population history of the Sahel/Savannah belt has been studied thus far mainly through genetic variation of the uniparental markers ( Pereira et al 2010 ; Černý et al 2011 ; Nováčková et al 2020 ; Diallo et al 2022 ), or specific genes, such as LCT , NAT2 , TAS2R16 , or HLA-B ( Podgorná et al 2015 ; Triska et al 2015 ; Sanchez-Mazas et al 2017 ; Vicente et al 2019 ; Priehodová et al 2020 ; Kulichová et al 2021 ). It has been shown that the genetic differentiation among pastoralists and farmers does not represent significant population structure and that intensive gene-flow or shared ancestry might be among the possible reasons for this ( Černý et al 2021 ).…”