Population Genetics and Reproductive Strategies of African Trypanosomes: Revisiting Available Published Data

Abstract

Trypanosomatidae are a dangerous family of Euglenobionta parasites that threaten the health and economy of millions of people around the world. More precisely describing the population biology and reproductive mode of such pests is not only a matter of pure science, but can also be useful for understanding parasite adaptation, as well as how parasitism, specialization (parasite specificity), and complex life cycles evolve over time. Studying this parasite’s reproductive strategies and population structure can also contribute key information to the understanding of the epidemiology of associated diseases; it can also provide clues for elaborating control programs and predicting the probability of success for control campaigns (such as vaccines and drug therapies), along with emergence or re-emergence risks. Population genetics tools, if appropriately used, can provide precise and useful information in these investigations. In this paper, we revisit recent data collected during population genetics surveys of different Trypanosoma species in sub-Saharan Africa. Reproductive modes and population structure depend not only on the taxon but also on the geographical location and data quality (absence or presence of DNA amplification failures). We conclude on issues regarding future directions of research, in particular vis-à-vis genotyping and sampling strategies, which are still relevant yet, too often, neglected issues.

Is Predominant Clonal Evolution a Common Evolutionary Adaptation to Parasitism in Pathogenic Parasitic Protozoa, Fungi, Bacteria, and Viruses?

“…LD is recorded in T. brucei gambiense (Morrison et al, 2008b) and T. brucei rhodesiense (Duffy et al, 2013). T. brucei gambiense I seems to be strictly clonal (Koffi et al, 2009(Koffi et al, , 2015, a hypothesis that is strongly supported by WGS analysis (Weir et al, 2016).…”

“…It has been postulated that mating was frequent in the Savannah group ), a proposal that has to be confirmed by more data and has been questioned in 2015 (Koffi et al, 2015). Strong LD is observed within this group ).…”

“…These are (1) homoplasy ('loci mutationally saturated'; Pearson et al, 2009b), which can be very important for microsatellites (Lehmann et al, 2004;Messenger et al, 2012;Sch€ onian et al, 2010;Sibley and Ajioka, 2008), although Koffi et al (2015) consider its impact as 'insignificant'; (2) different selective pressures; (3) different molecular clocks; and (4) different modes of genetic inheritance (mitochondrial versus nuclear genome).…”

“…On the contrary, the Wahlund effect (separation by physical obstacles: space and/or time) may restrain recombination in separate populations mistakenly pooled together and mimic the effects of PCE, a bias thoroughly exposed by Koffi et al (2015) and Rougeron et al (2014Rougeron et al ( , 2015. The Wahlund effect may operate at microgeographic scales (Rougeron et al (2014(Rougeron et al ( , 2015 and has certainly to be carefully taken into account in population genetic surveys.…”

“…The occurrence of stable near-clades and RD patterns in close sympatry, including in the same host, with therefore ample opportunity for genetic recombination, is a strong argument against the hypothesis that they are caused by a Wahlund effect (see further the case of T. cruzi). As a counterexample, the genetic subdivisions evidenced within T. brucei gambiense I by Koffi et al (2015) are obviously linked to geographical distance, and could be equated to near-clades only if they are both observed together in sympatry or are recorded each over different countries in further studies.…”