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

Hybridization in Trypanosoma congolense does not challenge the predominant clonal evolution model. A comment on Tihon et al., 2017, Mol. Ecol.

“…When the whole T. congolense species is considered, the subgroups Kilifi, Savannah and Forest, which can be equated to near‐clades from an evolutionary point of view (Tibayrenc & Ayala, , ), are confirmed by congruent data, including multilocus enzyme electrophoresis and microsatellites (congruence criterion). In the study by Tihon et al.…”

“…Contrary to what has been asserted (Ramírez & Llewellyn, ), the PCE model has not been challenged by the advent of genomics. Whole genome sequencing and typing by thousands of SNPs have fully confirmed widespread, stable clonal genotypes, near‐clading and Russian doll patterns up to a microevolutionary scale in parasitic protozoa (especially Leishmania ), pathogenic fungi and bacteria (Tibayrenc & Ayala, ,b). The hypotheses of the PCE model are all the more easily testable as they rely on the observation of an abundance of crude data that are accessible to anybody.…”

“…acknowledge that “this model [PCE] does not exclude the occurrence of hybridization,” but state that “a pattern of clonal population structure (Tibayrenc & Ayala, )… is generally characterized by genetically homogenous parasite populations containing a few predominant genotypes that propagated mitotically.” This is a glaringly wrong interpretation of the PCE model. To illustrate this point, we advance a brief review of the main points of the model (for detailed recent references, see Tibayrenc & Ayala, ,b):…”

“… PCE should be explored first in the complete ecogeographical range of the whole species (here: T. congolense ), as the species is defined and delimitated by specialists. Clonality is defined as strongly restrained recombination, a definition shared by many, if not most, authors working on pathogen population structure (Tibayrenc & Ayala, table 2) and also, by specialists of uniparental metazoans. This definition is not limited to mitotic clonality, as wrongly stated by Tihon et al. On the contrary, it includes other modes of reproduction leading to genetic clonality: selfing, strong homogamy, and, when metazoans are concerned, several forms of parthenogenesis, gynogenesis and hybridogenesis. The model does not state that recombination “plays a minor role in the evolution of micropathogens” (Tihon et al.…”

“…Their observation over space and time, in various ecosystems, ascertains their stability and widespreadness in the long run. The near‐clade concept therefore gives a common, clear evolutionary definition to entities that were previously described using a proliferating and disparate terminology that was a manifestation of a considerable conceptual uncertainty (Tibayrenc & Ayala, , table 4).…”