Multifaceted Population Structure and Reproductive Strategy in Leishmania donovani Complex in One Sudanese Village

Abstract

Leishmania species of the subgenus Leishmania and especially L. donovani are responsible for a large proportion of visceral leishmaniasis cases. The debate on the mode of reproduction and population structure of Leishmania parasites remains opened. It has been suggested that Leishmania parasites could alternate different modes of reproduction, more particularly clonality and frequent recombinations either between related individuals (endogamy) or between unrelated individuals (outcrossing) within strongly isolated subpopulations. To determine whether this assumption is generalized to other species, a population genetics analysis within Leishmania donovani complex strains was conducted within a single village. The results suggest that a mixed-mating reproduction system exists, an important heterogeneity of subsamples and the coexistence of several genetic entities in Sudanese L. donovani. Indeed, results showed significant genetic differentiation between the three taxa (L. donovani, L. infantum and L. archibaldi) and between the human or canine strains of such taxa, suggesting that there may be different imbricated transmission cycles involving either dogs or humans. Results also are in agreement with an almost strict specificity of L. donovani stricto sensu to human hosts. This empirical study demonstrates the complexity of population structure in the genus Leishmania and the need to pursue such kind of analyses at the smallest possible spatio-temporal and ecological scales.

Reproductive clonality of pathogens: A perspective on pathogenic viruses, bacteria, fungi, and parasitic protozoa

“…Other authors, mainly working with Leishmania species (107,111,115,116,212) but also with T. cruzi (153) and fungi (87,197), assert, however, that clonality should be distinguished from selfing/ inbreeding and that clonality should be limited to "strict" clonality, that is, mitotic propagation. This restricted meaning is a matter of definition.…”

“…This restricted meaning is a matter of definition. Our opinion is that the broader definition of clonality, proposed by us and shared by most authors, which includes selfing/ homogamy, should be privileged for several reasons: (i) The evolutionary consequences of strict clonality and strong selfing/ homogamy are similar, in that they lead to linkage disequilibrium (LD) and the propagation of unchanged MLGs; (ii) restrained recombination is the important consideration in applied research, such as molecular epidemiology (strain tracking and typing) and tracing of genes of interest; (iii) although homogamy/selfing occurs in bacteria (51,58,199,200,213) and probably in viruses, most authors do not distinguish it from clonality; indeed, in the case of haploid organisms, the distinction is not relevant; (iv) most importantly, the population genetic means for distinguishing strict clonality from selfing/homogamy are questionable, because they rely on segregation tests designed mainly for diploid metazoa (107,111,115,116,148,195,197,208,209,212,214,215). The common observation is a deficit of heterozygotes, although it is argued that strict clonality (mitotic propagation) should lead to an excess, not a deficit of heterozygosity.…”

“…The probability of these factors should not be evaluated separately (107,111,115,116,148,212), because they are not mutually exclusive. (b) Deficit of heterozygotes, inferred from microsatellite analysis, clashes with single-nucleotide polymorphism (SNP) data for Leishmania mexicana and Leishmania braziliensis (106) and T. cruzi (160), where an excess of heterozygotes is recorded.…”

“…A widely used sampling strategy is to apply population genetic tests, first on the whole sample and then within each of the genetic clusters that subdivide it (88,115,148,157). The working hypothesis is that gene flow is inhibited between the clusters, but not, or less, within each of them.…”

No Evidence of Interspecific Genetic Exchange by Multi-Locus Microsatellite Typing Between Leishmania Killicki and Leishmania Major in a Mixed Focus of Cutaneous Leishmaniasis in Southeast Tunisia

“…Phlebotomus riouxi (or P. chabaudi), which is suspected to be linked to L. killicki transmission [9], was the dominant species in the semi-natural rocky habitats associated with the presence of Ctenodactylus (C.) gundi, described as a potential reservoir [7][8][9][10]. Concerning the reproductive strategy, the current assumption, mainly based on population genetics studies, is that Leishmania alternates between three modes of reproduction: clonality, allogamy (interspecific recombination), and endogamy (intraspecific recombination), varying according to the species and the environment [11][12][13][14][15][16][17][18].…”