Geographical distribution, genetic differentiation of haplotypes and population expansion
The pattern of polymorphism suggested non neutral selection as revealed by both Fu’s Fs statistic and Tajima’s D (Fs = -3.624, p = 0.016; D: -0.59858; not statistical significant, p > 0.10). Moreover, Ficher’s exact test used to investigate haplotypic differentiation within the overall population suggested the rejection of the null hypothesis of homogeneity of nucleotide substitutions (LD = 0.1958, p < 0.001) following the neutral theory of molecular evolution.
Within-continent gene diversity (Hs) varied from 0.57 (in Europe) to 0.85 (in Africa), with the majority of haplotypes being specific to certain regions. For instance, of the 21 haplotypes found in Africa, 16 were specific to the continent; of the 14 haplotypes found in Asia, eight were specific; of the nine found in Europe, six were specific; and of the four recovered from America, two were specific to that region (see Figs. 2 - 5).
Haplotypes of C. mucosospermus were almost uniquely restricted to West Africa, and C. amarus haplotypes appeared specific to southern Africa. Haplotypes of C. colocynthis shared by Namibia, Ethiopia, and northern Africa were also found widespread throughout Asia. Across that continent, some haplotypes of C. colocynthiswere specific to different countries (Fig. 1). Six C. colocynthishaplotypes were specific to Asia, and six were specific to Africa. For this species, Iran contributed the highest number of haplotypes in Asia (Fig. 1), as Egypt did in Africa (Fig. 1).
Within C. lanatus , although all regions shared most haplotypes, Africa exhibited the highest number of singletons. The ancient haplotype H1 was found not only among West African countries but also in Europe (Georgia, Yugoslavia, Italy and Ukraine), Asia (Russia, Japan, China, India), and North America (USA and Canada). North Africa (Egypt) and southern Asia (India) shared C. colocynthis haplotype H12; and haplotype H4, specific to C. amarus , was shared by African countries (e.g. South-Africa and the Democratic Republic of Congo) and Russia (Fig. 1). Haplotype H2 was found throughout West Africa (Benin, Burkina-Faso, and Ghana) as well as in Asia (China, Japan, Yemen, North-Korean Republic, Mongolia, and Armenia), France, and North America (USA and Canada). Haplotype H2 is shared by C. lanatus andC. amarus ; and haplotype H6 is shared by C. mucosospermusand C. amarus species (see Figs. 2 - 5).
Analysis of interspecific genetic differentiation revealed a high level of total genetic differentiation among continents (Tables 4 and 5). Coefficients of pairwise genetic differentiation values were highest between Africa and Europe, on the one hand, and Asia and Europe, on the other; Gst was lower between Africa and Asia (0.006). The coefficient of population differentiation Gst was 0.196, and the pairwise difference between haplotypes Nst = 0.374.