To estimate the level of gene flow and whether pherotype defined diverging populations, the classic FST parameter [38], the K*ST statistic [39] and the more powerful nearest-neighbor statistic Snn [40] were used. The FST, K*ST and Snn statistics are measures of population differentiation based on the number of differences Selumetinib chemical structure between haplotypes. The statistical significance of both the K*ST and Snn statistics were evaluated by permutation. The data in Table 4 shows that statistically significant K*ST values (p < 0.01) were obtained Selleckchem Adriamycin not only for the analysis of the concatenated sequences but also for most of the individual genes. The more sensitive Snn statistic presented significant values (p < 0.01) for the analysis of

the concatenated sequence as well as for all individual genes.

Table 4 Nucleotide variation and population differentiation parameters. Alleles π FST K*ST p (K*ST)a Snn p (Snn)a aroE 0.005 0.021 0.018 0.022 0.721 < 10-4 gdh 0.009 0.025 0.008 0.115 0.706 0.004 gki 0.019 0.134 0.045 < 10-4 0.810 < 10-4 recP 0.005 0.072 0.039 0.001 0.717 < 10-4 spi 0.009 0.190 0.062 < 10-4 0.677 0.004 xpt 0.007 0.133 0.042 < 10-4 0.790 < 10-4 ddl 0.012 0.018 0.012 0.033 0.738 < 10-4 Combinedb 0.009 0.115 0.025 < 10-4 0.833 < 10-4 aProbabilities evaluated by 1,000 permutations. bThe results correspond to the analysis of the concatenated see more sequences of the aroE, gdh, gki, recP, spi and xpt alleles. A different approach to test if the pherotype is a marker of genetic isolation consists of calculating the probability that pairs of isolates with increasing levels of genetic divergence

have of belonging to different pherotypes. Figure 1 shows that the closest pairs of isolates have a significantly lower probability of having different pherotypes. When genetic divergence increases, the probability of differing in pherotype also increases, reaching the levels expected by chance when selleck compound isolates differ in more than three alleles. Again, these results show that isolates that are phylogenetically closely linked have an increased likelihood of sharing the same pherotype. Figure 1 Probability of pairs of isolates with different alleles to belong to different pherotypes. The black line indicates the fraction of observed CSP-1/CSP-2 pairs differing at the indicated number of alleles and the grey line the expected number if there was a random association between pherotype and sequence type. As the allelic differences increase, the probability of diverging in pherotype also increases reaching levels undistinguishable from those expected by chance when strains differ in more than three alleles. One asterisk, p < 0.01 and two asterisks, p < 0.001. Infinite allele model The structured nature of the pneumococcal population and the geographically limited origin of our sample could explain, at least partially, the segregation of pherotypes seen in Figure 1 and the high Wallace indices of Table 1.