Evidence for a more recently evolved clade within a Candida albicans NorthAmerican population

Candida albicans is diploid and displays a primarily clonal mode of reprodu ction. There is, however, evidence for meiosis and the degree to which this occurs in nature is unknown. Although random mating would act to obscure c lonal lineages, previous studies have demonstrated that collections of Nort h American isolates display three major partitions with no evidence of geog raphic clustering. To better understand the extent of sexuality and its rol e in the phylogeny of the species, a reference subset of 50 isolates repres enting this tripartite division was analysed using 1 minisatellite, 5 micro satellites (MSs) and 15 nuclear polymorphisms (NP). A total of 87 alleles w ere observed for 21 loci and 12/16 informative loci exhibited a departure f rom Hardy-Weinberg expectations (G(2) less than or equal to 0.05). We did n ot observe an absolute correlation between MSs and NP, although isolates wi th identical NP genotypes were correlated with a previously defined, predom inant class (putative group I). The use of additional markers did not give increased support for the tripartite structure of the population. However, (9/19) group I isolates were found to be highly related, differing by only one or a few alleles, Designated subgroup A, the interpretation is that the se isolates are related by descent and that they are of a more recent evolu tionary origin, diverging from an ancestral group I clone. The reason for t heir relative abundance in the population is unknown; one possibility is th at they may be under positive selection.