Microevolutionary analysis of the nematode genus Pristionchus suggests a recent evolution of redundant developmental mechanisms during vulva formation

To identify the mechanisms by which molecular variation is introduced into developmental systems, microevolutionary approaches to evolutionary develop mental biology have to be taken. Here, we describe the molecular and develo pmental characterization of laboratory strains of the nematode genus Pristi onchus, which lays a foundation for a microevolutionary analysis of vulva d evelopment. We describe 13 laboratory strains of the Pristionchus genus tha t are derived from natural isolates from around the world. Mating experimen ts and ITS sequence analysis indicated that these 13 strains represent four different species: the gonochoristic species P. Iheritieri and three herma phroditic species, P. pacificus, P. maupasi, and an as yet undescribed spec ies Pristionchus sp., respectively. P. pacificus is represented by five dif ferent strains isolated from California, Washington, Hawaii, Ontario, and P oland. Developmental differences during vulva formation are observed betwee n strains from different species but also between strains of P. pacificus, like the strains from California and Poland. In particular, redundant devel opmental mechanisms present during vulva formation in P. pacificus var. Cal ifornia are absent in other strains. Amplified restriction fragment length polymorphism (AFLP) analyses of the P. pacificus strains revealed that the American strains are highly polymorphic. In contrast, the developmentally d istinct strain from Poland is identical to the Californian strain, suggesti ng that the developmental differences rely on a small number of changes in developmental control genes rather than the accumulation of changes at mult iple loci.