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Abstract

To obtain an understanding of the microevolution of developmental processes, we study vulva development in closely related species and strains of the nematode genus Pristionchus. Like in C. elegans, the vulva in Pristionchus is formed from the vulva precursor cells P5.p, P6.p, and P7. The most striking developmental difference between these two nematodes is the fate of the posterior epidermal cell P8.p that has special properties in P. pacificus. P8.p has an epidermal fate in wild-type animals and is part of a novel signaling center in the posterior body region. It inhibits P5.p and P7.p from adopting a 1j fate after ablation of the other vulva precursor cells, a phenomenon known as ‘‘lateral inhibition’’. Here we present cell ablation data showing that P. pacificus strains differ in the developmental properties of P8.p. A strain from Poland differs from five strains from North America in that lateral inhibition by P8.p is markedly reduced. To study the genetic basis of lateral inhibition, we generated 180 recombinant inbred lines (RIL) by crossing the strains from Poland and Washington. Lateral inhibition is completely absent in at least 3 out of 62 tested RILs. We have determined the genotypes of the RILs to define those regions of the genome (QTLs) that contain the underlying ‘‘evolutionary’’ mutations. Lateral inhibition is also absent in sister species of P. pacificus, suggesting that the ancestral condition can be re-established in P. pacificus hybrid lines.