Microevolution of vulva development in Pristionchus pacificus

The comparison of vulva formation between P. pacificus and C. elegans represents a macro-evolutionary approach because both nematodes were separated from one another appr. 200-300 million years ago. Such an approach can identify the developmental alterations that gave rise to important evolutionary innovations. However, it cannot detect what micro-evolutionary variations are the basis for molecular changes. Which types of mutations generate evolutionarily important phenotypic variations? What types of molecular changes, i.e. changes of regulatory regions and/or protein coding regions, do they involve? Such questions can only be addressed by micro-evolutionary approaches involving the comparison of closely related species or even populations of the same species. Only micro-evolutionary studies can identify the mechanisms by which molecular variation is introduced into developmental processes and how such variants are fixed at a population level.
By now, a large number of different P. pacificus strains from several continents is available in the laboratory. Before entering a micro-evolutionary analysis of developmental processes, we carried out detailed studies in P. pacificus population genetics. These studies revealed that the amount and pattern of genetic variation in P. pacificus is much higher than in C. elegans (Zauner et al., 2007).
Vulva formation in P. pacificus is a promising system for micro-evolutionary studies in evolutionary developmental biology. In particular, the functional properties of one particular epidermal cell, P8.p, are attractive for micro-evolutionary studies. We began an experimental and genetic analysis of the microevolution of P8.p function. We showed that lateral inhibition and developmental competence of P8.p, two functions that are unknown from C. elegans and other nematodes, evolved within the genus Pristionchus and even between natural isolates of P. pacificus. Surprisingly, in some recombinant inbred lines of two distinct P. pacificus isolates, P8.p gained competence to form vulva tissue, a trait that was never observed in P. pacificus isolates. These results suggest differences in developmental stability between natural isolates and we hypothesize that the remarkable evolvability of redundant cell-cell interactions allows for adaptive evolution of robustness to developmental noise (Zauner & Sommer, 2007).



Scientist(s) involved:

Simone Kienle, Ph. D. Student




Selected References:


Sommer, R. J. (2009): The future of evo-devo: model systems and evolutionary theory. Nature Rev. Genetics, 10, 416-422.

Zauner, H. and Sommer, R. J. (2007): Evolution of robustness in the signaling network of Pristionchus vulva development, Proc. Natl. Acad Sci., 104, 10086-10091.

Zauner, H., Mayer, W., Herrmann, M., Weller, A., Erwig, M., and Sommer, R. J. (2007): Distinct patterns of genetic variation in Pristionchus pacificus and Caenorhabditis elegans, two partially selfing nematodes with cosmopolitan distribution. Mol. Ecol. 16, 1267-1280.