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Developmental plasticity: A facilitator of novelty

Developmental of phenotypic plasticity has long been proposed to facilitate the response of organisms towards changing environmental conditions. More recently, developmental plasticity is also considered to play a crucial role in facilitating phenotypic novelty at the morphological level. Pristionchus represents an interesting case study to test this hypothesis.

Pristionchus species, like others in the family Diplogastridae, show a case of developmental plasticity in the form of the buccal cavity. The mouth-form dimorphism includes one simple form (stenostomatous) that is reminiscent of outgroups, including Caenorhabditis elegans, in which the buccal cavity is narrow and has limited internal armature. The alternate form (eurystomatous) in Pristionchus is much wider and has distinctive teeth, including a claw-like dorsal tooth and an additional, opposing subventral tooth. The dimorphism is qualitative, irreversible, and discrete, suggesting that distinct genetic modules regulate the development of either form. The variation in buccal cavity morphology is thought to be related to different feeding habits:
stenostomatous nematodes primarily feed on bacteria, whereas eurystomatous nematodes can also feed on fungi and other nematodes. The dimorphism therefore has implications for the evolution of novel feeding forms and expansion into otherwise inaccessible ecological niches.

The aims of this project are to understand the genetic basis of a case of developmental plasticity and understand its significance for the evolution of novelty. We have shown that changing environments (e.g. starvation) strongly influence the response of the organism. Moreover, the phenotype decision has co-opted an endocrine signaling mechanism (DAF-12/∆ 7-dafachronic acid) that is involved in development of the resistant dauer stage. Using forward genetics we have produced mutants that are constitutive for each of the two forms; we are now mapping the genes responsible for executing the phenotype decision in development. Studies of inheritance in males suggest that dimorphism is also sex-linked. Ultimately, mechanistic details of the dimorphism will inform comparative analysis, enabled by a robust phylogenetic framework. In such an approach we can test whether genes in mutant animals reflect processes in natural history, such as by how they correlate with observed variation within the species (microevolution) and across the genus (macroevolution). 



Scientist(s) involved:

Dr. Erik Ragsdale, PostDoc
Manuela Müller, Ph.D. Student 
Vahan Serobyan, Ph.D. Student


Selected Reading:

Sommer, R. J. & Ogawa, A. (2011): Hormone signaling and phenotypic plasticity in nematode development and evolution. Curr. Biol., 21, R758-R766.
Ogawa, A., Bento, G., Bartelmes, G., Dieterich, C. & Sommer, R.J. (2011): Pristionchus pacificus daf-16 is essential for dauer formation but dispensable for mouth form dimorphism. Development, 138, 1281-1284.
Bento, G., Ogawa, A. & Sommer, R. J. (2010): Co-option of the hormone-signalling module dafachronic acid–DAF-12 in nematode evolution. Nature, 466, 494-497.
Featured in:
Kiontke, K., Fitch, D. H. A. (2010): Phenotypic Plasticity: Different Teeth for Different Feasts. Current Biology, 20, pp. R710-R712.


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last modified 2012-01-13