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Abstract

Genome sequencing projects have revolutionized biology and together with functional tools, such as RNA interference and gene knockout by CRISPR/Cas9, allow novel insight into nonLmodel organisms including parasites of human, livestock and agricultural plants. One unexpected finding from genome sequencing projects over the last decade is that essentially all organisms harbor a large number of genes that are not conserved over larger evolutionary distances. Basically, two distinct evolutionary mechanisms can be responsible for such taxonomically restricted genes, often called “orphan” genes. First, such genes might evolve rapidly, for example under the influence of positive selection, resulting in the (near) absence of sequence homology between distantly related taxa. Second, such genes might also evolve de!novo. Indeed, recent studies in molecular evolutionary biology provide evidence for de!novo gene evolution. Considering that orphan genes are present in all parasitic genomes, it is an important question, if such orphan genes are of functional importance for biology and for the functional understanding of the organisms, i.e. its parasitic life style. I will provide insight from the nematode Pristionchus!pacificus that we have established as model system in evolutionary biology to integrate developmental biology and other laboratory approaches with fieldwork in ecology and population genetics. P.! pacificus lives in association with scarab beetles. One key feature of its life style is a mouthLform dimorphism that enables predatory feeding. The development of teethLlike denticles of two different forms represents an example of developmental plasticity and we test the hypothesis that developmental plasticity is a facilitator of phenotypic diversification and the evolution of novelty. Similarly, we study the regulation of dauer development, another example of phenotypic plasticity. By studying the regulation of plastic traits in P.! pacificus by forward and reverse genetic tools and genomeLwide association stuides, we made the surprising finding that taxonomically restricted orphan genes seem to be functionally overrepresented. I will provide several case studies to highlight this finding. Therefore, orphan genes seem to play key roles in the interaction of the organism with the environment. I will argue that similar patterns might be the rule in parasites as well, as parasitism is essentially the interaction of the parasite with the host “environment”. Thus, functional approaches that aim to elucidate the role of orphan genes are most likely inevitable for a thorough analysis of animal parasitism.