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Abstract:
The morphological diversity of vertebrates is a beautiful example of phenotypic evolution. Although their archetypical body plan makes nematodes little less glamorous model organisms, they represent one of the most successful animal phyla and have adapted to almost all ecological niches including extreme abiotic environments and, in the case of parasitic nematodes, multiple host species. This makes them promising model systems to study molecular innovations. Our group focuses on the shark-tooth nematode Pristionchus pacificus which belongs to a clade that evolved teeth-like structures that allow them to predate and kill other nematodes. When its genome was sequenced, around one third of genes were classified as taxonomically-restricted orphan genes that lack homologs in other nematodes. Over the past years, we have characterized the origin and evolution of P. pacificus orphan genes using deep taxon phylogenomics. This revealed multiple mechanisms of new formation including divergence, de novo gene birth and mixed origin. While recent reports of thousands of noncanonical translated elements emphasize the potential impact of de novo gene birth on genomic novelty, we recently proposed to assess their evolutionary impact by studying their dynamics across multiple time scales and explicitly comparing these patterns with products of gene duplication which represents another major source of novelty. Comparative genomic and population-scale analysis in P. pacificus demonstrate a high abundance of de novo candidates relative to duplicates at shorter time-scales but opposite patterns across longer time-scales. Thus, both processes appear to operate at different time-scales whereby de novo genes may carry out more transient functions in fluctuating environments but more stable evolutionary changes are implemented by duplication events.
