The demise of the Platonic worm

Nematodes are generally considered to have an adult cell number that does not vary among wildtype individuals as a consequence of invariant cell lineages (eutely). However, there is extensive evidence that at least some cell lineages can be variable in nematodes. In a comparative study of 13 free-living nematode species, we have shown that the adult epidermis of most species contained variable numbers of nuclei and that this variance was positively correlated with mean epidermal nuclear number. Here we present simulations of the lateral seam cell lineages of four species and show that variance in cell number is influenced by lineage topology, as well as by the frequency of lineage variants. We show that the epidermal variability of Panagrellus redivivus cannot be accounted for by the complexity of its lineage, but requires higher levels of lineage variability than are found in Caenorhabditis elegans, Oscheius myriophila and Rhabditella octopleura. Our findings suggest that many nematodes may have tissues composed of indeterminate numbers of cells formed from variable lineages and, as such, resemble other metazoans.