Somatic chromosome fragmentation and telomere elimination is found in several Rhabditidae species.

A. Embryos from different species and at various stages of development (from the youngest on the left to the oldest on the right) were fixed and stained. DNA is shown in blue. The contours of the cells are shown in dotted white lines. The DNA of the germline precursor cell is shown in red. Polar bodies, when visible, are circled with a solid white line. For the pseudogamous species Mesorhabditis simplex, the paternal DNA stay highly condensed after fertilization [33] and is shown circled with a solid yellow line. White arrows point towards cytoplasmic fragments that become visible from the 5-cell stage in Mesorhabditis simplex and later in Cruznema sp. and Rhabditella axei. The name of the strain for each species is shown in parentheses. A zoomed-in view of the image of each embryo in the third column is shown in the inset on the right. In the inset, the nuclei are encircled in white and the DNA fragments excluded from the nuclei are indicated by an arrow. B. Embryos from different species are shown and at various stages of development, after DNA FISH treatment against telomeric repeats. On the left, embryos are undergoing chromosome fragmentation in a least one of their somatic cells. Enlargement of one cell is shown in the inset. DNA is in blue and telomeres are in red. In the inset, the nuclei are encircled in white and the telomeres excluded from the nuclei are indicated by an arrow. Older embryos, after chromosome fragmentation are shown on the right. In Caenorhabditis elegans, all cells in young and old embryos maintain their telomeres, whereas in species undergoing PDE, somatic telomeres do not reappear (Oscheius tipulae, Caenorhabditis monodelphis) or reappear progressively (Rhabditis rainai and Pelodera teres).

Phylogenetic distribution of species undergoing Programmed DNA Elimination in family Rhabditidae

Cladogram of species analysed in this study, based on the 18S and 28S rDNA sequencing. Species in which we detected PDE are shown in blue and others in orange. PDE has not been scored in Bunonema reticulatum, which serves here as an outgroup for the phylogeny only. Species undergoing PDE are grouped in two main monophyletic groups. We also found that Caenorhabditis monodelphis undergoes PDE whereas other Caenorhabditis species do not. The reproductive modes are shown on the right (asexual, male/female, hermaphrodite and three sexes), as well as chromosome numbers (also visible on Supp. Fig. 1). Pelodera strongyloides is not monophyletic with Pelodera teres, (see discussion in the main text).

Origin and strain of the 18S and 28S rDNA sequences used to build our Rhabditidae phylogeny.

For each of our 28 species (rows), the origin columns show whether we used our sequencing, where successful (‘This study’), or if publicly-available data was used, in which case we provide the NCBI Nucleotide accession. The sequenced strains, of our study, or of the publicly-available data, are also provided. ‘-’ indicates we did not sequence and no public data was available - this was only the case for 28S sequences.