A catalogue of chromosome counts for Phylum Nematoda

Abstract

Nematodes are important biological models in genetics and genomics, with research driven by basic biological as well as applied questions. The presence of holocentric chromosomes, clades with frequent polyploidy and the phenomenon of programmed DNA elimination make nematode karyotypic diversity of particular interest. Here we present a catalogue of published karyotypes of nematode species, rationalising and normalising descriptions from the previous 135 years. Karyotypes of 257 species are presented in taxonomic context. Nuclear chromosome counts range from 2 to 60. Tylenchina is identified as particularly diverse in karyotype. We highlight that Rhabditida and especially parasitic Rhabditina are well-represented, but there is a paucity of data from Enoplea, Dorylaimia, and from free-living marine groups in Chromadorea. The data have been uploaded to the Genomes on a Tree (GoaT) datasystem ( https://goat.genomehubs.org/) for integration with ongoing, large-scale genome sequencing efforts.

Keywords: Genomes on a Tree (GoaT); Nematoda; chromosome counts; karyotype.

Figure 1.. Chromosome numbers of Nematoda.

A Distribution of female nuclear karyotypes, grouped by suborder. B Variability of female karyotype within families (ordered by average [red diamond] with lowest [orange triangle] and highest [brown triangle] count per family) The data for both panels of this figure are available at https://tinyurl.com/NematodeKaryotypes-Table2-2023.

Figure 2.. Phylogenetic distribution of nematode chromosome numbers.

Average (dark blue) and maximum (light blue) counts of female chromosome numbers across the 90 genera (named with NCBI TXID) analysed that are present in the NCBI TaxonomyDB . Five genera are not currently represented in TaxonomyDB. Clades are coloured by suborder as in Figure 1A. Note that while the NCBI TaxonomyDB recognises “Strongylida'' as a distinct order, it is by molecular analysis actually nested within Rhabditina (sister to Heterorhabditis), and hence Rhabrditina (brown) is paraphyletic in this representation. Figure developed in iToL and available at https://itol.embl.de/export/77999098256461685686507. An interactive version is available through https://itol.embl.de/shared/mblaxter2.