Fonseca, G.; Derycke, S.; Moens, T. (2008). Integrative taxonomy in two free-living nematode species complexes. Biological Journal of the Linnean Society. 94(4): 737-753.
Integrative taxonomy considers species boundaries from multiple, complementary perspectives, with the main
objective being to compare the observed data against the predictions of the methodologies used. In the present
study we used three methods for delineating species boundaries within the cosmopolitan nematode species
Rhabditis (Pellioditis) marina and Halomonhystera disjuncta. First, phylogenetic relationships among molecular
sequences from the mitochondrial cytochrome oxidase c subunit 1 gene (COI), and from two nuclear regions,
internal transcribed spacer (ITS) and D2D3, were analysed. Subsequently, multivariate morphometric analysis was
used to investigate whether concordant molecular lineages were also morphologically distinct. When morphological
differences were found, typological taxonomy was performed to identify fixed or non-overlapping characters
between lineages. Interbreeding experiments were conducted between the two closest related lineages of R. (P.)
marina to investigate potential reproductive isolation. This integrative approach confirmed the presence of several
species within each nominal species: molecular lineages were concordant across two independent loci (COI and
ITS), and were characterized by significant morphological divergence. Most lineages were also detectable in the
D2D3 region, but were less resolved. The two lineages investigated in our study did not produce offspring. Our
results highlight that classical taxonomy grossly underestimates species diversity within the phylum Nematoda.
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