The tree was built upon an alignment of nAChR subunit deduced amino-acid sequences. The tree was rooted with the Parascaris equorum ACR-26 and ACR-27 sequences that are absent from C. elegans and clade I nematode species [34]. Scale bar represents the number of substitutions per site. Bootstrap values are indicated on branches. Accession numbers for sequences used in the phylogenetic analysis are provided in the Material and Methods section. C. elegans nAChR subunit groups are named as proposed by Mongan et al. [31], Cel, Tsu, Ttr, Tmu, Tsp and Peq refer to Caenorhabditis elegans, Trichuris suis, Trichuris trichiura, Trichuris muris and Parascaris equorum, respectively.