Although the monophyly of Ecdysozoa is now well established ( 2, 3), the phylogenetic relationships within this group have proven difficult to resolve ( 4– 7). Our study confirms the monophyly of the legged ecdysozoans, shows that past support for a Tardigrada + Nematoda group was due to long-branch attraction, and suggests that the velvet worms are the sister group to the arthropods.Įcdysozoa ( 1) is the clade of molting invertebrates that includes two of the ecologically most important and evolutionarily most successful animal phyla-the arthropods and the nematodes-as well as several other, less diversified taxa, including the tardigrades (water bears), the onychophorans (velvet worms), and the priapulids (penis worms). In addition, Onychophora and Arthropoda were found to share a second miRNA (miR-305). Our small RNA libraries fully support our EST results no miRNAs were found to link Tardigrada and Nematoda, whereas all panarthropods were found to share one unique miRNA (miR-276). Using careful experimental manipulations-comparisons of model fit, signal dissection, and taxonomic pruning-we show that support for a Tardigrada + Nematoda group derives from the phylogenetic artifact of long-branch attraction. Our EST analyses, based on 49,023 amino acid sites from 255 proteins, significantly support a monophyletic Panarthropoda including Tardigrada and suggest a sister group relationship between Arthropoda and Onychophora. Here we present results from the analyses of two independent genomic datasets, expressed sequence tags (ESTs) and microRNAs (miRNAs), which congruently resolve the phylogenetic relationships of Tardigrada. However, molecular data generally do not support the inclusion of tardigrades within the Panarthropoda, but instead place them closer to Nematoda (roundworms). Morphological data traditionally group Tardigrada (water bears), Onychophora (velvet worms), and Arthropoda (e.g., spiders, insects, and their allies) into a monophyletic group of invertebrates with walking appendages known as the Panarthropoda.
0 kommentar(er)
