Echiniscus

Guil, Noemí, Jørgensen, Aslak, Giribet, Gonzalo & Kristensen, Reinhardt Møbjerg, 2013, Congruence between molecular phylogeny and cuticular design in Echiniscoidea (Tardigrada, Heterotardigrada), Zoological Journal of the Linnean Society 169 (4), pp. 713-736 : 723

RELATIONSHIPS WITHIN ECHINISCUS

Deep phylogenetic structure within Echiniscus is missing for the most part, but a sister group relationship to D. oihonnae was well supported in all analyses. The majority of species or complexes of species (all but E. bigranulatus ) were supported but with different data sets: the blumi-canadensis complex, E. granulatus , E. spiniger , and E. testudo with 18S rRNA information ( Fig. 4A ), and E. merokensis , E. wendti , E. spiniger , and E. testudo with 28S rRNA data ( Fig. 4B ). Instead, the parsimony network constructed with the 18S rRNA data revealed three groups based on cuticular design that had statistical support (AMOVA: F ST = 0.944, P <0.001, genetic variation explained: 52.3% among cuticular design groups, 42.2% among populations within cuticular design groups, and 5.5% within populations). These three groups ( Fig. 5 ) are composed of: (1) blumicanadensis ; (2) viridissimus , spiniger , testudo , bigranulatus , jenningsi , and wendti ; and (3) trisetosus Tar 612 and 635, granulatus and merokensis . By contrast, other classical groups based also on cuticle designs (presented in Table 1 and Fig. 1 : bigranulatus , blumi-canadensis , merokensis , arctomys, and viridis ; Ramazzotti & Maucci, 1983; Peluffo et al., 2002; Pilato et al., 2007, 2008) did not find statistical or phylogenetic support from any of the genetic markers used, whether analysed individually or in combination. The parsimony network constructed with the 28S rRNA data or combining 18S and 28S rRNA sequences (networks not shown) did not yield any interpretable groups as specimens appeared mixed, and with no statistical (AMOVA) support (P> 0.05) in any case.

When considering uncorrected pairwise p -distances ( Table 5), differences within each Echiniscus species were up to 0.3% for 18S rRNA and up to 0.8% for 28S rRNA. Comparing uncorrected P -values among Echiniscus species , differences for 18S rRNA were 0.5–1.7% and for 28S rRNA 0.5–4.3%. Diploechiniscus oihonnae (sister group of Echinsicus ) had differences between 2.6 and 3.5% for 18S rRNA with respect to the Echiniscus species , and for 28S rRNA were 1.7–5.0%.

The sequence fragment delimited by primer pair 28Sa to 28S7b1 presented problems because the majority of the sequences were incomplete. A shorter fragment between primers 28Sa and 28S5b was complete in the majority of taxa and had enough differences to discriminate among species (a gap was present between within- and among-species differences; Table 5): within Echiniscus species genetic differences were 0.0–0.8%, and among Echiniscus species , 1.0–3.7%, this range being 2.4–4.1% for the sister group of Echiniscus , D. oihonnae , with respect to the Echiniscus species. In comparison, differences between Echiniscus species and Testechiniscus species were 1.8–4.1% for 18S rRNA and 2.8–4.5% for 28S rRNA fragment a-5b. Differences among other Heterotardigrada genera (from the same order) were 4.4–8.7% for 18S rRNA and 4.3–10.4% for 28S (a-5b) rRNA, and in Eutardigrada genera were 3.1–8.1% for 18S rRNA and 4.6–7.8% for 28S (a-5b) rRNA.

Figures

Figure 1. The five types of cuticular designs traditionally used to group Echiniscus species and the recently described genus Diploechiniscus (Ramazzotti & Maucci, 1983; Peluffo et al., 2002; Pilato et al., 2007, 2008): A, bigranulatus; B, blumi-canadensis; C, merokensis; D, arctomys; E, viridis; F, D. oihonnae. A to D and F were made using phase contrast. E was made using differential interference contrast. Scale bars: 10 μm.

Figure 4. Bayesian phylogram obtained from the analysis of 18S rRNA (A) and 28S rRNA (B) information for Echiniscus species and Diploechiniscus oihonnae, using Testechiniscus spitzbergensis as outgroup. Values above branches indicate posterior probabilities obtained with the Bayesian analysis. Bootstrap support values from ML analysis are provided below

Figure 5. Parsimony network obtained with TCS for the 18S rRNA information from Echiniscus species. A photo with the cuticular design for each species is provided. E. merokensis SP, Spanish Echiniscus merokensis merokensis. E. merokensis Tar759 SUE, subspecies Echiniscus merokensis suecicus. The three supported groups found among the Echiniscus species, based on cuticle design, are identified with dotted squares, and named as I, II, and III.