Corresponding author: Matthew T. Wayland (
Academic editor: Boyko Georgiev
The acanthocephalan genus
Wayland MT, Vainio JK, Gibson DI, Herniou EA, Littlewood TDJ, Väinölä R (2015) The systematics of
The acanthocephalan genus
Historical record of species discovery in
Given the species diversity and genetic divergence within
Cement gland arrangements of the genera recognised by
Although molecular systematics have revealed that species of
A further problem for Petrochenko’s classification is the taxonomic status of
The incompatibility between
Further attempts at revising
Sample information.
Species | Host | Locality | Date collected | Genus |
Environment | GenBank # |
Voucher specimens |
---|---|---|---|---|---|---|---|
Lake, Bleasby, Nottinghamshire, UK | 4/06/1997 |
|
Freshwater | BM(NH) 2002.2.4.284–292 | |||
|
Lake Keitele, central Finland | 10/10/1996 |
|
Freshwater | BM(NH) 2002.2.4.102–122 | ||
|
Lake Pulmankijärvi, northern Finland | 11/06/1990 |
|
Freshwater | NA | ||
|
Porcupine Seabight, |
13/08/1997 |
|
Marine, deep-sea | BM(NH) 1997.12.8.3 (holotype); BM(NH) 1997.12.8.4–28 | ||
Kuopio, Finland | 15/10/1996 |
|
Freshwater | BM(NH) 2002.2.4.123–131 | |||
Baltic Sea, off Tvärminne, Hanko | 21/10/1992 |
|
Marine | BM(NH) 2002.2.4.90–101 | |||
|
Mys Kartesh, Gulf of Kandalaksha, White Sea | 31/08/1994–2/09/1994 |
|
Marine | NA | ||
|
Mys Kartesh, Gulf of Kandalaksha, White Sea | 31/08/1994–2/09/1994 |
|
Marine | NA | ||
|
Bothnian Bay, Baltic Sea | 27/08/1996 |
|
Freshwater | BM(NH) 2002.2.4.132–226 | ||
|
Loch Walton Burn, River Carron catchment, central Scotland (National Grid Reference NS 668 865) | 24/06/1996 |
|
Freshwater | BM(NH) 2002.2.4.264–275 |
Acanthocephalans from
Collection data for the samples are provided in Table
Cement gland arrangement in male
Species | A | B | C | D | E |
---|---|---|---|---|---|
|
0 | 1 (5.3%) | 4 (21.1%) | 10 (52.6%) | 4 (21.1%) |
|
0 | 0 | 0 | 4 (44.4%) | 5 (55.6%) |
|
1 (8%) | 7 (54%) | 3 (23%) | 2 (15%) | 0 |
|
218 (100%) | 0 | 0 | 0 | 0 |
|
0 | 0 | 0 | 3 (8%) | 34 (92%) |
|
0 | 1 (3%) | 16 (53%) | 13 (43%) | 0 |
|
6 (37.5%) | 10 (62.5%) | 0 | 0 | 0 |
As explained in the Introduction,
In order to root the phylogenetic trees, sequence data were also determined from
All acanthocephalans were washed in saline and then fixed in 90–100% alcohol immediately after collection, or alternatively frozen in liquid nitrogen and stored at -80 °C. Single specimens of each sample were used for the sequencing of each gene, but different individuals were analyzed for the different genes (in different laboratories). The anterior ends of the worms were removed before DNA extraction to avoid contamination of the samples with any host tissue attached to the proboscis. For the 28S analysis, individual acanthocephalans were washed in TE, ground in 150 µl TE (pH 8.0), 0.5% SDS, and digested overnight with the addition of 6 µl proteinase K (10 mg ml-1) at 37 °C. DNA was phenol-chloroform extracted and precipitated for 15 minutes at -20 °C with 0.1 vol. sodium acetate, at pH 5.0, and 2.5 vols 100% ethanol. DNA pellets were washed in 70% ethanol, dried, resuspended in TE (pH 8.0) and stored at -20 °C. Spectrophotometry was used to estimate the concentration of nucleic acids. Alternatively, for the COI data set, the CTAB extraction protocol of
For most taxa, a c.1,600 base-pair segment of the 28S rRNA gene spanning variable regions D1 to D6 was amplified using the primers LSU5 (5´-TAGGTCGACCCGCTGAAYTTAAGCA-3) and LSUD6-3 (5´-GGAACCCTTCTCCACTTCAGTC-3´) (
For analysis of a part of the mitochondrial COI gene, the universal “barcoding” primers of
The 28S rDNA and COI sequences were analyzed independently and also concatenated into a single dataset. Three methods of phylogenetic reconstruction were applied to each dataset: Bayesian inference (BI), maximum likelihood (ML) and maximum parsimony (MP).
Mr Bayes version 3.2.2 (
ML analysis was carried out using the genetic algorithm implemented in MetaPIGA 3.1 (
MP analysis was performed using PAUP version 4.0b10 (
Phylograms and other graphics were created using R (
All sequence data have been submitted to GenBank; accession numbers are provided in Table
The aligned partial 28S rDNA sequence data consisted of 1,607 nucleotide sites for all taxa except
Observed sequence divergence (%) between pairs of echinorhynchid species for the 28S rDNA (below the diagonal) and COI sequence data (above the diagonal).
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | |
---|---|---|---|---|---|---|---|---|---|---|
|
— | 36.1 | 33.3 | 34.5 | 32.8 | 34.2 | 34.4 | 34.0 | 34.0 | 34.7 |
|
18.5 | — | 29.7 | 27.7 | 28.7 | 29.7 | 29.7 | 29.4 | 28.7 | 28.9 |
|
31.1 | 23.1 | — | 21.7 | 22.2 | 21.5 | 21.7 | 22.9 | 22.9 | 23.1 |
|
19.1 | 15.5 | 6.6 | — | 16.8 | 17.4 | 17.3 | 19.0 | 17.1 | 18.0 |
|
19.3 | 15.3 | 7.5 | 0.8 | — | 8.2 | 8.4 | 9.1 | 8.9 | 8.9 |
|
19.2 | 15.4 | 7.1 | 0.5 | 0.3 | — | 0.2 | 7.2 | 6.5 | 6.3 |
|
19.2 | 15.4 | 7.1 | 0.5 | 0.3 | 0.0 |
— | 7.4 | 6.5 | 6.3 |
|
19.2 | 15.4 | 7.1 | 0.5 | 0.3 | 0.0 |
0.0 |
— | 3.3 | 3.1 |
|
19.2 | 15.4 | 7.1 | 0.5 | 0.3 | 0.0 |
0.0 |
0.0 |
— | 1.5 |
|
19.2 | 15.4 | 7.1 | 0.5 | 0.3 | 0.0 |
0.0 |
0.0 |
0.0 |
— |
sequences are identical
In the 585 base-pair alignment of the COI sequences, 249 (42.6%) of the nucleotide sites were variable within
Since identical sequences were obtained from members of the
Phylogram estimated using Bayesian inference analysis of 28S rDNA sequence data. Numbers at nodes are clade support values (%) for each method of phylogeny reconstruction (BI/ML/MP). Tree is rooted on the outgroup
A fully resolved tree was recovered from the mitochondrial COI data-set (Fig.
Phylogram estimated using Bayesian inference analysis of COI sequence data. Numbers at nodes are clade credibility values (%) for each method of phylogeny reconstruction (BI/ML/MP). Tree is rooted on the outgroup
MP analysis of the COI data-set produced a single most parsimonious tree, 542 steps long (CI = 0.795, RI = 0.615), which differed from the BI and ML phylograms at a single point, regarding the basal placement of
Phylogenetic relationships of
BI, ML and MP analysis of the combined data-sets all yielded the same phylogram, which was topologically identical to the BI/ML tree for the COI data-set and displayed similar support for most clades (Fig.
Phylogram estimated using Bayesian inference analysis of concatenated 28S rDNA and COI sequence data. Numbers at nodes are clade support values (%) for each method of phylogeny reconstruction (BI/ML/MP). Tree is rooted on the outgroup
The following discussion is based on the fully resolved phylogeny recovered from the total molecular data. It is important to note that, whereas the deeper branches in the phylogeny are supported by sequence data from both genes, the interrelationships of the five most closely related species were resolved using the COI data-set alone.
No support for
Aquatic environment (freshwater/marine) mapped on to the fully resolved phylogeny inferred from the concatenated 28S and COI sequences. Bold letter indicates genus according to
Cement gland arrangement displays continuous variation, from the pattern of three regular pairs through to the strictly moniliform pattern, with each
Further and more conclusive evidence that the ancestral cement gland arrangement is three regular pairs is available from both outgroup comparison and ontogeny. Firstly, outgroup comparison is based on the assumption that the character state found in related groups is the plesiomorphic condition (
Structure of the vagina in
The acanthors of
Another taxonomic finding of the current study is paraphyly of the
One significant problem in the systematics of
Since our phylogeny represents only a small proportion of the species in the genus, it is impossible to make any definitive claims about the zoogeography of this group of worms. However, the limited observations do suggest hypotheses that could be tested with additional data.
From this suggested freshwater origin and radiation,
Evidence of a re-invasion of freshwater by marine stock can also be found in the fully resolved phylogeny (Fig.
This preliminary investigation of the phylogenetic relationships within
We would like to thank Professor Tellervo Valtonen (University of Jyväskylä, Finland) for collecting the specimens of
Aligned and concatenated partial sequences of COI and 28S rDNA
Nexus file
Aligned and concatenated partial sequences of COI and 28S rDNA in nexus format. Aligned partial sequences of COI and 28S rDNA from each acanthocephalan population have been concatenated. Gaps are indicated by ‘-’. The first 585 characters in each block correspond to COI and the remainder to 28S rDNA. The file contains data for all nine Echinorhynchus samples and the outgroup taxon, Acanthocephalus lucii. This nexus file was used in all phylogenetic analyses.
Maximum likelihood model parameters
Adobe PDF file
Model parameters used in the maximum likelihood approach to phylogenetic reconstruction.
Nucleotide substitutions
Comma-separated-value file of measurements
Substitutions of nucleotides (transitions/transversions) for 28S rDNA (below the diagonal) and COI sequence data (above the diagonal).
Patterns of COI sequence variation
Adobe PDF file
Patterns of COI sequence variation. Graphs and discussion of patterns of nucleotide substitions in the COI data-set.