Corresponding author: Matthew Thomas Wayland (
Academic editor: Christos Arvanitidis
The hooks of the acanthocephalan proboscis exhibit serial variation in size and shape. The Meristogram was developed by
The Meristogram algorithm was implemented in the
Acanthocephalans are characterized by the presence of a retractable proboscis armed with recurved hooks which provides the means of attachment to the definitive host's gut wall. In many acanthocephalans the proboscis hooks are arranged in longitudinal rows and display positional variation in size and shape. The Meristogram was developed by
Presumably anticipating the adoption of the Meristogram as a taxonomic character,
All of the previous Meristogram studies were conducted before molecular markers were in widespread use and so genetic data were not collected to demonstrate reproductive isolation between populations, detect morphologically cryptic species or resolve phylogenetic relationships between taxa. Now both hook measurements and molecular data are available for a number of
Is the Meristogram consistent with species?
Can the Meristogram discriminate taxa, including morphologically cryptic species?
Are hook patterns phylogenetically informative?
Additional aims of this study were to implement a freely available and easy to use software tool for creating Meristograms and to evaluate the accuracy of the algorithm's estimation of cross-sectional hook area.
All hook measurement data were extracted from the
Nuclear and mitochondrial DNA sequences have elucidated the phylogenetic relationships of six of these taxa:
For the original description of the Meristogram algorithm, please refer to
Hook position is standardized to allow homologous regions of the proboscis to be compared across specimens with different numbers of hooks per row. Counted position number is multiplied by 100 and divided by n + 1, where n is the total number of hooks in the row and the constant 1 is a corrective factor for centring the data-points in graphs.
Two additional variables are computed for each hook: area = length × base/2 and ratio = base × 100/length.
Hook variables length, base, area and ratio are standardized within each row by conversion to percentages of their respective maximum value.
A moving average routine is used to extract the trends in positional variation for each of the hook variables. The moving average routine considers a user-defined segment of the percent-position axis for each character and moves through the data from the distal end to the proximal end of the proboscis in 1% increments. With each advance of the segment, the arithmetic means of the standardized hook variables and the percent-position value are calculated for all hooks located in the segment.
A moving average routine is used to extract the trends in positional variation for each of the hook variables. The moving average routine considers a user-defined segment of the percent-position axis for each character and moves through the data from the distal end to the proximal end of the proboscis in 1% increments. With each advance of the segment, the arithmetic means of the standardized hook variables and the percent-position value are calculated for all hooks located in the segment.
For each hook variable, each of the segment means is multiplied by 100 and divided by the largest segment mean for that hook variable, yielding a "percent-max-collection-value".
The percent-max-collection-values of all four hook variables are plotted against percent-position to produce the Meristogram.
The moving average routine results in a non-uniform distribution of data-points along the percent-position axis. In the current implementation of the Meristogram algorithm an optional linear interpolation procedure is introduced between steps 4 and 5. The 'approx' function in R is used to calculate hook metrics (L, B, A & R) at each integer value in the range of percent-position values yielded by the moving average routine. This linear interpolation step often improves the appearance of the Meristogram, but more importantly, by providing common percent-position coordinates it facilitates comparison of Meristograms using multivariate statistics (please see next section).
This new implementation of the Meristogram algorithm also enforces a minimum moving average segment size. It seems reasonable to argue that each proboscis in a collection should be represented in every moving average segment. The minimum moving average interval is thus defined as 100/(x+1), rounded up to the nearest integer, where n is the length of the shortest row of hooks in the collection.
The Meristogram algorithm has been implemented in
All data analyses were performed using the
Before considering inter-taxon differences in Meristogram, intra-taxon variation related to sex and choice of moving average interval was investigated. For each taxon, a set of Meristograms were plotted for each sex using the following moving average segment sizes: (1) minimum moving average interval (MMAI) for the taxon; (2) 1.5 × MMAI; (3) 2 × MMAI.
To assess inter-taxon variation, hook measurement data for females and males were pooled and a Meristogram was generated for each taxon using a moving average segment of 17% and linear interpolation. For comparative purposes it was important to use the same moving average segment for all Meristograms and 17% was the MMAI which could be applied to all taxa.
In addition to visual inspection of Meristograms, a more objective comparison of Meristograms was achieved with the aid of statistical pattern recognition methods. Meristogram data from all taxa were concatenated into a single matrix, where columns were hook variables at each integer percent-position and rows were taxa. Principal component analysis (PCA) was then used to reduce the number of dimensions in this data-set. Similarity of Meristograms was further assessed by hierarchical clustering of the scores for the first two principal components (accounting for most of the variation in the data-set) using the unweighted pair group method with arithmetic mean (UPGMA) algorithm and four different distance metrics (Euclidean, Manhattan, maximum and Minkowski).
No new data are presented in this study. However, files of hook measurement data in the appropriate format for input to the Meristogram software have been prepared and these are available as supplementary material (Suppl. materials
Measurements of hook cross-sectional area, obtained using a digitizing tablet, were available for
Strong evidence of sexual dimorphism was not found in the Meristograms for
The new software implementation of the Meristogram includes an optional linear interpolation step. Fig.
Meristograms for each of the taxa in this study are presented below along with a brief description. For each taxon the meristogram characteristics which differentiate it from the other taxa in the study are identified. These differences have been termed 'Potential diagnostic features', because they have yet to be validated using independent data.
Arched pattern with maximal values for L, B, A and R at positions 55%, 58%, 58% and 59%, respectively (Fig.
The following features of the Meristogram of
The curves for all four hook variables converge at a percent-position of approximately 60% and all four variables have maximal values at this location.
On the distal third of the proboscis the order or the curves from top to bottom is length, ratio, base, area; in the other taxa the order of these hook characters is typically length, area, base, ratio.
The largest values of length are found in the middle of the proboscis, whereas in the other taxa maximum values of length are found towards the distal end.
Absence of loops formed by the intersection of curves.
Of the taxa in this study, only
In female worms the dorsal row maxima for raw L, B, A and R had the following ranges 95.7-126.7µm, 25.5-45.5µm, 1,265-2,494µm2 and 29.1-43.8, respectively; corresponding values for ventral rows were 99.9-129.4µm, 25.7-47.2µm, 1,410-2,678µm2 and 26.9-41.7, respectively. The hooks of male worms were typically smaller with dorsal row maxima for L, B, A and R of 70.1-91.3µm, 21.7-27.7µm, 720.4-1,095.0µm2 and 31.3-39.8, respectively; and ventral row maxima of 76.9-97.5µm, 25.2-27.7µm, 896-1,278µm2 and 31.4-35.5, respectively.
There is a region of very small hooks (low values of A and L) on the dorsal surface of the proximal end of the proboscis (positions > 79%), corresponding to a flattening of the tail of the Meristogram. Length and area of the last and smallest hook in dorsal rows of female worms ranged from 34.3-59.2µm and 137-477µm2, respectively. In male worms the final hook in a dorsal row had a length of 26.4-42.1µm and an area of 94.8-242.1µm2. On the ventral surface, hooks also become much smaller proximally, but not to the extent observed on the dorsal surface. The final hook in ventral rows of female worms measured 42.8-76.8µm in length and had an area of 218-782µm2; the corresponding hook in male worms had a length of 41-62µm and an area of 211-527µm2. The smallest hooks are not the weakest; the latter are found at the distal end of the proboscis. In female worms the stoutness ratio of the first hook in a row was 15.5-25.1 on the dorsal surface of the proboscis and 12.7-23.9 on the ventral. The most distal hooks of male worms had stoutness ratios of 18.3-27.8 and 17.6-30.1 for dorsal and ventral rows, respectively.
Radial asymmetry
Hooks are markedly reduced in size at the proximal end of the proboscis, especially on the dorsal surface.
The Meristograms of
The Drummore collection has peak values of L, B, A and R at positions 40%, 72%, 70% and 77%, respectively (Fig.
In the collection from the River Carron catchment maximal values of L, B, A and R are found at positions 33%, 64%, 43% and 75%, respectively (Fig.
The curves for B, A and R follow a similar trajectory in the distal half of the Meristogram, with a particularly strong monotonic relationship between B and A (Fig.
The longest hooks (57.2-66.0µm in females and 50.0-60.6µm in males) are located around a third of the way along a row from the distal end of the proboscis, and the shortest hooks (30.2-42.4µm in females and 24.7-43.3µm in males) at the proximal end of a row. The stoutest hooks (ratio values of 35.8-39.0 in females and 32.0-35.0 in males) are found just proximal to the middle of the row and the weakest (20.7-24.2 in females and 20.8-28.9 in males) at the distal end of the row. The hooks with the broadest base (18.7-22.5µm in females and 16.1-19.5µm in males) and greatest area (507-676µm2 in females and 393-547µm2 in males) are located in the middle of the row.
Apparently unique characteristics for this Meristogram are:
Similar curves for A, B and R in distal half of the Meristogram, with B and A almost superimposed.
Absence of large loops. Only two prominent loops, both of which are very narrow relative to those displayed in the Meristograms of the other taxa.
The Meristogram of
The Meristogram for
Maximal values of L, B, A and R occur at positions: 27%, 67%, 57% and 67% (Fig.
The Meristogram of
The Meristograms of all of the
In the 45-80% position region of the Meristogram are three obvious loops (Fig.
Meristogram characteristics which may differentiate
Visual inspection of Meristograms reveals some similarities and differences between taxa. For a more objective comparison, statistical pattern recognition was used to measure Meristogram divergence between taxa. In this analysis, a single Meristogram was generated for
Principal component analysis (PCA) revealed the major sources of variation in the Meristograms. Fig.
Hierarchical clustering of the scores for the first two PCs depicts relationships between Meristograms as a dendrogram (Fig.
The differences in Meristogram between the central and southwest Scotland collections of
None of the eight
Not surprisingly, Meristogram analysis appeared to be most effective at discriminating taxa for which conventional characters are diagnostic, such as
Morphology and ecology suggest that the NE Atlantic
Hierarchical clustering shows relationships between taxa based on overall similarity (Fig.
Concordance between the dendrograms and the molecular phylogeny is evidence of a strong phylogenetic signal in the Meristogram. This raises the prospect of using Meristogram characteristics to define monophyletic groups within
The formula used by the Meristogram for estimating hook cross-sectional area has been shown to be accurate. However, since hook metrics are standardized, estimates of hook area are only required to be proportional to the actual area. Although no evidence of sexual dimorphism was found in this study, users of the Meristogram should be alert to this possible source of intra-specific variation. In
Meristograms have been shown to be sensitive to the choice of moving average interval and so in comparative studies it is important to use the same value of this parameter for all hook collections. The systematic homogeneity of a sample of acanthocephalans should be assessed before applying the Meristogram. Molecular markers are the first choice of tool for detecting cryptic species, but when they cannot be applied, the
Users of the Meristogram are encouraged to share their hook measurement data, either by including them as supplementary files to publications or submitting them to public repositories (e.g.
Having demonstrated the utility of the Meristogram in acanthocephalan systematics, the author is keen to facilitate its use. Free software is provided for systematists who would like to apply the technique themselves. Additionally, the author would welcome the opportunity to analyse hook morphometric data for other acanthocephalan workers as part of a collaborative project.
The Meristogram is not limited to the analysis of the hooks of the acanthocephalan proboscis. It can potentially be applied to any organism in which there are patterns in the longitudinal variation of serially homologous structures,
The author would like to thank the reviewers, Drs David Huffman and Scott Monks, for their constructive comments which greatly improved this paper.
Screen-grab of the graphical user interface to the Meristogram tool. The slider control provides dynamic control of the moving average interval and linear interpolation can be toggled on/off using the checkbox. Plots and data can be downloaded using the buttons at the bottom of the screen.
Relationship between hook area estimated by the Meristogram and hook area measured using a digitising tablet in three species of the
Meristogram of
Meristogram without linear interpolation.
Meristogram with linear interpolation.
Meristograms of dorsal and ventral hooks of
Dorsal
Ventral
Meristograms for
Drummore – 35 females (Suppl. material
River Carron catchment – 11 females (Suppl. material
Drummore, southwest Scotland
River Carron catchment, central Scotland
Meristograms of species of the
Principal component analysis of Meristograms. The first (PC1) and second (PC2) principal components describe 56% and 27% of the variance in the data, respectively. Meristograms were generated from hook measurement data in Suppl. materials
Scatterplot of the scores for the first two principal components (PC1 and PC2).
Scatterplot of the loadings for the first two principal components (PC1 and PC2). Hook variables (L, B, A and R) are colour coded to indicate standardized position (%).
Dendrograms showing the relationships between Meristograms for the
UPGMA clustering using Euclidean distance metric.
UPGMA clustering using Manhattan distance metric.
UPGMA clustering using maximum distance metric.
UPGMA clustering using Minkowski distance metric.
Phylogenetic relationships of six of the
Taxa analysed using the Meristogram. Data files contain hook measurement data in the appropriate format for input to the Meristogram software.
Acanthocephalan | Host(s) | Locality | Accession Numbers | Number of Specimens | Source | Data Files |
---|---|---|---|---|---|---|
|
Bothnian Bay, Baltic Sea and Lake Keitele, central Finland | BM (NH) 1987.1070–1074 (paratypes); BM (NH) 2002.2.4.102–122; BM (NH) 1989.1474–1491 | 10 |
|
F: Suppl. material |
|
|
Lake Pulmankijärvi, northern Finland | NA | 2 |
|
Suppl. material |
|
|
Porcupine Seabight, |
BM(NH) 1997.12.8.3 (holotype); BM(NH) 1997.12.8.4–28 | 11 |
|
F: Suppl. material |
|
northern North Sea | NA | 6 |
|
F: Suppl. material |
||
northern North Sea | NA | 8 |
|
F: Suppl. material |
||
|
Baltic Sea, off Tvärminne, Hanko | BM(NH) 2002.2.4.90–101 | 6 |
|
F: Suppl. material |
|
|
Bothnian Bay, Baltic Sea | BMNH 2002.2.4.132-226; BMNH 2002.2.4.227-263 | 42 |
|
F dorsal: Suppl. material |
|
|
Drummore, southwest Scotland | BM (NH) 1986.764–793 | 54 |
|
F: Suppl. material |
|
|
|
River Carron catchment, central Scotland | BM (NH) 2002.2.4.264–275; BM (NH) 2002.2.4.276–283 | 18 |
|
F: Suppl. material |
Data analysis script
Data type: R language script
Brief description: The commands in this script will perform all of the data analyses described in this paper and generate all of the figures. The script is included here to enable readers to verify the findings of this study.
File: oo_73745.R
Area of hooks from
Data type: morphometric
Brief description: Comma separated value file with the following nine columns: species, sex, specimen, hook, position, length, base, measured_area and estimated_area.
species - species of the
sex - sex of acanthocephalan
hook - numerical position of hook in longitudinal row as counted from the distal end of the proboscis
length - length of hook blade (micrometres)
base - width of hook base (micrometres)
measured_area - cross-sectional area (square micrometres) of a hook viewed in profile and measured using a digitising tablet
estimated_area - cross-sectional area (square micrometres) of hook estimated using the formula: area = length x base / 2
Source:
File: oo_63675.csv
Hook measurement data from female
Data type: morphometric
Brief description: The file is a comma separated value (CSV) format suitable for input to the Meristogram software. The file has four columns: specimen, hook, length, base.
specimen - unique identifier for the specimen
hook - numerical position of hook in longitudinal row as counted from the distal end of the proboscis
length - length of hook blade (micrometres)
base - width of hook base (micrometres)
Source: Wayland (2013)
File: oo_63705.csv
Hook measurement data from male
Data type: morphometric
Brief description: The file is a comma separated value (CSV) format suitable for input to the Meristogram software. The file has four columns: specimen, hook, length, base.
specimen - unique identifier for the specimen
hook - numerical position of hook in longitudinal row as counted from the distal end of the proboscis
length - length of hook blade (micrometres)
base - width of hook base (micrometres)
Source: Wayland (2013)
File: oo_63706.csv
Hook measurement data from female
Data type: morphometric
Brief description: The file is a comma separated value (CSV) format suitable for input to the Meristogram software. The file has four columns: specimen, hook, length, base.
specimen - unique identifier for the specimen
hook - numerical position of hook in longitudinal row as counted from the distal end of the proboscis
length - length of hook blade (micrometres)
base - width of hook base (micrometres)
Source: Wayland (2013)
File: oo_63707.csv
Hook measurement data from female
Data type: morphometric
Brief description: The file is a comma separated value (CSV) format suitable for input to the Meristogram software. The file has four columns: specimen, hook, length, base.
specimen - unique identifier for the specimen
hook - numerical position of hook in longitudinal row as counted from the distal end of the proboscis
length - length of hook blade (micrometres)
base - width of hook base (micrometres)
Source:
File: oo_63694.csv
Hook measurement data from male
Data type: morphometric
Brief description: The file is a comma separated value (CSV) format suitable for input to the Meristogram software. The file has four columns: specimen, hook, length, base.
specimen - unique identifier for the specimen
hook - numerical position of hook in longitudinal row as counted from the distal end of the proboscis
length - length of hook blade (micrometres)
base - width of hook base (micrometres)
Source:
File: oo_63695.csv
Hook measurement data from female
Data type: morphometric
Brief description: The file is a comma separated value (CSV) format suitable for input to the Meristogram software. The file has four columns: specimen, hook, length, base.
specimen - unique identifier for the specimen
hook - numerical position of hook in longitudinal row as counted from the distal end of the proboscis
length - length of hook blade (micrometres)
base - width of hook base (micrometres)
Source:
File: oo_63710.csv
Hook measurement data from male
Data type: morphometric
Brief description: The file is a comma separated value (CSV) format suitable for input to the Meristogram software. The file has four columns: specimen, hook, length, base.
specimen - unique identifier for the specimen
hook - numerical position of hook in longitudinal row as counted from the distal end of the proboscis
length - length of hook blade (micrometres)
base - width of hook base (micrometres)
Source:
File: oo_63711.csv
Hook measurement data from female
Data type: morphometric
Brief description: The file is a comma separated value (CSV) format suitable for input to the Meristogram software. The file has four columns: specimen, hook, length, base.
specimen - unique identifier for the specimen
hook - numerical position of hook in longitudinal row as counted from the distal end of the proboscis
length - length of hook blade (micrometres)
base - width of hook base (micrometres)
Source:
File: oo_63712.csv
Hook measurement data from male
Data type: morphometric
Brief description: The file is a comma separated value (CSV) format suitable for input to the Meristogram software. The file has four columns: specimen, hook, length, base.
specimen - unique identifier for the specimen
hook - numerical position of hook in longitudinal row as counted from the distal end of the proboscis
length - length of hook blade (micrometres)
base - width of hook base (micrometres)
Source:
File: oo_63713.csv
Hook measurement data from female
Data type: morphometric
Brief description: The file is a comma separated value (CSV) format suitable for input to the Meristogram software. The file has four columns: specimen, hook, length, base.
specimen - unique identifier for the specimen
hook - numerical position of hook in longitudinal row as counted from the distal end of the proboscis
length - length of hook blade (micrometres)
base - width of hook base (micrometres)
Source:
File: oo_63714.csv
Hook measurement data from male
Data type: morphometric
Brief description: The file is a comma separated value (CSV) format suitable for input to the Meristogram software. The file has four columns: specimen, hook, length, base.
specimen - unique identifier for the specimen
hook - numerical position of hook in longitudinal row as counted from the distal end of the proboscis
length - length of hook blade (micrometres)
base - width of hook base (micrometres)
Source:
File: oo_63715.csv
Hook measurement data from dorsal rows of female
Data type: morphometric
Brief description: The file is a comma separated value (CSV) format suitable for input to the Meristogram software. The file has four columns: specimen, hook, length, base.
specimen - unique identifier for the specimen
hook - numerical position of hook in longitudinal row as counted from the distal end of the proboscis
length - length of hook blade (micrometres)
base - width of hook base (micrometres)
Source:
File: oo_63696.csv
Hook measurement data from ventral rows of female
Data type: morphometric
Brief description: The file is a comma separated value (CSV) format suitable for input to the Meristogram software. The file has four columns: specimen, hook, length, base.
specimen - unique identifier for the specimen
hook - numerical position of hook in longitudinal row as counted from the distal end of the proboscis
length - length of hook blade (micrometres)
base - width of hook base (micrometres)
Source:
File: oo_63699.csv
Hook measurement data from dorsal rows of male
Data type: morphometric
Brief description: The file is a comma separated value (CSV) format suitable for input to the Meristogram software. The file has four columns: specimen, hook, length, base.
specimen - unique identifier for the specimen
hook - numerical position of hook in longitudinal row as counted from the distal end of the proboscis
length - length of hook blade (micrometres)
base - width of hook base (micrometres)
Source:
File: oo_63701.csv
Hook measurement data from ventral rows of male
Data type: morphometric
Brief description: The file is a comma separated value (CSV) format suitable for input to the Meristogram software. The file has four columns: specimen, hook, length, base.
specimen - unique identifier for the specimen
hook - numerical position of hook in longitudinal row as counted from the distal end of the proboscis
length - length of hook blade (micrometres)
base - width of hook base (micrometres)
Source:
File: oo_63703.csv
Hook measurement data from female
Data type: morphometric
Brief description: The file is a comma separated value (CSV) format suitable for input to the Meristogram software. The file has four columns: specimen, hook, length, base.
specimen - unique identifier for the specimen
hook - numerical position of hook in longitudinal row as counted from the distal end of the proboscis
length - length of hook blade (micrometres)
base - width of hook base (micrometres)
Source: Wayland (2013)
File: oo_68461.csv
Hook measurement data from male
Data type: morphometric
Brief description: The file is a comma separated value (CSV) format suitable for input to the Meristogram software. The file has four columns: specimen, hook, length, base.
specimen - unique identifier for the specimen
hook - numerical position of hook in longitudinal row as counted from the distal end of the proboscis
length - length of hook blade (micrometres)
base - width of hook base (micrometres)
Source: Wayland (2013)
File: oo_68463.csv
Hook measurement data from female
Data type: morphometric
Brief description: The file is a comma separated value (CSV) format suitable for input to the Meristogram software. The file has four columns: specimen, hook, length, base.
specimen - unique identifier for the specimen
hook - numerical position of hook in longitudinal row as counted from the distal end of the proboscis
length - length of the hook blade (micrometres)
base - width of the hook base (micrometres)
Source: Wayland (2013)
File: oo_68464.csv
Hook measurement data from male
Data type: morphometric
Brief description: The file is a comma separated value (CSV) format suitable for input to the Meristogram software. The file has four columns: specimen, hook, length, base.
specimen - unique identifier for the specimen
hook - numerical position of hook in longitudinal row as counted from the distal end of the proboscis
length - length of the hook blade (micrometres)
base - width of the hook base (micrometres)
Source: Wayland (2013)
File: oo_68466.csv
Meristograms for female and male
Data type: morphological
Brief description: Meristograms for five female and five male specimens of
File: oo_64487.pdf
Meristograms for female
Data type: morphology
Brief description: Meristograms for two female specimens of
File: oo_64488.pdf
Meristograms for female and male
Data type: morphological
Brief description: Meristograms for four female and seven male specimens of
File: oo_64449.pdf
Meristograms for female and male
Data type: morphological
Brief description: Meristograms for four female and two male specimens of
File: oo_64463.pdf
Meristograms for female and male
Data type: morphological
Brief description: Meristograms for four female and four male specimens of
File: oo_64464.pdf
Meristograms for female and male
Data type: morphological
Brief description: Meristograms for five female and one male specimens of
File: oo_64466.pdf
Meristograms for female and male
Data type: morphological
Brief description: Meristograms for 36 female and 6 male specimens of
File: oo_64457.pdf
Meristograms for female and male
Data type: morphological
Brief description: Meristograms for
File: oo_68417.pdf