Research Article |
Corresponding author: Bangon Kongim ( kongimb@yahoo.com ) Corresponding author: Somsak Panha ( somsak.pan@chula.ac.th ) Academic editor: Richard Willan
© 2015 Bangon Kongim, Chirasak Sutcharit, Somsak Panha.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Kongim B, Sutcharit C, Panha S (2015) Cytotaxonomy of unionid freshwater mussels (Unionoida, Unionidae) from northeastern Thailand with description of a new species. ZooKeys 514: 93-110. https://doi.org/10.3897/zookeys.514.8977
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Morphological and chromosomal characteristics of a number of unionid freshwater mussels were studied from northeastern Thailand. Karyotypes of eight species from seven genera (Chamberlainia, Ensidens, Hyriopsis, Physunio, Pseudodon, Scabies and Trapezoideus) were examined. Six species possess 2n = 38 karyotypes, whereas Scabies crispata and an unidentified Scabies sp. lack three small chromosome pairs, giving a diploid number of 32. Moreover, the karyotypes of the unidentified Scabies differ from S. crispata as it exhibits a telocentric chromosome pair (6m + 7sm + 2st + 1t). Most of the conchological characters also differ between the two species – adult size, colour pattern, muscle scars, pseudocardinal and lateral teeth. The name Scabies songkramensis sp. n. is proposed for the unidentified species, and its description is included in this paper. Interestingly, seven species contain mostly bi-armed chromosomes, but only the mud-dweller in stagnant water, Ensidens ingallsianus, contains predominantly five telocentric pairs. In addition, the marker chromosome characteristics of an unbalanced long arm, twisted centromere, a wider angle 180° arrangement, a twisted arm and telomeric end union reported in this study are described for the first time for unionid mussels.
Chromosome, mussel, karyotype, systematics, Southeast Asia, cryptic species
The Unionidae is numerically the largest family of both extant and extinct freshwater mussels and includes over 670 species worldwide with about 220 species occurring in Indotropica (
Most studies have dealt with American, European and Australasian taxa (
Several sympatric species have been recorded in numerous Thai localities (
Data summary. This table shows the number of specimens examined (No.), locality, diploid number (2n), fundamental number (FN), karyotype pattern and chromosome markers of the Unionidae species included the present study. The numbered localities are presented in Figure
Species | No. | Locality | 2n | FN | Karyotype formula | Marker chromosome (pair number) |
---|---|---|---|---|---|---|
UNIONIDAE | ||||||
Subfamily Hyriopsinae | ||||||
Chamberlainia hainesiana | 2 | 2,3 | 38 | 76 | 4m + 9sm + 6st | 5 and 13 unbalance of long arm |
Hyriopsis bialatus | 10 | 1, 2, 3 | 38 | 72 | 6m + 7sm + 4st + 2t | 6 telomeric end union |
Subfamily Parreysiinae | ||||||
Scabies crispata | 10 | 1, 2, 3 | 32 | 64 | 6m + 7sm + 3st | 10 twisted arm |
Scabies songkramensis sp. n. | 10 | 4, 5 | 32 | 62 | 6m + 7sm + 2st + 1t | 15 small and twisted arm |
Subfamily Pseudodontinae | ||||||
Pseudodon mouhoti | 6 | 1, 2, 3 | 38 | 74 | 6m + 6sm + 6st +1t | 7 twisted centromere |
Subfamily Rectidentinae | ||||||
Ensidens ingallsianus | 6 | 1, 2, 3 | 38 | 46 | 3m + 4sm + 7st + 5t | 1 unbalance of long arm 6 and 13 wider angle 180° arrangement and twisted centromere |
Physunio inornatus | 10 | 1, 2, 3 | 38 | 74 | 3m + 9sm + 6st + 1t | 4 wider angle 180° arrangement 8 twisted centromere |
Trapezoideus exolescens | 10 | 1, 2, 3 | 38 | 74 | 3m + 10sm + 5st + 1t | 3 unbalance of long arm |
Here we examine the karyotypes of eight species of unionids from northeastern Thai that represent seven genera (and four subfamilies): Chamberliania, Hyriopsis (Hyriopsinae); Scabies (Parreysiinae); Pseudodon (Pseudodontinae); Ensidens, Physunio, Trapezoideus (Rectidentinae). All these genera are considered to be completely different from each other on a morphological basis (
The localities and shell characteristics of each species are given in Figs
Sampling locations for unionids in northeastern Thailand: 1 Ban Tha Nanglian, Chonnabot, Khon Kaen (16°1'21"N; 102°33'34"E) 2 Ban Tha Khonyang, Kantharawichai, Maha Sarakham (16°14'1"N; 103°16'1"E) 3 Ban Tha Krai, Selaphum, Roi Et (16°2'0"N; 103°56'2"E) 4 Ban Klang Charern, Pangkon, Sakon Nakorn (17°24'22"N; 103°50'1"E) 5 Kamtakla, Sakon Nakorn (17°49'32"N; 103°47'10"E).
Abbreviations for figures and measurements: aa, anterior adductor; muscle scar; lt, lateral teeth; pa, posterior adductor muscle scar; pl, pallial line; pt, pseudocardinal tooth; H, height of valves; L, length of valves; W, width of valves.
CUMZ Chulalongkorn University, Museum of Zoology, Bangkok, Thailand
SMF Forschungsinstitut und Naturmuseum Senckenberg, Frankfurt, Germany
ZMMSU Zoological Museum of Mahasarakham University, Thailand.
The karyotype of six species consists of 2n = 38 chromosomes, but two species (Scabies crispata and an unidentified Scabies sp.) showed 2n = 32. In all samples examined, no sex chromosome heteromorphism or secondary constrictions were evident. The fundamental numbers (FN) varied among species, ranging from 46 to 76 (Figs
Karyotypes of unionids studied: A Chamberlainia hainesiana B Hyriopsis bialatus C Scabies crispata D Scabies songkramensis sp. n. E Pseudodon mouhoti F Ensidens ingallsianus G Physunio inornatus H Trapezoideus exolescens. Abbreviations: m, metacentric; sm, submetacentric; st, subtelocentric; t, telocentric; numbers 1, 5, 10, 11, 15 represent the pair numbers.
The karyotype of Scabies crispata is almost identical to that of Scabies songkramensis sp. n., but the latter differs in having a telocentric pair 7. The FN values were dissimilar at 64 and 62, respectively (Figs
The karyotypes of Pseudodon mouhoti consists of 6m + 6sm + 6st + 1t with twisted centromere pair 7. The three members of the subfamily Rectidentinae (i.e. Ensidens ingallsianus, Physunio inornatus and Trapezoideus exolescens) are different from each other in FN value, size arrangement and morphology of chromosomes (Table
(by subsequent designation of
Holotype ZMMSU 00500 (length 30 mm, height 18 mm, width 7.5 mm) Paratypes: ZMMSU 00501 (20 shells; length 29–33 mm, height 17–19 mm, width 7–8 mm); CUMZ (five shells).
Houy Plahang stream in Songkram River Basin, Ban Klang Charern, Pangkon, Sakon Nakorn, Thailand – 17°24'22"N, 103°50'1"E. Type locality indicated in Fig.
The specific name songkramensis refers to the Songkram River, type locality of this new species. Authorship of this new species is to be credited to Kongim and Panha in Kongim, Sutcharit and Panha.
Shell of medium size (length 29–33 mm), ovate in outline, H/L ratio = 0.59, anterior portion rounded, umbonal area elevated and sloping downwards posteriorly. Underlying shell colour brown. Shell sculptured with a series of coarse, v-shaped ribs radiating outwards from umbo; v-line arrangement loose, with 4-fold number on 10 mm; posterior slope with coarse and distinct ridges. Sculpture reduced to nearly obsolete near ventral and posterior shell margin. Periostracum brown, tending towards dark green where ribs are worn. Hinge plate well-developed; pseudocardinal tooth (pt) forming a thickened plate and raised lamelliform on right valve, but thinner and also raised lamelliform on left valve. Two well-developed posterior lateral teeth (lt) present in each valve, long and sharp. Anterior adductor muscle scar (aa) prominent and deeply impressed; posterior adductor muscle scar (pa) shallow; pallial line (pl) faintly impressed. Nacre bluish-white with little iridescence.
Shell valves of A, B Scabies songkramensis sp. n., A holotype ZMMSU 00500 and B paratype ZMMSU 00501. C Scabies crispata, Brandt collection SMF 188682 from Bangkok, Thailand D Scabies nucleus Brandt collection SMF 198394 from Mekong River, Pakse, Laos E Scabies phaselus Brandt collection SMF 188695 from Takrong River, Nakon Ratchsrima, and F hinge plates of Scabies songkramensis sp. n., holotype, with illustrating and measurements terminology. Abbreviations: aa, anterior adductor muscle scar; lt, lateral teeth; pa, posterior adductor muscle scar; pl, pallial line; pt, pseudocardinal tooth; H, height of valves; L, length of valves; and W, width of valves.
The new species differs from the closely related Scabies crispata (Gould) and S. phaselus (Lea) by having a smaller, harder, thicker, ovate shell that is brown in colour, with dark brown v-line sculpture. The two other species have larger, more elongate shells that are yellowish brown in colour, combined with greenish v-line sculpturing in S. crispata and a nearly smooth shell surface in S. phaselus. Scabies songkramensis sp. n. differs from S. nucleus (Lea) in having a larger shell and v-line sculpture, compared with w-line sculpture in S. nucleus.
Scabies songkramensis sp. n. occurs in a small tributary of the Songkhram River. It lives in shallow water in a sandy-gravel substrate, or less frequently in sandy-mud. This new species is currently known only from the type locality, approximately 100 km from the main stem of the Songkhram River (Fig.
The diploid numbers of six species in the three subfamilies, Hyriopsinae, Pseudodontinae and Rectidentinae, showed the same chromosome number (2n = 38), which is similar to unionid taxa in other regions (
The diploid (2n), haploid (n) and fundamental number (FN) for the Unionoida. Data for the Unionidae plus three additional families (Hyriidae, Mutelidae and Margaritiferidae) are included in the table. References as follows: (1)
Species | 2n | n | FN | Karyotype | Locality | References |
---|---|---|---|---|---|---|
Family Hyriidae | ||||||
Diplodon chilensis | 34 | – | – | 9m + 8sm | Chile | 9 |
Family Mutelidae | ||||||
Alathyria pertexta | 34 | – | – | – | Australia | 2 |
Mutela rostrata | 20 | – | – | 2m + 2sm + 6a | Egypt | 8 |
Velesunio ambiguus | 34 | – | – | – | Australia | 2 |
Velesunio legrandi | 34 | – | – | – | Tazmania | 2 |
Family Margaritiferidae | ||||||
Margaritifera margaritifera | 38 | – | – | – | USA | 5 |
Margaritifera laevis | 38 | 19 | 76 | 19sm | Japan | 4 |
Family Unionidae | ||||||
Alasmidonta arcula | 38 | – | – | – | USA | 5 |
Alasmidonta marginata | 38 | – | – | 10m + 7sm + 2sm | USA | 5 |
Anodonta anatina | 38 | – | 76 | 10m + 3s/m + 6sm | Netherlands | 3 |
Anodonta anatina | 38 | – | 76 | 6m + 12sm + 1st | Poland | 14 |
Anodonta cygnea | 38 | – | 76 | 6m + 12sm + 1st | Portugal | 15 |
Anodonta grandis | 38 | – | – | 6m + 12sm + 1st | USA | 5 |
Anodonta woodiana | 38 | – | 76 | – | Poland | 13 |
Anodonta woodiana woodiana | 38 | – | 76 | – | China | 11 |
Anodontoides ferussacianus | 38 | – | – | 9m + 10sm | USA | 5 |
Elliptio complanata | – | 16 | – | – | USA | 1 |
Elliptio complanata | 38 | – | – | – | USA | 7 |
Gonidea angulata | 38 | – | – | – | USA | 5 |
Hyriopsis cumingii | 38 | – | – | – | China | 10 |
Inversidens japonensis | 38 | – | 76 | 6m + 13sm | Japan | 4 |
Lampsillis radiate luteola | 38 | – | – | – | USA | 5 |
Lasmigona costata | 38 | – | – | 9m + 7sm + 3st | USA | 5 |
Potamilus alatus | 38 | – | – | – | USA | 5 |
Pseudodon obovalis omiensis | 38 | – | 76 | 9m + 10sm | Japan | 4 |
Ptychobranchus fasciolaris | 38 | – | – | 8m + 10sm + 1st | USA | 5 |
Quadrula quadrula | 38 | – | – | – | USA | 5 |
Solenaia khwaenoiensis | 37 | 19 | – | 3m + 15sm + 1st | Thailand | 12 |
Toxolasma lividus grans | 38 | – | – | – | USA | 5 |
Tritigonia verrucosa | 38 | – | – | – | USA | 5 |
Unio elongatulus | 28 | – | – | 10m + 4sm | Egypt | 8 |
Unio elongatulus | – | 19 | – | – | Italy | 6 |
Unio pictorum | 38 | – | 76 | 8m + 1m/sm + 10sm | Netherlands | 3 |
Villosa iris | 38 | – | – | 11m + 6sm + 2st | USA | 5 |
Villosa lienosa | 38 | – | – | – | USA | 5 |
Comparisons of shell characteristics of the new species compared with those of the three other Thai species of Scabies.
Characteristics | S. songkramensis sp. n. | S. crispata | S. nucleus | S. phaselus |
---|---|---|---|---|
Length of valves; L (mm) | 29–33 29.60 ± 0.57 |
30–39 35.40 ± 2.33 |
16–19 18.00 ± 0.40 |
30–35 32.60 ± 1.85 |
Height of valves; H (mm) | 17–19 17.60 ± 0.57 |
14–17 15.88 ± 0.68 |
11–13 12.20 ± 0.67 |
13–17 15.26 ± 0.55 |
Width of valves; W (mm) | 7–8 7.51 ± 0.35 |
5.5–7.5 6.57 ± 0.42 |
3.5–4.5 4.23 ± 0.87 |
5.5–7 5.95 ± 0.39 |
H/L ratio | 0.59 ± 0.01 | 0.46 ± 0.31 | 0.71 ± 0.01 | 0.48 ± 0.32 |
Shell shape | Ovate | Elongate cuneiform | Subquadrate | Elongate with ventral margin concave |
Shell colour | Greenish brown | Dark greenish | Greenish | Dark greenish |
Shell sculpture | Coarse, obtuse | Fine, glossy | Coarse, obtuse | Fine, glossy |
Line of shell sculpture | Loose, distinct v-line | v or w-line | v-line | Dense, wavy line |
Fold number on shell sculpture on 10 mm | 4 | 6 | 6 | 9 |
Shell thickness | Thick | Thin | Thick | Thin |
Nacre colour | Bluish-white | Milky-white | Bluish-white | Milky-white |
Pseudocardinals tooth | Thick plate | Large, deep fracture | Thick, stumpy, short, deep fracture | Large, short, triangular, pointed crest |
Muscle scars | Deep and narrow in anterior, shallow in posterior | Deep in anterior, very shallow in posterior | Distinct, deep in anterior | Deep in anterior |
The karyotypes of all eight species of unionids studied here differ in the degree of asymmetry (sub-telocentric and telocentric). Primitive karyotypes typically exhibit low asymmetry and derived karyotypes show higher asymmetry (
Marker chromosomes such as telomeric end union, wider angle arrangement and others, are useful in taxonomy and systematics (
The karyotype is generally a species-specific character, and as such is useful in species discrimination (
We are indebted to R. Janssen (SMF, Frankfurt) for kindly permitting SP and CS to study type specimens. We also thank K. Kongim and P. Ekkawat for their kind assistance with fieldwork. This project was funded by: the Research Unit, Mahasarakham University (2013) to BK; the Ratchadaphiseksomphot Endowment Fund of Chulalongkorn University (RES560530658-FW) to CS; and the TRF Senior Research Scholar, Thailand Research Fund (RTA5580001) to SP. Our warmest thanks go to the reviewers and the subject editor (Dr Richard Willan) for patiently improving this manuscript and to Dr Robert Butcher of the PCU unit, Faculty of Science, Chulalongkorn University, for critically correcting the English.