/. MolL Stud. (1998), 64,309-318
© The Malacological Society of London 1998
CHROMOSOMES OF MELANOPSIS DUFOURI FERUSSAC,
1823 (CAENOGASTROPODA: MELANOPSIDAE)
IJ
'J. BARSlENE, 2G. TAPIA and 3 D. BAR$YTE
Institute of Ecology, Akademijos 2, 2600 Vilnius, Lithuania. 'Department of Animal Biology,
University of Valencia, Dr. Moliner, 50, 46100 Burjassot (Valencia), Spain. 3School of Biological Sciences.
Stop ford Building, Oxford Road, Manchester University, Ml 3 9PT, Manchester, U.K.
(Received 27 February 1997; accepted 10 October 1997)
ABSTRACT
The most frequent chromosome numbers were 2n =
36 and n = 18 in Melanopsis dufouri F6russac inhabiting the Ullal de Baldovf, an ancient spring of the
Albufera lake (Valencia province), and the small
stream Rambla de Gaibiel (Castellon province) in
Spain. Subtelocentric and subtelo-telocentric chromosomes predominated in the sets of snails from
both populations. Pericentric inversions were basic
factors in the interpopulational differentiation of
karyotypes. Intrapopulational karyotype polymorphism (specimens with 2n = 36, 2n = 34, rarely 2n =
35) and mosaic molluscs occurred in the Ullal de Baldovf population as a result of small chromosome
elimination. The rather frequent appearance of one
or two non-homologue small chromosomes in hypodiploid nuclei 2n = 35, 2n = 34 was obviously
connected with fragmentation of chromosomes. Karyological findings are in accordance with phenotypic
diversity of M. dufouri from the Ullal de Baldovf
population.
INTRODUCTION
Karyological information on the prosobranch
family Thiaridae, in which the genera Melanopsis was included until recently, is comparatively
scarce: chromosome numbers of only 7 species
were listed in the review by Patterson (1969).
Haploid numbers of 16, 18 and 19 chromosomes in diploid species were reported and also
polyploid species with haploid chromosome
complements of 35-60 elements. Yaseen (19%)
reported the diploid number of 2n = 22 for
Melanoides tuberculata (Muller). This species
has also been found to be polyploid (Jacob,
1959; BarSiene, Tapia & BarSyte, 19%). Cleopatra bulimoides (Olivier) has a reported
diploid chromosome number of 2n = 28, as
well as different levels of polyploidy for certain
phenotypes (Yaseen, 1994).
The aim of this investigation was to examine
the chromosomes of Melanopsis dufouri F6russac inhabiting the small stream Rambla de
Gaibiel in Castellon province and the Ullal de
Baldovi (a spring which in the past was connected to the Albufera lake and is nowadays
separated from it by rice fields), in Valencia
province, Spain. The taxonomic status for this
species is still uncertain as phenotypic diversity
is very wide. This paper presents a quantitative
karyological assessment of intra- and interpopulational polymorphism in M. dufouri.
MATERIAL AND METHODS
Specimens of M. dufouri were sampled from two
populations during May-June 1994. One hundred
specimens from the Ullal de Baldovd spring and 35
from the Gaibiel population were collected from an
area around 10 m2 in each site and were taken to the
laboratory. Blocking of gonadal and somatic cell divisions at metaphase was achieved by injection of a
0.1-0.2% aqueous solution of colchicine into the
snails 4-10 hours before they were dissected. The
different stages of sample fixation, chromosome
preparation and identification were the same as those
previously described by BarSiene (1978) and
BarSiene & Grabda-Kazubska (1988). Despite the
fact that we collected many M. dufouri specimens for
study, the investigation of their chromosomes proved
notably difficult. This was mainly due to the low
mitotic activity found, which made finding suitable
preparations for individual analysis troublesome.
Cells undergoing mitosis rarely occurred in May and
were more frequent in June. Meiotic cells in
pachytene and diakinesis were found from the
middle of June onwards.
Karyometric parameters were determined in 10
karyotypes of snails from the Gaibiel population and
in 20 karyotypes of those from the Ullal de Baldovf
spring. The absolute length, relative length (100 X
chromosome length/total haploid chromosome set
length) and centromeric index (100 X length of the
short chromosome arm/total chromosome length)
were obtained. These chromosome measurements
J. BARSlENE, G. TAP1A & D. BARSYTE
310
were taken from photomicrographs. Classification of
chromosomes was based on Levan, Fredga & Sandberg (1964). Where the standard deviation of the
centromeric index was at the borderline between two
types of chromosomes, the nomenclature for both
chromosome types is shown.
RESULTS
The most frequent chromosome numbers 2n =
36 and n = 18 were found in both populations
of M. dufouri. The chromosome number variability in specimens from the Ullal de Baldovf
locality was higher than in the Gaibiel population (Fig. 1).
The chromosomes of 314 mitotic metaphase
spreads and meiotic nuclei from somatic and
gonadal tissue of 22 specimens of M. dufouri
from the Ullal de Baldovf spring were counted.
Modal chromosome numers 2n = 36 and n =
18 appeared in 36.3% of the cells studied. The
other most frequent values were 2n = 34 and
n = 17 (29.6% of cells) and 2n = 35 (15.3% of
cells). There was an insignificant amount of
polyploid nuclei (4.7%) (Figs. 1,2).
The karyological analysis of M. dufouri from
the Ullal de Baldovf population showed the
existence of specimens with a predominance of
I Baldovi
cells possessing different chromosome numbers: 2n = 36 (16 snails), 2n = 35 (one snail)
and 2n = 34 (5 snails). In the tissues of four
specimens (with prevalence 2n = 36), nuclei
with 35,34 and 33 were very frequent and their
distribution was analogous to mosaic organisms. The comparison of the karyotypes of
snails with prevalence of 36 and 34 chromosomes showed the existence of not only numerical differences but also intrapopulational
differences in the relative lengths of 7th and
8th chromosome pairs. The predominance of
subtelocentric chromosomes in the modal sets
was remarkable. Two pairs of metacentric
elements were present in both karyotypes
(2n = 36 and 2n = 34) (Tables 1,2).
An additional one or two small chromosomes, and sometimes acentric fragments, were
present in most of the cells of the specimens
with predominance of 2n = 34 and 2n = 35
chromosomes (Figs. 3, 4). Such small supernumerary elements only occasionally appeared
in cells with 2n = 36. There were multiple sites
of homologous non conjugation, univalents,
polyvalents and other meoitic disturbances in
the gametogenesis of M. dufouri from Ullal de
Baldovf (Fig. 5).
Karyological analysis of ten specimens from
the Gaibiel population was also performed.
0 Gaibiel
70 -f
60-
50-
40-
30-
20-
10-
Flgure 1. Variability of chromosome number of M. dufouri from the two populations.
CHROMOSOMES OF MELANOPSIS
311
Iff M KKft*h\ hh
2
3
a
$)
Aft <A ftA
K)
11
t*
AA IA 4A
13
VI
115
Figure 2. Modal chromosome sets of Af dufouri inhabiting the Baldovf irrigation system. A. Mitotic
metaphase and Waryotype 2n = 36. B. Meiotic diakinesis, n = 18. Scale bars = 10 mm.
Table 1. Chromosome measurements in ten mitotic metaphases of M. dufouri from the Baldovf
population, 2n = 36.
Chromosome
pair No
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Chromosome
length ((j.m)
M
SD
6.13
5.54
5.23
5.12
4.80
4.53
4.25
4.17
3.82
3.63
3.43
3.33
3.21
3.10
2.87
2.80
2.62
2.35
1.77
1.76
1.51
1.48
0.90
0.84
1.14
1.01
0.73
0.79
0.86
0.80
0.76
0.80
0.77
0.74
0.59
0.53
Relative length
of chromosome (%)
M
SD
8.60
7.73
7.37
7.19
6.62
6.46
5.97
5.88
5.44
5.14
4.82
4.70
4.53
4.36
4.03
3.93
3.79
3.45
0.50
0.57
0.42
0.48
0.81
0.46
0.21
0.21
0.32
0.26
0.31
0.25
0.25
0.23
0.16
0.19
0.27
0.15
Centromere
index (%)
M
SD
20.20
48.52
12.11
22.54
11.62
11.14
22.92
20.93
15.38
16.63
20.48
13.15
26.72
32.34
27.09
38.44
24.06
45.02
3.41
0.58
4.08
8.05
4.58
2.75
0.94
4.88
3.07
2.70
5.09
3.73
4.15
5.20
1.15
7.10
7.34
3.08
M - average mean, SD - standard deviation, m - metacentric, sm - submetacentric,
st - subelocentric, t - telocentric chromosomes
Chromosome
type
st
m
st-t
st-sm
st-t
t-st
st
st
st
st
st
st-t
sm-st
sm
sm
m-sm
st-sm
m
J. BARSIENE, G. TAPIA & D. BARSYTE
312
The chromsomes were counted in 173 good
metaphase plates and in spermatocyte nuclei-at
meiotic pachytene and diakinesis stages. A
diploid complement of 2n = 36 chromosomes
and n = 18 bivalents was determined in 64.4%
of the investigated cells (Figs. 1, 6). Polyploid
nuclei were noted in 12.4% of cells. The poly-
ploidization level in some cases was very high,
reaching 8-12n (140-200 chromosomes) and
even higher levels (Fig. 7).
Table 3 shows the main karyometrical
parameter values and standard deviations of
each chromosome pair in modal karyotypes for
the Gaibiel population. The absolute length of
Table 2. Chromosome measurements in ten mitotic metaphases of M. dufouri from the Baldovt
population, 2n = 34.
Chromosome
pair No
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Chromosome
length (p,m)
M
SD
Relative length
of chromosome (%)
M
SD
Centromere
index ( %)
M
SD
Chromosome
type
4.16
3.71
3.34
3.42
3.20
3.07
2.99
2.86
2.72
2.73
2.49
2.34
2.21
2.15
2.04
1.96
1.83
8.71
7.72
7.35
7.12
6.67
6.43
6.36
6.01
5.79
5.68
5.26
4.93
4.67
4.56
4.38
4.28
3.99
23.37
48.80
13.71
23.29
14.74
12.44
16.41
13.67
12.88
13.49
23.26
17.53
26.52
33.90
30.22
24.48
46.52
st-sm
m
st-t
st
st-t
st-t
st
st-t
st-t
st-t
st-sm
st-t
sm-st
sm-m
sm-st
st-sm
m
0.99
0.99
0.98
0.88
0.81
0.68
0.64
0.60
0.61
0.59
0.51
0.47
0.31
0.34
0.27
0.23
0.28
0.31
0.53
0.56
0.44
0.33
0.17
0.15
0.08
0.13
0.13
0.21
0.26
0.32
0.25
0.45
0.46
0.21
3.68
1.50
7.23
3.03
9.08
3.34
4.52
3.53
3.97
5.68
10.53
4.34
9.80
10.19
9.67
9.88
2.86
Notes see Table 1
Table 3. Chromosome measurements in ten mitotic metaphases of M. dufouri from the Rambla de
Gaibiel population, 2n = 36.
Chromosome
pair No
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Notes see Table 1
Chromosome
length (jjim)
M
SD
Relative length
of chromosome (%)
M
SD
Centromere
index 0fc)
M
SD
Chromosome
type
4.91
4.65
4.29
4.01
3.95
3.77
3.64
3.50
3.38
3.31
3.17
2.99
2.76
2.69
2.52
2.37
2.23
2.19
8.10
7.71
7.18
6.64
6.52
6.23
6.02
5.80
5.63
5.48
5.24
4.95
4.59
4.48
4.23
3.98
3.77
3.48
23.50
49.51
13.98
26.84
13.17
12.91
19.55
16.84
17.18
19.90
18.94
12.86
30.54
32.09
22.00
30.80
17.91
47.81
st-sm
m
st-t
sm
st-t
st-t
st
st
st
st
st
st-t
sm
sm
st-sm
sm
st
m
1.25
1.04
0.64
0.92
0.95
0.91
0.88
0.75
0.66
0.74
0.72
0.65
0.48
0.50
0.36
0.29
0.19
0.43
0.45
0.29
0.50
0.29
0.28
0.27
0.24
0.08
0.15
0.15
0.19
0.21
0.17
0.14
0.23
0.29
0.41
0.38
3.47
0.84
3.95
2.09
3.45
3.17
5.27
4.20
2.44
2.70
1.00
3.01
1.59
5.01
5.35
6.88
2.64
2.49
CHROMOSOMES OF MELANOPSIS
A«
313
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AH
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H#l
13
»
A^
14
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ITA
To
10
A A
Ki
11
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17
A*
1,
A n
7
1:1
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4
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5)
10
14
r.s
K>
IS
AA
11
r/
1»
is)
Figures 3 and 4. Mitotic metaphases and karyotypes of M. dufouri from the Baldovf population. 3. 2n = 34
and small additional chromosome. 4. 2n = 35 and small additional chromosome. Scale bars = 10 mm.
J. BARS>IENE, G. TAPIA & D. BAR$YTE
314
5b
M U tk.1
'I
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AA W A6 ii
IK IA
7
11
II
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1
V.
tk U
U
A4 A^ «*
13
"IIS
H>
14
T/
1H
CHROMOSOMES OF MELANOPS1S
315
Figures 5 and 6. Chromosomes of M. dufouri. 5A. Abnormal meiosis; pachytene with non-conjugating sites of
bivalents and univalent (arrows). 5B. Abnormal meiosis; metaphase I with normal bivalents and one very
small bivalent (arrow). 6A. Oaibiel population; mitotic metaphase and karyotype 2n = 36. 6B. Gaibiel population; meiosis at metaphase I, n = 18. Scale bars = 10 mm.
Figure 7. 205 chromosomes from a highly polyploid (12n) cell of M. dufouri from the Gaibiel locality. Scale
bar = 10 mm.
chromosomes ranged from 2.19 to 4.91 (xm.
Their relative sizes changed from 3.48 to 8.10%
of the total haploid set length. Ten pairs of
complement consist of submetacentric, subtelocentric or subtelotelecentric chromosomes
(Fig. 6A). The 2nd and 18th pairs are metacentric elements.
Interpopulational differences in the ideograms of karyotypes (Fig. 8) were found in
the relative lengths of the 1st, 4th, 10th and
11th chromosome pairs. Interpopulational
differences of centromere indices occurred in
the 1st, 4th, 7th, 11th, 15th and 16th chromosome pairs. Intrapopulational differences of
chromosome morphology among the snails
from the Ullal de Baldovf spring (with 2n = 36
and 2n = 34) were found in the 7th, 8th, 10th
and 16th pairs. We hypothesize that the 17th
pair of the karyotype 2n = 36 was the missing
element in the karyotype 2n = 34, judging from
the chromosome measurements (Fig. 8).
DISCUSSION
Melanopsis species-level taxonomy has proved
a difficult problem for a long time. The wide
range in shell form led some authors to
describe many different species (Bourguignat,
1884, 1886; Pallary, 1926). Others recognised
far fewer species (FeYussac, 1823; Pujante,
1987; Glaubrecht, 1993).
There are several reports of the M. dufouri
morphotype in the Albufera lake (Bofill, 1914;
2 •
0
1
1
2
L1
y
w
!
i
\
\
13
1
1
n n
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x
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a bc
i
3
1
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,\
s3
U>
i
1
L
;
i
•
'
16
;
I <
;
i
•
'
!
'
;
;
«
1
t
'<
x
1
i ; A
!
3
P
y
\
1
17
s
;
I
|
1
i
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j
jl
x
<1
',
\
\
:
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18
«u
j
i
XX )
•
x
)
j
l
(1
i
j
,•
[ I38 1; x(1
;
;
6
8
;
j
)
i
i
y
]
1
*
i
?
i
I
1
;
11
1
(Rambla de Gaibiel)
H. dufouri, 2n=34 (Baldovi)
M. dufouri, 2n=36 (Baldovi)
J
12
i
i
•
i
*
j
^U L
I;
\
;
J
j i
i
3r 1
,
\l I 1 1
10
1
i
n II
S
HelanopsiB dufouri, 2n-36
J
'1
•
!
•
j
j
i
S
1
i
Figure 8. Ideograms of centromere indices of M. dufouri inhabiting the Gaibiel and Baldovi localities.
I
0
i-i
Vx
CD
>
73
p
m
p
•2.
m
CO
>
JO
(sx
CHROMOSOMES OF MELANOPSIS
317
Haas, 1924; Gasull, 1971), whereas in the Ullal sites of the Atlantic Ocean (Staiger, 1950,1954;
de Baldovi (Muntanyeta dels Sants) Gasull Bantock & Cockayne, 1975; Page, 1988; Dixon,
(1971) reported the ocurrence of the morpho- Pascoe, Gibbs & Pasantes, 1994). Robertsonian
type Melanopsis graellsi Villa & Villa (=M. translocations were considered to be one of
tricarinata Bruguiere). These morphotypes the main mechanisms by which chromosome
only differ in their shell morphology and were numbers have changed in this species.
sympatric in the past, as the Ullal de Baldovf
The existence of M. dufouri individuals with
spring was part of the Albufera lake. Robles, predominance of 36,34 and, rarely, 35 chromoCollado & Borreda (1985) state that M. dufouri somes in their tissues cells was observed only in
disappeared in the Albufera lake because of
the Baldovf population, and in addition there
the strong eutrophication it has suffered in were mosaic snail specimens. In many cells
the last years. The separation of the Ullal de containing 35 and 34 chromosomes, small
Baldovf spring from the Albufera lake pre- supernumerary elements indicated considervented the extinction of the current population able meiotic transformation and karyological
and it is possible that the M. dufouri morpho- heterogeneity. We suggest that this phenotype also survived there, though in a very small menon results from interbreeding between
proportion.
snails possessing non-homologous chromosoThe modal karyotype of M. dufouri from mal features. Meanwhile, small supernumerary
both the studied populations consists of 36 elements in the cells of 2n = 35 and 2n = 34
chromosomes. This chromosome number was may be derived by way of chromosome fragdetermined in 36.3% of cells in snail tissues mentation.
from the Ullal de Baldovf spring and in 64.4%
As mentioned previously, our study revealed
of those from the Gaibiel locality. Exceptions significant levels of intra- and inter-individual
to the basic karyotype (2n = 34 and 2n = 35) divergence in the chromosome number of M.
were found in 45% of nuclei in snails from the dufouri collected from the Baldovf locality.
Ullal de Baldovf spring. The high frequencies Possibly the effects of Baldovf water pollution
of these chromosome sets mainly appeared as a were expressed at a cytological level as various
result of inter-individual variation. The intra- chromosomal disturbances. A positive correlaand inter-individual variability of chromosome tion between bioaccumulation of xenobiotics in
number is not influenced by Robertsonian mollusc tissues and chromosome set transfortranslocations. However, hypodiploidy, and to mations has been described (BarSiene, 1994).
a lesser degree, polyploidy, have played a pri- However, the karyotypes of M. dufouri from
mary role. The hypodiploid formation was the Gaibiel locality were more stable. It should
mainly connected with the elimination of small be noted that ecological conditions in this
chromosomes. Pericentric inversions were biotope, located in the mountain region, were
basic factors in the interpopulational differenti- less disturbed than in the agricultural area of
ation of M. dufouri chromosome complements. the Albufera lake irrigation system. The modal
A wide range of chromosome number (from karyotype 2n = 36 was dominant in all speci14 to 36) has been reported in other proso- mens from the Gaibiel population and there
branch species (Patterson, 1969; Nakamura & was no evidence for karyological instability.
Ojima, 1990). The differences in chromosome
On the basis of karyological data it can be
number have occurred without large genome assumed that reproductive barriers between
alterations or Robertsonian translocations various karyomorphs of M. dufouri, or sepa(Nakamura & Ojima, 1990). According to rate species from the Baldovf site are not
Nakamura & Ojima (1990), the tandem fusion
absolute. Abnormal meiosis in some specimens
of smaller chromosomes produced large shows cytogenetical heterogeneity exists.
elements in karyotypes of the genus Semi- These karyological considerations agree with
sulcospira (Mesogastropoda, Pleuroceridae; findings of phenotypic diversity and the exisrelative to Thiaridae). These authors also tence of intermediate morphological forms of
reported that the DNA values of Semisul- M. dufouri from the same locality of Ullal de
cospira are, very constant (3.4-3.7 pg/diploid Baldovf.
cell).
The variation in chromosome number in M.
Significant levels of intra- and inter-individ- dufouri inhabiting Baldovi spring, as well as
ual or interpopulational variation in chromo- interpopulational karyologycal differences of
some number were also shown in dog-whelks those from Baldovf and Gaibiel populations
Nucella lapillus Linne\ prosobranch snails are in accordance with phenotypic diversity of
inhabiting different geographically isolated the genus Melanopsis. Further karyological
318
J. BARSIENE, G. TAPIA & D. BARSYTE
information for other M. dufouri populations
and other Melanopsis species would be useful
for elucidation of problems of their taxonomy
and speciation.
ACKNOWLEDGMENTS
This research was supported by the Valencia Government (Cultural, Educational and Scientific Office)
award to Janina BarSiene, order of 15/04/1993. We
are grateful to Prof. V. Roca, F. Robles and to Dr. A.
Pujante for their valuable discussion on the biology
and ecology of Melanopsis. Many thanks are due to J.
Martin and M. Lafuente (University of Valencia) for
their assistance in the collection of field samples, and
to D. Elder and P. Scarlett for the supervision of the
English. We are also grateful to anonymous reviewers for their helpful comments.
sujet Memoires de la Society d'Histoire Naturelle,
Paris, 1:132-164.
GASULL, L. 1971. Fauna malacoldgica de las aguas
continentales dulces y salobres del sudeste ibenco.
Boletin de la Sociedad de Historia Natural,
Baleares, 16: 23-83.
GLAUBRECHT, M. 1993. Mapping the diversity:
Geographical distribution of the freshwater
snail Melanopsis (Gastropoda: ? Cerithioidea:
Melanopsidae) with focus on its systematics in the
Mediterranean Basin. Mitteilungen aus den Hamburgischen Zoologisch Museum und Institut, 90:
41-97.
HAAS, F. 1924. Los moluscos de agua dulce de la
Albufera de Valencia. Annales del Instituto Genetica y Ttcnico, Valencia, 16:1-13.
JACOB, J. 1959. The chromosomes of six melaniid
snails (Gastropoda: Prosobranchia). Cytologia, 24:
487-197.
LEVAN, A., FREDGA, K. & SANDBERG, A. 1964.
Nomenclature for centromere position on chromosomes. Hereditas, 52: 201-220.
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