Content uploaded by Kōji Yokogawa
Author content
All content in this area was uploaded by Kōji Yokogawa on May 18, 2025
Content may be subject to copyright.
SUISANZOSHOKU 47(3), 363-368 (1999)
Morphological and Genetic Characteristics in Two Forms
of Gibbose Conch, Gibberulus gibberulus gibbosus
Kð¯ji YOKOGAWA *1
(Accepted July 16, 1999)
Abstract: Morphological and genetic features in two forms (white form and purple form) of gibbose
conch, Gibberulus gibberulus gibbosus, were examined. Morphological characters of the two forms
showed no significant differences except the shell coloration. Isozymes detected by horizontal
starch-gel electrophoresis were used as genetic markers of 22 loci presumed. There were no
significant differences between the two forms in the genetic variability and allelic frequencies at any
of the loci examined. The genetic distance (D value) between the two forms, calculated from
isozymic allele frequencies was 0.0019, being below the inter-subpopulational level. The
morphological and genetic results suggested that the white form and the purple form compose the
unique Mendelian population, they represented an intra-specific variation.
Key words: Gibberulus gibberulus gibbosus; Morphology; Genetics; Isozyme
Gibbose conch, Gibberulus gibberulus gibbosus
(Roiling) (Gastropoda: Strombiidae), is a com-
mon tropical shell species in the Pacific tidal
waters. It is utilized as food in some tropical
region where it abundantly occurs1,2). In this
species, it is known that there are two distinct
forms; aperture with white coloration (hereafter
called white form) and that with purple coloration
(hereafter called purple form)1-4). In addition, the
purple form has a more contrasty dappled pat-
tern on the shell surface than the white form1).
Since the two forms do not represent sexual
dimorphism2,4), probabilities that they are intras-
pecific variation or distinct species can be consid-
ered. For this reason, the present study was
carried out to examine morphological and genetic
features in the two forms and assess their tax-
onomic status.
Materials and Methods
Specimens examined in this study were col-
lected around sandy bank located between
Fukapanari (Sotobanare) Island and Uchipanari
(Uchibanare) Island, which are adjacent to
Iriomote Island, Taketomi-cho, Okinawa Prefec-
ture, Japan, on September 13, 1997 by snorkel-
ing. The sampled specimens were immediately
transported to the author's laboratory by a cool
delivery service, and they were preserved in a
deep refrigerator at -80•Ž. The specimens com-
prised 36 individuals of the white form and 8 in-
dividuals of the purple form. Sizes (shell height)
of the specimens were 32.8-54.6 mm (average
41.8 mm) in the white form and 34.7-46.2 mm
(average 41.0 mm) in the purple form.
Morphologically, 9 sections in the shell shown
in Fig. 1 were measured and each proportion
was expressed as a percentage of the shell
height (SH, in mm). In addition, total body
weight (shell with soft part, BW, in g) was
weighed and weight index (WI) was calculated
by the following formula:
WI=BW/SH3•~105
Immature individuals whose shells were in-
complete at the outer lip part were omitted from
the morphological analysis. Number of the omit-
ted individuals was both one in the two forms.
Isozymes detected by horizontal starch-gel
*1 Kagawa Prefectural Fisheries Experimental Station , 75-5 Yashimahigashimachi, Takamatsu, Kagawa 761-0111, Japan.
364 K. Yokogawa
Fig. 1. Measured sections of shell. SH, Shell height; SD, Shell diameter; SW , Shell width; AL,
Aperture length; BWL, Body whorl length; SPH, Spire height; BWD , Body whorl diameter;
SWD, Second whorl diameter; TWD, Third whorl diameter.
electrophoresis were used as genetic markers.
Each about 0.5g of muscle and visceral mass
tissue was removed from the specimens in partial
frozen condition, and it was put into a 1.5 ml micro
tube. The sampled tissue was homogenized with
100 ƒÊl and 50 ƒÊl of distilled water, respectively.
The samples were centrifuged at 15, 000 rpm for
10 minutes under 0•Ž condition, and the super-
natant fluid was used for the electrophoresis. The
following experimental methods and expression of
loci and alleles were as described by Yokogawa5).
For esterase from the muscle tissue in particular,
the thin polyacrylamide-gel electrophoresis after
Taniguchi and Tashima6) was introduced. For the
genetic analysis, all the collected individuals were
examined.
Results
Morphological Characters
Results of the morphological examinations are
shown in Table 1. All the proportions and the
Table 1. Morphometric characteristics of white form and purple form with results of t tests between both average values
*1 Risk percentage for t value .
*2 Percentage of shell height .
Letters in parenthese represent numbers of individuals examined in each form.
365
Features in Two Forms of Gibbose Conch
weight index (WI) of the two forms showed very
close values to each other and the t tests be-
tween the two forms did not give significance of
less than 5% at any of the characters (Table 1).
This indicated that there were no morphological
differences between the two forms except for
the shell coloration mentioned earlier.
Genetic Characters
By electrophoresis, 14 enzymes and 1 non-
enzymic protein were detected and 22 loci were
presumed (Table 2).
Fitness of the allelic frequencies in polymor-
phic loci, according to Hardy-Weinberg equilib-
rium, was examined by chi-square test in the
white form, purple form and both the forms
pooled (Table 3). Because no ƒÔ2 values were
significant at the 5% level in the white and
purple forms, they were both regarded to be
originated from simple Mendelian populations.
Also, the pooled population did not show signifi-
cance at any locus, unlike the case of the two
Table 2. Enzymes, protein and tissues examined
Table 3. Chi-square tests of fitness for Hardy-Weinberg equilibrium in groups of white form, purple form and both forms
pooled
* 1 Number of individuals in which genotypes were revealed at each locus.
* 2 Risk percentage to reject the equilibrium .
366 K. Yokogawa
forms of a pen shell, Atrina pectinata reported
by Yokogawa7), in which the two forms were
clarified to be the distinct species.
Values to indicate the genetic features in the
white form, purple form and both the forms
pooled, are shown in Table 4. These values
were fairly similar in the two forms and the
pooled population. The heterozygosity ratio
(Ho/He) indicated approximately 1 in both the
forms (Table 4), suggesting no prominent excess
of homozygotes or heterozygotes.
Allelic frequencies at the 22 loci with ƒÔ2
heterogeneities between the two forms are
shown in Table 5. In general, the allelic frequen-
cies were very similar between the two forms.
The ƒÔ2 heterogeneities between the two forms
resulted in too small values to reach the signifi-
cant level of 5% at any of the loci examined
(Table 5).
The genetic distance (D value)8) between the
two forms, calculated from isozymic allele fre-
quencies resulted in 0.0019, being a figure below
the inter-populational level9,10)
Discussion
The results given in this study showed that
there were no morphological and genetic differ-
ences except for the shell coloration between
the two forms of Gibberulus gibberulus gibbosus.
This suggests that the two forms are not distinct
species, they may reflect the genetic variation
within a species. The probability can be
supported by the facts that the two forms do not
represent sexual dimorphism2,4) and they are not
caused by environmental factors because the
two forms inhabit together anywhere1,2,4), furth-
er the two forms do not represent distinct spe-
cies.
Ueno4) mentioned that there were no morpho-
logical differences except the aperture coloration
and regarded the two forms as the same species
although he showed no data on that. While
Tsuchida and Shimura1) examined a regression
between shell height (SH) and shell diameter
(SD) in the two forms of this species from
Fiji by using many specimens, detecting a statis-
tically significant difference between the two
forms at the inclination of the linear regression
formulae. Namely, the SD of the purple form is
relatively greater than that of the white form. In
this study, however, the difference of the
SD/SH between the two forms was not signifi-
cant (Table 1)
. Supposing the phenomenon detected by
Tsuchida and Shimural) were universal, no sig-
nificance recognized in this study could be
caused by the small numbers of specimens, in
particular by that of the purple form. If so, the
proportional difference detected by them can
reflect the genetic variation as same as the shell
coloration.
Yokogawa11-14) examined total biological fea-
tures in two forms of Hirase's scallop, Volachla-
mys hirasei, concluding that the two forms rep-
resent genetic dimorphism, and both the forms
including much variation in the shell coloration
and morphology. This suggests that there can be
genetically coded morphological polymorphism
also in the shell proportion. Thus in G. gibberu-
lus gibbosus, the allele(s) for the morphological
characteristic(s) can link with that(those) for
the coloration.
Tsuchida and Shimura1) purchased an amount
of this species, which comprised 266 individuals
(41.2%) of the white form and 380 individuals
(58.8%) of the purple form at Suva Market, Fiji.
Similarly, Cernohorsky (1965) reported that the
Fijian G. gibberulus gibbosus populations compris-
ed almost equal numbers of the two forms.
Table 4. Genetic features in groups of white form, purple
form and both forms pooled
P* : Polymorphism less than 0.95.
P : Polimorphism over 0.95.
Ho : Observed heterozygosity.
He : Expected heterozygosity.
Letters in parenthese represent numbers of individuals
examined in each group.
367
Features in Two Forms of Gibbose Conch
Table 5. Allelic frequencies of white and purple forms with ƒÔ2 heterogeneities between both frequencies
* 1 Degree of freedom .
* 2 Risk percentage for chi -square value .
In this study, however, the specimens consist
of 36 individuals (81.8%) of the white form and 8
individuals (18.2%) of the purple form, consider-
ably differing from the Fijian populations. This
may reflect the differences in genetic composi-
tion between the Fijian and the Japanese popula-
tions, especially in the frequencies of alleles for
the shell coloration. The Japanese archipelago is
located at the northern margin of distribution of
this species15), where genetically independent
local populations of the tropical shell species
occasionally can be established by the Black
Current * 2. This may be a reason why the Fijian
and the Japanese populations genetically differ
* 2 Yokogawa , unpublished data.
368 K. Yokogawa
from each other.
Masuda and Shinomiya16) examined genetic
characteristics of a nautilus, Nautilus pompilius,
populations from Fiji and the Philippines, detect-
ing considerable differences between the two
populations. This information suggests that there
can be genetic isolation between distant popula-
tions, and add weight to the probability that the
Fijian and the Japanese G. gibberulus gibbosus
populations are genetically different.
Acknowledgements
The author is grateful to Miss Ikuko Makino,
Nihon Veterinary and Animal Science University,
who assisted in transporting the specimens used
in this study. Also, I wish to thank Mr. Thomas
Verghese, University of Malaya, Malaysia, for
grammatically checking the manuscript.
References
1) Tsuchida, E. and S. Shimura (1996): Some commercial
mollusks collected at Suva market, Fiji (2). Chiribotan,
27(1), 16-20 (in Japanese).
2) Cernohorsky, W. O. (1965): The Strombiidae in Fiji.
Rec. Fiji Mus., 1(1), 1-18, 6 pls.
3) Wang, R., Q. Zhang, X. Qu, Y. Cai, and Y. Zhang
(1988): Coloured illustrations of aquatic mollusks in
China. Zhejiang Publ. House Sci. Tech., Hangzhou, iii
+v+x+255 p. (in Chinese).
4) Ueno, S. (1994): Why does gibboue conch, which in
-habits sandy beach of Iriomote Island gather? Mar.
Sci. Mus. Tokai Univ., 24(5), 2-3, 1 pl. (in Japanese).
5) Yokogawa, K. (1997): Morphological and genetic dif-
ferences between Japanese and Chinese red ark shell
Scapharca broughtonii. Fisheries Sci., 63(3), 332-337.
6) Taniguchi, N. and K. Tashima (1978): Genetic varia
tion of liver esterase in red sea bream. Bull. Japan.
Soc. Sci. Fish., 44(6), 619-622 (in Japanese).
7) Yokogawa, K. (1996): Genetic divergence in two
forms of pen shell Atrina pectinata. Venus, 55(1), 25-
39 (in Japanese).
8) Nei, M. (1972): Genetic distance between populations.
Amer. Nat., 106, 283-292.
9) Nei, M. (1990): Molecular evolutionary genetics (Trans
-lated from English by T. Goj•¬bori and N. Sait•¬). Baifu
kan, Tokyo, vii+433 p. (in Japanese).
10) Japanese Society to Protect Aquatic Resources (Nihon-
Suisanshigen-Hogokyokai) eds. (1989): Population
analyses of fishes and shellfishes by isozyme. Nihon-
Suisanshigen-Hogokyokai, Tokyo, 555 p. (in Japanese).
11) Yokogawa, K. (1997): Characteristics in two forms of
Hirase's scallop Volachlamys hirasei-1, shell morpholo-
gy. Venus, 56(4), 319-329 (in Japanese).
12) Yokogawa, K. (1997): Characteristics in two forms of
Hirase's scallop Volachlamys hirasei-2, soft part mor
phology and its seasonal changes. Venus, 56(4), 331-
339 (in Japanese).
13) Yokogawa, K. (1998): Characteristics in two forms of
Hirase's scallop Volachlamys hirasei-3, age and growth.
Venus, 57(1), 49-56. (in Japanese).
14) Yokogawa, K. (1998): Characteristics in two forms of
Hirase's scallop Volachlamys hirasei-4, genetic charac
- ters. Venus, 57(1), 57-71 (in Japanese).
15) Arakawa, Y. (1986): Gibbose conch Gibberulus gibberu
lus gibbosus (Rð±ding), in •gThe Great Animal Illustrated
Encyclopedia, Mollusca•h(ed. by T. Okutani), Sekai-
bunkasha, Tokyo, pp. 94 (in Japanese).
16) Masuda, Y. and A. Shinomiya (1986): Genetic variabil
ity in a nautilus Nautilus pompilius. Monthly Ocean Sci
ence, 18(10), 661-665 (in Japanese).
ネ ジマ ガキ ガ イ2型 の形 態 的お よび遺伝 的特 徴
横川浩治
ネ ジマ ガキ ガ イ2型(殻 口の 白 色型 と紫 色型)の 形 態 的 お よび遺 伝 的差 異 に つい て 調べ た 。殻 の 外
部形 態 につ い て,型 の標 徴 で あ る殻 の色 彩 を 除 き,調 べ た す べ ての形 質 に お いて 両型 の 平 均値 に は全
く有 意差 は認 め られ なか った 。遺 伝 形 質 と して ア イ ソザ イ ム を調 べ22遺 伝 子 座 を推 定 したが,両 型 の
遺伝 的諸 特 性 値 は非 常 に類 似 した値 を示 し,さ らに 遺伝 子 頻 度 につ い て も両 型 問 で有 意差 が 認 め られ
た遺 伝 子座 は全 くな か った。 ア イ ソザ イ ム系 遺 伝子 に よる両 集 団 問の 遺 伝 的距 離(D値)は0.0019と
な り,地 域集 団 問 以下 の 水 準 であ っ た。 以 上 の形 態 的 お よび 遺伝 的 解析 結 果 か ら,ネ ジマ ガキ ガ イの
白色型 と紫色 型は同一 種内の遺伝 的多型現 象で ある可能性 が強 く示唆 された。
