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[Original] Regional Difference of Ray Number Variation in a Starfish, Patiria pectinifera

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Patiria pectinifera, a common littoral starfish in Japan, is a 5-rayed species, including the individuals with 4 or 6 to 9 rays. In this research, the frequency of non-5-rayed individuals was investigated in the Pacific coast of eastern Japan (Miyagi, Ibaraki and Kanagawa). Interestingly, the frequency in Kanagawa (5.6%) was significantly greater than those in Miyagi (3.0%) and Ibaraki (3.0%). The 6-rayed individuals occupied 81% of non-5-rayed population similarly in these areas. These results imply that similar mechanism produces non-5-rayed individuals in these areas, but it functions more actively in Kanagawa. Furthermore, the mechanism might be specific in P. pectinifera, because the individual variation was not found in Aquilonastra minor, a closely-related 5-rayed species, inhabiting the same area to P. pectinifera.
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[Original]
Regional Difference of Ray Number Variation in a Starfish,
Patiria pectinifera
Osamu Kawase*1, Ryohei Furukawa*2
*1 Department of Biology, Premedical Sciences, Dokkyo Medical University, Mibu-machi,
Shimotsuga-gun, Tochigi, 321-0293, osamuk@dokkyomed.ac.jp
*2 Iwate Tohoku Medical Megabank Organization, Iwate Medical University, Nishitokuta,
Yahaba-cho, Shiwa-gun, Iwate 028-3694, rfuru@iwate-med.ac.jp
Abstract
Patiria pectinifera
, a common littoral starfish in Japan, is a 5-rayed species, including the
individuals with 4 or 6 to 9 rays. In this research, the frequency of non-5-rayed individuals
was investigated in the Pacific coast of eastern Japan (Miyagi, Ibaraki and Kanagawa).
Interestingly, the frequency in Kanagawa (5.6%) was significantly greater than those in
Miyagi (3.0%) and Ibaraki (3.0%). The 6-rayed individuals occupied 81% of non-5-rayed
population similarly in these areas. These results imply that similar mechanism produces
non-5-rayed individuals in these areas, but it functions more actively in Kanagawa.
Furthermore, the mechanism might be specific in
P. pectinifera
, because the individual
variation was not found in
Aquilonastra minor
, a closely-related 5-rayed species, inhabiting
the same area to
P. pectinifera
.
Key words: starfish,
Patiria pectinifera
, ray number, individual variation
1. Introduction
Pentaradial symmetry is one of the common
features of echinoderms, i.e. starfish, brittle
stars, sea urchins, sea cucumbers, and sea lilies.
However, starfish include some species with
individual variation in ray number. Practically,
the species with more than 5 rays (multi-rayed
species), for example
Luidia maculata
(7 to 10
rays),
Acanthaster planci
(14 to 18),
Solaster
dawsoni
(8 to 13), have the variation (Saba and
Irimura, 2011). Furthermore, asexual
reproduction causes the variation owing to the
frequent unequal division and inaccurate
regeneration, as it is seen in
Aquilonastra
5-rayed
Non-5-rayed
Figure 1 Individual variation in ray
number in
P. pectinifera
Pictures of 5-rayed and non-5-rayed (4-, 6-
and 7-rayed) individuals were taken on the
board ruled into 10 mm squares.
受領日 2014 年 1 月 29 日
Annual Report of Premedical Sciences, Dokkyo Medical University, 3: 49-52, March, 2014
獨協医科大学基本医学年報 第 3 号 49-52 頁 2014 年 3
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anomala
,
Pseudonepanthia briareus
,
Echinaster luzonicus
,
Coscinasterias acutispina
and
Calasterias toyamensis
(Hayashi, 1975, Saba and Irimura, 2011).
A pentagonal shaped starfish,
Patiria pectinifera
is common in Japanese coast. Although
they are not multi-rayed species and do not reproduce asexually, they have individual ray
number variation, in which 4-rayed or 6- to 9-rayed individuals exist besides major 5-rayed
individuals (Fig. 1). Therefore, the mechanism, producing the variation in this species,
might be different from the cases in multi-rayed species and asexually reproducing species.
In this research, we investigated the frequency of non-5-rayed individuals in
P.
pectinifera
, to create the basis for understanding the ray number determinant.
2. Materials and Methods
Specimens of
P. pectinifera
were observed at Kappazawa, Bentensaki and Tsubakishima,
Minamisanriku in Miyagi, at Hiraiso, Hitachinaka in Ibaraki, and at Morito, Hayama and
Hashirimizu, Yokosuka in Kanagawa. Specimens of
Aquilonastra minor
were observed at
Sakamoto and Kanera, Minamisanriku. In each point, the ratio of non-5-rayed individuals
was investigated, and SCUBA was used depending on the depth. The density of
P.
pectinifera
in each point was measured by line census in Minamisanriku. To analyze the
regional difference, chi-square test and following Ryan's method were used.
3. Results and Discussion
We investigated the frequency of non-5-rayed individuals of
P. pectinifera
in three areas,
Miyagi, Ibaraki and Kanagawa (Fig. 2, Table 1). Surprisingly, the frequency in Kanagawa
was 5.6%, which was significantly greater than those in Miyagi (3.0%) and Ibaraki (3.0%).
According to the research of Sanin Kaigan Nature Museum, it was 1.0% (3/260) in Iwami,
Tottori (The article on 3 September 2010 in MSN
Sankei News, http://sankei.jp.msn.com/). Thus, the
regional difference was clearly indicated although
the cause of it was unknown.
If the ray number is determined genetically,
some selective pressures, which profit non-5-rayed
individuals, increase the frequency. It was reported
that the degree of genetic polymorphism in this
species was much higher than many other shallow
water echinoderms and the degree was diverse
regionally (Matsuoka and Asano, 2003). Therefore,
the frequency of non-5-rayed individuals might
reflect the degree of polymorphism of genes,
designing the body shape.
Figure 2 Sites of investigation
Minamisanriku,
Miyagi
Hitachinaka,
Ibaraki
Hayama,
Kanagawa
Yokosuka,
Kanagawa
Osamu Kawase
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Table 1 The frequency of non-5-rayed individuals in each area
Area
(City/Town) Point Date Frequency
Density
(/10 m2)Frequency
(Area Total)
Ray Number
(Area Total)
Four Six Seven
Miyagi
(Minamisanriku)
Kappazawa 2010.01.13 4.1%
(5/122) 2.0
3.0%
(54/1799) 5 44 5
Bentensaki 2011.10.05 3.3%
(3/92) 2.7
Tsubakishima 2010.01.28 2.9%
(42/1457) 146.0
2011.10.11 3.1%
(4/128) 32.0
Ibaraki
(Hitachinaka) Hiraiso 2012.06.04 3.0%
(42/1391) - 3.0%
(42/1391) 5 34 3
Kanagawa
(Hayama) Morito
2010.04.15 7.2%
(13/181)
- 5.6%*
(21/371) 3 17 1
2012.05.07 5.8%
(7/121)
(Yokosuka) Hashirimizu 2012.05.06 1.4%
(1/69)
* The value was significantly greater than the others (p < 0.05).
Moreover, the water quality is possibly related to the regional difference. The seawater
quality in Kanagawa should be different from the others, because the warm Kuroshio
current, flowing northeast along the Pacific coast, should influence the quality in Kanagawa
more strongly than the other areas. Furthermore, Kanagawa (the population density:
3760/km2) is congested much more than Miyagi (320/km2) and Ibaraki (480/km2). The water
pollution in Kanagawa might disrupt the body formation and increase the frequency of
non-5-rayed individuals.
Tsunami after the Eastern Japan Earthquake severely damaged the animals and algae
in Minamisanriku, and the starfish should have suffered accidental body breakage (Aoki
et
al.
, 2013). If the inaccurate regeneration had occurred after the breakage, non-5-rayed
individuals would have increased after the Tsunami. But, the frequencies were similar at
Tsubakishima before (28 January 2010) and after (11 October 2011) the Tsunami. These
results indicated that the ray number variation is not the result of regeneration error.
Therefore, the frequency of non-5-rayed individuals does not reflect the seriousness of the
natural disturbance in each area (Table 1).
On the other hand, the relation between animal density and the frequency was not
observed by comparing three points in Minamisanriku. Although the density at
Tsubakishima (146 animals/10m2) was much higher than those at the others, the ratios of
non-5-rayed individuals were similar in these points (Table 1).
Whichever factor affects, the similar mechanism should produce non-5-rayed individuals
in these areas. This presumption was supported by the results that 6-rayed individuals
accounted for 81% of non-5-rayed population similarly in these areas (Table 1). But, the
factor, affecting the frequency, seemed to be more active in Kanagawa.
The closely-related species,
A. minor
, is a standard 5-rayed starfish and inhabits similar
area to
P. pectinifera
(Hayashi, 1974). We also investigated the frequency of non-5-rayed
individuals in
A. minor
. But, no individual, carrying more or less than 5 rays, was found in
87 individuals observed in Minamisanriku. Therefore, the mechanism and factor,
Ray number variation in starsh
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determining individual ray number in
P. pectinifera
, is probably species specific.
In this research, we showed the regional difference in the frequency of non-5-rayed
individuals. Various causes, such as genetic difference, environmental effect, etc., are
considered as the candidates to determine the individual ray number. The animal
experiments must give answer conclusively. For example, breeding the starfish in seawaters
from different areas will indicate the effect of water quality. Crossbreeding of non-5-rayed
individuals will prove the genetic regulation. The mechanism, designing the animal body
shape, is an important subject in biological research, and we hope that ray number variation
in starfish will be a clue to unravel the mystery.
4. Acknowledgments
We were grateful to Osamu Abe, Akihiro Dazai, Junko Miura and Masanori Sato
(Shizugawa Nature Center), and Takuji Kintaka (Aqua World, Ibaraki Prefectural Oarai
Aquarium) for helping us to observe animals.
5. References
Aoki M., Endo H., Horikoshi A., Agatsuma Y., 2013, Dynamics of the rocky subtidal
ecosystem after the Tohoku Pacific Earthquake, Journal of Integrated Field Science, 10:
32
Hayashi R., 1974, A new sea-star from Japan,
Asterina minor
sp. nov., Proceedings of the
Japanese Society of Systematic Zoology, 10: 41-44
Hayashi R., 1975, A new sea-star of Coscinasterinae from Toyama bay, Annotationes
Zoologicae Japonenses, 48: 198-202
Matsuoka N., Asano H., 2003, Genetic variation in northern Japanese populations of the
starfish
Asterina pectinifera
, Zoological Science, 20(8): 985-988
Saba M., Irimura S., 2011, Sea stars and brittle stars in Japanese waters, 135 pages,
Hankyu Communications, Japan
Osamu Kawase
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ResearchGate has not been able to resolve any citations for this publication.
Article
The starfish Asterina pectinifera of the family Asterinidae is endemic Japanese species and commonly found in Japanese waters. In order to examine the degree of genetic variation and the maintenance mechanism of polymorphism within population, we studied the allozyme variation in five northern Japanese local populations of the starfish by electrophoresis. The species showed much higher genetic variability than many other shallow water echinoderms. Based on other allozyme studies and the ecological data, it was suggested that the high genetic variation of the starfish was closely related to the population size. Additionally, the relation between the degree of enzyme variation and the quaternary structure of enzymes was also examined, and the results suggested the close relation between the enzyme variability and functional constraints.
Dynamics of the rocky subtidal ecosystem after the Tohoku Pacific Earthquake
  • M Aoki
  • H Endo
  • A Horikoshi
  • Y Agatsuma
Aoki M., Endo H., Horikoshi A., Agatsuma Y., 2013, Dynamics of the rocky subtidal ecosystem after the Tohoku Pacific Earthquake, Journal of Integrated Field Science, 10: 32
A new sea-star from Japan, Asterina minor sp
  • R Hayashi
Hayashi R., 1974, A new sea-star from Japan, Asterina minor sp. nov., Proceedings of the Japanese Society of Systematic Zoology, 10: 41-44
A new sea-star of Coscinasterinae from Toyama bay
  • R Hayashi
Hayashi R., 1975, A new sea-star of Coscinasterinae from Toyama bay, Annotationes Zoologicae Japonenses, 48: 198-202