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nes vENus (Jap. Jour. Marac.) Vol. 3S, No. 2 (1979) : 135-140

t] v 7" h" i Crass ostrea rhizophorae (GUILDING,1828) ot9W

pt pt pt .(: . k7V F. Ti7Lttr"-`p , M. E. v Y 7IL= 'f-iY

･ £ ' A. 7 fj"!vpt' 7d if'7-, M. 7' u'ri tJk

The Karyotype of CTassostTea rhizophorae (GulLDING, 1828)*

Faustino RoDRIGuEz-RoMERo, Manuel URIBE-ALCocER,

Alfredo LAGuARDA-FIGuERAs and Maria Esther DIUPOTEX-CHoNG

(Universidad Nacional Aut6noma de Mexico, Centro de Ciencias del

Mar y Limnolegia, Mexico, D.F., Mcxice)

Abstraet

The chromQsomes of Ce"assostrea rhizophorae (GulLDING, 1828) from

Estero del Pargo, Isla del Carmen, Campeche, Mexico, were analysed by using routine eytogenetie teehniques of genadal tissue to obtain mitotic and meiotic chromosomes.

The diploid number (2n) was 20. All chromosomes were biarmed and the

arm number was 40. From the cytogenetic point of view, the karyotype of

this species was only metacentrie and submetacentric chromosomes as in the

ease of other Crassostrea species alreudy studied.

Introduction

Cra,ssostrea rhizophoo'ae, as other speeies of the genus, has been confused

with respect to the identifieation ef its populations in the different localities

where they are found.

This problem has been solved in part by studies of the morphology of

the shell. Nevertheless, these studies have not been useful when the charae-

teristics of each species are not well defined. For this reason it has been

necessary to consider other aspects related to the biology of these molluscs.

0ne important aspeet that has helped to deterrnine whether an individual

belongs to the genus Crassostrea or the genus Ost?'ea is the differenee in internal

anatomy. In seareh of features at the eytological level that can be utilized

in resolving the systematics Qf oysters of closely related populations, AHMED

and SpARKs (1967a, 1967b), LoNGwELL et al. (1967), MENZEL (1968a, 1968b)

and others, made studies at the ehrornosomic level in order to compare the

';` Contribution 189 of the Centro de Cicncias del Mar y Limno]ogfa, U.N.A.M.

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l36 VENUS: Vol. 38, No.2(1979)

eytotaxonomy of these organisms. However, karyotypic studies of the two

genera have not been completed and although various Crassostrea species have

been already studied (LoNGwELL et al., 1967; RoDRIGuEz-RoMERo et al., 1979),

the genus Ostrea has been less studied from the eytogenetieal point of view. These chromosomic studies, and others dealing with physiology (STAuBER, 1947) and biochemistry (WILKINs and MATHERS, 1972; NASCIMENTO and

RODRIGuEs, 1976), ean be valuable in eomparing and better understanding the

biology and taxonomy of the Ostreidae at interespecifie Ievel.

For these reasons, it is of interest to know the characteristies of the

ehromosomie cernplement of these speeies in order to have cytogenetie data

that can add to the knowledge of the taxonomy and phylogeny of the oysters. In this present work, the results of karyotypie analysis of the mangrove oyster Crassostrea･ rhi2ophorae are reported for specimens of populations located in Isla del Carmen, Campeche, Mexieo.

Material and methods

Ten specimens from Estero del Pargo, Ciudad del Carmen, Campeehe,

Mexico, were proeessed to obtain chromosomes by the air drying technique

used by RODBIGuEz-RoMERo et al. (1978). In each organism, the ehromosomes of one mitotic field were measured, statistically analyzed and classified aecording to LEvAN et at., (1964) and AL-

AIsH (1969).

Results

The diploid number obtained was 20 (2n). All ehromosomes were biarmed

asxtK"2 k" } as IS 3 4 s

"･k "K7 IX -x as s 6 8 g !e

Fig. 1.The"pkaryotype of Crassostrea rhi2obhorae -7" h' i･ 0 ･tu' av

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RODRIGuEz-RoMERo et al. :Karyotype of Crassostrea rhixophorae 137

tt/t.t/tt ..tt .tt/.. tt.t. tt tt t. t.t tt ,e '///'/"'. ti,titl':,,t.; '.1;'.. i/'.' ,. "'i ' '"' ttttt ttt"t tt t/ t/ t t/ tt e tt lsi:･'';i･ ' 'ti''":/1"1'11"'l''" s ' "' ".tw, 'tt pt - \k. 1･ /xi･ , ilSki･fieN'"xs"!x,''k/ - '1,･,･k ,,' ･ ･"･

n-･ ts

t t/ ' ' ' '･t/it.L･,i･･･,',/,,/,･･';',･,l,･･ /ttt"･,?'/, ,i,-.-.･･, ･,･. , st1 ,,t; ttt/ ,, ttt tt.tttt .//tt//ttt/ ttt. tt tt ' ''.lnt./// ,," /t/ t /t ttt./ ttt..t.ttttt.. t/ //t tt,' t/ ',,',t t '', .,',L/, t, ,, ,, tttt. t..t.tt ,, ttt tt ttt ttt t t., .. , ,ttt/. . t ,,. , ,. t/ ., ./., /,. /, / t tt t., //t=, , t/tttt, 'lx･- t , . , .g, te $eqesasts ･ tltt/t/t t /,t//,,./t,. '"' ' ""ts ･ t t"'tt tt tt tt t/ / tt tt t tt/ Nsiyt/ t tt ttt ' ,,,. ･11･ k*ts ,.,,,･･,,,･･1,,' ,Xl･ag.･･-,･ .t ',l / .t tttt . ttt t/ t/tt tttt tt t t ttt.tttt . /t .t t/t . ttt .//tt t ,, t '.tt//'tl. 't/ti.t/t/,.,.ttt /t,,;',t'' ' t,' t/ ,'t '.. , /t,,' t /t /t t t ,as,.-, 'Se}''i t /t t t tttttt ttt/t t ,wk',･･''i,･'IL,//,,i,Y,'.'',':'･/i.,'-/1, ,',' 1,i'' ttt ' t tt tt t ttll/"ttt '. ttt ',,, - ･ # s'.' ･'･ -',･ pt tt t '.･･'･ ,,,i;' r.,,,,,,'i:.･ ,{ t･'' /･t/t't'"r:..tt/''/t,/' t./t,'t,ttt, ,' ,ta. ,,? ," ,' ny, ts'･･'l･,t･lit･,1,,･l-ill･･i･,,eq･;l}･ll･Elilliiii･', ee Sgi//i,?rci',,t/t t Waseetsigeliee' "'''"""S,:i',-'i,l'{, ,.t.t...t,t,t,.t.t/:,..,/t:./t.ll:l.' ,. ･., ,,/･,,,･ }･Silifii,eex- , t".,,l, ,/.･ t,,l, /tttttt/t!tttttil/ttt/tttt: ' t/t tt t/t/tt ･ tttttt t tttt / /''t'''tt't;'''tt'/t''//ti"'t'//"'t"/' ,, l,iiillg,･x･ig,,:,{,･ , ,;si//i

Fig. 2. Mitotlc fields of Crassostrea rhi=oPhorae. h V 7' V)'i Ol>paue 2a-d: 2n-20. 2e: Tetrapleid g!iNPS

and the arm number was 40,

The ehromosomes of C. rhi2ophorae differ little in size except for the first and the last pairs. The pairs 1, 3, 5, 8 and 10 are metacentries and the pairs 2, 4, 6, 7 and 9 are submetaeentrics (Table 1, Fig. 1).

Other features of ehromosome morphology, sueh as seeondary eonstrictions,

satellites and sexual ehromosomes, were not identified (Figs. 2-3).

Meiotic eomplexes at diakinesis showed 10 bivalent figures.

Discussion

Sincethe original descriptiens of GulLDING in 1828, populations of

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VENUS ： VoL 38 No ．2 1979 138 ， （ ）

lDEOGRAM OF

Fig ．3． The iCleogram of Crassostrea rhizoPhorae showing only biarmed chromosomes ordered in two groups ： metacentrlcs and submetacentrics ． カ リ ブ ガ キ の 染 色 休 図 つ 2 表 。 双 腕 を も 群 （中 部付 着， 次 中 部 付 着 ） の み か ら な る 。

Table 1． Relative values for the identification of the chromosomes of

CrassostrearhigoPhorea （GulLDING ， 1828 ）． カ リ ブ ガ キ 各 染色 体 同定 の た め の 相 対 値 Total Chromosome P11 Q Length RL138 CI AR Classificatien

1 ．727 13 ．7813 25．5021 ．86116 45．9634 1．171 m

2 ．59 ，9811 ．4820 ．97113 ．9145 ．861 sm

3 ．56 ．3312 ．8319 ．43108 ．6034 ．101 m

4 ．938 ．9410 ．8718 ．20102 ．8745 ．861 sm

5 ，516 ．3811 ．8917 ．8697 ，0534 ，2J1 m

6 ．175 ．8011 ．9716 ，8589 ．3332 ．912 sm

7 ，276 ．118 ．3815 ．2085 ．1743 ．IOl sm

8 ．784 ．949 ．7314 ，6680 ，1032 ，312 m

9 ．735 ．956 ．7012 ．0566 ，1744 。101 sm

10 ．5 ，78 ．28 ．87 ．78 ．23 m

183 ．63 999 ，95

P ；Length of the shQrt arm 短 腕 長 ； Q Length of the long arm 長 腕 長 Total length” ’ 総 染色 体長 に 対 す る 各 染 色 体 の 比 長 RL ＝R ・ 1・ tive 1・ ngth ＝ × 1・ OOO ・ S 。 th 。 f T6fit ［ e 。g th （千 分 比 ）

＝ P CI ＝Centromeric index × 100 短 腕 比 （動 原体指数 ） Total length PQ AR ＝Arm ratio ＝ 染 色 体 の 腕 長 比

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RoDRIGuEz-RoMERo et al.: Karyotype of Crassostrea rhizophorae 139

CTassostrea rhizophorae (named Ostrea Thizophorae by the author) have been

reported in other areas of the Caribbean i. e. in Venezuela, Cuba and Brazil.

The reports, in some eases, have referred to this speeies under different

seientific names, thereby causing confusion as to its nomenclature (MATTox, 1949; BoNILLA, 1969). This eonfusion has hindered the efforts to have a better understanding of organisms. From the aquaculture point of view, these oysters are of eonsiderable importance as there now exists the possibility of experi- mental eultivation as is done in Venezuela (MANDELLI and ACUNA, 1975;

VELEz, 1968) and Cuba (NIKOLIc and MELENDEz, 1968). This interest in

aquaculture motivated studies, partieularly eeological and of seasonal gonadic

changes, that led to a better understanding of the requirements necessary for

good suceess with experimental eultivation (MATTOX, 1949; ANGEL, 1972; VELEz, 1972; VELEz and BoNILLA, 1972). However, other biologieal studies

of Crassostrea rhi2ophorae are searce.

Studies of chromosome analysis have produced the cytotaxonomy whieh ean be used to solve similar problems with other oyster species.

In the genus CrassostTea it is possible to apply this criterion onee the

studies on the karyotypes of this taxon have been eompleted.

In the ease of C. rhizophoTae, the presenee in its karyotype of a diploid number of 20, an arm number of 40, and a chromosomic morphology integrated

exclusively by metaeentric and submetaeentric chromosomes, indicates that it is closely related to other parental speeies already studied. This has been

confirmed in part by MENzEL (1968li), in studies on experimental interspecific hybridization.

It is of furidamental importanee to know the karyotypic features of all the species of this genus to determinate the various similarities and differenees

that ean be used to recognize eaeh speeies by means of this eytotaxonomie

method, even in the Iarval stages.

g ts

,s *-y-, thivIvea)xA7p . 7'iv . .V}ditnth V 7'ir=} Crassostrea rhi2oPhorae a)vats Lrr, Ctsigg2thfiesvt-oLiFC"Vir()caesLt!. cotetsC･t 2n=20 t"(v(>"Ien`e, vawadwt40eC'th-,t:. pt

ecoMagvttwe=anve"ttkMMofillptNB}}, igstI･1'EW (ee 1, 3, s, s, 10 XD Moetst[P$ftifU 'ptkt) '(i･ (ee 2, 4, 6, 7, 9 O Sk iE, . Vi:.

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