Asiatic Herpetological Research

Qu ne 1995

Vol.

ft,pp.

167-171

Cytotaxonomic Studies on Chinese Pelobatids VI. The Karyotypes, C-bandsand Ag-NORs of Megophrys minor and Oreolalax major

XIAO-MAO ZHENG AND GUAN-FU WUChengdu Institute of Biology, Accidentia Sinica, Chengdu, Sichuan, China-Chromosome preparations were successfully stained for C-bands and Ag-NORs in two Chinese
pelobatids, Megophrys minor and Oreolalax major. The results were analyzed and compared. The karyotype
formula of O. major was 6+7 like most species of Chinese Oreolalaxinae whereas M minor was 5+8 just as
in most species of Chinese Megophryinae. The SC on the long arm of chromosome No. 6 associated with
the C-band-positive was speculated the Standard NORs of genus Oreolalax. The NOR just in the conspicuous
SC was not emerged firmly in the genus Megophrys.
Abstract:.

Key words: Anura, Pelobatidae, Megophrys, Oreolalax, cytotaxonomy, China

Introduction
Chinese pelobatids axe attributed to two
subfamilies with about 50 species (Tian etThe karotypes of 15 speciesal., 1986).
among those 50 species, with the majority
distributed in the Heng Duan Mountains
region where the karyotypic characteristics
of some anurans are unusual (Zeng and Wu,
In this paper, twoOreolalax
other species,major andminor
wereanalyzed by means
Megophrys
andof C-banding
silver-staining NORs

1989), were reported.

techniques.

Materials and Methodsminor(3 males and 1
Megophrys
werecollectedon Mt. Emei,female)
Sichuan Province, China and in Maowen
County, Sichuan Province, China,respectively. Oreolalax major (3 males)
were captured from Mt. Emei in 1989-90.
Chromosome preparations were performedAll specimens of M.

minor from twoplaces, Mt. Emei and Maowen had 2n=26
and the complement included five pairs oflarge (Nos. 1-5) and eight pairs of small
Nos. 1, 4-5(Nos. 6-13) chromosomes.
weremetacentricand 8-12(m), whereas
Nos. 2-3 and 6-7 were submetacentric (sm)chromosomes. The last pair was telocentric(t). The highly differentiated heteromorphic
sex chromosomes as seen in Pyxicephalus
adspersus (Schmidt, 1980a) were not foundwhen males and females were compared.

Three males of O. major also had 2n=26
with the complement of six pairs of large(Nos. 1-6) and seven pairs of small (Nos.
7-13) chromosomes. The chromosomes
were metacentric except for Nos. 3-5 and 9with submetacentric and No. 6 with sub- or
Whether or not highly
metacentric.

sex
heteromorphic
chromosomes are present is not known, duedifferentiatedto the lack of female animals.

by centrifugal air-drying method (Wu et al.,KC1 as hypotonic
1981) using 0.4
40
minutes.
solution forC-banding wasSumnermade following(1972), for 5
minutes with Barium Hydroxide treatment at54° C. Silver-staining NORs was prepared

The conspicuous secondary constriction
was found in a pericentric position on thelong arm of chromosome No. 6 of O. major

following Tan et al. (1986), AgN03 acting
time for about 5 minutes at about 55° C.

1Mwhereas the small inconspicuous one can beseen in a proximal position on the short armof chromosome No. 6 of M. minor (Figuresand 2).

The
Results

resultrevealed thatof silver-staining

Ag-NORs

NORs

were present onchromosome No. 6 associated with theThe measurements of chromosomes forthe two species are shown in Table 1.

© 1995 by Asiatic Herpetological Researchsecondary constriction in both species (Figs.
1, 2). The strongly C-band-positive was inVol. 6, p. 168

TABLE 1.

Asiatic Herpetological Research

The arm ratio and relative length of Megophrys minor and Oreolalax major.

April 1995

4i
B

Vol. 6, p. 169

Asiatic Herpetological Research

April 1995

UiIIsiu »II*iu

1<H »iiII•

j{ii_•i*.
SIU• •.

.

-'FIG. 2

TABLE 2. The karyotypes of three Megophrys species and six Oreolalax species.
Species. »Vol. 6, p. 170

Asiatic Herpetological Research

species were only reflected on thearrangement of m and sm chromosomes.

Compared with the genus Megophrys,
Oreolalax species had no st
chromosomes and all chromosomes in the 6
known species were m or sm except
chromosome No. 13 of O. schmidti (Table2) which was t chromosomes. That their
theJune 1995

bands and only had one interstitial C-band
positive on chromosome No. 6 which wasjust associated with the position of the SC.

Apart from one on chromosome No. 6, O.
major had the other interstitial C-band on
chromosome No. 1. This is different fromthe other species of this genus.
If theinterstitial C-bands revealed the relics ofchromosome rearrangement (Schmidt,SC always appeared firmly on the long arm

1978a; King, 1980), it should be possibleof chromosome No. 6 was different fromthat the karyotype of O. major shows more

Megophrys, in which 3 species had 3

higher evolutionary level in the Oreolalax.

different positions of SC.

Furthermore, thenumber of the large sm chromosome pairsof the Oreolalax species were much morethan that of Megophrys. Oreolalax was asubgenus of the Scutiger (Duellman, 1985)
and it was considered as a genus (Myers andLeviton, 1962) which was attributed toMegophryniae. The differences of the twosubfamilies (most species mentioned above)were present on two different karyotype
formulas: the former was 6+7, whereas thelatter was 5+8. It was thought that the moreprimitive karyotypic characteristics thekaryotype of pelobatids had, the more t, stand sm pairs of chromosomes incomparison with that of the higher Anura(Duellman, 1985; Morescalchi, 1973). This
position is still similar to the point of view

on morphological taxonomy.

C-bands and NORs
C-bands in pelobatids were found more
weakly and in less number than those inhigher Anura (Bufonidae, Ranidae, andHylidae). The C-banding of M. minor wasvery similar to those of the other two speciesof Megophyrs, M. nasuta (Schmidt, 1980b)
and M. omeimontis.
The constitutive
heterochromatin emerged on the precentricarea of each pair of chromosomes. The Cband associated with the SC onchromosome No. 6 (M. nasuta, M.
omeimontis) and No. 5 (M. minor) was notenhanced to be particularly distinguishedwith centric C-band. The result of the Cbanding treatment to Oreolalax species wereless active than that to Megophrys.

TheC-bands were always weak (O.
omeimontis, 0. pingii, and 0. rugosa) orinvisible (O. schmidti, O. major, and thispaper). Most of them had no centric Ccentric

It is said that stable and conspicuous SC
always the location of NORs. In respect
to the genus Rana, Schmidt (1978b)
concluded that the Standard NORs werealways emerged in this SC on the long armof chromosome No. 10 and thought it as asign of Rana. The result of silver staining inO. major and O. schmidti proved that NOR
was just in the SC on the long arm ofchromosome No. 6. In terms of the otherfour species of this genus, Oreolalax withthe same SC, it is speculated that the SC
region on chromosome No. 6 should be inisthe location of the standard NORs of thisgenus. Furthermore, it is possible the close
relationship between species in this genus
was shown due to them having the sameNORs (Tymoska, 1977). The NOR of M.
minor and M. omeimontis emerged on theplace associated with themselves SC.
Compared with Oreolalax, they did not havethe same SC associated with NOR, thus
species showing higher interspecificdifferentiation.

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