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THE CHROMOSOMES OF TWO SPECIES OF THE GENUS A USTRALOTETTZX RICHARDS (GRYLLACRIDOIDEA:

MACRO PATHINAE)

By ALEJO MESA* [Manuscript received October 15, 19691

Abstract The chromosomes of Australotettix montanus Richards and A. carraiensis Richards have been studied. Both species share the following characteristics: the chromosome number is 2n=45 d 4 6 9 ; the sex mechanism is of the XO 8-XX 9 type with the X submetacentric; the X chromosome as well as two bivalents (H, and H,) are heterochromatic during first prophase.

The species differ in: (a) the pattern of distribution of heterochromatic blocks in H,; (b) the H, pair consists of two metacentric autosomes in A. carraiensis while these chromo- somes are acrocentric in A . montanus; (c) a medium-sized pair of autosomes is formed by subacrocentric elements in A. carraiensis while they are acrocentric in A. montanus.

The karyotypes of both species do not differ basically from that which is typical for the Macropathinae.

INTRODUCTION

It is in general accepted that, within Orthoptera (i.e. Caelifera plus Ensifera) the superfamily Gryllacridoidea is the most ancient group still living. The subfamily Macropathinae in particular, presents an interesting geographical distribution, with species scattered in the southern regions of South America and South Africa (one species), the south and east of Australia and the whole of New Zealand, besides some isolated sub-Antarctic islands. This circum-Antarctic distribution, with groups of genera apparently isolated during millions of years, provides an interesting basis for comparative chromosomal studies.

Surprisingly enough, all the species of South American and Australian origin so far studied, show similar chromosomal characteristics, the differences recorded consisting of relatively minor modifications of an ancient basic karyotype.

The chromosomes of several species of Macropathinae have been described in previous papers (Mesa 1965; Mesa et al. 1968, 1969). In 1964, Richards described the genus Australotettix including in it two species : carraiensis and montanus. Mesa et al. (1968) briefly mentioned the number of chromosomes, the sex mechanism and the morphology of the chromosomes in A. montanus. It is now possible to compare the karyotypes of the two species in detail.

MATERIAL AND METHODS The specimens studied in this paper were collected by the author at the follow-

ing localities :

Australotettix montanus Richards 4 8 8 from Horseshoe Falls, Hazelbrook, New South Wales, 15.iv.1968. 2 6 8 from Horseshoe Falls, Hazelbrook, New South Wales, 25.xi.1968.

7 8 8 from 40 mi. W of Kempsey, New South Wales, 24.xi.1968, in an old mine.

Australotettix carraiensis Richards

All the specimens were fixed in a mixture of ethyl alcohol and acetic acid (3: l ) . The squash preparations of the chromosomes were stained by the Feulgen method, after hydrolysing the tissue in N HCl at 60°C for 8 minutes.

'Department of Genetics, University of Melbourne, Parkville, 3052, Victoria.

J . Ausi. ent. Soc., 1970, 9: 7-10.

8 ALEJO MESA

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PLATE I A,C.-Austrulorettix curraiensis Richards: ( A ) diplotene stage; (C) heterochromatic bi- valent (HI) during pachytene stage. B,D.-A: montunus Richards: (B) diplotene stage; (D) heterochromatic bivalent (HI) during pachytene stage.

CHROMOSOMES OF AUSTRALOTETTIX SPP.

OBSERVATIONS

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Australotettix montanus The chromosome number in this species is 2n=45 6 4 6 9, and the sex chromo-

some mechanism is of the XO 6-XX 9 type. The X chromosome is a large submeta- centric chromosome that during first prophase remains entirely heterochromatic.

The twenty-two autosomal bivalents form an evenly graded series with respect to size and for this reason it is difficult to group them. From their configuration during first metaphase, all the autosomes appear to be acrocentric. Two of the bivalents ( H I and H2 in Plate IB) are clearly heterochromatic during first prophase, though two small pairs are also in some degree heterochromatic; H I is the longest pair of the set and as shown in Plate ID, presents three blocks of heterochromatin separated by short, less stained segments. The first and second segments (left to right in Plate ID) are very large and separated by a weakly stained segment which sometimes shows an internal spherical granule. The third block is short, sometimes rounded and separated from the second by a short weakly stained region.

H2 is medium-sized and largely heterochromatic although its detailed structure is difficult to determine.

Aus tralo tet t ix carraiensis The chromosome number is 2n=45 346 3 with an XO &-XX 3 sex deter-

mining mechanism. The X chromosome is a large submetacentric element. The X is heterochromatic during the whole of first prophase.

It can be seen at first metaphase that the largest bivalent consists of two meta- centric chromosomes. One of the medium-sized pairs (the tenth in Plate IA) is formed by two subacrocentric chromosomes. The remaining chromosomes look acro- centric though it is difficult to observe the morphology of the three smallest pairs.

The twenty-two pairs form a graded series. During first prophase it can be seen that two pairs of chromosomes are clearly heterochromatic (Plate IA, H I and H2). The first pair ( H I ) is the largest and metacentric, as observed in first metaphase. At pachytene stage, H I shows three segments of heterochromatin separated by short less stained segments. The first heterochromatic block (left of Plate 1C) is not intensively stained, although relatively long. The second block is the largest and comprises about a half of the chromosome length. The third block is approximately a third of the length of the second block.

H2 is medium-sized and also extensively heterochromatic. Two more small chromosomes show some degree of heteropycnosis.

DISCUSSION While showing a similar karyotype to that typical for Macropathinae, the two

species of Australotettix present some features that allow us to differentiate them

X

FIGS. 1, 2.-Australotettix species, first metaphase with the bivalents arranged in order of size, the X at the end: ( 1 ) A. montanus Richards; (2) A . carraiensis Richards.

10 ALEJO MESA

at the specific level. In both species, the largest of the autosomal pairs (H,) is hetero- chromatic during first prophase, but if analyzed in detail, a distinctive pattern of chromatin blocks is evident. Moreover, this pair is formed by acrocentric chromo- somes in A . montunus, while in A . curruiensis they are metacentric. It is not possible to determine at present in which direction the change in centromere position occurred, but since the chromosome number in both species remains the same, the origin of such a change could be a pericentric inversion.

H2 has approximately the same size in both species, and this is also true for the remaining two small partially heterochromatic pairs.

Bearing in mind that in the majority of species of Macropathinae only two pairs of autosomes are heterochromatic, we believe that the heterochromatin in the two small pairs has been acquired more recently.

Another distinctive characteristic is the presence of a medium-sized subacro- centric chromosome in A . caruuiensis while in A . montunus this chromosome is acrocentric.

P. CK NO w LEDGEMENTS

The author is greatly indebted to Professor M. J. D. White, Department of Genetics, University of Melbourne. for critical reading of the manuscript.

REI ERENCES MESA, A. (1965).-Caryology of four Chilean species of Gryllacridoids of the genus Hereromallus (Ortho-

ptera, Gryllacridoidea, Rhaphidophoridae). OCC. Pap. Mus. Zool. Univ. Mich. 640: I - 13. MESA, A., FERREIRA, A. and DE MESA, R. S. (1968).- The karyotype of some Australian species of Macro-

pthinae (Gryllacridoidea-Rhaphidophoridae). Chromosoma 24: 456-466. MESA, A., ERREIRA, A. and DE MESA, R. S. (1969)-The chromosomes of three Australian species of

gryllacridids (Gryllacridoidea-Rhaphidophoridae-Macropathinae). Curyologia 22: 149-160. RICHARDS, A. (1964).-The Rhaphidophoridae of Australia. Part 2. A new genus. Proc. Linn. SOC. N.S. W.

84: 313-379.