R. H. Crozier.
The Chromosomes of Three Australian Dacetine Ant Species (Hymenoptera: Formicidae).
Psyche 75:87-90, 1968.

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THE CHROMOSOMES OF
THREE AUSTRALIAN DACETINE ANT SPECIES
(HYMENOPTERA: FORMICIDAE)
Genetics Department, University of Melbourne, and Department of Entomology and Limnology, Cornell University
Although more species of Myrmicinae have been studied cytolog- ically than of any other ant subfamily (Imai, 1966; Hauschteck, I 965 ) , there have been no reports on the chromosomes of dacetines. The tribe Dacetini is a very distinct group whose members are mostly specialized
feeders on Collembola and whose evolution has been traced in unusual depth for ants (Brown and Wilson, 1959). The species treated here fall into three Australasian genera. Pharate pupae (prepupae), male pupae, and embryos were pre- treated with colcemid. Aceto-carmine-orcein squash preparations were made from Epopostruma and Orectognathus material, and an acetic acid dissociation, air drying technique with aceto-lactic orcein staining (Crozier, 196th) was also used for Colobostruma and Orectognathus.
The criteria used for chromosome classification are those of Levan, Fredga and Sandberg (1964). The nomenclature followed is that indicated by Brown and Wil- son (1959). Identification of the ants was by W. L. Brown, and specimens will be deposited in the Australian National Insect Col- lection, C. S. I. R. O., Canberra.
Orectognathus clarki (figures I & 4)
2n = 30
Material from Narbethong Victoria, and Ferntree Gully State Park, Victoria, showed that the karyotype of this species comprises nine pairs of metacentric to submetacentric and six pairs of sub- acrocentric and acrocentric chromosomes; thus two chromosome groups are discernible (figure 4).
Epopostruma sp. (figure 2)
n = 10, 2n = 20
Material from 5 miles W. of Hopetoun, Victoria, has a karyotype ^Present address: Department of Entomology and Limnology, Cornell University, Ithaca, New York, 14850, U.S.A. Manuscript received by the editor February 12, 1968 Pu&e 75337-90 ( 1968). hup Ytpsychu einclub orgi75175-087.htd



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Psyche [March
Figures 1-3. Metaphase
plates of dacetine species: (1) Orectognathus clarki, Ferntree ~ u l l ~ sample.
Diploid cell from air dried preparation
of pharate pupal cerebral ganglion (2) Epopostruma sp. Haploid cell from squash preparation of pupal testis. (3) Colobostruma al.;nodis. Dip- loid cell from air dried preparation of pharate pupal cerebral ganglion. Line in figure 3 represents 10 microns.
in which all the chromosomes are metacentric, with a more or less continuous gradation in size. A lack of consistent differences pre- cluded grouping the chromosomes.
Colobostruma ulinodis (figure 3)
n = 11, 2n = 22
Material from Ferntree Gully State Park, Victoria, shows a karyotype with eleven metacentric chromosomes. As in the case of
the Epopostrunzu karyotype above, there is a range in size of the chromosomes, but without consistent discontinuities enabling an ar- rangement of the chromosomes into groups. DISCUSSION
In Brown and Wilson's (1959) phylogenetic scheme for the Dace- tini, Colobostruma and Epopostruma are placed very close together, with Orectognathus some distance away. The cytogenetic results tend to support this placement although, even between the Colobos- truma and Epopostruma karyotypes, at least three changes must have occurred (one centric fusion or dissociation, and two pericentric in- versions).
The difference between these karyotypes and that of Orectognath~us clarki is substantial, and speculation about the changes involved would be idle.




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19681 Crozier - Chromosomes of Dacetine Ants 89 Variation in chromosome number within a genus has now been demonstrated for eight ant genera (Iridomyrmex, Camponotus, Lasius, Formica, A~haeno~aster, Pheidole Leptothorax and Myrmica s e e references), and it would be surprising in view of the diver- gence between the kai-yotypes reported here if such variation were not found in further work on the three dacetine genera. In the case of Epopostruma in particular, cytotaxonomy could prove a val- uable aid in a genus whose taxonomy is rendered difficult by the tendency of populations to mimic some other locally common ant species ( Brown, pers. comm. ) .
Figure 4.
Diploid karyogram of Orectognathus clarki from cell in figure 1. Line represents 10 microns.
Interpopulation variation in chromosome morphology is indicated in Iridonzyrmex of the "detectus" group (Crozier, 1g68b), and populations of Rhytidoponera metallica vary in chromosome number (Crozier, unpub.) , indicating that single-sample karyotype analyses in ants can be misleading, even though karyotypic stability does seem the rule in some ant groups.
Unfortunately, few dacetine species
are common enough to permit repeated sampling. Ant cytogenetics is still in a survey period, but this should not prevent the gathering of data on intraspecific ka.ryotypic variation in suitable species.
SUMMARY
Two samples of Orectognathus clarki showed a haploid chromo- some number of 15, comprising g metacentric to submetacentric and 6 subacrocentric to acrocenti-ic chromosomes. A sample of Colobos- truma alinodis had I I metacentric chromosomes and one of a species of Epopostruma 10 metacentric chromosomes, as haploid numbers.



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90 Psyche [March
These observations tend to support present taxonomic placement of these genera, but no simple relationship can be demonstrated be- tween any of the genera.
The work on Epopostruma and part of that on Orectognathus is part of a thesis submitted as partial fulfillment of the requirements for the M. Sc. degree, University of Melbourne, and was supported by grants from the C. S. I. R. 0. and the University of Melbourne. The work on Colobostruma and part of that on Orectognathus is part of a thesis partially fulfilling the requirements for the Ph.D. degree, Cornell University, and was supported by an Allied Chem- ical Foundation Grant, and U. S. N. S. F. grant GB5574X, W. L. Brown, Jr., principal investigator. The work was carried out in the Genetics Department, University of Melbourne, and the En- tomology Department, Cornell University. I thank Professors M. J. D. White and W. L. Brown for much encouragement and help- ful advice.
REFERENCES
BROWN, W. L. AND E. 0. WILSON
1959. The evolution of the dacetine ants. Quart. Rev. Biol., 34: 278- 294.
CROZIER, R. H.
1968a.An acetic acid dissociation, air drying technique for insect chromosomes, with aceto-lactic orcein staining. Stain Technol. 43 (in press).
1968b. Interpopulation karyotype differences in Australian Iridomyrmex of the 'detectus' group (Hymenoptera: Formicidae: Dolicho- derinae). J. Australian Entomol. Soc., 7 (in press). HAUSCHTECK, E.
1965. Halbe haploide Chromosomenzahl im Hoden von Myrmica sul- cinodis Nyl. (Formicidae) . Experientia, 21 : 323-325. IMAI, H. T.
1966. The chromosome observation techniques of ants and the chromo- somes of Formicinae and Myrmicinae. Acta Hymenopterologica, 2: 119-131.
IMAI, H. T. AND T. H. YOSIDA
1964. Chromosome observations in Japanese ants. Annual Report Nat. Inst. Genet., Japan, 15: 64-66.
KUMBKARNI, C. G.
1965. Cytological studies in Hymenoptera Part 111. Cytology of par- thenogenesis in the formicid ant, CamPonotus compressus, Cary- ologia, 18 : 305-311.
LEVAN, A., K. FREDGA AND A. A. SANDBERG
1964. Nomenclature for centromere position on chromosomes. Here- ditas, 5 2 : 201-220.




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