No. 1] Proc. Japan Acad., 63, Ser. B (1987) 21

6. B Chromosomes in a Male of pardalina (Bates) (Coleoptera: Cerambycidae), with special regard to their Association at MI

By Hirokazu KIDOand Kazuo SAITOH Departmentof Biology,Hirosaki University, Hirosaki 036 (Communicatedby Sajiro MAKINO,M.J. A.,Jan. 12, 1987)

In the course of a chromosome survey of male cerambycid , B chromo- somes were observed in germ cells of a X enicotela pardalin.a male of the and their behavior at MI was especially complicated, often forming a tripartite complex which is regarded as an Xyp incorporated with a B. As has been known from the monograph of Jones and Rees (1982) , the information on the B chromo- somes of cerambycids is currently meagre. So, some findings on the B chromo- somes of the present male are outlined below, with special regard to their be- havior at MI analysed on the basis of the visible configuration. Material and methods. Adult males, collected from Nurukawa, Kuroishi- shi, Aomori-ken, were used for the present study. Their testes taken out were first kept in 0.075 M KCl soln. for 15-20 min. at the room temperature. Chromo- some spreads were then prepared by the method of Crozier (1968) and stained with Giemsa (4%, pH 6.8) as usual. Results. B chromosomes were observed in spermatogonia and primary spermatccytes in one of the two males examined. Since the anaphase-I and telophase-I configurations were not encountered in this male, the later meiotic fate of Bs could not be determined. In the non-B-carrying male examined, the diploid chromosome number was 22, including a y of the smallest size. Consequently, eleven elements (10+Xyp) were observed at MI. The sex-bivalent was a bipartite complex of the usual parachute-shape. In the B-carrier, the second smallest element was the B chromosome. So, distinction between y and Bs was certain. Of the eleven metaphase spermatogonia examined, one carried a B, six two Bs (Fig. 1), two four Bs (Fig. 2), one five Bs and one six Bs. These Bs were of course free. Table I summarizes the results of an analysis of the behavior of Bs at MI based on their visible configurations. Of the 259 MI-cells examined, 244 (94.2%) carried from one to five Bs with the majority in the 2B class. Non-B-carrying, OB cells were also observed (5.8%). In the cells carrying more than two Bs, the association of a pair of Bs (BII; Fig. 7) was observed not infrequently. In the 2B cells in particular such associated Bs (B11) occurred in 49% of them. In addition, the B chromosome sometimes incorporated with an Xyp forming a tripartite complex (ByBp; Figs. 4 and 5). The XyBp was quite peculiar in its visible configuration, because it is a complex of three chromosomes of the differ- ent size in the parachute-association: their size relation was X>B>y. Its identi- fication was therefore easy and about 13% of the total B-carrying cells examined were characterized by its presence. On the contrary, Bs did not associate with any of the regular autosomal bivalents. .

22 H. KIDO and K. SAITOH [Vol. 63(B),

Figs. 1-8. Chromosome complements of a male with Bs. 1: Spermatogonial mitosis, 2B. 2: Ditto, 4B 3: MI, 1B1. 4: Ditto, XyBp. 5: Ditto, XyBp+1BI. 6: Ditto, 2BI. 7: Ditto, B11. 8 Ditto, 3BI. Arrow indicates B chromo- some and arrowhead XyBp, respectively. . Bottom bar: ca. 10 um. No. 1] B Chromosomes of a Longicorn 23

Table I. The type of association of Bs in the first division of a X enicotela pardalina male

Remarks. As evident from the table, the present specimen is a mosaic male containing both of non-B- and B-carrying germ cells, with a preponderance of the B-carrying ones. However, whether these OB cells might directly have derived from the spermatogonia lacking Bs, or, as Smith and Virkki (1978) referred to, resulted from the premeiotic elimination of the B in some mitoses has re- mained unknown. The behavior of Bs at MI of this male was complicated as shown in the table, not infrequently featuring the association of two Bs and the incorporation of a B to the sex-pair that resulted in the formation of the tripartite complex designated XyBp. Previously, Lanier and Raske (1970) observed in the Mono- chamus-males of the Lamiinae another kind of the tripartite sex-chromosome complex, XXYp, which consisted of the three elements of nearly the same size. Virkki (1984) concluded the two Xs of the complex to be the fission products of the normal X. Thus, the XyBp and XXYp are different in their basic organization and of course their visible configurations at MI are dissimilar to each other. Summary. A Xenicotela pardalina male of the Cerambycidae (Coleoptera) has been found to contain both non-B- and B-carrying germ cells, showing an overwhelming preponderance of the B-carrying ones. One to six Bs are observed in the examined spermatogonia and one to five Bs in about 94.2% of the examined MI-cells. The behavior of the Bs at MI is varied as shown in Table I and the association of a pair of Bs (B11) and the incorporation of an Xyp with a B (XyBp) are especially noted, but the B did not associate with any of the regular autosomal bivalents. Acknowledgements. We are very grateful to Dr. Y. Obara and Dr. S. Sato of the Department of Biology in Hirosaki University for their critical comments. Our cordial thanks are also due to Professor Emeritus Dr. S. Makino, M. J. A., for his refinement of the manuscript. 24 H. KIDO and K. SAITOH [Vol. 63(B),

References

Crozier, R. H. (1968) : Stain Technol., 43, 171-173. Jones, R. N., and H. Rees (1982) : B Chromosomes. Academic Press, 266 pp. Lanier, G. N., and A. G. Raske (1970) : Can. J. Genet. Cytol., 12, 947-951. Smith, S. G., and N. Virkki (1978) : Cytogenetics. vol. 3, Insecta 5. Gebruder Borntraeger, 366 pp. Virkki, N. (1984) : Chromosomes in Evolution of Eukaryotic Groups (eds. Sharma, A. K., and A. Sharma). vol. 2, CRC Press, pp. 41-76.