368 Proc. Japan Acad., 60, Ser. B (1984) [Vol. 60(B),

94. The Early Emerging Male of the Japanese Paper , snelleni Saussure (, ) and its Chromosome

By Hidehiro HosHIBA*) and Masato ONo**> (Communicated by Saj ira MAKING,M. J. A., Nov. 12, 1984)

In the temperate o f social , the foundress (queen) usually produces her first brood as workers. However, according to Kasuya (1983) , the early emerging males (EEM) produced by the foundress have been known in three species of the Japanese Polistes wasps (P. chinensis antennalis, Morimoto, 1954; Suzuki,1981; Kasuya, 1983. P. rothneyi iwatai, Yamane, 1972. P. jadwigae, Yamanaka, 1928; Kasuya, 1983). Strassmann (1981) observed most of the f oundress of P. ex- clamans produced the EEM. She found that the EEM mated with workers and some of the inseminated workers founded satellite nests. She considered that this phenomenon was probably an adaptation to long Texas summers. Kasuya (1983) applied this role to the EEM of the Japanese temperate region. On the other hand, Suzuki (1981) claimed that the EEM was considered as the result of the accidental haploid by any cases and/or the failure of mating of the foundress in P. chinensis antennalis. The chromosome number of the genus Polistes has been studied in the 12 species (5 subgenus;), and the wide range in number of chromosomes was reported (Table I). While, the diploid males have been reported in several species of Hymenoptera under the sibling mating condition (Page and Metcalf, 1982), and the cytological conf ermation was made on Apis melli f era (Hoshiba, 1979). Their sex was determined by the multiple sex alleles (Whiting, 1940). This mechanism of sex determination seems to be a common rule among Hymenoptera. Therefore, the cytological studies of the EEM which was unusually produced by the f oundress, have been required. In the present paper, the EEM of P. snelleni and its karyological analyses were reported.

*' Daito Bunka University , Daiichi High School, Takashimadaira, Itabashi, Tokyo. *' Laboratory of Entomology, Faculty of Agriculture, Tamagawa Univer- sity, Tokyo. No, 9] The Early Emerging Male of Polistes snelleni and its Chromosome 369

Table I:. The haploid chromosome numbers o f 12 Polistes species*

Materials and method. Young larvae including the EEM of P. snelleni were collected at Tokumaru, Itabashi, Tokyo in June, 1984, which was an isolated region where the sibling matings have probably occurred. The larvae of normal males and females were collected at Tamagawagakuen, Machida-shi, Tokyo in August, 1984. They were dissected to obtain the testes and the ovaries when they were in the spermatogonial (oogonial) stage, then pretreated by the hypotonic solution (0.4% KCI, 0.01% colchicine) for 30 min and fixed in acetic-methanol (1: 3). The preparations were made by the usual air-dried method, and stained by the Giemsa solution. Results and discussion. We expected that some of the EEM of P. snelleni which were found in this study were diploid males, since they were nested in the isolated region ; we have observed the nest of this species at an isolated area for 6 years. In this area, the possibility of sibling mating is high (Ono and Hoshiba, unpublished). However, as far as this case was concerned, no diploid males were found. Probably they will be found in the future. All of the nests including the EEM were to be degenerated until about the middle of July. This may be caused by the accidental parthenogenesis, but the possibility of the mating between the EEM and the workers could not be ignored. Further studies on their be- haviour are to be required. The chromosome number of P. snelleni had already been reported by Machida (1934). He counted n=13 (male), 2n=26 (female) and he also observed that the haploid set was divided into two groups, 6 long chromosomes and 7 short chromosomes. But the present study made clear, i.e., n=30 (male), 2n=60 (female) and the EEM was n=30 as shown in Figs. 1-3. The longest chromosome is about 2.57 370 H. HOSHIBA and M. ONo [Vol. 60(B),

Figs. 1-3. 1: Metaphase plate of the female (queen) of Polistes snelleni, 2n=60. 2: Metaphase plate of the male of Polistes snelleni, n=30. 3: Meta- phase plate of the early emerging male of Polistes snelleni, n=30.

Fig. 4. Temporary arranged karyotype of haploid Polistes snelleni (early emerging male).

and the shortest, about 1.25 (average of 17 cells). Most of the chromosomes seem to be meta- or submetacentrics. The haploid set seems to be consisted of 15 pairs (Fig. 4), if so, it is an interesting finding from the view point of the karyotype evolution in genus Polistes. Acknowledgements. The authors wish to express their sincere appreciation to Professor Emeritus, Dr. S. Makino, M. J. A., of the Hokkaido University for his helpful suggestions for the improvement of this manuscript. They are also greatly indebted to following pro- fessors; Drs. I. Okada of the Tamagawa University, S. Sakai of the No. 9] The Early Emerging Male of Polistes snelleni and its Chromosome 371

Daito Bunka University, H. Yamamoto and S. Toshioka of the Dokkyo University of Medicine.

References

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