No. 2] Proc. Japan Acad., 53 (1977) 71

20. Chromosomal Studies on Interspeci fcc Hybrids of (Papilionidae, Lepido ptera) . VIII

Crosses among P, machaon hippocrates, P, xuthus, P, benguetana, and P, pot yxenes

By Kodo MAEKI* ) and Shigeru A. AE* (Communicated by Saj iro MAKINO,M. J. A., Feb. 12, 1977)

Through the application of cytogenetical methods, striking con- tributions have recently been made to the analysis of many problems associated with systematics and evolution that are not always avail- able by non-cytogenetists on the basis of merely external searches. A series of investigations have been undertaken by us in an aim to make a new approach to understanding of evolutional features of groups, based on data derived from hybridization experi- ments. Relevant data have been provided in hybrids among P. poly- ctor, P. bianor, P. maackii, P. polytes, P. helenus, P. protenor, P. macilentus, P. Paris, P. nepheles, P. aegeus, P, f uscus, P. memnon, P. ascalaphus, P. polymnestor, and P. rumanzovia (Maeki and Ae 1964, 1966, 1970, 1975, 1976a, 1976b, 1976c, 1976d), with special attention paid toward pairing of the chromosomes at male meiosis. In the present paper are described the results derived from the fol- lowing crosses: P. xuthus x P. benguetana, P. polyxenes x P. xuthus, and P. xuthus x P. machaon hippocrates. The hybridization experi- ments were performed by Ae (1959, 1964, 1966), and chromosome studies were carried out by Maeki according to the routine paraffin method. Results. Two out of four parental Papilio species (P, xuthus and P. benguetana) here dealt with were uniformly characterized by a n-number of 30, along with an apparently similar karyotype. P. polyxenes from North America was remarkable by showing a chromosomal dimorphism, n, 30 and n, 31, at male meiosis-I. The basic number is 30, while the dimorphism results from the presence of a single m-chromosome (Maeki and Remington 1960). A chromo- somal polymorphism was noted in P. machaon hippocrates in which the n-number varied from 30 to 34 in male meiosis-I cells. In this species the basic number was also 30, and the above numerical varia- tion was due to the occurrence of supernumerary chromosomes,

*' The Biological Laboratory , Faculty of Science, the Kwansei Gakuin University, Nishinomiya, Japan. **) The Biological Laboratory , the Nanzan University Nagoya, Japan. 72 K. MAEKI and S. A. AE [Vol. 53, probably resulted from the fragmentation (Maeki 1976). 1. ? ` (from Japan) X Papilio benguetana (from Philippines). Chromosome counts were possible for 20 cells at M-I and 10 cells at M-II derived from three hybrid males in the above cross (Nos. 3, 4 and 5 from Brood X-316). In the F1 hybrids the chromosome number of the M-I cells was shown as uniformly 30 in all cells so far examined (Fig. 1). Studies of 36 cells at M-I and 28 cells at M-II which came from 10 back cross males (P. xuthus x F1, nos. 5, 6, 10, 11, 15, 17, 19, 24, 25, and 31 from Brood X-337) demonstrated the n-number of 30 in them without exception. The feature is indicative of that P. xuthus and P. benguetana are very closely related. 2. (from U.S.A.) X Papilio xuthus (from Japan). In this cross, 26 cells at M-I derived from two hybrid males (No. 1 from Brood P-43 and Brood P-28) were available for chromosome study. The chromosome-number of the M-I cells in the above hybrids ranged in variation from 44 to 55 (Figs. 2, 3, 4). The cells having 48 and 52 elements were most frequent, being 15 in each. It is apparent from this feature that there are many chromo- somes which remain not being paired in the meiosis-I. The chromo- some-number distributions in the M-I metaphase based on the 26 cells are as follows :

n,44...... 1ce11 n, 50...... 3 cells n,45...... 2 cells n, 51...... 2" n,46...... 3 n, 52...... 4 n,47...... 2 n,54...... 2" n, 48...... 4 n,55...... 2 ~~ n,49...... lcell

3a. Papilio xuthus (from Japan) X Papilio machaon hippocrates (from Japan). 3b. Papilio machaon hippocrates (from Japan) X Papilio xuthus (from Japan). Chromosomes of hybrids were investigated in 29 cells at M-I from three hybrid males which were derived from above reciprocal crosses (Nos. 1 and 2 from Brood X-26; and No. 1 from Brood H-3). The observations revealed the occurrence of a single cell with 43 chromosomes, as well as of 28 cells in which 50-60 chromosomes were counted. In the latter cells the exact number was difficult to obtain because of severely aberrant meiosis, showing a very irregular distribution of chromosomes in the equatorial plate (Figs. 5, 6). This seems to be an indication suggesting that systematically the two parental species are distantly related with each other. No. 2] Chromosomes of Papilio Hybrids. VIII 73

Figs. 1-6. Meiotic chromosomes of Papilio hybrids (M-I, M-II, 1-4: X2100, 5-6: x1200). 1-2: P, xuthus X P, benguetana, Fl. 3-4: P, polyxenes X P. xuthus, F1. 5-6: P, xuthusXP, machaon hippocrates, Fl. 1: n, 30, 2: n, 30 (M-II), 3: n, 44, 4: n, 51, 5-6: highly disorganized chromosomes in M-I metaphases of xuthus/machaon hybrids.

Remarks. Based on some hybridization experiments, Ae (1971) is of opinion that Papilio machaon forms a group systematically related to P. polyxenes and to some other North American species, and that P. xuthus is related with P. benguetana. Morphologically,

Fig. 7. Diagram illustrating the relationship of four species of Papilio, based on the analysis of meiotic pairing of chromosomes in hybrids.

P. xuthus was noted as a species of the Papilio machaon group on account of the morphological resembrance of male genitalia (Shirozu 1960). However, hybridization experiments made by Ae (1971) have shown that the two are not closely related, because P. xuthus and P. machaon have produced very frail male hybrids. Viewed from the chromosomal pairing observed in the M-I cells of these hybrids, certain gene differences are remarkable from the standpoint of genie homology. It then appears that P. machaon is closer to P. maackii 74 K. MAEKIand S. A. AE [Vol. 53, than to P, xuthus (Maeki and Ae 1964) on the basis of genie homology. Ranges of the chromosome-number variation and the number- mode observed in the interspecific hybrids from three combinations with P. xuthus were obtained as below: Cross Number variation Mode xuthus x benguetana 30 30 polyxenes x xuthus 44-55 48, 52 machaon hippocrates x xuthus 50-60 50-60 Based on the above cytogenetic data on hybrid chromosome pairing, the statements can be allowed that phyletically P. xuthus and P. benguetana are most closely related, and that the phylogenetic relation between P. polyxenes and P. xuthus, and that between P. machaon hippocrates and P. xuthus, rank in order.

References Ae, S. A.: Spec. Bull. Lep. Soc. Jap., No. 2, 75 (1966) and No. 5, 89 (1971). Lorkovic, Z.: Glasnik Hrv. Priridosl. Drustvo, Zagreb 2B, 2-3, 57 (1950). Biol. Glasnik, 21, 95 (1968). --: Period. biol., 76, 93 (1974). Maeki, K.: Trans. Lep. Sod. Jap., 25, 85 (1976). Maeki, K., and Ac, S. A.: Kwansei Gakuin Univ. Ronko, 11, 111 (1964). Spec. Bull. Lep. Soc. Jap., No. 2, 121 (1966). Spec. Bull. Lep. Soc. Jap., No. 4, 131 (1970). Proc. Japan Acad., 51, 577 (1975). Proc. Japan Acad., 52, 236 (1976). Proc. Japan Acad., 52, 308 (1976). --: Proc. Japan Acad., 52, 509 (1976). --: Proc. Japan Acad., 52, 567 (1976). Maeki, K., and Remington, C. L.: Journ. Lepid. Soc., 13, 193 (1960). Makino, S.: A Review of the Chromosome Numbers in . Rev. ed., pp. 300. Hokuryukan, Tokyo (1956). Remington, C. L.: Proc. 10th Int. Congr. Ent., 2, 787 (1958). White, M. J. D.: Cytology and Evolution. 3rd ed. Univ. Press, Cam- bridge (1973).