Bull. Biogeogr. Soc. Japan VoI. 44 Dec. 20, 1989
Geographic Variation of Chromosomes in Sabacon makinoi Suzuki (Arachnida, Opiliones, Sabaconidae)
Nobuo Tsurusaki
Abstract. Chromosomes of Sabacon makinoi Suzuki were surveyed from five populations in Hokkaido and the northernmost part of Honshu, Japan. Chromosome numbers (2n=1O to 14) were found to vary among and sometimes within populations. Out-group comparison and the spatial distribution of the chromosome variants suggest that 2n=14 is the plesiomorphic state and the evolution proceeded with a decrease in the chromosome number. Centric fusion is considered the most important type of chromosome rearrangement responsible for the karyo typic change.
Harvestmen of the family Sabaconidae are the details of the method, see Tsurusaki (l985a), represented by two genera and about 40 species, and Tsurusaki and Cokendolpher (in press). The and are sporadically distributed in temperate format of the description of karyotypes including regions of the Northern Hemisphere (Martens, idiograms follows Tsurusaki and Cokendolpher 1972, 1983; Suzuki, 1974; Shear, 1975, 1986; (in press). The samples were collected from the Cokendolpher, 1984). Their cytology has been following localities: 1) Asamushi, Hachiman-gu seriously neglected due to the rarity and the small Shrine, a site in Japanese red ceder, Cryptomeria size of these opilionids. Chromosome numbers japonica forest, 20 malt., Aomori Pref.; 2) Onuma are known for only two species: Sabacon par adoxum Simon from Europe (2n=16; Juberthie, 2n-14 1956) and S. pygmaeum Miyosi from Japan (2n= 14; Suzuki, 1966). This paper reports observa tions on an additional species, S. makinoi Suzuki sampled from five different populations in north ern Japan. Sabacon makinoi Suzuki is mainly found in eastern Japan, namely Hokkaido, Honshu (Chubu , district and northward, northeastern part of Hiroshima Prefecture), and Shikoku (Mt. Tsurugi, Tokushima Prefecture) and in Korea (Suzuki, 1974; Suzuki & TSUfusaki, 1983). This species is found in leaf litter and under stones and logs on o the forest floor. The life cycle of S.makinoi is , , Sabacon •• .akinoi not fully known. However, the results obtained ", from periodical field surveys conducted at two -- localities in and near Sapporo, Hokkaido, in 1979 show that this species overwinters as eggs and Sabacon •• sugi.atoi various stages of juveniles (Tsurusaki, unpubl.). • • Materials and Methods Fig. I. Distribution and chromosome numbers of Sabacon makinoi in Hokkaido and the north The cytological data were obtained from air ernmost part of Honshu. A, Asamushi; B, dry preparations of testes or ovaries of field-col Onuma; C, Maruyama; D, Nopporo; E, Wak lected adults and juveniles of later instars. For kanai.
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Park, ca. 150 malt., Nanae-ch6, Kameda-gun, with 2n = 12 and its haploid idiogram are shown Hokkaido; 3) Maruyama, Sapporo; Hokkaido; 4) in Fig. 2B and Fig. 3, respectively. Autosomes Nopporo, Ebetsu, Hokkaido; 5) Wakkanai Park, are composed of one pair of metacentrics (No. 4), 60 malt., Wakkanai, Hokkaido (Fig. 1). The two pairs of submetacentrics (Nos. 1, 2), one pair of data are tabulated in Table 1 together with the subtelocentrics (No. 5), and one pair of acrocel) results. S. makinoi is divided into two subspecies tries (No. 3). The X chromosome is a metacentric by the difference in the degree of developement of being second largest in size, while Y is sub abdominal scutum in females. Females of S. metacentric and somewhat smaller than the X. makinoi makinoi Suzuki, inhabiting Hokkaido, The outstanding feature of the karyotype is the always have a somewhat sclerotized scutum on presence of large submetacentric chromosomes their abdomens. Females of S. makinoi sugimotoi which occupies about one fourth of the total Suzuki et Tsurusaki, inhabiting Honshu and chromosome length (TCL) (Fig. 3). Further Shikoku, have no marked scutum (Suzuki & study is needed to comprehend this discrepancy Tsurusaki, 1983; Affiliation of Korean popula in chromosome numbers. tions remains unknown, since no female has been collected from those areas). Of the present Onuma population: 2n = 10 (0') materials, only the Asamushi population belongs Diploid chromosomes were clearly counted to S. makinoi sugimotoi. as 10. Unfortunately, chromosome slides stored under inappropriate condition were so severely deteriorated before photographing that its karyo Results type remains unknown. The results are summarized in Table 1 and karyotypes are shown in Fig. 2. Haploid id i Maruyama population: 2n = 10 (0', 'fl) ograms obtained from some karyotypes are pre The karyotype is composed of four pairs of sented in Fig. 3. autosomes and one pair of sex chromosomes (0': XY,'fl: XX) (Figs. 2C-D, 3). Autosomes are ig. 2. Karyotypes of Sabacon makinoi. A, Asamushi, male (2n=14); B, Asamushi, male (2n=12); C, D, Maruyama(2n=10). C, male; D, female; E, Nopporo, male (2n=12); F, Wakkanai, female Asamushi population: 2n = 12 (0', 'fl) and 14 (0'). metacentric without exception. The X chromo (2n= 14). Scale=5 (tm. Chromosome observations were made for spe some is metacentric similar in size to chromosome cimens collected from the same site at Asamushi No. 3, and Y is the shortest metacentric. MARUYAMA, 2n=10 in two consecutive years (1981 and 1982). Two -l 20 males used in 1981 preparations showed 2n = 14, Nopporo population: 2n = 12 (0') ...u whereas two males and two juveniles (one male The karyotype consists offive pairs of autosomes ....o and one pair of sex chromosomes (Figs. 2E, 3). Cl> and one female) in 1982 showed 2n = 12 without "4 exception. Figure 2A shows the male karyotype Autosomes comprise of two pairs of metacentrics ~ 10 30 with 2n = 14. Unfortunately, the detailed karyo (Nos. 1,2), one pair of subtelocentrics (No. 3), 8... type is unknown. The sex chromosome com and two pairs of acrocentrics (Nos. 4, 5). The X ~ ASAMUSHI,2n=12 position is probably XY. The male karyotype chromosome is a metacentric similar in size to o 20 x Y Table 1. Chromosome numbers in five populationsof Sabacon makinoi. j=juvenile(s).
20 NOPPORO,2n=12 2n chrom. number No. modal cells Locality Date No. indiv. obs. (CS/';f) CS ';f 10 Asamushi 23-YII-1981 2CS 14 7/- 2-YII-1982 2 CS 2j(CS, ';f) 12 12 27/ 4 10 Onuma 29-Y-1984 I CS 10 3/- o Maruyama 22-YI-1982 2 CS 2j(CS, ';f) 10 10 44/ 6 x Y 15-YII-1982 3CS 10 14/- 22-X-1982 8j(4CS,4';f) 10 10 66/19 o Nopporo 20-IX-1982 I CS 2j (CS) 12 5/- x Y Wakkanai 7-YJI-1984 1 ';f 14 -/8 ig. 3. Idiograms of some populations of Sabacon makinoi. TCL (total chromosome length) is a total of lengths of all haploid autosomes and an X chromosome.
-112- -113- Tsurusaki, N. Chromosomes of Sabacon makinoi chromosome No. 2, while Y is the shortest meta 2n=12 and 14, respectively. The proposed origin yama population) was formed by centric fusion Sabacon Simon 1879 (Arachnida: Opiliones: 'Saba centric. of this geographic pattern of chromosome varia of two acrocentric pairs (Nos. 4 and 5 in Nopporo conidae). Senckenb. BioI., 63: 265-296. tions is presented in Fig. 4 and is explained as population). Likewise, the Asamushi popula Minato, M., 1972. Late Quaternary geology in northeni Japan, pp. 63-71. In: Fyles, J. G., Stalker, Wakkanaipopulation: 2n=14 (~) follows: tion with 2n=12 has two acrocentric or sub Only one female was karyotyped. 2n chromo Stage 1: Ancestral populatipn of S. makinoi A. M. and W. O. Kupsch (eds.), International Geo telocentric pairs. Derivation of 2n=10 form from logical Congress, 24th Session, Section 12. HarpeII's, some number was determined as 14 (Fig. 2F). The had invariably 2n=14 chromosomes. this variant can also be envisaged in the same Gardenvale, PQ, Canada. detailed karyotype is unknown, although it seems Stage 2: A new chromosomal form with 2n= manner. However, centric fusion is not likely --- (ed.), 1978. Atlas of the Geologic Develop to contain some pairs of acrocentrics and some 12 occurred somewhere in what is now the south to be the only mechanism causing the changes in ment of the Japanese Islands. Tsukiji-Shokan, pairs of submeta- or metacentrics. Since no western part of Hokkaido/northern Honshu and karyotypes. The presence of a large chromosome Tokyo. 124 pp. (In Japanese.) male could be studied, no information on sex displaced the former chromosomal type with 2n = (No. 1) in the Asamushi population, for instance, Juberthie, c., 1956. Nombres chromosomiques chez chromosomes is available. 14. This event should have preceeded the com suggests that also other rearrangement mech les Sironidae, Trogulidae, Ischyropsalidae, Phalangi pletion of the Tsugaru Straight between Hokkaido anisms, such as tandem fusion or pericentric inver idae (Opilions). C. R. Acad. Sci., Paris, 242: 2860 Discussion and Honshu (ca. 18,000 years ago; Minato, 1972). sion, participated in the changes of chromosome 2862. Stage 3: Following the completion of the morphology. Further study is needed to infer Shear, W. A., 1975. The opilionid genera Sabacon and Tomicomerus in America (Opiliones, Troguloidea, Diploid chromosome numbers in Sabacon maki Tsugaru Straight,another new chromosomal detailed process of karyotype evolution. Ischyropsalidae). J. ArachnoI., 3: 5-29. noi range from 10 to 14. Of these numbers, 14 is form with 2n=10 arose in the midst of the range Effects of this karyotype diversity on the mor --- 1986. A cladistic analysis of the opilionid considered to be primitive by out-group com occupied by the northern 2n=12 variant and phological evolution or speciation are unclear. superfamily Ischyropsalidoidea, with descriptions parison. Its immediate sister species, S. pygmaeum spread over the southwestern part of Hokkaido. As stated earlier, among the populations studied of the new family Ceratolasmatidae, the new genus (Suzuki, 1974; Suzuki & Tsurusaki, 1983), is Comparisons among the various karyotypes the Asamushi population differs from the others Acuclavella, and four new species. Amer. Mus. distributed in the western part of Japan and has suggest that centric fusion was the main cause on Hokkaido in morphology of the abdominal Nov., 2844: 1-29. 2n=14 (Suzuki, 1966). Spatial distribution of responsible for the reduction in chromosome num integument of females. Both karyotypes (2n = Suzuki, S., 1966. Opiliones, pp. 90-139. In: Uchida, known chromosome numbers also supports this ber. Namely, there seems to be a general trend 12 and 14) from Asamushi seem to differ from T. (ed.), "Dobutsu KeitobuDfuigaku (Systematic supposition. Namely, there is a nested pattern, that the number of meta- or submetacentrics any other karyotype found in Hokkaido. How Zoology)" 7 (2A). Nakayama-shoten, Tokyo. (In populations with lower numbers intervene between decreases with an increase in the number of acro ever, it is premature to discuss the involvement Japanese.) ---, 1974. The Japanese species of the genus the two isolated populations with identical higher or subtelocentrics. For example, Maruyama popu between the karyotype change a~ddifferentiation Sabacon (Arachnida, Opiliones, Ischyropsalididae). numbers (Fig. 1). When such a nested pattern is lation with 2n = 10 is composed entirely of met of external morphology in this species. observed, it is most likely that the character state acentrics, whereas the Nopporo population is 2n = J. Sci. Hiroshima Univ., (B), (1), 25: 83-108. & N. Tsurusaki, 1983. Opilionid fauna occupying the more central geographical position 12 with two typical acrocentric pairs (Nos. 4, 5). Acknowledgments of Hokkaido and its adjacent areas. J. Fac. Sci. is apomorphic (Tsurusaki, 1985b). Thus 2n=1O It is most probable that one metacentric pair of Hokkaido Univ., (VI), 23: 195-243. and 12 can be considered apomorphic relative to autosomes (possibly No. 1 chromosomes in Maru- I am grateful to Mr. James C. Cokendolpher of Tsurusaki, N., 1985a. Taxonomic revision of the Texas Tech University for his review of the draft. Leiobunum curvipalpe-group (Arachnida, Opiliones, The following persons and institutes provided Phalangiidae). I. hikocola-, hiasai-, kohyai-, and facilities during this work: Dr. Haruo Katakura platypenis-subgroups. J. Fac. Sci. Hokkaido Univ., (Hokkaido Univ.); Dr. Masanori Sato (Kagoshi (VI), 24: 1-42. ma Univ.) and the staff of the Asamushi Marine ---1985b. Geographicvariationof chromosomes Biological Station, Tohoku University; Dr. and external morphology in the montanum-subgroup Masaki Takahashi (Marine Biomedical Institute, of the Leiobunum curvipalpe-group (Arachnida, Sapporo Medical College). This study was Opiliones, Phalangiidae) with special reference to its presumable process of raciation. ZooI. Sci., 2: partly supported by a Grant-in-Aid (no. 63740434) 767-783. from the Ministry of Education, Science and --- & J. C. Cokendolpher, in press. Chromo Culture, Japan. somes of sixteen species of harvestmen (Arachnida, , Opiliones, Caddidae and Phalangiidae). J. ArachnoI. References (Tsurusaki, N.: Department of Biology, FacuIty of Cokendolpher, J. c., 1984. A new species of Sabacon Education, Tottori University. Tottori, 680 Japan) from Oregon (Arachnida: Opiliones: Sabaconidae). Fig. 4. A hypothetical process of differentiation of karyotypes in Sabacon makinoi. Thick solid contour Can. J. ZooI., 62: 989-991. lines in stages 1-2 show shore lines around Hokkaido and the northernmost part of Honshu in the Martens, J., 1972. Opiliones aus dem Nepal-Himalaya, mid main WOrm ice age (late Pleistocene; ca. 20,000-18,000 years ago) and in stage 3 the postglacial I. Das Genus Sabacon Simon (Arachnida: Ischy period (Holocene, ca. 6,000 years ago) (after Minato, 1978). Present-day shore lines are depicted ropsalididae). Senckenb. BioI., 53: 307-323. with thin solid lines. Explanation in text. --- 1983. Europaische Arten der Gattung
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