Propithecus Verreauxi Coquereli (Primates, Indriidae)
International Journal of Primatology, Vol. 4, No. 4, 1983
The Banded Chromosomes of Coquerel's Sifaka, Propithecus verreauxi coquereli (Primates, Indriidae)
P. A. Poorman ~
Received September 9, 1982; revised November 30, 1982
The karyotype of Propithecus verreauxi coquereli is described in this report using G-, Q-, and C-banding and silver staining for nucleolus organizer regions. The banded chromosomes of P. v. coquereli (family Indriidae) are compared with those of Lemur fulvus fulvus (family Lemuridae), revealing few karyotypic similarities between the two groups and suggesting a well- established phylogenetic divergence between these families.
KEY WOKD~: l-'roplthecus; Indriidae; banded karyotype; chromosomal evolution.
INTRODUCTION
The family Indriidae, composed of three genera, Propithecus, Indri, and Avahi, is included in the infraorder Lemuriformes, all of whose members are restricted to the island of Madagascar and the Comoro Islands. The anatomical and behavioral features of the indriids indicate that they form a cohesive group; however, their unbanded karyotypes differ in both diploid number and fundamental number (Rumpler, 1975). The genus Propithecus is represented by two known species, P. verreauxi (A. Grandidier, 1867) and P. diadema (Bennett, 1832), each with different unbanded karyotypes. The diploid number determined from unbanded preparations is 48 for P. verreauxi and 42 for P. diadema (Rumpler, 1975). In this study a banded karyotype is established for P. verreauxi coquereli.
~Department of Anatomy, Duke University Medical Center, Durham, North Carolina 27710. 419
0164-0291/83/1200-0419503.00/0 1983 PlenumPublishing Corporation 420 Poorman
The banded karyotype of Propithecus might be expected to resemble more closely the banded karyotype of the Lemuriformes, of which it is a member, rather than the Lorisiformes. In order to look for karyotypic similarities between Propithecus and Lemur, the banded chromosomes of P. v. coquereli are compared with those of L. fulvus fulvus in this study.
MATERIALS AND METHODS
A 3-ml heparinized blood sample was drawn from one male P. v. coquereli housed at the Duke University Center for the Study of Primate Biology and History. The lymphocytes were cultured and processed using the procedures of Dresser and Hamilton (1979) and Poorman (1982). Slides were G-banded (Dresser and Hamilton, 1979), Q-banded (Miller et al., 1971; Poorman, 1982), C-banded (Schreck et al., 1977), or silver stained for nucleolus organizer regions (NORs) by the AgAS procedure (Goodpasture and Bloom, 1975). Six mitotic karyotypes were measured for relative lengths and arm ratios of the chromosomes using a Numonics graphics calculator (Moses et al., 1977). Metacentric, submetacentric, and acrocentric classifications are based on the centromeric nomenclature of Bender and Chu (1963). Chromosomes with arm ratios of 1.0-1.9 are metacentric, 2.0--4.9 are submetacentric, and greater than 5.0 are acrocentric.
RESULTS
The modal diploid number of P. v. coquereli is 48. The karyotype consists of 10 autosomal submetacentrics, 20 autosomal metacentrics, and 16 autosomal acrocentrics. The Y chromosome is a small acrocentric, and the X, a medium sized submetacentric. The autosomal fundamental number is 76. The largest chromosome pair, averaging 9.9 #m in early and midmetaphase spreads, is easily identifiable. The rest of the chromosomes show a serial reduction in length from 7.0 to 0.8 #m, with the X chromosome approximately 2.8 #m (falling in position 12) and the Y chromosome approximately 1.2 #m. G- or Q-banding allows the identifica- tion of each of the autosomal pairs and the sex chromosomes. Figure 1 shows one G- and one Q-banded chromosome for each pair in the karyotype of P. v. coquereli, together with an idiogram showing the bands typically seen at metaphase. The autosomes are ordered by relative length. C-banded preparations consistently show pronounced centromeric staining on each chromosome (Fig. 2). One of the small acrocentrics has Banded Chromosomes of Coquerel's Sifaka 421
1 2 3 4 5
6 7 8 9 10
11 12 13 14 15
16 17 18 19 20
21 22 23 X Y
Fig. 1. Haploid mitotic karyotype of P. v. coquereli: G-banded chromosome (left), idiogram of G- and Q-banded pattern (center), and Q-banded chromosome (right). Bar = 10 ~tm. additional C-positive material in its long arlia and is most likely the Y chromosome since the acrocentric Y of Lemur also has additional C- positive material. Sequential AgAS staining after either G- or Q-banding reveals two pairs of NOR-bearing chromosomes, pairs 16 and 18. In each case, the NOR is adjacent to the centromere in the long arm of the chromo- some. Only a few similarities exist between the G-banded Chromosomes of P. v. coquereli and those of L. f. fulvus (Hamilton and Buettner-Janusch, 1977). Propithecus chromosomes lq, 18, and 20 have banding patterns 422 Poorman
Fig. 2. C-banded metaphase spread of P. v. coquereli. Three chromosomes appear to be almost completely heterochromatic, the Y chromosome at 12:00 and the No. 23 chromosomes at center and at 9:00. The chromosome at 1:00, which appears to be a long acrocentric, is actually a sub- metacentric with the short arms folded under. Bar = 10~m.
identical to those of L. f. fulvus chromosomes lq, 21, and 25. The Y chromosome in both species is a small acrocentric with a terminal band. P. v. coquereli has a submetacentric X chromosome which does not resemble the acrocentric X of L. fulvus or the submetacentric X chromosomes of other species of Lemur. C-bands in P. v. coquereli are similar to those in L. f. fulvus in being very prominent and present at all centromeres.
DISCUSSION
Comparative studies of banded chromosomes of prosimians can provide information about the evolutionary relationships of different but related species. The extent to which the karyotypes of two groups resemble each other is a measure of the closeness of their relationship in a phylo- genetic sense. Correlation of the cytogenetic results with the classical morphological and geographical criteria, together with recent biochemical and immunological data, can help to resolve some of the conflicts in the taxonomic classifications of the prosimians. Although the precise relationship of the Indriidae with the other Lemuriformes and Lorisiformes is not clear, several lines of evidence have been used to construct cladograms which place the Indriidae among the other members of the Lemuriformes and Lorisiformes. In a systematic analysis of morphological and behavioral characteristics of the Strepsirhini, Eaglen (1980) constructed a cladogram in which the Indriidae are placed as Banded Chromosomes of Coquerers Sifaka 423 a sister group to the Lemuridae. This lemur-indriid dade then forms a sister group to the Lorisidae, Galagidae, and Cheirogaleidae. On the basis of Eaglen's results, the Indriidae would be expected to have some karyotypic similarities with the Lemuridae. TattersaU (1982) has constructed a cladogram primarily on the basis of craniodental morphology, in which an Indri group (composed of the Indriidae, their subfossil relatives, and Daubentonia) belongs to a lemur clade. In this scheme, the Indriidae would be expected to have more karyotypic similarities with Daubentonia and the Lemuridae than with other groups. Phylogenetic reconstructions using data from immunodiffusion tests (Dene et al., 1976; Goodman, 1975) show that Propithecus (Indriidae) is most closely related to the Lemuridae and that these two groups are closer to cheirogaleids than to Daubentonia. In turn, cheirogaleids, Daubentonia, Propithecus, and Lemur are closer to each other than to lorisoids. From these results, more karyotypic similarities would also be expected between the Indriidae and the Lemuridae than between the Indriidae and other groups. However, a comparison of the banded chromosomes of P. v. coquereli and L. f. fulvus reveals few karyotypic similarities. This is not what would be expected on the basis of the immunodiffusion tests and an analysis of morphological and behavioral characteristics. If Propithecus is more closely related to the Lemuridae than to any other group, the relationship based on a comparison of the banded karyotypes does not seem to be a very close one, suggesting a well-established phylogenetic divergence between the Indriidae and the Lemuridae. The Propithecus karyotype also differs to a similar degree from that of another of the Lemuriformes, Cheirogaleus medius. Most of the latter's chromosomes (27 of 32 autosomal pairs) are indistinguishable from those of L. f. fulvus, despite a few notable differences (Dresser and Hamilton, 1979). Thus, the chromosomes of Propithecus are more removed from those of Lemur than are those of Cheirogaleus. Propithecus has four small chromosomes which appear to be identical to chromosomes in C. medius (P. v. coquereli chromosomes 18, 19, 20, and 21 have the same G-banding patterns as C. medius chromosomes 22, 25, 28, and 27), two of which (chromosomes 25 and 27 in C. medius) are not present in L. f. fulvus. C. medius chromosome 1, which is thought to be primitive because it is acrocentric, is postulated to have given rise to L. f. fulvus submetacentric 1 by Robertsonian translocation to another acrocentric and loss of G-positive material (Dresser and Hamilton, 1979). 424 Poorman
The long arm of this submetacentric in L. f. fulvus is identical to the long arm of P. v. coquereli 1. Thus, it seems that both may have arisen from ari ancestral homologue of C. medius chromosome 1. All three Lemuriformes, Propithecus, Lemur, and Cheirogaleus, are distinctly different from the lorisoid Galago CrasMcaudatus. A comparison of the banded chromosomes of C. medius and G. crassicaudatus reveals few karyotypic similarities (only five chromosome arms are the same; Poorman, 1982). The banded karyotype of P. v. coquereli is also very different from that of G. crassicaudatus but has at least 10 chromosome arms which are identical to arms in G. crassicaudatus, only 2 of which are also present in C. medius and L. f. fulvus (P. v. coquereli 18 and 20). It cannot be determined at this time if the additional chromosome arms which are shared between Propithecus and G. crassicaudatus have been retained from an ancestor common to both groups or whether the shared chromosomes represent synapomorphies. Further studies are needed to see if the banded karyotype of P. v. coquereli more closely resembles that of other members of the Lemuriformes, in particular Daubentonia, or even other Lorisiformes. The intrageneric karyotypic relationship of P. verreauxi with P. diadema and with other members of the Indriidae also needs to be determined. The results so far suggest that karyotypes of the Indriidae may set them apart from all other groups of prosimians, as do certain of their morphological and behavioral features, but still allow them to retain their cohesiveness as a family. Further studies will show whether the cytogenetic results are in agreement with classical taxonomy, as well as data from the studies of anatomy, behavior, ecology, immunology, and biochemistry.
ACKNOWLEDGMENTS
I would like to thank the management and staff of the Duke University Center for the Study of Primate-Biology and History, especially Mr. Michael Stewart and Ms. Andrea Katz, for providing the blood samples used in this study. I am very grateful to Dr. Montroge J. Moses and Mr. Michael Dresser for their helpful advice and comments on the manuscript and to Dr. Elwyn Simons, Dr. Matt Cartmill, and Mr. John Wible for their useful suggestions. I especially wish to acknowledge the expert assistance of Ms. Meredith Drapkin, Ms. Beth Hockey, Ms. Marlene Johnson, and Mr. Todd Gambling in the course of this work. Funding for this project was provided by NIH Grant GM-23047 to Dr. M: J. Moses. Banded Chromosomes of Coquerel's Sifaka 425
REFERENCES
Bender, M. A., and Chu, E. H. Y. (1963). The chromosomes of primates. In Buettner- Janusch, J. (ed.), Evolutionary and Genetic Biology of Primates, Vol. 1, Academic Press, New York, pp. 261-310. Dene, H. T., Goodman, M., and Pryehodko, W. (1976). Immunodiffusion evidence on the phylogeny of the primates. In Goodman, M., Tashian, R. E., and Tashian J. H. (eds.), Molecular Anthropology, Plenum Press, New York, pp. 171-195. Dresser, M. E., and Hamilton, A. E. (1979). Chromosomes of Lemuriformes. V. A com- parison of the karyotypes of Cheirogaleus medius and Lemur fulvus fulvus. Cytogenet. Cell Genet. 24: 160-167. Eaglen, R. H. (1980). The Systematics of Living Strepsirhini, with Special Reference to the Lemuridae, Ph.D. thesis, Duke University, Durham, N.C. Goodman, M. (1975). The protein sequence and immunological specificity: their role in phylogenetic studies of primates. In Luckett, W. P., and Szalay, F. S. (eds.), Phylogeny of the Primates, Plenum Press, New York, pp. 219-248. Goodpasture, C., and Bloom, S. E. (1975). Visualization of nucleolar organizer regions in mammalian chromosomes using silver staining. Chromosoma 53: 37-50. Hamilton, A. E., and Buettner-Janusch, J. (1977). Chromosomes of Lemuriformes. III. The genus Lemur: Karyotypes of species, subspecies, and hybrids. Ann N.Y. Acad. Sci. 293: t25-159. Miller, O. J., Miller, D. A., Kouri, R. E., Allderdice, P. W., Dev, V. G., Grewal, M. S., and Hutton, J. J. (1971). Identification of the mouse karyotype by quinacrine fluorescence and tentative assignment of seven linkage groups. Proc. Natl. Acad. Sci. USA 68: 1530-1533. Moses, M. J., Slatton, G. H., Gambling, T. M., and Starmer, C. F. (1977). Synaptonemal complex karyotyping in spermatocytes of the Chinese hamster (Cricetulus griseus). III. Quantitative evaluation. Chromosoma (Berl.) 60: 345-375. Poorman, P. A. (1982). Banded chromosomes of Galago crassicaudatus monteiri, G. c. gernetti; and a subspecific hybrid. Cytogenet. Cell Genet. 34: 296-304. Rumpler, Y. (1975). The significance of chromosomal studies in the systematics of the Malagasy lemurs. In Tattersall, I., and Sussman, R. W. (eds.), Lemur Biology, Plenum Press, New York, pp. 25-40. Schreck, R. K., Breg, W. R., Erlanger, B. F., and Miller, O. J. (1977). Preferential derivation of abnormal human G-group-like chromosomes from Chromosome 15. Hum. Genet. 36: 1-12. Tattersali, I. (1982). The Primates of Madagascar, Columbia University Press, New York.