Chromosomes of lemuriformes. I. A chromosome complement of Lepilemur mustelinus (I. Geoffroy 1851)код для вставкиСкачать
Chromosomes of Lemuriformes I. A CHROMOSOME COMPLEMENT OF LEPlLEMUR MUSTELlNUS (I. GEOFFROY 1851) JOHN BUETTNER-JANUSCH,l ANDREW E. HAMILTON 1 AND JAN A. BERGERON Departments of A n a t o m y , Zoology, and Anthropology, Duke University. D u r h a m , North Carolina 2771 0 KEY WORDS Chromosomal satellites type . Lemur chromosomes. . Cytogenetics . Karyo- ABSTRACT The diploid chromosome number of two specimens of Lepilemur m u s t e l i n u s (I. Geoffroy 1851) is 2 N = 20. All of the chromosomes, except the Y chromosome, are metacentric or submetacentric; the Y chromosome is acrocentric and is the shortest chromosome in the complement. Satellites on autosoma1 pair 5 provide marked chromosomes for the animals studied and may be a marked pair for the species. The chromosomes of primates are significant data in the study of phylogenetic relationships among various living species in this mammalian order. Each karyotype enables us to increase the number of statements we can make about the probable direction of karyotype evolution in the primates (Bender and Chu, '63; Rumpler and Albignac, '70). The data available in the literature on primate chromosomes support the view that variation in chromosome complements is one of the mechanisms by which differentiation of populations into species occurs. Rearrangements in chromosome complements may eventually produce a reproductive barrier between two segments of what had been a single species. The purpose of this report is to describe the chromosome complement of two male individuals of Lepilemur mustelinus (fig. l), a small nocturnal member of the family Lemuridae. The diploid number we report, 2N = 20, is at the lower end of the range of diploid numbers reported by Rumpler ('72). Rumpler reports diploid numbers ranging from 2 N = 2 0 to 2 N = 3 8 from a number of specimens of Lepilemur m u s telinus (Rumpler, '72 and personal communication). The variety of diploid numbers and karotypes found within what is considered a single mammalian species is a remarkable example of intraspecific variation and imAM. J. PHYS. ANTHROP., 39: 1-6. plies that we must consider the systematics of that species, so we shall make a few remarks here about the systematics of Lepilemur. In 1960 Petter and PetterRousseaux revised the nomenclature and systematics of the genus. They concluded that the number of species that ForsythMajor (1894) constructed was not valid. Instead they defined one species, LepiLem u r mustelinus, with two subspecies, L. m. mustelinus and L. m . ruficaudatus. A discussion of the confusion produced by Forsyth-Major is to be found in Petter and Petter-Rousseaux ('60) and in Schwarz ('31). As we said, variation in diploid numbers and karyotypes of the sort reported by Rumpler is unusual for a single mammalian species, and it is possible that Forsyth-Major recognized valid specific distinctions despite the internal inconsistencies in his work noted by Schwarz ('31). MATERIALS AND METHODS Two male Lepilemur mustelinus (probably L. m. mustelinus, fig. 1) captured in Madagascar were sent to the Duke University Primate Facility in October 1969. Blood samples were taken immediately upon arrival. Both animals appeared to be in good health, and one of the two is still 1 Present address. Department of Anthropology, New York University, New York, New York 10003. 1 2 BUETTNER-JANUSCH, HAMILTON AND BERGERON Fig. 1 Lepilemur mustelinus, male (animal 1202, Duke University Primate Facility). 3 CHROMOSOMES OF LEPILEM U R M U S T E L I N U S alive and well, but the other died shortly after arrival for reasons not determined upon autopsy. Standard techniques for culturing leukocytes were used (Moorhead et al., '60). The cultures were prepared with TC Chromosome Microtest reagents (Difco). Slides were made by placing three or four drops of the suspension of cells on clean, dry microscope slides. The fixative was ignited and the slides allowed to dry (Moorhead et al., '60). Slides were stained for 30 minutes in a 2% Giemsa solution in phosphate buffer at pH 6.4, dried, and mounted in Permount (Fisher). Photomicrographs at a magnification of 720 X were taken on a Zeiss research microscope equipped with a Wild Photo-automat. Kodak high-contrast copy firm was used. Measurements were made on well-spread metaphase chromosomes with clearly defined centromeres. The figures were photographed and enlarged to a magnification of 3450 X , and the chromosomes were measured with calipers. Both arms of each chromosome were measured in 23 spreads. These results were verified by measuring the chromosomes visually at a magnification of 1000 X with a calibrated eyepiece. Chromosomes were classified as metacentric, submetacentric (subtelocentric), or acrocentric according to the definitions of Bender and Chu ('63). RESULTS AND DISCUSSION We counted 42 cells, 40 of which had a chromosome number of 20 (table 1). The autosomes were arranged in order of decreasing size and the sex chromosomes determined by elimination (fig. 2). The mean lengths of the autosomes in the metaphase figures vary between 2.8 pm and 10.5 pm. The mean arm ratios of the autosomes vary from 1.36 to 4.26 (table 2). The longest chromosomes in the compleTABLE I Diploid chromosome n u m b e r s of two m a l e Lepilemur mustelinus Diploid n u m b e r Animal Cells counted 19 20 21 1 20 0 20 0 2 22 1 20 1 ment, pairs 1, 2, and 3 (fig. 2), are not easy to distinguish from one another. They are similar in length and have similar arm ratios; the ratios for pairs 1 and 2 fall within the range defined as submetacentric; the ratio for pair 3 is in the metacentric range. Pairs 4 and 6 are submetacentric and are easily distinguished from each other by length and arm ratios (table 2). The chromosomes of pair 5, which are metacentric, are the most distinctive in the karyotype. In the distal third of the short arm, each has a conspicuous secondary constriction forming a characteristic satellite that marks the chromosome (fig. 2). Pairs 7, 8, and 9 (table 2) are the shortest autosomes, from one-third to onehalf the length of any one of the first six pairs. Pair 7 is submetacentric; pairs 8 and 9 are metacentric. The X chromosome, 3.29 0.17 pm in length, is submetacentric. The Y chromosome is the shortest in the karyotype, 0.7220.09 pm, and it represents only 1.3% of the total complement length. Its minuscule short arms make it the only acrocentric member of the karyotype ( r = 12.06). The fundamental number, NF (Matthey, '49), calculated by assigning a value of two to metacentric and submetacentric autosomes and one to acrocentric and sex chromosomes, is NF = 38. Rumpler ('72) reports NF ranging from 36 to 42 among the specimens of Lepilemur he examined. The values of NF for other members of the Lemurinae, the genera Hapalemur and Lemur, range from 62 to 70, outside the range of values reported for Lepilemur. When more results are available, the fundamental numbers should enable us to interpret the direction of evolution of the karyotypes of Lemurinae, if karyotype evolution proceeds primarily by the Robertsonian mechanism of centric fusion. The two animals whose karyotypes are reported here were captured in their native habitat and probably represent normal members of the species. However, karyotypes of only two individuals of a population must be considered tentative, especially for a species that appears to have so much karyotypic variation. The diploid number for Lepilemur mustelinus, 2N = 20, is the smallest reported for members of * 4 BUETTNER-JANUSCH, HAMILTON AND BERGERON Fig. 2 Karyotype and chromosome spread from male Lepilemur mustelinus. Arrows in chromosome spread indicate pair 5, the two chromosomes with secondary constrictions and satellites. 5 CHROMOSOMES OF L E P I L E M U R M U S T E L I N U S TABLE 2 Morphology of the chromosomes of two male Lepilemur mustelinus Relative length 2 Chromosome 1 2 3 4 5 6 7 8 9 X Y Mean S.E. 0.155 0.147 0.135 0.124 0.122 0.093 0.057 0.055 0.051 0.062 0.013 0.001 0.003 0.001 0.003 <0.001 < 0.001 < 0.001 0.002 0.001 0.001 0.002 5 1 Ratio ( r ) 3 Mean S.E. 2.29 2.16 1.95 3.78 1.76 4.26 2.01 1.36 1.69 2.84 12.06 0.05 0.06 0.04 0.10 0.04 0.30 0.07 0.07 0.08 0.20 0.30 5 Morphological classification 4 SM SM M-SM SM M SM SM M M SM A Calculations are based on measurements of 23 metaphase spreads. Relative length is the length of the chromosome as a proportion of the length of the haploid complement including the X chromosome. 3 r = Z/s where 1 is mean length of the long a r m and s is mean length of the short arm. 4 M, metacentric, r = 1.0-1.9; SM, submetacentric (subteloceutric), r =2.0-4.9; A, acrocentric, r = 5.0-m (Bender and Chu, ' 6 3 ) . 5 S.E., standard error of the mean. 1 2 the order Primates. The chromosome pair (pair 5 ) that characteristically has satellites may be a marked chromosome that will enable us to evaluate similarities and differences among karyotypes from individuals of the genus Lepilemur. Because of the intraspecific or intrageneric variation in diploid numbers, NF, and karyotypes reported for Lepilemur (Rumpler, '72), comparisons of many individuals of the genus are desirable and necessary. Techniques of chromosome banding (Finaz and de Grouchy, '71; Lomholt and Mohr, '71; Utakoji, '72) will certainly be useful. ACKNOWLEDGMENTS We wish to thank M. Georges Ramanantsoavina, Ingenieur en Chef des Eaux et For& de la Direction des Eaux et For& et de l a Conservation des Sols, Republique Malgache, for the two animals studied. We are particularly grateful to Dr. Yves Rumpler of the Laboratoire dHistologie, Embryologie-Cytogenetique, Ecole Nationale de Medecine, Universite de Madagascar, €or his advice and assistance. Mr. Victor Lukas and Mr. Richard Hackel provided invaluable advice with photographic techniques. The work was supported in part by NIH GM16722 (RCDA), NIH RR00388, and NSF GS2508 (BuettnerJanusch); by a n NIMH training grant to the Department of Sociology-Anthropology (Hamilton); and by Duke Endowment research funds (Bergeron). LITERATURE CITED Bender, M. A , , and E. H. Y . Chu 1963 The chromosomes of primates. In: Evolutionary and Genetic Biology of Primates. Vol. 1. J. BuettnerJanusch, ed. Academic Press, New York, pp. 261-31 0. Finaz, C., and J. de Grouchy 1971 Le caryotype humain aprks traitement par l'a-chymotrypsine. Ann. Genet., 1 4 : 309-311. Forsyth-Major, C. I. 1894 Diagnosis of a new species of the genus Lepidolemur. Ann. Mag. Nat. Hist., 6 (13): 211-219. Lomholt, B., and J. Mohr 1971 H u m a n karyotyping by heat-giemsa staining a n d comparison with fluorochrome techniques. Nature New Biology, 234: 109-110. Matthey, R. 1949 Les Chromosomes des Vertebres. F. Rouge, Lausanne. Moorhead, P. S., P. C. Nowell, W. J. Mellman, D. M. Battips a n d D. A. Hungerford 1960 Chromosome preparations of leukocytes cultured from h u m a n peripheral blood. Exper. Cell Res., 20. 613416. Petter, J. J., and A. Petter-Rousseaux 1960 Remarques sur la systematique du genre Lepilemur. Mammalia, 24: 76-86. Rumpler, Y. In press Cytogenetic contributions to a new classification of lemurs. Research Semin a r on Prosimian Biology, 1972, London. Rumpler, Y., and R. Albignac 1970 Evolution chromosomique des lemuriens malgaches. Ann. Univ. Madagascar, 12-13: 123-131. Schwarz, E. 1931 A revision of the genera and species of Madagascar Lemuridae. Proc. Zool. SOC.London: 399-428. Utakoji, T. 1972 Differential staining patterns of h u m a n chromosomes treated with potassium permanganate. Nature, 239: 168-170.