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7. Chromosonlal Evolution in Gazelles and its Relevance to Conservation Steven C. Kingswood and Arlene T. Kumamoto Abstract: Chromosomes ofgazelles (genus Gazella) vary in diploid number (2n) from 30 to 58. The fundamental number (FN) has been reported to range from 58 to 72. Chromosomal evolution in the genus is believed to have been predominated by Robertsonian translocations of the centric fusion type. Autosome-to-sex chromosome trans locations have been documented in all species in which banding analyses have been conducted. Comparative cytogenetic studies support affinities, as established by morphological data, between certain taxa of gazelles. Chromosomal studies are unique in their ability to quickly document the complete genetic constitution ofan organism, albeit at a gross level of resolution. Intraspecific chromosomal variation demonstrated in G. dama, G. soemmerringi, and G. subgutturosa illustrates the importance of cytogenetics in identifying biological diversity not detectable through other measures. Chromosomes have a major role in the concept of biological species because of the potential for chromosomal rearrangements to effect reproductive isolation. Thus, conservation efforts aimed at preserving biological diversity are served by studies that document chromosomal variation in gazelles. Keywords: Gazella, chromosomes, evolution, cytogenetics, conservation, wildlife management. Introduction Nine taxa of gazelles (genus Gazella) are currently recognized by the World Conservation Union as threatened (IUCN, 1990). Conservation efforts for gazelles are complicated, however, by the uncertain taxonomy of the genus. Reviews by Gentry (1971), Corbet (1978), and Groves (1988) place 12 to 16 species in the genus Gazella, and taxonomic revisions based on morphological data continue to be made on a regular basis. Cytogenetic studies have demonstrated considerable chromosomal variation among gazelles, both interspecifically and intraspecific ally , but the relationships between chromosomal and morphological variation are complex and not wellunderstood. However, chromosomal variation is well-established as a potential reproductive isolating mechanism, and the identification of chromosomal variation serves in the identification of biological species. Cytogenetic studies are relevant to conservation through the identification of biological diversity that may not be apparent morphologically and in documenting potential reproductive isolation among chromosomally divergent populations. The purposes of this paper are to discuss chromosomal evolution in gazelles, comparing the evolutionary implications of these data with taxonomic relationships inferred from morphological data, to discuss the role of chromosomes in the biological species concept, and to establish the relevance of chromosomal studies to the conservation of gazelles. 77
Chromosomal evolution in gazelles Chromosomes of Gazella vary in diploid number (2n) from 30 in female G. dorcas, G. granti, and G. subgutturosa, to 58 in G. ruftfrons and G. thomsoni (Table 7.1). Variation in diploid number among gazelles is primarily the result of fusions or fissions between chromosomal arms. This is evidenced by the fact that the chromosomal arm number (commonly referred to as the fundamental number or FN) for gazelles has little variation. The FN is usually 58 to 62 but may be higher in G. thomsoni and G. saudiya (Table 7. 1) . Compound sex chromosomes, formed by the fusion of an autosome (i.e. a chromosome other than a sex chromosome) to the X and/or Y chromosome, are common among gazelles. The findings of all known chromosomal studies of gazelles are summarized in Table 7.1 . Todd (1975) proposed that chromosomal evolution in artiodactyls, including gazelles, has been predominated by karyotypic fissioning, whereby metacentric (bi-armed) chromosomes of putative ancestors split at their centromeres. This resulted in an increase of the number of chromosomes as fission of a metacentric produced two acrocentric (single-armed) chromosomes. However, the most widely accepted theory emphasizes centric fusion events. Centric fusion between two acrocentrics would produce a single metacentric chromosome and result in lowering the diploid number. Chromosomal rearrangements of autosomes that involve centric fusions are often termed Robertsonian translocations. In studies of mammalian karyotypic evolution, Robertsonian trans locations are the most frequently encountered chromosomal rearrangements. Gallagher and Womack (1992) presented evidence supporting centric fusions as driving chromosomal evolution in the family Bovidae. Chromosomal evolution in the form of Robertsonian translocations has resulted in both interspecific and intraspecific variation in the diploid number of gazelles. Variation in the diploid number between gazelles of the subgenus Nanger (G. granti, G. soemmerringi, and G. dama) can be attributed to four Robertsonian rearrangements and an autosome-to-Y chromosome translocation. Intraspecific variation in the diploid number of G. dama, G. soemmerringi, and G. subgutturosa is due to Robertsonian translocations (Effron et ai., 1976; Benirschke et ai., 1984; Benirschke and Kumamoto, 1987). G. dama and G. subgutturosa are polymorphic for single centric fusions; G. soemmerringi is polymorphic for three centric fusions. It is important to note that Robertsonian translocations involve a change in the structure of the chromosomes, but do not involve loss or gain of genetic material, except for theoretical loss of minute centromeres. Autosome-to-X chromosome translocation is another common chromosomal rearrangement found in gazelles. Twelve species studied to date have a compound X chromosome (Table 7.1). Previous studies did not identify G. thomsoni as having the autosome-to-X chromosome translocation, but banding analysis resulting in higher resolution of chromosomal structure indicates that G. thomsoni possesses this translocation (Kumamoto, unpublished data). This rearrangement involves the fusion of an acrocentric autosome to the X chromosome. Since males have only one X chromosome, one member of the autosomal pair remains unfused, and this usually results in males having an additional chromosome. However, in G. soemmerringi, G. dama, G. ruftfrons, and G. thomsoni, an autosome-to-Y chromosome translocation also exists, giving these species compound X and compound Y chromosomes (Table 7.1). Analyses of G-banded karyotypes indicate that the autosome translocated to the X chromosome is the same in G. soemmerringi (Benirschke et ai., 1984), G. subgutturosa (Kingswood and Kumamoto, 1988), G. dama (Arroyo Nombela et al. , 1990), 78
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CONSERVATION OF ARABIAN GAZELLES
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• 14 Survey of Gazelle Populatio
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List of Contributors Prof. Abdulaz
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Foreword HRH Prince SAUD AL-FAISAL
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1. Recent Developments in Gazelle C
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• April, 1988: Survey of the Fara
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- May, 1991: Capture of rheem from
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References Abuzinada, A., 1987. Int
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until Groves (1983) re-examined the
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Figure 2.1 a Figure 2.1 b
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Dissatisfaction with the BSC over t
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Nixon & Wheeler (1990) are not so d
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In order to test the PSC (phylogene
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(2) FEMALES Variable gazella cora
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two adult male and one adult female
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4 4 * 4 3 2 *33 1 1 * 1 * 2 1 1 I 5
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(2) FEMALES Variable G. bennelli (
Page 36 and 37: In the two other equally parsimonio
Page 38 and 39: ufifrons benneui saudiya subguuurcs
Page 40 and 41: By branch-swapping, using Macelade,
Page 42 and 43: On my first visit to AI-Areen, in 1
Page 44 and 45: anch of the premaxilla generally to
Page 46 and 47: J.R., and Morrison-Scott, T.C.S. 19
Page 48 and 49: Aden: 12°50'N, 45°03'E (4 skins,
Page 50 and 51: species is currently the subject of
Page 52 and 53: One area where local people are ins
Page 54 and 55: 4. The Relationship Between Taxonom
Page 56 and 57: 'I1Ie current status of taxonomy Ad
Page 58 and 59: There is much scope for conflict be
Page 60 and 61: The Controversial Subject of Gazell
Page 62 and 63: • Taxonomic argument: The divisio
Page 64 and 65: conventional taxonomic characters t
Page 66 and 67: divergence between the mitochondria
Page 68 and 69: Morphometries: Some morphological c
Page 70 and 71: operative progranune could be set u
Page 72 and 73: museum specimens (data extracted fr
Page 74 and 75: Acknowledgements This work was carr
Page 76 and 77: Lange, 1. 1972. Studien an Gazellen
Page 78 and 79: 6. Modern Techniques in Taxonomy an
Page 80 and 81: protein electrophoresis still a val
Page 82 and 83: "molecular clock") has been establi
Page 84 and 85: Beni~hke, Nombela, J.J., Rodriguez
Page 88 and 89: and C. gazella (Vassart et ai., Art
Page 90 and 91: analysis. Systematic relationships
Page 92 and 93: management efforts, whether managem
Page 94 and 95: Kumamoto, A.T., and Bogart, M.H. 19
Page 96 and 97: Table 8.1 Mammalian cells in cultur
Page 98 and 99: genetic diversity in a subspecies w
Page 100 and 101: amount of change between individual
Page 102 and 103: pardus, at positions 38, 61, 64, an
Page 104 and 105: Wildlife Research Center (KKWRC), n
Page 106 and 107: grown m MEM medium supplemented wit
Page 108 and 109: was involved in a V-autosome transl
Page 110 and 111: and heterozygosi ty values found in
Page 112 and 113: Viegas-Pequignot, E., and Dutrillau
Page 114 and 115: cellular and molecular biology requ
Page 116 and 117: structures in terms of visible morp
Page 118 and 119: Although a Robertsonian translocati
Page 120 and 121: Groves, c.P. 1969. On the smaller g
Page 122 and 123: G. bilkis and the dark forms of G.
Page 124 and 125: survey was carried out in February
Page 126 and 127: Conservation action: International
Page 128 and 129: 12. Genetics of Saudi dorcas gazell
Page 130 and 131: Genetic research can clarify the ta
Page 132 and 133: dorcas gazelles Gazella do rcas ssp
Page 134 and 135: y less than 2% from each other. How
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Groves, c.P. 1969. On the smaller g
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eflect the truly remarkable output
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• National (central) government p
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past colonial Africa and Asia, and
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• Studies of gazelle growth rates
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References Child, G., and Grainger,
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14. Survey of Gazelle Populations i
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Sony IPS-360 Global Positioning Sys
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1. Mahkshush The gazelle habitat co
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5. Jabal Jandaf A small population
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A slight caveat is required to thes
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• Appoint one local auxiliary ran
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Recommendations on park zoning, man
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'9~ ~~~
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flamingos Phoenicopterus ruber; her
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salt marshes and associated sand du
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Many projects were initiated at KlS
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CG: Taxonomy is the essential backg
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WR: On a mitochondrial DNA basis, w
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CM & AG: We should not forget in si
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- AG: What could the taxon called G
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Gazella dorcas 1) Survey Al-Khunfah
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3 Male mountain gazelle (Thumamah)
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7 Female Arabian sand gazelle (Thum
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