CONSERVATION OF ARABIAN GAZELLES - Nwrc.gov.sa

If the karyotype is adaptive as other biological characteristics are to an organism, the
chromosomal constitution of a taxonomic group of organisms can be expected to demonstrate
evolutionary trends. This pattern of chromosomal evolution is referred to as karyotypic
orthoselection (White, 1973). The numerous Robertsonian trans locations found in the Bovidae are a
good example of karyotypic orthoselection at the family leveL Autosome-to-sex chromosome
translocations are common rearrangement patterns found in two bovid genera, Tragelaphus and
Cazella (Wurster, 1972; Effron et al., 1976; Wallace, 1978). Wurster (1972) has documented similar
relationships between characteristics of the sex chromosomes and taxonomic groups in other
subdivisions of manunals.
Chromosomal variation among gazelles is considerable, both interspecifically and
intraspecifically, but observed relationships between chromosomal and morphological variation can
only be explained on theoretical grounds. For example, chromosomal evolution among marine
mammals (cetaceans and pinnipeds) demonstrates phylogenetic relationships; however, the karyotype
has not evol ved in the same way as anatomical and physiOlogical characteristics. Amason (1972)
attributed thi s to two factors; their reproductive biology (late sexual maturity) and ecology (mobility
in a relatively uniform environment). Because of these factors , the chances are unlikely that two
individuals with the same chromosomal rearrangement will meet and become founders of a
population with a new karyotype.
In contrast to marine marrunals, the reproductive biology and ecology of gazelles would seem
to favour karyotypic change. Sexual maturity in gazelles is reached at an earlier age than in marine
mammals. Perhaps most influential in the development of karyotypic diversity among gazelles were
the series of Pleistocene climatic changes in Africa and Asia that diversified the environment by
fragmenting habitats (Bishop and Clark, 1967). Savannas inhabited by gazelles receded due to the
advance of forests during alternating periods of dry and moist climates. These geologically recent
events might explain the interspecific karyotypic diversity among gazelles as the geographic isolation
of populations facilitated the fixation of chromosomal rearrangements. Intraspecific chromosomal
variation observed in C. dama, C. soemmerringi and C. subgutturosa indicate that the fixation of
existing chromosomal rearrangements in some gazelle populations is not complete.
Cytogenetics can reinforce, or even clarify, evolutionary relationships postulated on the basis
of morphological studies. For example, Thomson's gazelle C. thom soni has historicaJiy been
consi dered a separate species from the red-fronted gazelle C. rufifrons. Groves (1985) contended,
however, that Thomson's gazelle was a subspecies of the red-fronted gazelle with "a chain of
gradually changing subspecies which simply cannot be broken up into species". Chromosomal reevaluation
of Thomson's gazelle (Kumamoto, unpublished data) along with recent preliminary data
from the red-fronted gazelle (Kumamoto et ai., unpublished data) seems to support the contention of
Groves (1985) that they are conspecific. Cytogenetic data also support relationships of C. cuvieri to
C. leptoceros and C. subgullurosa based on skull measurements (Groves, 1985). G-banded
karyotypes of C. cuvieri and G. leptoceros are nearly identical (Kumamoto and Bogart, 1984).
The systematic value of G-band studies has been reviewed by Baker et al. (1987). In
phylogenetic analyses, variation in G-band patterns among taxa can be used as character states.
Evolution of chromosomal rearrangements can be determined through the identification of primitive
character states. Cladistic methods utilizing data from G-bands can be used to test phylogenetic
relationships inferred from other data sets, such as morphology, protein electrophoresis, or DNA
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