CONSERVATION OF ARABIAN GAZELLES - Nwrc.gov.sa

Fonnation of nonnal gametes is dependent upon proper progression of chromosomal events
at meiosis (Moses, 1980). Chromosomal homology is necessary for meiotic pairing and
recombination; prerequisites to segregation, production of chromosomally balanced gametes, and
reproductively fit individuals. The level of chromosomal homology required for recombination
seems to be influenced by the particular species involved and the degree to which homology has been
changed, or reduced, by chromosomal rearrangement. C. dorcas and C. gazella differ
chromosomally by two Robertsonian translocations. They have hybridized in captivity when a C.
gazella dam was involved; FI females had reduced fertility and males were sterile (Wahnnan el al,.
1973). However, based on extensive breeding records, reproductive fitness of sheep (Ovis aries) was
not affected by three different Robertsonian translocations that produced heterozygotes with two to
five translocation chromosomes (Bruere and Ellis, 1979).
Autosome-to-X chromosome translocations often have a considerable detrimental effect on
fertility. Genn-cell death during meiosis is typical for male autosome-to-X translocation
heterozygotes in humans (Speed, 1989) and mice (De Boer and De long, 1989). In cattle, there have
been few reports of autosome-to-X translocations (Long, 1988). but reduced fertility was observed in
female cattle heterozygous for an autosome-to-X translocation (p. K. Basrur, pers. comm.).
However, autosome-to-sex chromosome trans locations in two species of marsupials (Shannan, 1961)
and several species of the rodent family Gerbillidae (Viegas-Pequignot el ai., 1982) apparently do not
reduce fertility. Occurrence of autosome-to-X translocations in 12 gazelle species studied to date
(Table 7. 1) suggest that pairing of the sex chromosomes is not disrupted. Meiotic studies in C.
subgullurosa males, having both a Robert sonian and an autosome-to-X translocation, give no
indication of reduced fertility in heterozygotes (Kingswood, 1992). Thus, chromosomal
rearrangements can define potential reproductive isolation between karyotypically divergent
populations, but are limited in defining reproductive isolation by the variability of meiotic systems.
Baker and Bickham (1986) have proposed a model of chromosomal speciation by
monobrachial centric fusions in which fixation of single Robertsonian translocations is facilitated in
populations by nonnal segregation and minimal meiotic problems. The model is based on the
fixation of single fusions, involving different acrocentric chromosomes, by geographically-isolated
populations. If secondary contact between the populations leads ' to hybridization, metacentric
chromosomes having monobrachial homology (i.e. homology limited to only one of the two
chromosomal anns) may experience meiotic problems. The finding that single Robertsonian
translocations do not appear to cause meiotic problems in male C. subgullurosa (Kingswood, 1992)
is consistent with this model. Extensive monobrachial homology among gazelles and other bovid
taxa (Effron el ai., 1976; Gallagher and Womack, 1992) suggests the involvement of monobrachial
centric fusions in their speciation.
Relevance to conservation
From a conservation standpoint, it is important to recognize and preserve chromosomal variation
simply because it exists. There is a need to consider quantitative measures of taxonomic distinctness
in conservation (May, 1990), and chromosomal variation can and should be used with other measures
to quantify biodiversity. The role of chromosomes in effecting reproductive isolation and biological
speciation makes cytogenetics an important tool in identifying species diversity. As a practical
application , cytogenetics can identify cryptic chromosomal variation that might jeopardize
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