CONSERVATION OF ARABIAN GAZELLES - Nwrc.gov.sa

Cytogenetic analysis: Chromosomal studies can help to identify subspecies by the
comparative study of their karyotypes. Karyotypes obtained with conventional colouration as well as
with different banding techniques should be compared for each pair of chromosomes. Chromosomal
differences could explain any observed reduced fertility of hybrids between two subspecies.
Thus, karyotypes of the two subspecies of orang-utan, Pongo pygmaeus pygmaeus and P. p.
abelii, differ by a pericentric inversion involving chromosome pair 2 (Seuanez el al., 1979). These
two taxa can also be identified by morphological and behavioural differences.
- Protein electrophoresis: Allozyme study can be a powerful tool in identifying subspecies,
but only if there is a sufficiently large degree of protein heterozygosity within the species, with
poly morphic loci and variation in allele frequency (Ryder el ai., 1988). The required level of
heterozygosity is not present in all mammalian families. Protein polymorphism may be low, as, for
example, in the Mustelidae (O'Brien el al., 1989). Some alleles may be discriminant between the two
samples. Genetic distances between subspecies may also be calculated and compared with data in
related species, and used as a criterion for distinguishing subspecies.
For example, a study of six different Alpine chamois Rupicapra rupicapra populations
revealed Nei genetic distances that allowed the validation of one population as a subspecies, R. r.
ca rlUsiana (Pemberton el al. , 1989). No loci displaying fixed differences were detected but the
genetic di stances calculated on allele frequencies were of the same order of magnitude as the
distances between named red deer Cervus elaphus subspecies (Gyllensten el al., 1983).
- Mitochondrial DNA analysis: The mitochondrial genome consists of a closed circular
DNA molecule. This DNA has a rapid rate of evolution in comparison with the rates of change in
nuclear genes (Brown el ai., 1979). The rate is also relatively constant and provides an "evolutionary
molecular clock". It has been suggested that the evolution rate ranges from 0.5% to 2% per million
years (Brown el al., 1979; Harrison, 1989). Mitochondrial DNA is haploid, maternally inherited
without recombination, has a simple sequence organization, and thus, represents an unambiguous
marker of maternal phylogeny (Harrison, 1989). It can therefore be used to investigate systematic
relationships between related taxa with recent times of divergence (Avise el aI., 1979; Brown and
Simpson, 1981; George and Ryder, 1986). Nevertheless, it is apparent that there is considerable
variability among taxa in relative and absolute rates of change, which necessitates caution about the
hypothesis of the molecular clock (Hillis, 1987). This clock should first be demonstrated as valid
within a taxonomic group. The relative rate test, using phylogenetic data (Sarich and Wilso"n , 1973)
and the study of fossils can provide comparative data for this purpose. Molecular data should always
be analyzed in parallel with unrelated suites of characters and historical biogeographic data.
Taxonomic subdivisions should be recognized when all this information is concordant and clear
phylogenetic discontinuities resulting from long-term population separation appear (Avise, 1989).
Analysis of the mitochondrial DNA of the bontebok and the blesbok shows 0.47% sequence
divergence which would translate into a time of divergence of about 250,000 years ago (Essop el al.,
1991). This confirms the subspecific level for these two taxa.
Another study estimated the genetic distances between the two most numerous subspecies of
the black rhinoceros, Diceros bicomis michaeli and D. b. minor, to determine whether they could be
mixed for conservation management purposes (Ashley el al., 1990). The estimated percent sequence
56