CONSERVATION OF ARABIAN GAZELLES - Nwrc.gov.sa

Genetic research can clarify the taxonomic status of taxa which have been difficult to classify
(Benirschke, 1977; FurJey et al., 1988). The techniques used here are karyOlyping. which involves
comparison of chromosomes. and DNA sequencing of the mitochondrial cytochrome b gene. The
number of chromosomes is relatively characteristic for each species. and banding techniques enable
identification of individual chromosomes. which is useful for comparing chromosomes within and
between species. Mitochondrial DNA is a fa st "evolutionary clock" (several times faster than most
nuclear DNA) and is therefore valuable for estimating evolutionary relationships between species and
subspecies (Irwin et al., 1991). There is a difference between mitochondrial genes. although each
gene evolves at a constant rate. However. during analysis one should be aware of the different types
of error in the data (Harley and Vassar!. this volume). For closely related taxa one should analyze a
relatively large amount of sequence data to minimize stochastic error. For very divergent taxa.
successive mutations and parallel mutations at a single base pair site can cause problems (transitions
can be saturated). so only transversions should be looked at. When one is confident that only single
changes are detected (changes take place at a linear rate in time) the data can be used to estimate the
time of divergence of species from their common ancestor. The cytochrome b gene evolves at a
linear rate between approximately 5 and 10 million years (Irwin et al .• 1991 ). and therefore is useful
to detect evolutionary relationships in the Antilopinae. Comparison of cytochrome b sequences
reveals phylogenetic distances between the various genera of the Antilopinae and between species.
respectively. The combination of different genetic techniques (karyotyping and DNA sequencing)
using identical samples gives the taxonomic results a solid basis (Ryder and Chemnick. 1990). Many
gazelle species are threatened with extinction (Ryder. 1987; IUCN. 1990). which makes it important
to clarify the taxonomic status of animals which will be used as founders for captive breeding
programmes.
xx
1:1 XI
,. I. AD
Figure 12.2 Dorcas gazelle Gazella dorcas isabella from Africa female A76 (2n=30). KKWRC.
121