to prevent others from eating it and so they are territorial. Since females are widely
dispersed (because of the food they eat), males can obtain mates only by keeping a
female in his territory, and so a monogamous pair bond develops.
At the other end of the scale is the African buffalo (Syncerus caffer) (500 kg), which
lives in herds of several hundred animals, often in open savanna, and which eats abun-
dant but low-quality grass. By living in herds they obtain protection from predators- only lions (Panthera leo) are big enough to attack them. Because grass tends to
be closely and uniformly distributed, buffalo are able to live in herds and still find
enough to eat. It is not worth their while defending a patch of grass because there
is plenty more beyond. Thus the mating system has evolved into a dominance hier-
archy among males in which the dominant males obtain most of the matings – this is
a polygynous system. These comparisons suggest that an adaptation to one thing, say
food type, leads to complementary adaptations to habitat utilization, antipredator
responses, and social behavior.
Mitochondrial DNA can be used to determine the geographical areas from which
specimens have been taken. Thus, black rhinoceros (Diceros bicornis) have become
highly endangered because of illegal hunting for their horns. Conservation and
enforcement strategies are helped because mtDNA samples from individuals can
identify their geographic origins (O’Ryan et al. 1994). This approach is used in
detecting illegal hunting of other species (Manel et al. 2002). Similarly, differences
in the frequency of mtDNA genotypes among conspecific nesting populations of green
turtles (Chelonia mydas), loggerhead turtles (Caretta caretta), and hawksbill turtles
(Eretmocheles imbricata) show little interrookery exchange of maternal lineages.
Thus, evidence is consistent with natal homing by females (Bowen and Avise 1996).
Mitochondrial DNA has been used to examine genetic differences among wolf
populations. Wayne et al. (1992) and Wayne (1992) used mtDNA to conclude that
the red wolf (Canis rufus) is a modern hybrid of the gray wolf (Canis lupus) and the
coyote (Canis latrans), with a predominance of the latter. Nowak (1992) has sug-
gested that the red wolf is a true species and not just a hybrid, but that it has recently
hybridized in some areas with the other canids.
Allozyme and mtDNA data explained the peculiar distribution of clouded salamanders
( Jackman 1998). One species, Ameides vagrans, is found in California and Vancouver
Island, British Columbia, while a second species, A.ferreus, occurs in Oregon
between the disjunct distribution of the former. The DNA evidence shows that the
Vancouver Island population was introduced from California in the 1800s.
Analysis of mtDNA in gray seal (Halichoerus grypus) populations in the western
North Atlantic (Canadian coast) and eastern North Atlantic (Norway, Baltic Sea) showed
no shared haplotypes and an estimated divergence of 1.0–1.2 million years ago. In
contrast, Norwegian and Baltic stocks diverged 0.35 million years ago, while popu-
lations along the Canadian coast show no divergence (Boscovik et al. 1996). Degrees
of divergence are important factors when considering issues such as the conserva-
tion of genotypes and the reintroduction of lost populations.
Endangered populations are often at the edge of a species range and are subject to
unusually high abiotic and biotic pressures. These may contribute to a population
decline and range contraction. Mitochondrial DNA is not suitable for identifying causes
of these sorts. In contrast, quantitative traits such as morphology, reproductive
capacity (clutch size), and behavior may provide useful information because they expose34 Chapter 3
3.8.2Uses of genetic
techniques