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Intl. J. of Mol. Ecol. and Conserv. 2012, Vol. 2, No.1, 1-7
http://ijmec.sophiapublisher.com
3
revealed more variation in Class I MHC, but not Class
II MHC and also the amount of DNA sequence
variation among the alleles was fairly high thus they
could recognize a wide array of foreign proteins.
However, they noted that although wild cheetahs
appear to have enough MHC variation for defense
against current common diseases, they may still be at
risk from other new emerging diseases. The importance
of low genetic variation in cheetah might have been
over-estimated as Castro-Prieto et al (2011) concluded
by noting that the long term survival of free-ranging
cheetahs in Namibia seemed more likely to depend on
human-induced rather than genetic factors.
Genetic variability is lost slowly (over hundreds to
thousand generations) and the rate of loss is inversely
proportional
N
e
. This implies that variability loss
mainly depends on the size of the lowest population to
date and for how many generations it has been held at
that level; it is slow compared to the timescales over
which conservation biology operates (Amos and
Balmford, 2001). Thus, although some studies
claimed to show a link between known bottlenecks to
low levels of genetic variability like in cheetah
(O'Brien, 1994) and in Elephant seals (Hoelzel et al.,
1993), closer examination reveals that the expected
loss of heterozygosity might be far less than thought
(Amos and Balmford, 2001). The level of threat posed
by genetic variability considering this aspect is
therefore currently not very serious but there is no
guarantee that situation will remain the same given the
ongoing challenges in threats like habitat degradation,
fragmentation, pollution and climate change.
2 Inbreeding depression
Inbreeding depression is reduced fitness in a
population caused by mating between related
individuals. Genetic theory predicts that inbreeding
will reveal deleterious recessive alleles, that might be
shown in reduced growth rates, lower fecundity and
high infant mortality that could lead to population
extinction (Caro and Laurenson, 1994). In a large pop
with random mating these detrimental alleles are
present in heterozygous state and therefore their
effects are partially masked. In small populations
however, mating among relatives becomes common
and the proportion of individuals that are homologous
at many loci increases and results in inbreeding
depressions. Following this theory, inbreeding
depression should be a real cause for concern in
conservation for many species that are in decline or
that survive in small isolated populations.
Researchers have questioned the importance of
inbreeding for the persistence of wild populations
since most inbreeding evidence comes from
domesticated/captive populations. There are also
theories suggesting that most of inbreeding depression
can be purged considering the many ways in which
species avoid inbreeding (Keller and Waller, 2002).
However, there have been accumulation of evidence
for inbreeding in wild animal populations, for
example the Soay sheep (
Ovis aries
) in the UK,
homologous sheep suffered high parasitism and lower
overwinter survival in comparison to heterozygous
sheep (Coltman et al., 1999). In south-eastern USA,
inbreeding reduced hatching rates, fledging survival
and recruitment to the breeding population of
red-cockaded woodpeckers (
Picoides borealis)
(Daniels and Walters, 2000). Also, evidence for
inbreeding in natural populations of plants exist and
purging does not appear to act consistently as a major
force in these populations (Byers and Waller, 1999). In
an experiment using
Clarkia pulchella
that differed in
founders` relatedness, persistence time was found to
be lower in individuals whose founders were related
(Newman and Pilson, 1997). This then suggest that
inbreeding depression is important in the conservation
of these species.
It has been noted that the importance of inbreeding
depression in the wild does not necessarily imply
population decline (Caro and Laurenson, 1994).
Environmental stress such as food and water shortages
can reveal effects not seen under less demanding
conditions. Inbreeding depression and its interaction
with environmental stress was demonstrated in an
experiment with mice (Jimenez et al., 1994). Wild
caught mice subjected to full-sib mating in captivity
showed greater mass loss and lower survivorship
when they were returned to their habitat compared to
the progeny of outbred matings. When equivalent
mice were retained under laboratory conditions,
inbreeding depression was less severe. This suggests