Lecture 9: Conservation genetics Flashcards
The 6th Extinction
Geological records show there have been 5 mass extinctions. Currently witnessing the 6th mass extinction. Human activities are to blame: habitat destruction/fragmentation/poaching/hunting.
Habitat destruction -
biggest threat. Causes populations to become small and geographically isolated.
Genetic drift…
the process of losing genetic variation by chance.
What genetic drift governed by?
population size:
- loss of genetic variation by drift is faster in small populations
- Small populations tend to be less polymorphic
Genetic drift can play an important role in..
Evolution
Northern and Southern elephant seals
Northern elephant seal: once abundant, but heavily exploited, almost went extinction by 1900.
southern elephant seal: exploited, however always abundant.
Genetic variation in the Northern Elephant seal
-Hunting ceased in 1884
-one population survived -Isla Guadalupe
-possibly 20-30 individuals. Maybe only 1 breeding male.
This severe bottleneck has led to a decline in variation.
The Mauritius Kestrel (bird)
Native forest destruction and DDT insecticide usage (1940s) caused a decline in population size.
- Only four left; breeding from a singe pair
- 400-500 birds
Small populations do have..
less genetic variation (northern elephant seals, Mauritius kestrel)
Populations that are small in size or lac genetic variation are…
less capable of evolving in response to new challenges (high extinction risk) e.g. genetically homogenous host populations are more vulnerable to infection than genetically diverse populations
monoculture effect means
genetically homogenous host populations are more vulnerable to infection than genetically diverse populations
Inbreeding:
mating between close relatives. In small populations there are fewer potential mates. Therefore the probability of mating with relatives increases.
when are two alleles IDENTICAL BY DECENT (ibd)
if they trace their ancestry back to the same ancestral allele
Wrights inbreeding coefficient (f)
The standard measure of the degree of inbreeding of an individual. Developed by Sewall Wright (1922)
The greater the value of f (wrights inbreeding coefficient) means
the more inbred
do inbred or outcrossed progeny have higher f values?
INBRED progeny. If ibd the individual must be homozygous at the locus
homo or heterozygosity frequencies higher in inbred populations?
HOMOZYGOSITY.
- reveal recessive deleterious alleles (e.g. cystic fibrosis)
- Less likely to benefit from heterozygote advantage (e.g. kuru)
Inbred progeny often suffer from…
INBREEDING DEPRESSION (less fit than outcrossed progeny)
Small, isolated populations are particularly vulnerable to
- loss of genetic variation due to genetic drift
- inbreeding depression
- these often lead to lowered evolutionary potential, compromised reproductive fitness and elevated extinction
Captive breeding programmes and e.g.
For endangered species. Populations are inevitably small. Some inbreeding may be unavoidable.
-Californian condor
California condor:
Largest bird in North America.
Captive breeding programme based on last 27 birds in the world.
Now 150-200, some returned to the wild. However, recessive lethal allele has reached high freq (p=0.17) Homozygous birds suffer from CHONDRODYSTROPHIC DWARFISM (die at hatching)
Breeding programs avoid hetero carriers mating or 1/4 would die.
Florida Panther:
Once down to a pop of 60-70 in Southern Florida. Road kill main cause of morality. Culverts under highways have reduced the problem. REMAINING PROBLEM: persistent inbreeding means that most males suffer CRYPTORCHIDISM (undescended testes) Poor sperm quality.
SOLUTION: introduce 6-8 females from close related subspecies in Texas. 32 surviving progeny
example of bad recovery programme:
KOALAS Cause: A succession of bottlenecks
Amish people of North America
Isolated human populations and disease:
- small founder population from Rhineland, Germany.
- marriage outside the community is forbidden
- excellent genealogical records - pedigrees used to understand inheritance.
- high incidence of some disorders e..g Ellis-van Creveld syndrome
- Amish collaborated with geneticists & the gene was discovered in 2000
Gene mapping in the Finnish population
- Geographically remote
- Small founder population and several bottlenecks
- Uralic language - barrier to immigration and admixture
- some genetic diseases are virtually absent (CF)
- others ~30 at quite high freq and well characterised
- Good genealogical records
Genetic drift…
the random loss of genetic variation
Genetic variation is lost quickest in …
small populations
Loss of genetic variation appears to affect
extinction tisk
inbreeding is more likely in
smaller populations
inbreeding is measured by
the inbreeding coefficient (f)
inbreeding depression is the
reduction in fitness due to inbreeding
conservation genetics aims to
reduce the loss of genetic variation & avoid inbreeding
Isolated human populations have high
incidence of some genetic diseases & can be used to map disease genes
