Transcript Continue genetic diversity

Nile Perch from Lake Victoria
Genetic Diversity
Fitness
• evolutionary fitness is a measure of the
number of offspring an individual produces
Loss of Fitness
• Another important aspect of polymorphism
is that it tends to maintain fitness • populations of animals in zoos, which are
typically low in genetic diversity, often
have low fitness - low fertility and high
mortality among offspring
Fitness of Zoo Animals
Reasons for Loss of Fitness
1. increased incidence of deleterious recessive
homozygous individuals
2. lack of heterosis – heterosis (hybrid vigor) is the
phenomenon where heterozygous individuals have
higher fitness than do homozygotes - often
heterozygotes are more resistant to disease
3. lack of evolutionary potential - with all
homozygotes there is lack of variation and all
individuals will be susceptible to the same
problems
Inbreeding Depression
• Inbreeding depression is the loss of fitness
resulting from the breeding of closely
related individuals - it occurs due to the
three reasons listed before
Ngorongoro Crater
Lions at Ngorongoro Crater
Vipera berus - adder
Glanville Fritillary Butterfly
Outbreeding Depression
• The loss of fitness that occurs when
distantly related individuals breed –
• This occurs because certain populations
may have been selected for traits that are
successful in their environment, so that
introducing novel traits may reduce fitness
for that environment
Austrian Ibex – Capra ibex ibex
Turkish Ibex – Capra ibex aegagrus
Nubian Ibex – Capra ibex nubiana
Optimum outbreeding in Japanese
Quail
Fitness
• evolutionary fitness is a measure of the
number of offspring an individual produces
Maintenance of Polymorphism
without natural selection • random mating tends to
maintain polymorphism –
due to the benefits of
sexual reproduction –
recombination,
independent assortment,
and crossing over
Maintenance of Polymorphism
• The effects of nonrandom mating are
variable - species may either mate
assortatively (like with like) or
disassortatively (like with unlike)
• assortative mating results in many
homozygous individuals
• disassortative with many polymorphic,
heterozygous individuals
Assortative Mating - Three spined
stickleback
Disassortative Mating –
Nonbreeding Ruff
Disassortative Mating - Breeding male
ruff and variations on head pattern
Maintenance of Polymorphism
• environmental variance - the environment
may affect development of different
genotypes so that which genotype
dominates changes with the environment if the environment varies or different
habitats exist within the species range, then
different genotypes will exist
Backswimmers – winged or
wingless forms
Maintenance of Polymorphism
With Natural Selection
with selection, we would expect the most fit
genotype to come to dominate the population, but
polymorphism may still occur:
1. selection acts to maintain stable polymorphism so
that different genotypes are most fit under
different situations
2. fixation of a particular genotype is counteracted
by mutation
3. fixation of a particular genotype in one
population is counteracted by gene flow from
another population
Polymorphism under selection –
in the Grove Snail - Cepaea
Clines
• in many species, local populations have
little variation, but the entire species
exhibits much variation as local populations
are adapted to different conditions - if these
changes in genes change in response to
certain environmental variables, we may see
a cline - a gradual change along a
geographic transect
Clines with Body Size
• Bergmann's rule - many animals get larger
in size as the species range approaches the
poles - it is related to ability to keep warm larger bodies maintain warmth better
• Allen’s Rule – size of extremities decreases
towards the poles – heat is lost through
things like large ears
Bergman’s Rule in same aged
White-tailed Deer
Allen’s Rule in Foxes
Arctic Fox
Desert (Kit) Fox
Allen’s Rule in Hares
Cline in Cyanide Production in
White Clover
Cline in
cyanide
production
by white
clover
Greater Racquet-tailed Drongo
cline in crest size
Reductions in Polymorphism
• Gene Flow - the movement of alleles from
one population to another tends to maintain
genetic similarity among populations
African Wild Dog
Rates of Gene Flow
– Ne (effective population size) = 120
Minimum Viable Population
• The smallest population for a species which
can be expected to survive for a long time
• Many factors effect MVP – the study of
those factors is often called Population
Viability Analysis – or Population
Vulnerability Analysis – or PVA
Factors that make populations
vulnerable to extinction
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Environmental fluctuations
Catastrophes
Demographic uncertainties
Genetic problems
Habitat fragmentation
Environmental Fluctuations
Kirtland’s Warbler
Cheetah
Habitat Fragmentation
• Fragmentation is the transformation of large
expanse of habitat into a number of smaller
patches of smaller total area isolated from
each other by a matrix of habitat unlike the
original
Habitat Fragmentation
Habitat fragmentation occurs due to:
• Natural climatic shifts
• Human caused habitat loss: logging,
agriculture, urbanization, dams, road
construction, etc.
• Overexploitation of species
• Species introduction
• Secondary effects due to extinctions
Domesday Book – 1085-86
Selection from the Domesday Book
Factors that make populations
vulnerable to extinction
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Environmental fluctuations
Catastrophes
Demographic uncertainties
Genetic problems
Habitat fragmentation
Heath Hen – Extinction Vortex
Minimum Viable Population Size
• Another definition - often defined as 95%
probability of 100 year survival, but can
also plan for longer survival (500 or 1000
years)
• MVP is usually determined by modeling
Forces which may cause extinction
1) deterministic - something essential is
removed (habitat loss) or something lethal
is added (pollutant, disease, introduced
species) - presumably we can act to
minimize these risks
Forces which may cause extinction
2) stochastic (random) - environmental, catastrophic,
demographic and genetic - this is what we need to
worry about and what is hardest to prevent
• environmental randomness effects resources and
conditions and we can't do much about it
• catastrophic randomness - floods, fires, hurricanes,
volcanoes - can't really prevent but can spread
individuals around to minimize the impact
• demographic - just natural random variation in
birth and death rates can lead to extinction
• genetic - lack of genetic variability can lead to
problems of inbreeding and poor response to
diseases and environmental change
Bighorn Sheep and MVP
Bighorn Sheep and MVP
Grizzly Bear and 50/500 Rule
MVP – 50/500 Rule?
Reductions in Polymorphism
Reductions in population size can lead to
losses of genetic polymorphism
Two special cases of reductions in population
size are:
1. A few individuals move to a new area and
start a new population that is isolated from
other populations – founder effect
2. We can also experience a population
bottleneck where a formerly large
population is drastically reduced in size
Founder Effect – Galapagos Tortoise
Founder effect – Amish and
Polydactyly
Population Bottleneck – Northern
Elephant Seal