Download adaptive evolution

EVOLUTION IN LARGE
POPULATIONS:
SELECTION
Influences upon genetic diversity and the
evolution of populations
Genetic
Drift
Mutation
Natural Selection
Migration
The need to evolve
• environmental change is ubiquitous
– Pests, parasites, novel competitors, anthropogenic
change, global warming, new diseases
• Species must adapt and evolve to avoid extinction
Adaptation
• 3 forms of adaptation: Physiological, behavioural and
genetic
Physiological adaptation: change in metabolism or
biochemistry to deal with an environmental problem
Example: High-altitude adaptations in vertebrate haemoglobins
• Increased blood O2 affinities
at altitude
• Linked to structural changes
in haemoglobin molecules
Weber (2007) Respiratory
Physiology & Neurobiology vol 158
132–142
Adaptation
Behavioural adaptation: the things organisms do to survive
Example: feeding specialisations in bottlenose dolphins in
Shark Bay, WA
• Subset of population uses
sponges to probe substrate
for fish
• Recent co-ancestry
• Vertical social
transmission among
females
• Cultural transmission of
tool use? Krützen et al. (2005) PNAS vol 102 8939-
Adaptive evolution
Adaptive evolution: long term evolutionary changes in
response to natural selection upon superior genetic
variants
• Adaptive evolutionary changes in animals have been
documented in:
- morphology, behaviour, colour, prey size, body size, life
history, disease tolerance and resistance, biocide
resistance, tolerance to pollutants.
• Plants evolve in response to:
- soil conditions, light regimes, water stress, flooding, air
pollution and herbicides. Plant populations adapted to
diverse ecological conditions are so common that they
have their own term, called ecotypes.
Adaptive evolution and explosive
speciation in cichlid fish
Kocher, T (2004) Nature Reviews Genetics 5: 288-29
• Genetic adaptation and adaptive evolution is ubiquitous in
species that have genetic diversity
Adaptive evolution
• Take home message: Adaptive evolution is ubiquitous in
plants and animals that have genetic variation
• Adaptive evolution is important in the following
conservation contexts:
- Preserving evolutionary potential
- Adaptation to marginal environments
- Genetic adaptation to captivity
- Adaptation of invasive species
- Outbreeding depression
Natural Selection
Evolving populations are complex
systems
• Evolving populations are complex systems influenced by
mutation, migration, selection and chance operating within the
context of the breeding system
Competition
Climate
Disease
Loss of
genetic
diversity
Zygotes
SELECTION
CHANCE
SAMPLING
deaths
Adults
Mating
MIGRATION
Gametes
Selection of mates
MUTATION
Introduction to Conservation Genetics 2
Fig 6.1 Evolving pop as complex systems.ppt
Is Natural Selection the Same Thing as Evolution
evolution is directional in producing
all the life-forms on earth today from
one or several ancestral life-forms
billions of years ago
Natural selection is an
observable process that is
often purported to be the
underlying mechanism of
unobservable molecules-toman evolution.
Through natural selection, genetic
information (variety) was lost.
The long-fur dogs survive better in
a cold environment; they are less
able to survive in a warm
environment and vice versa.
A particular characteristic in the dog
population was selected for.
Dogs are still dogs since the
variation is within the boundaries
of “kind.”
Selection on quantitative characters
• Variation is determined by several loci and environmental
effects
• Selection affects phenotypic means and variances
3 forms of selection
Directional
selection:on quantitative characters:
favours phenotypes toward
one end of the distribution
and shifts mean towards
that extreme
Stabilizing selection: favours
phenotypic intermediates
and reduces variation about
the mean
Disruptive Selection: favours
both phenotypic extremes
and increases variation
Case study: directional selection
Undesirable evolutionary consequences of trophy hunting in
Bighorn sheep Coltman et al. (2003) Nature 426, 655-658
Directional selection: favours phenotypes toward one end of
the distribution and shifts mean towards that extreme
Case study: stabilizing selection
Stabilizing selection for birth weight in humans after Mather,
1973
Stabilizing selection: favours phenotypic intermediates and
reduces variation about the mean
Case study: disruptive selection
Disruptive Selection: favours both phenotypic extremes and
increases variation about the mean
Disruptive selection and then what? Rueffler et al. (2006)
TREE 21, 238-245; Schulter and McPhail (1992) The
American Naturalist 140: 85-108
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