Download The Origin of the Species

The Origin of Species
The “mystery of mysteries”
Macroevolution
• Speciation=Evolution of new species
– Source of biodiversity
• Appearance of “evolutionary novelties”
2 patterns of evolutionary change
• Anagenesis
– Accumulation of heritable changes
– micorevolution
• Cladogenesis
– Branching of species
– macroevolution
What makes a species?
• Biological species
concept
– Population(s) that can
interbreed to produce
viable offspring
• Reproductive isolation
– Behavior
– Geography
– physiology
Reproductive Isolation
• Prezygotic Barriers-impede mating
• Postzygotic Barriers-impede hybrid
development
Habitat Isolation
• Occupy different habitats within the same
area
– Garter snakes
– Anolis
Temporal Isolation
• Breeding seasons are asynchronous
– Eastern and Western Skunks
Behavioral Isolation
• Courtship rituals that rely on unique traits
Mechanical Isolation
• Structural differences prevent cross
mating
– Differently shaped pollen
– Different pollinators
– Drastic differences in size
Gametic Isolation
• Zygotes don’t fuse
– Sperm lack proper receptor proteins
Reduced hybrid viability
Hybrid Sterility
• Hybrids are weaker than “pure-breds”
• Hybrids are sterile
– Mule
– Liger
Hybrid Breakdown
• Hybrids are strong, their offspring are less
viable
– Coydog
Speciation
• Allopatric- population becomes
geographically divided
• Sympatric- Populations live in overlapping
habitats, no geographical separation is
necessary
Allopatric Speciation
• Individuals colonize new areas
• Geologic changes (oxbow lakes, rivers,
mountains)
• Small, isolated populations are more likely to
change
• Isolated populations develop separately
Sympatric Speciation
• Chromosomal changes
• Non-random mating that reduces gene
flow
– Polyploidy
– Habitat differentiation
– Sexual selection
Adaptive Radiation
• Evolution of many species from single
common ancestor
• Hawaiian islands
– Colonizers arrive, diverge into different
microhabitats
Punctuated Equilibrium
• Periods of stability, interrupted by periods
of rapid evolution and change of species.
• Fossil record isn’t exact, species can
seem to just appear (could have taken
200,000 years to evolve into a unique
form)
• Transitional states aren’t always captured
in fossil record
Evolutionary Novelties
• Complex structures evolve in increments
from simpler versions
• Thousands of “speciation events” take
place as an evolutionary novelty is formed
The Eye
• Complex structures
evolve from
simpler structures
Exaptations
• Traits don’t evolve for future use, have to
be beneficial in the present
• Structures that evolved for one use can be
used for other purposes
– Ex. Feathers used for courtship or
camouflage were also beneficial for flight
Evolution of Development Genes
• Depends on rate, timing and spatial
patterns of changes
• Heterochrony-change in rate or timing of
developmental events
Evolution is not goal oriented
Species selection
• Species that are around for the longest,
and have the most successful offspring
influence the direction of evolution
• Species that are easily dispersed can give
rise to many new species
– Birds
– Fish
• Evolution is the
interaction between
organisms and their
current environments
• When conditions change,
evolutionary trends
change as well