The Origin of Species
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Transcript The Origin of Species
The Origin of Species
Chapter 24
Basics
Speciation
Macroevolution
Two basic patterns of
evolution:
Anagenesis
Cladogenesis
Species
Biological species concept: a
population/group of whose members can
potentially reproduce & create fertile
offspring, but are unable to do so with
other populations
Reproductive isolation is the key!
Often this is a combination of several types of
barriers
Reproductive Isolation
Prezygotic barriers
Habitat isolation
Temporal isolation
Behavioral isolation
Mechanical isolation
Gametic isolation
Postzygotic barriers
Reduced hybrid viability
Reduced hybrid fertility
Hybrid breakdown
Reproductive Isolation Charades
Your group will be assigned one of the
reproductive isolation mechanisms
Your job is to create a silent skit to teach
this to the class…remember, you’re at
school so this needs to be appropriate
Your skit doesn’t have to be very long
You have ten minutes before we start the
presentations. GO!
Limitations to Biological Species Concept
Reproductive isolation is difficult to
determine for extinct species & those that
are asexually reproducing which limit the
use of bsc
These definitions focus on the unity found
within species:
Morphological species concept
Paleontological species concept
Ecological species concept
Phylogenetic species concept
Speciation
Allopatric speciation
Gene flow of a population is prevented due to
geographic isolation creating two distinct subspecies
The size of the geographic barrier is dependent on
the species & their motility
Example: antelope squirrels at the Grand Canyon
Speciation
Sympatric speciation
Populations with geographic overlap become
isolated leading to speciation
Driven by chromosomal changes & nonrandom
mating that reduce gene flow
Polyploidy (changes in the number of sets of
chromosomes during meiosis) in plants
Habitat differentiation
Sexual selection
• Example: cichilids with coloration preference
Sympatric Speciation
Autopolyploidy
Sympatric Speciation
Allopolyploidy:
A hybrid plant that is infertile may reproduce asexually
& eventually mutate to become fertile polyploid
Sympatric Speciation
Habitat Differentiation
Genetic factors allow new generations to exploit a
resource that was unused by previous generations
(the parent population)
Example: apple maggot flies had speciation as new
generation inhabited European introduced apple trees
with different apple production season
Allopatric vs Sympatric Speciation
Adaptive Radiation
The evolution of many diverse species from a
common ancestor after introduction to new
environments
Usually results from new populations being established
in distant areas
This is what happened to mammals after the
dinosaurs went extinct!
This can be seen in the Hawaiian islands as
species invaded the naked islands & then had
allopatric & sympatric speciation events occur
Silversword Alliance in Hawaii
The Tempo of Speciation
Gradualism
Punctuated
Equilibrium
Evolution & Developmental Biology
(Evo-devo)
Slight genetic differences can can lead to
major morphological differences
Especially for genes that control the rate,
timing, & spatial pattern of an organism’s form
as it develops
Rate & Timing:
Heterochrony (general
term)
Allometric growth
(proportioning that gives a
body its specific form)
Paedomorphosis (sexually
mature species with
juvenile characters
because sexual
development was faster
than somatic
development)
Spatial Pattern:
Homeotic genes
(determine where a pair of
appendages will be
located)
Does evolution have a goal?
NOPE! There is no specific direction that a
species is trying to follow & that’s why you
see so many evolutionary branches that
end
Think about species selection: the species that
survives the longest will determine the next
evolutionary trend
Stanley compares species to an individual
(speciation is birth, extinction is death, & new species
created from this one are the offspring)