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)