Title: LECTURE 8: Macroevolution
1LECTURE 8Macroevolution
2What is microevolution?
- Evolution on a small scale
- Change in allele frequencies from one generation
to the next - A process that leads to a change in a species
- Natural selection
- Genetic Drift
- Gene Flow
- Mutation
- Microevolution explains how populations evolve
3What is Macroevolution?
- Origin of different species
- SPECIATION
- Extinction of species
- Evolution of major features
4What are the Macroevolution Processes?
- Divergent Evolution
- Formation of 2 descendent species from an
ancestral species - Homologous structures
- Convergent Evolution
- 2 species acquiring same characteristics from 2
different ancestral species - Analogous Structures
5What is Speciation?
How would we identify if a species is new?
6How can we see Speciation in the Fossil Record?
7What are the types of speciation?
- Coevolution
- A species evolves due another species evolving
- Predator/prey relationships
- Adaptive Radiation
- Appearance of numerous species over a short
period of time - Filling open niches
- When would this happen?
8What is adaptive radiation?
- Explosion of new species from common ancestor
that results in diverse species adapted to
different environments
ADAPTIVE RADIATION
9What is the tempo of speciation?
- Punctuated Equilibrium
- Long periods of little change
- Occurs after fast/rapid changes
- Adaptive radiation
PUNCTUATED EQUILIBRIUM
10Where was there an extinction?
PUNCTUATED EQUILIBRIUM
ADAPTIVE RADIATION
11What is the Biological Species Concept?
- Biological
- Group of individuals capable of interbreeding
- Is this an accurate definition of a species?
12- CASE 1
- A mule is the offspring of a female horse and a
male donkey. In contrast, the hinney is the
offspring of a male horse and female donkey. The
mule is easier to breed and larger in size than
the hinney. For these reasons, the mule became
an important domesticated animal. Horses have 64
chromosomes, donkeys have 62. The mule has 63
and cannot evenly divide, that is why the animal
is sterile.
13- CASE 2
- A liger is a cross between a female tiger and a
male lion. In contrast, the tigon is a cross
between a male tiger and a female lion. These
two species do not breed in nature because their
habitats are so different. Lions live in open
grasslands while tigers live in forests. In
captivity, it is possible to produce ligers and
tigons. Male ligors are sterile, but female
ligers are fertile and may reproduce with either
tigers or lions.
14- CASE 4
- E.coli is a bacterium normally found in the
intestines. It is harmless and may actually be
beneficial to the human digestive system. There
is a pathogenic strain of E.coli that produces a
toxin that can kill its human host. The two
strains look very similar under a microscope.
Comparison of their genomes reveals that the
pathogenic strain lacks 528 genes found in the
normal strain and has 1,387 genes not found in
the normal strain.
15What are other species concepts?
- 5 Types
- Morphological
- Group of individuals sharing similar
characteristics - Recognition
- Behavior/chemical recognition between individuals
- Genetic
- Range of variation in DNA- similar in individuals
- Cladistic
- Species defined as a branch in a cladogram
- Biological
- Group of individuals capable of interbreeding
16Why dont similar species interbreed?
- Reproductive Isolation
- Biological barriers preventing members of 2
species from producing fertile, viable offspring
hybrids - Geographic Isolation
17What is Geographic Isolation?
- Geographic Isolation
- Separation of a species due to obstruction
- Allopatric Speciation
18What is Reproductive Isolation?
- Sympatric Speciation
- Prezygotic (before fertilization)
- Timing
- Diff breeding seasons
- Behavior
- Mating rituals
- Habitats
- Diff living areas (niches)
- Mechanical
- Diff Reproductive Structures
- Gametic
- Sperm cannot survive in female reproductive tract
- Postzygotic (After fertilization)
- Reduced Hybrid Viability
- Abort embryonic development
- Reduced Hybrid Fertility
- Cannot breed
19What are the Modes of Speciation?
- Two general modes of speciation are distinguished
by the way gene flow among populations is
initially interrupted - Allopatric speciation
- geographic separation of populations restricts
gene flow - Sympatric speciation
- speciation occurs in geographically overlapping
populations when biological factors, such as
chromosomal changes and nonrandom mating, reduce
gene flow
20What is Allopatric Speciation?
- Geological processes can fragment a population
into two or more isolated populations - Mountain ranges, glaciers, land bridges, or
splintering of lakes may divide one population
into isolated groups. - Some individuals may colonize a new,
geographically remote area and become isolated
from the parent population - For example, mainland organisms that colonized
the Galápagos Islands were isolated from mainland
populations.
21What is Allopatric Speciation?
- Once geographic separation is established, the
separated gene pools may begin to diverge through
a number of mechanisms - Mutations
- Sexual selection favors different traits in the
two populations - Different selective pressures in differing
environments act on the two populations. - Genetic drift alters allele frequencies.
22- HOW DO WE CONFIRM THAT ALLOPATRIC SPECIATION HAS
OCCURRED? - EXPERIMENT!!!!!
23What is Sympatric Speciation?
- New species arise within the range of the parent
populations - Reproductive barriers must evolve between
sympatric populations - In plants, sympatric speciation can result from
accidents during cell division that result in
extra sets of chromosomes, a mutant condition
known as polyploidy - In animals, it may result from gene-based shifts
in habitat or mate preference.
24IN SUMMARY
- In allopatric speciation, a new species forms
while geographically isolated from its parent
population. - As the isolated population accumulates genetic
differences due to natural selection and genetic
drift, reproductive isolation from the ancestral
species may arise as a by-product of the genetic
change. - Such reproductive barriers prevent breeding with
the parent even if the populations reestablish
contact. - Sympatric speciation requires the emergence of
some reproductive barrier that isolates a subset
of the population without geographic separation
from the parent population. - In plants, the most common mechanism is
hybridization between species or errors in cell
division that lead to polyploid individuals. - In animals, sympatric speciation may occur when a
subset of the population is reproductively
isolated by a switch in food source or by sexual
selection in a polymorphic population.
25Microevolution or Macroevolution
- Change in allele frequencies
- Creation of new species
- Giraffe necks getting longer
- A species of birds going extinct
- A species of beetle have evolved harder shells,
so a species of bird has evolved beaks that can
crush the beetles shells - -What is this called?
- There is variation within a snake species, one
variation survives the other does not survive