Download Chapter 14

Introduction
The Origin of Species
  A species can be defined as a group of organisms
whose members can breed and produce fertile
offspring, but who do not produce fertile offspring
with members of other groups
Chapter 14
Copyright © 2009 Pearson Education, Inc.
14.1 The origin of species is the source of
biological diversity
  Speciation is the emergence of new species
  The many millions of species on Earth have all
arisen from an ancestral life form that lived around
3.6 billion years ago
Copyright © 2009 Pearson Education, Inc.
14.2 There are several ways to define a species
CONCEPTS OF SPECIES
  Taxonomy is the branch of biology that names and
classifies species and groups them into broader
categories
  Carolus Linnaeus developed the binomial system of
naming organisms using physical characteristics to
distinguish over 11,000 species
  Similarities between some species and variation
within species can make defining species difficult
Copyright © 2009 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
14.2 There are several ways to define a species
14.2 There are several ways to define a species
  The biological species concept defines a species
as a population or group of populations whose
members have the potential to interbreed in nature
and produce fertile offspring
  Can the biological species concept always
distinguish species from each other?
  Reproductive isolation prevents gene flow and
maintains separate species
Copyright © 2009 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
14.2 There are several ways to define a species
14.2 There are several ways to define a species
  The morphological species concept classifies
organisms based on observable phenotypic traits
  The ecological species concept defines a species
by its ecological role or niche
  It can be applied to asexual organisms, fossils, and
in cases when we don t know about possible
interbreeding
–  Consider the cichlids, which are similar in appearance
but feed at different depths in the lake
  There is some subjectivity in deciding which traits to
use
Copyright © 2009 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
14.2 There are several ways to define a species
14.3 Reproductive barriers keep species separate
  The phylogenetic species concept defines a
species as a set of organisms representing a specific
evolutionary lineage
  Reproductive barriers serve to isolate a species
gene pool and prevent interbreeding
–  Morphological or DNA similarities or differences can be
used to define a species
  Reproductive barriers are categorized as prezygotic
or postzygotic, depending on whether they function
before or after zygotes form
–  Defining the amount of difference required to
distinguish separate species is a problem
Copyright © 2009 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
Zygote
Gametes Prezygotic barriers
• Temporal isolation
• Habitat isolation
• Behavioral isolation
• Mechanical isolation
• Gametic isolation
Postzygotic barriers
• Reduced hybrid
viability
• Reduced hybrid
fertility
• Hybrid breakdown
Viable,
fertile
offspring
14.4 In allopatric speciation, geographic isolation
leads to speciation
MECHANISMS
OF SPECIATION
  In allopatric speciation, populations of the same
species are geographically separated, separating
their gene pools
  Changes in the allele frequencies of each population
may be caused by natural selection, genetic
drift, and mutation
Copyright © 2009 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
14.4 In allopatric speciation, geographic isolation
leads to speciation
14.4 In allopatric speciation, geographic isolation
leads to speciation
  Gene flow between populations is initially prevented
by a geographic barrier
  Likelihood of allopatric speciation increases when
a population is small and isolated
–  The Grand Canyon and Colorado River separate two
species of antelope squirrels
–  A small population may have a different gene pool
due to the founder effect
–  Genetic drift and natural selection may have a
greater effect in a small population in a new habitat
Copyright © 2009 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
14.5 In sympatric speciation, speciation takes
place without geographic isolation
14.5 In sympatric speciation, speciation takes
place without geographic isolation
  In sympatric speciation, new species may arise
within the same geographic area as the parent
species
  Many plant species have evolved by polyploidy,
the multiplication of the chromosome number due
to errors in cell division
  Gene flow between populations may be reduced
by factors such as polyploidy, habitat
differentiation, or sexual selection
  A tetraploid (4n) plant can arise from a diploid
parent
Copyright © 2009 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
14.5 In sympatric speciation, speciation takes
place without geographic isolation
  Most polyploids arise from hybridization of two
different species
  Haploid gametes from two different species
combine to produce a sterile hybrid
1
Species A
2n = 4
Chromosomes not
homologous
(cannot pair)
2
3
Gamete
n=2
  Chromosome duplications may produce a fertile
polyploid species
Sterile hybrid
n=5
Species B
2n = 6
Gamete
n=3
Viable, fertile
hybrid species
2n = 10
Copyright © 2009 Pearson Education, Inc.
14.5 In sympatric speciation, speciation takes
place without geographic isolation
  Sympatric speciation in animals more commonly
occurs through habitat differentiation and sexual
selection
14.6 EVOLUTION CONNECTION: Most plant
species trace their origin to polyploid
speciation
  80% of all living plant species are the descendants
of ancestors that formed by polyploid speciation
  Hybridization between two species accounts for
most of these species
–  What advantage might there be to hybridization?
  Polyploid food plants include oats, potatoes,
bananas, peanuts, barley, plums, apples,
sugarcane, coffee, and bread wheat
  Cotton is also polyploid
Copyright © 2009 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
14.6 EVOLUTION CONNECTION: Most plant
species trace their origin to polyploid
speciation
AA
BB
×"
Triticum monococcum
(14 chromosomes)
  Wheat has been domesticated for 11,000 years
1
Wild
Triticum
(14 chromosomes)
Hybridization
AB
Sterile hybrid
(14 chromosomes)
–  It is the most widely cultivated plant in the world
2
  Bread wheat, Triticum aestivum, is a polyploid with
42 chromosomes
Cell division error
and self-fertilization
AA BB
DD
×"
T. turgidum
Emmer wheat
(28 chromosomes)
T. tauschii
(wild)
(14 chromosomes)
3
Hybridization
ABD
Sterile hybrid
(21 chromosomes)
4
Cell division error
and self-fertilization
AA BB DD
T. aestivum
Bread wheat
(42 chromosomes)
Copyright © 2009 Pearson Education, Inc.
14.10 Adaptive radiation may occur when new
opportunities arise
14.11 Speciation may occur rapidly or slowly
  In adaptive radiation, many diverse species
evolve from a common ancestor
  What is the total length of time between speciation
events (between formation of a species and
subsequent divergence of that species)?
  Adaptive radiations occur
–  When a few organisms colonize new unexploited
areas
–  After a mass extinction
  Adaptive radiations are linked to new
opportunities: lack of competitors, varying habitats
and food sources, evolution of new structures
–  In a survey of 84 groups of plants and animals, the
time ranged from 4,000 to 40 million years
–  Overall, the time between speciation events averaged
6.5 million years and rarely took less than 50,000
years
Animation: Macroevolution
Copyright © 2009 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.