1. Chapter 24 The Origin of Species
Evolutionary theory must explain how new species originate and how populations evolve
Speciation
the origin of new species
within a population
Microevolution consists of adaptations that evolve ______________________, confined to one gene pool
Macroevolution refers to evolutionary change above the _________________
species level
Biologists compare morphology, physiology, biochemistry, and DNA sequences when grouping organisms

2. The biological species concept is based on the potential to interbreed rather than on physical similarity
Figure 24.2 The biological species concept is based on the potential to interbreed rather than on physical similarity
(a) Similarity between different species

3. (b) Diversity within a species
Figure 24.2 The biological species concept is based on the potential to interbreed rather than on physical similarity
(b) Diversity within a species

4. Reproductive Isolation
Reproductive isolation is the existence of biological factors (barriers) that impede two species from producing ___________, fertile offspring
Hybrids are the offspring of crosses between _______________ species
Reproductive isolation can be classified by whether factors act before or after fertilization
viable
different
block fertilization
Prezygotic barriers _______________________ from occurring by:
Impeding different species from attempting to mate
Preventing the successful completion of mating
Hindering fertilization if mating is successful

5. Zonkey
Liger
Wholphin

6. Grolar Bear
Zorse

10. Prezygotic barriers
Habitat isolation: Two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers
Temporal isolation: Species that breed at different times of the day, different seasons, or different years cannot mix their gametes
Behavioral isolation: Courtship rituals and other behaviors unique to a species are effective barriers
Mechanical isolation: Morphological differences can prevent successful mating
Gametic isolation: Sperm of one species may not be able to fertilize eggs of another species

11. Postzygotic barriers developing
Postzygotic barriers prevent the hybrid zygote from _______________ into a viable, fertile adult:
Reduced hybrid viability
Reduced hybrid fertility
Hybrid breakdown
Reduced hybrid viability: Genes of the different parent species may interact and impair the hybrid’s development
Reduced hybrid fertility: Even if hybrids are vigorous, they may be sterile
Hybrid breakdown: Some first-generation hybrids are fertile, but when they mate with another species or with either parent species, offspring of the next generation are feeble or sterile

12. Prezygotic barriers
Habitat Isolation
Temporal Isolation
Behavioral Isolation
Mechanical Isolation
Individuals of
different
species
Mating
attempt
(a)
(c)
(e)
(f)
(d)
Figure 24.4 Reproductive barriers
(b)

13. Reduced Hybrid Viability Reduced Hybrid Fertility Hybrid Breakdown
Prezygotic barriers
Postzygotic barriers
Gametic Isolation
Reduced Hybrid Viability
Reduced Hybrid Fertility
Hybrid Breakdown
Viable,
fertile
offspring
Fertilization
(g)
(h)
(i)
(l)
(j)
Figure 24.4 Reproductive barriers
(k)

14. Speciation can take place with or without geographic separation
Speciation can occur in two ways:
_______________________
Allopatric speciation
Sympatric speciation
(a) Allopatric speciation
(b) Sympatric speciation

15. Allopatric (“Other Country”) Speciation
In allopatric speciation, gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations
The definition of barrier depends on the ability of a population to disperse
Separate populations may evolve independently through _____________, ___________________, and ___________________
mutation
natural selection
genetic drift
Regions with many geographic barriers typically have more species than do regions with fewer barriers
Adaptive radiation
- the emergence of numerous
- spreads to many new
species from a common ancestor
environments

16. Allopatric speciation of antelope squirrels on opposite rims of the Grand Canyon
A. harrisi
A. leucurus
Allopatric speciation in frogs
India
88 mya
65 mya
56 mya
Madagascar
Figure 24.6 Allopatric speciation of antelope squirrels on opposite rims of the Grand Canyon

17. Sympatric (“Same Country”) Speciation
In sympatric speciation, speciation takes place in geographically overlapping populations
Polyploidy
Polyploidy is much more common in __________ than in animals. Many important crops (oats, cotton, potatoes, tobacco, and wheat) are polyploids
plants
Polyploidy is the presence of extra _______ of chromosomes due to accidents during cell division
An autopolyploid is an individual with more than two chromosome sets, derived from ________________
sets
one species
2n = 6
4n = 12
Failure of cell
division after
chromosome
duplication gives
rise to tetraploid
tissue. 2n
Gametes
produced
are diploid.. 4n
Offspring with
tetraploid
karyotypes may
be viable and
fertile.

18. An allopolyploid is a species with multiple sets of chromosomes derived from ___________________
different species
Species B
2n = 4
Unreduced
gamete
with 4
chromosomes
Unreduced
gamete
with 7
chromosomes
Hybrid
with 7
chromosomes
Meiotic
error
Normal
gamete
n = 3
Viable fertile
hybrid
(allopolyploid)
2n = 10
Figure One mechanism for allopolyploid speciation in plants
Normal
gamete
n = 3
Species A
2n = 6

19. Habitat Differentiation
Sympatric speciation can also result from the appearance of new ecological ____________
For example, the North American maggot fly can live on native hawthorn trees as well as more recently introduced apple trees
niches
Sexual Selection
Sexual selection can drive _________________ speciation
Sexual selection for mates of different colors has likely contributed to the speciation in cichlid fish in Lake Victoria
sympatric
The Time Course of Speciation
Broad patterns in speciation can be studied using the fossil record, morphological data, or molecular data

20. Two models for the tempo of speciation
- branches diverge - most morphological
- continuous - long periods of stasis followed by
ex.
gradually
changes
evolution
episodes of punctuated speciation
polyploid plants