Chapter 20: Speciation and Macroevolution
1. Define and describe the biological species concept of speciation and the associated problems
2. Compare and contrast and give examples of prezygotic and postzygotic isolating mechanisms and
barriers for reproductive isolation (e.g. temporal, habitat, behavioral, mechanical, and gametic isolation;
hybrid isolating mechanisms) (knowledge/comprehension)
3. Define, compare and contrast and give examples of allopatric and sympatric speciation
4. Name, define, compare and contrast the three types of hybrid zones (knowledge/comprehension)
5. Name, define, compare and contrast the types of rate and pattern of speciation
6. Define, describe and discuss macroevolution in the context of novel features, including preadaptations,
allometric growth, and paedomorphosis (knowledge/comprehension)
7. Define, describe and discuss the macroevolutionary significance of adaptive radiation and extinction
(knowledge/comprehension) Some key words
Adaptive radiation evolution of several species from one or a few ancestral species; occurs in
relatively short time frame
Allometric growth growth of different body parts at different rates
Allopatric speciation formation of two new species following the physical separation of individuals of a
Gradualism evolution occurs as a result of slow steady changes over time
Hybrid inviability egg and sperm of two different species are genetically incapable of producing a
viable zygote and embryo
Hybrid sterility gametes of interspecies hybrid are not normal and able to produce a zygote
Hybrid breakdown the hybrid is unable to reproduce successfully; F1 and and F2 generations may be
Hybrid zone an area of overlap between closely related species or subspecies in which interbreeding
Macroevolution large-scale changes over long time periods resulting in phenotypic changes that warrant
placement of the organism into a new taxonomic group at or above the species level
Microevolution small-scale changes that occur within a species as a result of changes in the allele or
Paedomorphosis retention of juvenile features in the adult body form
Preadaptation a characteristic that functioned in one way originally but later changed in a way that was
adaptive to the structure having a different role
Prezygotic barrier something that prevents fertilization from occurring (prevents formation of a zygote);
prevents hybrid formation
Postzygotic barriersomething that occurs after fertilization (formation of a zygote) that prevents a hybrid
from living long enough to form a new species
Punctuated equilibrium evolution proceeds with period of little or no change and then rapid changes
occur over a relatively brief period of time
Sympatric speciation formation of two new species within the geographic region of the parent
population; no physical barrier is present but reproductive isolating mechanisms
are Chapter 20: Speciation and Macroevolution
Objective 1: Define and describe the biological species concept of speciation and the associated problems
What is a species?
I. What is a biological species?
Fertile offspring are produced
II. What are some problems?
Includes only sexual reproduction
Objective 2: Compare and contrast and give examples of prezygotic and postzygotic isolating mechanisms
and barriers for reproductive isolation (e.g. temporal, habitat, behavioral, mechanical, and gametic
isolation; hybrid isolating mechanisms) (knowledge/comprehension)
I. Reproductive isolation in biological species
A. What is the dividing point?
A zygote formed by the fusion of egg and sperm
B. What are the two barrier groupings?
1. Prezygotic reproductive barriers
Prior to zygote formation
2. Post zygotic
After zygote formation
II. Prezygotic barriers
A. Temporal (timing) isolation
species reproduce at different times of day, season, or year preventing cross fertilization
Slide 28 B. Habitat isolation
Species are in same geographic area, but live and breed in different habits in that area. IE: Frogs
that breed in temporary ponds in woods and living near frogs that breed in permanent pond along edge of
C. Behavioral isolation
Many animal species exchange a distant series of signals before mating(visual, chemical, oral)
D. Mechanical isolation
Structural differences in reproductive organs prevent mating.
E. Gametic isolation
Molecular and chemical differences between species gametes prevents formation of a zygote.
Eggs and sperm incompatible
F. What happens if prezygotic barriers fail?
Hybrid is produced
III. Postzygotic reproductive barriers(Skipped)
A. When do postzygotic barriers occur?
B. What do postzygotic barriers do?
IV. Barriers to hybrid longevity
A. Hybrid inviability
Embryo of interspecific hybrid spontaneously aborts
B. Hybrid sterility
Interspecific hybrid lives cannot reproduce
C. Hybrid breakdown
Hybrid lives and F1 hybrid mate produces F2 hybrid generation and unable to continue generation
because of some defect.
Objective 3: Define, compare and contrast and give examples of allopatric and sympatric speciation