Speciation occurs through reproductive isolation over long periods of time. There are three main types of speciation: allopatric speciation which occurs when populations become geographically isolated; parapatric speciation at habitat borders; and sympatric speciation within the same habitat. Reproductive barriers like behavioral, ecological, and mechanical isolation prevent interbreeding and lead to the evolution of new species. Over time, small changes through microevolution accumulate into macroevolutionary changes between species.

1. Speciation
Chapter 13

2. Evolution
• Microevolution—Relatively short term
changes in ALLELE FREQUENCIES within a
population or species
• Macroevolution—Large scale evolutionary
changes
– Over long periods
– Small scale microevolution leads to
macroevolution

3. Biological Species Concept
• Species—Group of populations whose
members have the potential to interbreed in
nature and produce viable, fertile offspring,
but do not produce viable offspring with
members of other groups.
• What maintains species?
– Gene flow
– Reproductive isolation (biological)

4. Other Species Definitions
• Morphological Species Concept
– Characterizes by body shape and other structures
• Ecological Species Concept
– Characterizes in terms of ecological niche
• Phylogenetic Species Concept
– Smallest group of organisms that share a common
ancestor

5. Reproductive Isolation
• Prezygotic Barriers—block fertilization from
happening
– Prevent different species from attempting to mate
– Prevent an attempted mating from being successful
– Hindering fertilization
• Postzygotic Barriers—occur after zygote is
formed
– Developmental errors
– Birth defects cause death
– Infertile offspring

6. Prezygotic Reproductive Isolating
Barriers
• Behavioral isolation—Absence of cross-attraction between individuals of
separate species inhibiting any courtship initiation or individual behavior
during copulation does not allow normal fertilization to occur.
• Ecological isolation—Variations in the ecology of species give rise to
barriers:
– Habitat isolation—Even when living in the same common locality, species
occupy diverse habitats due to different biological or genetic tendencies
thereby limiting gene flow during breeding seasons.
– Temporal isolation—Species living in the same area have different breeding
seasons preventing gene flow.
– Pollinator isolation—Flowering plants have varying interactions with
pollinators thereby reducing gene flow.
• Mechanical isolation—Reproductive structures are incompatible between
species inhibiting copulation or pollination.
• Gametic isolation–Gametes that are transferred during copulation or
pollination are ineffectual for fertilization due to problems with storage or
transfer of gametes or because of conspecific pollen or sperm partiality.

7. Prezygotic Barriers—Habitat Isolation

8. Prezygotic Barriers—Temporal
Isolation

9. Prezygotic Barriers—Behavioral
Isolation
• http://www.fiddlercrab.info/video/u_heteropleura02.html
• http://www.fiddlercrab.info/video/u_ornata01.html

10. Prezygotic Barriers—Mechanical
Isolation

11. Prezygotic Barriers—Gametic Isolation

12. Postzygotic Reproductive Isolating
Barriers
• Ecological unviability—Although normal development
occurs, hybrids cannot find a suitable ecological niche
thereby lowering viability.
• Hybrid unviability—Hybrid species have developmental
issues causing complete or incomplete lethality.
• Behavioral sterility—Although normal gametogenesis
occurs, hybrids are less fertile and typically exhibit
phenotypes or courtship behaviors that make them less
desirable mates.
• Hybrid sterility—Hybrids can have developmental problems
of the reproductive organs or gametes, or can suffer from
physiological or neurological issues that prevent effective
courtship.

13. Postzygotic Barriers—Reduced Fertility

14. Speciation
• Development of a new species through a
variety of factors
• Rate of speciation depends on generation
time, environmental conditions, etc.
• Can be caused by a change in just 1 gene or a
set of genes causing some sort of isolation

15. Types of Speciation
• Allopatric Speciation—gene flow is interrupted when a
population is divided into geographically isolated
subpopulations
• Parapatric Speciation—occurs when part of a population
enters a new habitat bordering the range of the parent
species
– Some gene flow may occur between populations in border zone
• Sympatric Speciation—occurs in populations that live in
the same geographic area
– Less common than allopatric speciation
– Happens when gene flow is diminished by:
• Polyploidy
• Habitat differentiation
• Sexual selection

16. Types of Speciation

17. Allopatric
Speciation

18. Parapatric
Speciation
Ephedra californica
Ephedra trifurca

19. Sympatric Speciation
Apple maggot flies (Rhagoletis pomonella) on domestic apple (left) and on much smaller
native hawthorn fruits (right). Flies that emerge from a given host generally return to
mate and lay eggs on the same type of fruit.

20. How Does Speciation Occur?
• Gradualism—one species gradually
transforming into another through a series of
intermediate forms
– Evolutions occurs in small, incremental changes
over MANY generations
– Should be able to see in fossil record but we do
not – intermediate forms NOT present in fossils
• Fossil record incomplete or;
• Missing links too rare in fossils or;
• See next slide 

21. Gradualism

22. How Does Speciation Occur?
• Punctuated Equilibrium—relatively brief
bursts of rapid evolution interrupting long
periods of little change
– Fits with allopatric speciation
– Can occur during adaptive radiation—population
inhabiting a patchy environment gives rise to
multiple specialized forms in short time period
• Common in island groups

23. Punctuated Equilibrium

24. Adaptive
Radiation A. loysiana
GULF
OF
MEXICO
Florida
ATLANTIC OCEAN
CUBA
JAMAICAHISPANIOLA
PUERTO
RICO
Upper trunk/canopy
A. evermanni
Midtrunk
Lower trunk/ground
A. cristatellus
Grass/bush
A. pulchellus

25. Adaptive
Radiation

26. Extinction
• A species goes extinct when ALL of its
members die.
• Many factors can cause—climate,
reproductive barriers, disease.
• No matter what it is, it is a FAILURE of that
species to adapt to the new conditions
• More prevalent in small, less genetically
diverse populations

27. Types of Extinction
• Background Extinction—gradual loss of species
over time.
– Loss of habitat, small climate change, etc.
• Mass Extinction—many number of species
disappeared over a relatively short period of
time.
– Open up new habitats for adaptive radiation
– Two theories:
• Impact Theory—meteor, comet crashes into earth making it
inhabitable for the life there
• Movement of Earth’s Crust—causes dramatic environmental
changes

28. Taxonomy
• How we name and classify organisms
• Binomial Nomenclature
– First name—Genus
– Second name—Species
– Homo sapiens
• Organisms are classified based on a hierarchy
of more specific categories

30. Phylogeny
• Phylogeny—Depiction of species relationships
based on descent from shared ancestors
• Phylogenetic Trees—pictures of these
relationships
– Anatomical features of fossils and living creatures
– Behaviors
– Physiological adaptations
– Molecular sequences

31. Cladistics
• Phylogenetic system based on ancestral and
derived characteristics
– Ancestral Characteristics—inherited attributes and
RESEMBLE those of ancestor
– Derived Characteristics—features that are different
from ancestors group
– Monophyletic—Group of organisms with 1 common
ancestor and ALL the descendants
– Paraphyletic—Group of organisms with 1 common
ancestor and some, but not all descendants
– Polyphyletic—Group of organisms that EXCLUDES the
most recent common ancestor

32. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Clades
Taxa at branch
tips
Birds
Nonavian
dinosaurs
Crocodiles
Lizards
and snakes
Amphibians
Mammals
Turtles
Time
Node
(common
ancestor)
Last
common
ancestorRoot
of tree
Cladogram

33. Cladogram

34. Cladogram

35. Constructing Cladograms
• Light bones
• 3-toed foot
• Wishbone
• Breastbone
• Loss of 4th
and 5th digits
• Down like
feathers
• Longer arms
and hands
• Complex
feathers
• Arms as long or
longer than legs
• Feathers
support flight
1
2
3
4
5
Coelophysis
Allosaurus Modern birdsProtarchaeopteryx
SinosauropteryxArchaeopteryx
Last
common
ancestor of
theropods
Coelophysis
Allosaurus
Sinosauropteryx
Protarchaeopteryx
Archaeopteryx
Modern birds
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1
2
3
4
5

36. Constructing Cladograms

37. Cladistics

38. Phylogenetics and Cladistics Cheat
Sheet
Term Definition
Ancestral characters a trait inherited from the ancestor of a clade
Clade a group consisting of an ancestor and all its descendants—a single "branch" on the "tree of life”
Cladistics the science that tries to reconstruct phylogenetic trees and thus discover clades
Cladogram tree-shaped diagrams; the result of cladistic analyses
Derived characters a trait that has evolved—not from the common ancestor of the clade
Monophyletic group a taxon (group of organisms) which forms a clade
Outgroup a monophyletic group of organisms that serve as a reference group when determining the evolutionary
relationship among three or more monophyletic groups of organisms
Paraphyletic group a group that consists of all the descendants of the last common ancestor of the group's members minus a
small number of monophyletic groups of descendants
Phylogenetic tree a branching diagram or "tree" showing the inferred evolutionary relationships among various biological
species or other entities—their phylogeny—based upon similarities and differences in their physical or genetic
characteristics
Polyphyletic group a group characterized by one or more homoplasies: character states which have converged or reverted so as
to appear to be the same but which have not been inherited from common ancestors
Systemactics the study of the diversification of living forms, both past and present, and the relationships among living
things through time

39. The World Around Us