Download Macroevolution updated fa14

SPECIATION &
MACROEVOLUTION
OBJECTIVES:
1) EXPLAIN WHY DEFINING SPECIES IS
DIFFICULT
2) IDENTIFY CAUSES OF SPECIATION
3) DESCRIBE MACROEVOLUTIONARY
PROCESSES/PATTERNS
Are these spiders the same
species?
What is a species??
 Different species
concepts…

Biological species
concept

Phylogenetic
species concept

Ecological species
concept
Biological Species Concept
 1 or more populations whose
members interbreed and produce
fertile offspring
 Reproductively isolated from other
species
 Has own gene pool
Problems with Biological Species…
 Asexual Reproduction..
 Hybrids…
Speciation
 Event that splits lineage and produces 2 or more
species
 Speciation can be difficult to identify…
 Ring species (ex. Ensatina)

All of these salamanders can interbreed with their immediate
neighbors except E. eschsholtzii and E. klauberi

Where did speciation occur?
What causes speciation?
ISOLATION
+
SELECTIVE PRESSURE
Types of Isolation
GEOGRAPHIC
REPRODUCTIVE
Geographic Isolation…


Event causes populations to separate
Gene flow ceases

Over time, the 2 populations experience different selective
pressures
Physical changes
 Food/Habitat preferences
 Courtship

 Species do not need to be completely separated
 Broad geographic range
 Reduced gene flow
 Hybrid zones
 May or may not = speciation
Reproductive Isolation
 Prezygotic barriers – prevent fertilization

Temporal

Habitat

Behavioral

Mechanical

Gametic
 Postzygotic barriers

Hybrid inviability

Hybrid sterility

Hybrid breakdown
Types of Speciation:
Allopatric
 Results from
Sympatric
 Same location
geographic isolation



Change in ploidy

Ecological change
Natural selection
Genetic drift
 Most common
 More common in
plants
Rate of change
 2 models try to explain fossil
record
 Gradualism
 Proposed by Darwin
 Evolution is a continuous process
 Change is slow and steady
 Series of transitional forms
 Millions of years
 Difficult to observe in fossil record
 Punctuated equilibrium
 Proposed by Gould and Eldridge
(1970s)
 Fossil record may not be as incomplete
as we believe
 Long periods with little change are
interrupted by short bursts of rapid
speciation (tied to speciation event)
 Macromutation
 Skip transitional forms
 Thousands of years
Macroevolution
 Large-scale Evolution
 Species level +
 Zooms out on tree of life
Patterns in Macroevolution
Stasis
 Lineage remains stable/little change for long period
of time
 What can this tell us?
Speciation
 Phylogenetic tree can reveal history, frequency of
speciation in a clade
Extinction
 Opens ecological niches
 Surviving species rapidly diversify
Adaptive Radiation
 Evolutionary diversification of many species
from one/few ancestral species in short amount
of time
 Divergent
 Adaptive zones – new ecological opportunities