speciation creation of unique gene pools. i. introduction a. microevolution vs. macroevolution –...

SpeciationCreation of Unique Gene Pools

I. Introduction

• A. Microevolution vs. macroevolution– 1. microevolution

• a. Definition• b. Example• c. Importance in evolutionary

process• d. Can be seen• e. Measurable• f. Natural selection

2. macroevolution

• a. evolution or creation of new taxonomic groups

• b. Novel innovations• c. New ways of making

living• d. Branching of

phylogenetic tree• e. Evolution of coelom• f. May not occur by natural

selection• g. Harder to understand

B. Speciation events may drive macroevolution

• 1. New species may be first of a new grade or branch

• 2. Two modes of speciation observed in fossil record– a. anagenesis– b. cladogenesis

C. Anagenesis-gradualism

• 1. species seem to slowly gradually change

• 2. from one springs another

• 3. driven by natural selection

• 4. not as often seen in the fossil record

D. Cladogenesis

• 1. branching pattern• 2. rapid speciation event• 3. punctuated equilibrium• 4. supported by many

records in fossil

II. What is a species?• A. Morphological species concept

– 1. places specimen together or separates them on structural basis– 2. convenient when working in a lab– 3. fossil organisms– 4. organisms that don’t come into contact

B. Biological species concept

• 1. definition• 2. particularly

good definition for population genetics

• 3. speciation occurs when two gene pools become separate and distinct

III. How does speciation occur

A. Allopatric speciation1. barrier2. gene flow interupted3. differences

accumulate4. when become

sympatric?

5. Generalizations

• a. Requires a lot of time generally

• b. Most often occurs in small populations

• c. What is barrier to one may not be barrier to another

• d. Adaptive radiation example of allopatric speciation

• e. End point of speciation event is hard to agree to

• f. Most common?

B. Parapatric speciation

• 1. two populations sort of separated

• 2. experience different selection pressures at edges of range

• 3. differences accumulate despite gene flow

• 4. gene flow becomes impossible

C. Sympatric speciation

• 1. most commonly seen in plants

• 2. common barrier to hybridization is meiotic failure of hybrid– a. Two distinct sets of

chromosomes– b. No homologous pairs– c. What happens at

prophase I of meiosis

3. Polyploidy occurs commonly in plants

• a. Haploid• b. Diploid• c. Polyploid• d. Generally

leads to sterility

• e. But in plants

4. Allopolyploidy

4. New species form this way in plants because they self pollinate

5. Very uncommon in animals-cichlids

6. Parasites and hosts-apple maggot fly

Flies tend to stay on host

V. Pre and postzygotic barriers to hybrid formation• A. Natural selection operates to

maintain separate gene pools when speciation has occurred

• 1. Imagine disruptive selection• 2. Specializations occur• 3. Overlap after speciation event• 4. Potential interbreeding• 5. Parental species have

specialized• 6. Hybrids dilute the

specializations• 7. Natural selection would come

down hard on the dilution

B. Prezygotic barriers

• 1. Habitat isolation

2. Behavioral isolation

Spotted Newts

Spermatophore and red eft

3. Temporal isolation

4. Vocalizations Eleutherodactylus coqui

5. Mechanical Isolation

Kangaroo penis types

Adapters?

C. Postzygotic barriers to hybridization

• 1. hybrid inviability• 2. hybrid sterility• 3. hybrid breakdown-F2 are sterile

D. Thought questions

• 1. Do prezygotic or postzygotic barriers to hybrid formation form first?

• 2. Which of these two mechanisms is favored by natural selection?

• 3. Which of these two methods is more cost effective?

VI. Potential forces behind macroevolutionary change• A. Chance– 1. cannot be

preadapted to a disaster

– 2. meteorite implosion will wipe out all but lucky few

– 3. who survives can direct future evolutionary paths

B. Macromutations

• 1. translocations

2. Inversions

3. Chromosomal duplications

C. Segmentation genes• 1. ancestral animals were

one continuous body piece

• 2. the evolution of segmentation genes produced a branch in the tree of life

• 3. segmentation of body parts allows specializations to occur in different regions of the body

• 4. feeding structures and locomotion appendages

D. Homeotic genes

• 1. specify developmental plan for each segment

• 2. mutations can cause one body part to be replaced by a second

• 3. leg growing from head

E. Hox genes control number of appendages• 1. ancestral fruit fly had

four wings• 2. more economical

and faster to fly with two wings

• 3. mutation in Hox genes can cause backward jump

• 4. devolution

F. Allometric growth

• 1. varied growth rates for different parts of the body during development

2. Mutation in the genes which govern allometric growth

• Might produce chances for rapid evolutionary chanage

• Growth rates altered, drastic changes in shape

• May or may not be adaptive

Ocean sun fish

G. Changes in timing of development-paedomorphsis

• 1. retention of larval characteristics into adulthood

• 2. aquatic salamander• 3. by being able to remain in water may

have escaped terrestrial predators• 4. aquatic environment is not as harsh-

may have escaped dessication• 5. genes that cause metamorphosis

may have been blocked• 6. adult neotenic salamanders given

injections may display adult traits

H. Neoteny –retention of juvenile traits into adulthood

H. Old genes being turned back on

• 1. modern birds lack teeth

• 2. aerodynamically not efficient

• 3. ancestral birds had teeth

• 4. genes for teeth still reside in bird chromosomes

• 5. unlock the past-raw material for future evolutionary jumps?

Inbreeding

I. Jumping genes-transposons

J. Viral transmission