Biology 106: Lecture Topic # 12 Speciation

I. Importance:

A. What are species?;

B. How do they evolve?

II. Levels of Variation

A. Variation within locally breeding populations or demes

B. Variation between populations or demes

C. Variation among GROUPS of populations

1. races,

2. subspecies,

3. often geographically isolated,

4. incipient species?

D. Development of ecotypes = ? and ecological races = ?: Turesson, Clausen, Keck, & Heisey

E. Variation Between Species

1. individuals appear very different

2. often reproductively isolated

3. individuals of a species appear more similar to one another than to other species

III. Definition:

A. History

1. Type concept: a. species is a special creation; b. variation around true "type"

2. John Ray

3. Linnaeus

B. Modern usage

1. Biological species concept; (Ernst Mayr) groups of actively or potentially cross fertilizing individuals which are isolated from other such groups

OR individuals whose genes can recombine with one another

OR similar indiv. which breed mostly among themselves & change as a unit through time

PHENOTYPE, BREEDING BEHAVIOR, EVOLUTIONARY UNIT?

IV. Problems

A. Are species reproductive units?

B. Is a species a unit of evolution?

V. Origin of Species

A. Microevolution ---> Macroevolution

1. Anagenesis =

2. Cladogenesis =

clade=group of species derived from a single common ancestral species

B. Processes of Reproductive Isolation

1. Sympatric Speciation

=evolution of reprod. isol within demes--LEAST LIKELY but

2. Parapatric Speciation

= evolution of reprod. isol among contiguous but non-overlapping demes--Uncommon

3. Allopatric= evol. of reprod. isolation after populations have become geographically isolated-- Most Frequent

VI. Reproductive Barriers or Isolating Mechanisms

A. Post-Zygotic: 1. zygotes do not develop normally/die, 2. if develop normally are sterile, 3. less fit

B. Pre-Zygotic

1. favored by natural selection after secondary contact

2. Mechanisms:

a. ecological isolation;

b. temporal isolation;

c. behavioral isolation

d. mechanical isolation = structural differences between species prevent copulation

VII. Rates of Speciation

A. Rapidly or gradually: Gradualism versus Punctuated Equilibrium

B. Polyploidy: - very important in plant evolution

VIII. Adaptive Radiation = rapid evolution of many divergent species from a common ancestor

Can account for rapid evolution following stasis via 1. empty niches

niche=all components of an environment with which an organism interacts

IX. Take Home Message

A. Species- one level of organizing variation;

B. Species - similar organisms which can interbreed

C. But are they reproductive units?;

D. New species form mostly in allopatry

E. Postzygotic ---> then Prezygotic ;

F. Species formation probably a gradual process

G. Except for plants-Polyploidy;

F. Importance of Adaptive Radiation

X. Terms to Know: ecotype, ecological race, Species, type, Biological species concept, Anagenesis, Cladogenesis, Sympatric Speciation, Parapatric Speciation, Allopatric Speciation, Post and Pre zygotic isolating mechanisms, stasis, polyploidy, adaptive radiation, Gradualism, Punctuated Equilibrium.