Bio 140 Handout. V. Speciation and Macroevolution

did not convert #39 into a question and include notes during class

Morphological species concept

Species concepts

based on distinctive morphological features

a. It is difficult to determine if a set of organisms represents multiple or a single species with extensive phenotypic variation.

b. Two populations morphologically similar are almost indistinguishable.

Species concepts

What are the difficulties of the Morphological species concept?

Phylogenetic species concept

Species concepts

species is an irreducible (basal) clust of organisms that is diagnosably distinct from other such clusters

Biological species concept

Species concepts

Species are groups of actually or potentially interbreeding natural populations that are reproductively isolaed from other such groups (Mayr 1942).

Biological species concept

Limitations:

a. not applicable to asexually reproducing species

b. cannot be applied to extinct organisms represented only by fossils

c. difficult to apply to two populations that are geographically segregated

Biological species concept

Limitations:

a. not applicable to __________ reproducing species

b. cannot be applied to __________ organisms represented only by fossils

c. difficult to apply to two populations that are ____________ _____________

1. Premating barriers

2. Post-mating, pre-zygotic barriers

3. Post-zygotic barriers

Barriers to gene flow

What are the 3 main types of barriers?

1. Premating barriers

   • Ecological isolation

     • Temporal isolation

     • Habitat isolation

   • Behavioral isolation

   • Pollinator isolation

Barriers to gene flow

1. Premating barriers

   • ________________

     • ________________

     • ________________

   • ________________

   • ________________

2. Post-mating, pre-zygotic barriers

   • Mechanical isolation

   • Gametic isolation

Barriers to gene flow

2. Post-mating, pre-zygotic barriers

   • ________________

   • ________________

3. Post-zygotic barriers

   • Extrinsic

     • Ecological inviability

     • Behavioral sterility

   • Intrinsic

     • Hybrid inviability

     • Hybrid sterility

     • F2 breakdown

Barriers to gene flow

3. Post-zygotic barriers

   • Extrinsic

     • ________________

     • ________________

   • Intrinsic

     • ________________

     • ________________

     • ________________

What do you call each mode of Speciation (Gradual) shown in the picture above?

A. ________________

B. ________________

C. ________________

D. ________________

Allopatric speciation (by vicariance)

Modes of Speciation (Gradual)

the evolution of genetic reproductive barriers between populations that are geographically separated by a physical barrier

Peripatric speciation

Modes of Speciation (Gradual)

occurs when a small subset of a population is isolated (becomes peripheral), and genetic drift and natural selection drive evolution of reproductive isolation between the source and founding populations

Parapatric speciation

Modes of Speciation (Gradual)

occurs when divergent selection is stronger than gene flow between populations in adjacent areas

Sympatric speciation

Modes of Speciation (Gradual)

occurs when a biological barrier to gene exchange arose within an initially randomly mating population without spatial segregation of incipient species.

Sympatric speciation

Modes of Speciation (Gradual)

sexual selection by females may drive __________ speciation

Sympatric speciation

Modes of Speciation (Gradual)

involves abrupt genetic changes that quickly leads to reproductive isolation of a group of individuals

Ex. polyploidization

Sympatric speciation

Modes of Speciation (Gradual)

genetic changes enable members of a species to occupy a new niche within the same geographic range

Speciation by polyploidy

the only known mode of instantaneous speciation by a single genetic event

Autopolyploidy

new species results from the genome of a single species

Allopolyploidy

new species/hybrid results from two (or more) different species

• Self-fertilization

• Vegetative propagation

• Higher fitness than diploid

• Niche separation from diploid

How do polyploids form a viable population?

diversity

Consequence of Speciation

Speciation is necessary for ____________ of organisms

speciation

Consequence of Speciation

Each branch in the great phylogenetic tree of life represents a __________ event.

reproductively isolated; divergent

Consequence of Speciation

Populations become ________________, hence, capable of independent, ________ evolution, including, eventually, the acquisition of differences that mark genera, families, and higher taxa.

microevolution; macroevolution

Consequence of Speciation

Speciation bridges ___________ (genetic changes within and among populations) and _____________ (evolution of the higher taxa in all their diversity).

Macroevolution

“evolution above the species level”

Macroevolution

evolution of great phenotypic changes, or the origin of characteristics that diagnose higher taxa

George Gaylord Simpson

Rates of Evolution

He pioneered study of evolutionary rates

George Gaylord Simpson

Rates of Evolution

distinguished Phylogenetic from Taxonomic rates

Phylogenetic rates

Rates of Evolution

how fast single or complexes of characters evolve

Taxonomic rates

Rates of Evolution

how fast taxa with different characteristics originate, become extinct, and replace one another

Gradualism

Each new species evolves continuously over long spans of time

Gradualism

Accumulation of many small genetic changes result to speciation

Punctuated equilibrium

long periods of little change (stasis) interrupted/punctuated by brief episodes of more rapid change

Punctuated equilibrium

Species exist relatively unchanged for many generations

Rapid evolution

It is explainable by mutation, genetic drift, natural selection, and speciation.

Stasis

evolution is very slow

Three hypotheses that explain stasis in evolution:

1. Genetic and developmental constraints

2. Stabilizing selection for a constant optimum phenotype

3. Erasure of divergence by gene flow between populations with ancestral and derived character states.

Three hypotheses that explain stasis in evolution:

1. ___________ and ___________ constraints

2. ___________ selection for a constant optimum phenotype

3. Erasure of divergence by ___________ between populations with ancestral and derived character states.

What accounts for the macroevolution of phenotypic characters?

1. A feature originates as a new structure, or a new modification of an existing structure

   • Ex. A slight thickening of bone in the nasal region of the earliest titanotheres could have been advantageous in contests that the males of many hoofed mammals engage in. Once this thickening originated, sexual selection could have favored a larger hornlike structure.

2. A feature is a developmental by-product of other adaptive features.

   • may not be adaptive initially, but later, may be recruited or modified to serve an adaptive function

   • Ex. By excreting nitrogenous wastes as crystalline uric acid, insects lose less water than if they excreted ammonia or urea. Excreting uric acid is surely an adaptation, but the white color of uric acid is not.
     
     However, pierine butterflies like cabbage white butterfly (Pieris rapae) sequester uric acid in their wing scales, making the wings white, which plays a role in thermoregulation and probably in other functions.

3. A change in the function of a feature alters the selective regime, leading to its modification.

   • Ex. A bee's sting is a modified ovipositor, or egglaying device.
     
     The wings of auks and several other aquatic birds are used in the same way in both air and water. In penguins, the wings have become entirely modified for underwater flight.

What accounts for the macroevolution of phenotypic characters?

1. A feature originates as a new structure, or a new modification of an existing structure

   • Ex. A slight thickening of bone in the nasal region of the earliest titanotheres could have been advantageous in contests that the males of many hoofed mammals engage in. Once this thickening originated, sexual selection could have favored a larger hornlike structure.

2. A feature is a developmental by-product of other adaptive features.

   • may not be adaptive initially, but later, may be recruited or modified to serve an adaptive function

   • Ex. By excreting nitrogenous wastes as crystalline uric acid, insects lose less water than if they excreted ammonia or urea. Excreting uric acid is surely an adaptation, but the white color of uric acid is not.
     
     However, pierine butterflies like cabbage white butterfly (Pieris rapae) sequester uric acid in their wing scales, making the wings white, which plays a role in thermoregulation and probably in other functions.

3. A change in the function of a feature alters the selective regime, leading to its modification.

   • Ex. A bee's sting is a modified ovipositor, or egglaying device.
     
     The wings of auks and several other aquatic birds are used in the same way in both air and water. In penguins, the wings have become entirely modified for underwater flight.