How Diversity Evolves

Macroevolution

The evolution of large scale diversity

Evolutionary novelties Wings, feathers,

brain sizes

Speciation: origin of new species

What is a species?

The morphological species concept: if it looks like a duck, and quacks like a duck…

What is a species?

The morphological species concept:

Mature leaves of arrowhead plants (Sagittaria sagittifolia)

What is a species?

The biological species concept: groups of interbreeding natural populations that are reproductively isolated from other such groups.

What problems might exist with this definition?

What is Speciation?

For speciation to occur, populations must attain reproductive isolation.

Genetic Divergence: when populations become reproductively isolated.

Reproductive Isolating Mechanisms

Any heritable features that prevent interbreeding between populationsIsolating mechanisms can be physical (body form), physiological (body function), or behavioralIsolating mechanisms can be prezygotic or postzygotic.

Note: a zygote is a fertilized egg.

Reproductive Barriers

Prezygotic Isolation

Temporal (reproduce at different times)

Prezygotic Isolation

Behavioral (courting behaviors are different)

Bird courtship behavior include visual, acoustic and tactile rituals that identify members of the same species.

Prezygotic Isolation

Mechanical (differences in reproductive organs)

Plants and their pollinators

Prezygotic Isolation

Habitat (same area but different habitats)

Microhabitats of Manzanita in Nevada

Prezygotic Isolation

Gametic Mortality (egg & sperm incompatibility)

Correct chemical signal needed for successful fertilization

Postzygotic Isolation

If fertilization does occur the embryo is often weak and dies.

In others, hybrids are vigorous but sterile.

Mules are produced by a male donkey and female horse.

Mechanisms of Speciation

Allopatric speciation: geographically isolated by a physical barrier.

Sympatric speciation: species form within home range of an existing species.

Allopatric Speciation

“allo” = different; “patric” = lands

Antelope squirrels and the Grand Canyon

Evidence for Allopatric Speciation

Allopatric Speciation

Archipelagos island chain and adaptive radiation low competition and

predation abundant habitats

and resources

Sympatric Speciation

“sym” = together

Cichlids of Lake Barombi Mbo Many species by

feeding modes (open water, bottom feeders, shoal feeders)

Sympatric Speciation

Polyploidy

How does this happen? Improper separation

during meiosis & mitosis

50% of all flowering plants are polyploidy

Animal problems

The Evolution of Wheat

Evolutionary Trees and Rates of Change

Trees summarize information about the relationship among species over time.

Two types of models:Gradual model: branches at slight angles

to show slow changes over timePunctuation model: horizontal branches

show abrupt speciation followed by stable conditions

Evolutionary Trees and Rates of Change

Macroevolution and “Evo-Devo”

Genetic changes in developmental biology

Homeotic genes Control timing, rate, and

spatial patterns in embryos

Subtle changes can have profound effects

Paedomorphosis Axolotl

“Evo-Devo” Research

Macroevolution and Earth’s History

Macroevolution and Historical Events

Evolution Today?