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 populations Isolating mechanisms can be physical (body form), physiological (body function), or behavioral Isolating 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 time Punctuation 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?