Speciation: The Origin of New Species Botany 4 Lecture #31 Speciation: The Origin of New Species

Evolution Produces Novel Organisms… But when, how and why do new SPECIES appear?

What is a species??????

Morphological Species: Members of a species are individuals that look similar to one another. Basis for most classification used today...

But… many organisms look similar, but are not members of the same species. (Monarch and Viceroy Butterflies) And… some organisms look vastly different, but are members of the same species…morphs, juveniles… (Caterpillars and Butterflies)

Biological Species: “Groups of potentially interbreeding populations that are reproductively isolated from other such groups.”

Speciation (Macroevolution) “When a new species emerges or splits from an existing species.” How can this occur? The key to Speciation is Reproductive Isolation.

Reproductive Isolation The inability to form fertile gametes. There are many mechanisms in nature that can preclude organisms from breeding. These barriers can occur before or after fertilization.

Barriers Before Fertilization (Prezygotic) Temporal - different mating times. Behavioral - different mating behaviors. Mechanical- sperm can’t get to egg. Gametic- sperm deposited, but no fertilization. Habitat – potential mates never meet.

Barriers After Fertilization (Postzygotic) Hybrids have problems – zygotes do not develop, are weak, have low fitness, or are sterile.

How Does Speciation Occur in Nature?

Two Main Types of Speciation.

Allopatric Speciation Speciation that occurs when two populations are geographically isolated from each other and therefore gene flow stops. Populations gradually diverge to form two distinct species.

Allopatric Speciation 4 Events that could drive Allopatric Speciation.

Adaptive Radiation An Example of Allopatric Speciation. A few members of a population migrate to a new area and eventually a new species evolves. Darwin’s Finches evolved this way.

Sympatric Speciation New species arises despite being in the same location (within the range of the parent species).

Sympatric Speciation Most common method is by Polyploidy. This type of Speciation can occur rapidly. Most common method is by Polyploidy.

Polyploidy Having more than 2n number of chromosomes. How could this occur? How would this cause Rapid Evolution?

Autopolyploidy Polyploid hybrid resulting from contributions from one species.

Allopolyploidy Polyploid hybrid resulting from contributions of two different species. Very important for plant evolution.

Allopolyploidy Evolution of modern wheat. Two separate Allopolyploidy events.

Extinction… Mass Extinctions are “common”: Occurs most when environment changes faster than genetic change (mutations). Mass Extinctions are “common”: Drastic environmental changes such as enormous volcanoes or meteor impacts. Gradual Changes such as continental drift.