slatkin8Answers - Bio 1B, Spring, 2007, Evolution section 1...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Bio 1B, Spring, 2007, Evolution section 1 of 3 Updated 3/13/07 1:29 PM Lecture 8 8 Modes of speciation. Reading 7 th edition 476-482; 6 th edition 468-476. The formation of new species requires some initial reduction of gene flow Two processes of speciation are thought to be important, allopatric speciation and sympatric speciation. Allopatric speciation, The first step in allopatric speciation is the restriction of dispersal between two (or more) populations that would otherwise freely interbreed. One possibility is that a geographic barrier such as a river or desert forms. The separation of two populations by such a barrier is called a vicariant event. A second possibility is that individuals from a source population colonize a new geographic area that is separated from the source population by a nearly complete barrier to gene flow. The establishment of a new population is a founder event. Both vicariant and founder events may reduce gene flow sufficiently that reproductive isolating mechanisms can evolve afterwards. Whether a geographic barrier leads to allopatric speciation or not depends on dispersal ability. A barrier may lead to speciation in some groups but not in other groups. For example, a river may be a barrier for a snake but not a bird. In the Origin , Darwin emphasized that isolation led to the evolution of separate species. The neo-Darwinian theory is essentially the same. If there is no gene flow between two populations, they will evolve independently under the combined effects of mutation, natural selection, and genetic drift and will eventually be recognized as different species. Reproductive isolating mechanisms will also evolve in the absence of gene flow. Female choice can play an important role in species formation, as illustrated by the
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 09/07/2008 for the course BIO 1B taught by Professor Carlson,mischel,power during the Spring '07 term at University of California, Berkeley.

Page1 / 3

slatkin8Answers - Bio 1B, Spring, 2007, Evolution section 1...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online