Chapter 9 March 18, 2008. Evolution – genetically controlled changes in physiology, anatomy, and...

Chapter 9

March 18, 2008

• Evolution – genetically controlled changes in physiology, anatomy, and behavior that occur to a species over time– Microevolution – evolutionary change within

an individual species or population– Macroevolution – evolutionary change within

larger taxonomic units such as families

• Speciation – development of two or more generically differentiable species from a single common ancestor

• Phenotypic variations – differences in physiology, anatomy, and behavior of different species or individuals of the same species

• Genotypic variations – differences in the genes between different species or members of the same species

Genotypic Variation• Geographic races - Genetically and phenotypically

distinct members of the same species that occur in different regions

Figure 9.1

• Can offspring of an organism inherit phenotypic traits that are acquired due to environmental conditions acting upon the organism?

• How then do new genes and genetically controlled traits appear in species?– Mutation– Genetic drift– Natural selection– Gene flow– Adaptation

• Mutation – changes in DNA

• Genetic drift

• Natural Selection – traits that provide an advantage in reproduction are selected fore, whereas disadvantageous traits are selected against

• Gene flow

• Adaptation

How does evolution lead to speciation?

• Reproductive isolation – must be barrier between newly formed species and original species

• Polyploidy – plants that are born with twice the chromosome as the parent making them reproductively isolated

• Allopatric speciation – formation of a new species by geographic isolation

Allopatric speciation

• Sympatric speciation – development of new species within the same geographic area

• Causes:– Life cycle timing, such as timing of

reproduction– Ethological isolation – barriers to breeding

caused by behavior, particularly mate choice– Stenophagy

Sympatric Speciation

• Cichlids of Lake Victoria, Africa

• Parapatric speciation – caused by the evolutionary divergence of populations that occupy different habitat or niches in the same geographic area– Iris fulva (lower left)– grows on drier riverbanks– Iris giganticaerulea (lower right) – grows in damp

marshes– Hybrids possible, but cant survive in either parental

niche