Chapter 9 March 18, 2008
Jan 19, 2016
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