Chapter 9 March 7, 2012

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

Clade – different species that arise from the same ancestor Cladogenesis = speciation Phenotypic variations – differences in physiology, anatomy, and behavior of different species or individuals of the same species –Spruce tree in forest versus spruce tree at treeline Genotypic variations – differences in the genes between different species or members of the same species –Yarrow plants

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? –No –Lamarck’s giraffes How then do new genes and genetically controlled traits appear in species? –Mutation –Mutants can sometimes only mate with siblings, creating instantaneous speciation

Genetic drift – random changes in the genetic composition of a population that arise via mutation of genes and loss of other genes Can lead to a new species if the population is small and geographically isolated

Darwin Natural Selection – traits that provide an advantage in reproduction are selected fore, whereas disadvantageous traits are selected against –A bird with a longer beak would have an easier time finding food – that trait could be passed down to offspring –A bird with a short beak would have a hard time finding food and not reproduce at all –Moth coloration

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

Temporal Patterns in Evolution Darwin’s phyletic gradualism – distinctive transitional forms in the fossil record showing gradual evolution Punctuated equilibria – When the environment is impacted by environmental change, a stable species is replaced by a new species

Cope’s Rule Cope’s Rule – species become larger as a lineage evolves

Evolutionary reductions – complex forms that evolve into simpler forms