{ Evolution & Speciation Mechanisms & Models Quizlet:

 Phylogenetic species concept: species = one or more populations that share a trait derived from a common ancestor which sets them apart from other organisms  Biological Species Concept: a species includes only individuals that could potentially produce fertile offspring and are isolated from others. Species defined

 #1 Reproductive Isolation of some type  #2 Genetic divergence due to different selective pressures or genetic drift  #3….. Evolution of differences that prevent interbreeding even if reintroduced to original home land Speciation Requires

 1) prezygotic = before zygote forms  2) Postzygotic = after zygote forms 2 Types of Reproductive Isolation Mechanisms

 A) Mechanical Isolation….parts don’t fit  Chihuahua and Great Dane  snail shells twist in different directions  B) Temporal Isolation… mate at dif. times  seasons, years, nocturnal vs diurnal  C) Behavioral Isolation: courtship/recognition  D) Ecological/habitat Isolation…field vs forest  E) Gametic Isolation: sperm fail to survive or penetrate egg Prezygotic Repro Isolation Mechanisms

 F.Geographic Separation:  1) different islands  2) different sides of the river  G. Polyploidy

 A) Embryo mortality  B) Death before maturity  C) Reduced hybrid fertility  D) Hybrid breakdown: offspring of hybrid weak or sterile Postzygotic mechanisms …zygote forms and then….

 1) Song birds change their mating song. (behavioral isolation & sexual selection)  2) Female fish select mates that are most similar in color to themselves (sexual selection)  3) One population of flowers blooms earlier than another (temporal isolation)  4) One group of fish feed at the top of the lake the other feeds at the bottom. They seldom encounter each other and do not mate. (ecological isolation also called Habitat isol.) Examples reproductive isolation

 Plants can be 3n or 4n or more  Polyploid individuals no longer interbreed with the 2n population = reproductive isolation = new species.  Autopolyploidy = just keep two full sets of your own chromosomes (4n can self pollinate)  Allopolyploidy = hybridize with other species Polyploidy Polyploidy

Autopolyploidy

allopolypoidy

 1) rates of change  a) gradual  b) punctuated equilibrium model, no change for long time then rapid change for ‘short’ time (10,000 – 100,00 years)  c) average time 6.5 million years  2) number of species formed  a) anagenesis = single line of descent  b) cladogenesis = branching line of descent Patterns of Evolution

 Lineage splits do to reproductive isolation & genetic divergence  Adaptive Radiation Cladogenesis = Branch creation

 Each branch point on a cladogram shows an extinct common ancestor of the organisms further down the branch  Outgroup = group at base of cladogram, shows the least number of shared derived traits

 Lines crossing the cladogram show when derived traits showed up.  All organisms further along the branch will have those traits unless they were lost due to natural selection

 Lines that don’t make it to the top went extinct

 Monophyletic group – All the descendants of a common ancestor.  Paraphyletic group – All members of group share a common ancestor but not all descendants of that ancestor are included in the group

 Attempts to measure absolute time of evolutionary change  # nucleotide substitutions proportional to time  Since divergence  Assumes constant rate of evolution of genes  Δ rates depend on importance of gene/mutation Molecular Clock Theory