{ 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 Mechanisms of Reproductive Isolation

 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

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

 1) Allopatric speciation = geographic isolation  different homeland, physical barriers prevent reproduction with other parts of a population  (prevent gene flow)  2)Sympatric speciation = reproductive isolation  together homeland, some part of population stops reproducing with the rest even though they are nearby  3) Parapatric Speciation = common border only  beside homeland 3 Models of Speciation

 Geographic barrier depends on mobility  reproductive isolation occurs by differential natural selection or genetic drift.  Lake levels subside to form 2 separate lakes  Human developments separate populations  Islands separated from mainland by water  (founder effect)  Continents separated by continental drift Allopatric

 Guppies in different pools of the same river.  Pools with predator = select for drab colors  Pools with no predator = select for bright color  Put the two together again they don’t recognize each other and won’t mate Example of Allopatric

 Requires some form of reproductive isolation  (repro isolation = biological barriers to repro)  1) Natural selection & habitat/food source Δ  2) Sexual Selection & mate choice  3) polyploidy  Sympatric

 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 and the other group feed at the bottom so they seldom encounter each other and do not mate. (ecological isolation also called Habitat isol.) Examples of Sympatric

 Plants can become 3n or 4n or more n rather than the standard 2n. Polyploid individuals can 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 5. Polyploidy

allopolypoidy

 Incomplete reproductive barriers create Hybrid zones  Hybrid organisms produced in border area No real gene flow because hybrids are either …  a) restricted to border land (die elsewhere)  Or  b) sterile and can’t pass on any genes Parapatric Hybrids:

 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) clagogenesis = branching line of descent Patterns of Evolution

 Results from directional selection  No branching  Only 1 species at a time exists Anagenesis = up/renewed creation

 Lineage splits do to reproductive isolation & genetic divergence  Disruptive selection or geographic isolation  Adaptive Radiation = many branches (new species) form as one species spreads into multiple new habitats (adaptive zones)  Major adaptive radiation after mass extinctions 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 brance will have those derived 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