Evolution & Speciation Mechanisms & Models Quizlet: http://quizlet.com/12797658/flashcards

I. Species defined A. Phylogenetic species concept: species = one or more populations that share a trait derived from a common ancestor which sets them apart from other organisms ** can be physically separate populations** B. Biological Species Concept: a species includes only individuals that could potentially produce fertile offspring in nature and are isolated from others (can’t/don’t reproduce with others).

II. Speciation Requires A. Reproductive Isolation of some type B. Genetic divergence(evolution) due to different selective pressures or genetic drift C Evolution of differences that prevent interbreeding even if reintroduced to original home land

III. Speciation occurs when 2 populations become reproductively isolated by: A) geographic barriers B) prezygotic mechanisms= before zygote forms C) Postzygotic mechanisms= after zygote forms

IV. Prezygotic Mechanisms of Reproductive Isolation A) Mechanical Isolation….parts don’t fit 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

V. Examples reproductive isolation 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.)

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

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

Autopolyploidy

allopolypoidy

VIII. Patterns of Evolution defined by…. A) rates of change 1) gradual 2) punctuated equilibrium model, no change for long time then rapid change for ‘short’ time (10,000 – 100,00 years) B) number of species formed 1) anagenesis = single line of descent 2) cladogenesis = branching line of descent

IX. Cladogenesis = Branch creation A) Lineage splits do to 1) reproductive isolation & 2) genetic divergence (evolution) B) Adaptive Radiation C) Graphical models: Cladograms and Phylogenetic Trees 1) mathematical models - computer generated 2) based on a) morphological homologies b) molecular data (amino acid/DNA sequence) 3) show when traits are derived or lost

D. Each branch point shows an extinct common ancestor of the organisms further down the branch E. Outgroup = group at base

F. lines that do not reach the top of the page show lineages that went extinct

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

X. Types of Cladistic Grouping Monophyletic group – All the descendants of a common ancestor in one group Paraphyletic group – All members of group share a common ancestor but not all descendants included in the group Polyphyletic group – includes descendants from more than one common ancestor

XI. Molecular Clock Theory A) Attempts to measure absolute time of evolutionary change B) # nucleotide substitutions proportional to time since divergence C) Assumes constant rate of evolution of genes D) Δ rates depend on importance of gene/mutation