The Origin of Species Macroevolution Biological Species Concept Ernst Mayr, 1942 defines species as a population who have the potential to interbreed. •Must be able to interbreed in nature •Produce viable, and fertile offspring (interfertility) •Must occur in nature Prezygotic Barriers Factors that impede mating between species or hinders fertilization. 1. Habitat Isolation: contact is rare b/w species because of habitat location 2. Behavioral Isolation: attractor signals are not the same between the species 3. Temporal Isolation: breeding occurs at different times, seasons, years. 4. Mechanical Isolation: mating can be attempted but not successful. 5. Gametic Isolation: fusion b/w gametes does not occur Postzygotic Barriers Barriers that prevent a fertilized egg from developing into a viable, fertile adult. 1. Reduced Hybrid Viability: development is not complete, or survivors are weak. 2. Reduced Hybrid Fertility: hybrids are sterile, gametes are not formed by meiosis. (Mule). 3. Hybrid Breakdown: 1st generations are viable and fertile, but next generations are feeble or sterile. Modes of Speciation Allopatric Speciation: a geographical barrier that isolates populations and prevents gene flow. Sympatric Speciation: chromosomal changes and nonrandom mating changes gene flow within a pop. Ring Species in Progress? Conditions favoring Allopatric Speciation 1. Gene pools differ between the outer population extreme clines created, differ from inner pop. Outer pop small founder effect 2. Genetic Drift occurs until outer pop. is large enough. Some may become fixed, causing more divergence. 3. Evolution by Natural Selection may differ between outer and inner pop. Sympatric Speciation Polyploidy: Creation of a new species when during cell division extra sets of chromosomes are generated. Occurs in plants species. Autopolyploidy: failure of meiosis results in 4n. Can self fertilize or mate with other 4n’s. Sterile offspring made when fertilize a 2n. Discovered by Hugo de Vries in 1900’s, Allopolyploid: two species contribute to a polyploid hybrid. Two different species interbreed. Propagation by asexual reproduction. May be more vigorous than parents, best of both. Sympatric Speciation • Reproductive Isolation • Different Figs, different wasps • Monkey & Fig • Lake Victoria, East Africa – Selective reproduction (blue back vs. Red back) – Mate choice based on color is main repro. Isolation – Can still interbreed……..if prezygotic barrier is breached. – Speciation recent. Tempo of Speciation •Punctuated Equilibrium •Abrupt changes •Period of stasis •Gradualism: •Slow divergence •Slight changes Evo-Devo • Interdisciplinary science b/w evolutionary biology and study of development. • Genes regulate (zygote to adult) – Control rate – Timing – Spatial pattern of change in form • Allometric growth: – Growth rates of different parts – Changes form/structure – Heterochrony: evolutionary change in the rate or timing of developmental events Paedomorphosis • At sexual maturity, species may retain body features that were juvenile structures in ancestral species. • Salamanders have larval stage to become adult. • Some become mature but still have gills and other structures (juvenile) Evolution is not goal oriented.