AP Biology Crosby High School The Origin of Species AP Biology Crosby High School

Reproductive Isolation Prezygotic Barriers: Habitat Isolation: Parasites in different hosts Behavioral Isolation: Generally courtship rituals Temporal Isolation: Different time, day, season, or year Mechanical Isolation: Square peg, round hole Gametic Isolation: Gamete recognition doesn’t match

Reproductive Isolation (cont.) Postzygotic Barriers: Reduced Hybrid Viability: Embryo may abort due to genetic incompatibility Reduced Hybrid Fertility: Hybrid can not backbreed due to sterility Hybrid Breakdown: May produce one generation of viable and fertile offspring, but future generations are not

Classifying a Species Biological Species: emphasizes reproductive isolation Ecological Species: Species defined by ecological niche Pluralistic Species: Reproductive or niche Morphological Species: Unique set of structural features Geneological Species: Unique genetic history

Allopatric Speciation Conditions Separated by a geographical feature Changes must prevent interbreeding Ring Species California Salamanders more distant to the south Adaptive Radiation Diversely adapted species from common ancestor

Evolution of Reproductive Barriers Prezygotic: Two populations of D. melanogaster Starch vs. Maltose for generations Maltose females only breed with maltose males

Sympatric Speciation Polyploid Speciation in Plants 2n  4n 4n can self pollinate or mate with other 4n Oats, cotton, potatoes, tabacco, wheat Sympatric Speciation in Animals Pundamilia pundamilia vs. Pundamilia nyererei Normal light vs. monochromatic orange

Evolutionary Time “Although each species must have passed through numerous transitional stages, it is probable that the periods during which each underwent modification, though many and long as measured by years, have been short in comparison with the periods during which each remained in an unchanged condition.” -Charles Darwin

Punctuated Equilibrium Evolution occurs so rapidly that there is no fossil record

Eye Development Pigmented Cells Eyecup Pinhole camera-type Eye w/ Primitive lens Complex Camera-type

Exaptations Develop for one purpose, but later end up serving another Birds Honeycombed bones Original: light for agility Present: light for flight Feathers Original: Display for mating Present: flight

Evo - Devo Allometric Growth: Growth rates create proportioning for each species Heterochrony: Evolutionary change in rate or timing of developmental events Paedomorphosis: Rate of reproductive development accelerates compared to somatic Homeotic genes: Determine placement and spatial organization of body parts Hox genes

Evolutionary Trends Evolution is not goal oriented Horse Evolution Equus is only surviving genus of the tree Not all adaptive radiations lead to same result Parahippus: Grazers Miohippus: Browsers Species Selection: Species that endure the longest and reproduce the most set the trend for macroevolution

Equus Evolution

Sympatric Speciation

Ring Species

Adaptive Radiation