Speciation & Rates of Evolution Biology 101B

Reproductive Isolation Two Types: 1. Prezygotic Isolation Prevents reproduction by making fertilization unlikely Geographic isolation- separated by barrier (river, canyon) Temporal- mating occurs at different times for different species (trout, fireflies, some flowers) Behavioral isolation- no sexual attraction or communication- use different mating songs or calls Mechanical- structural differences- sex organs “don’t fit” Gametic- gametes fail to unite & create viable offspring

Reproductive Isolation Two Types: Liger 2. Post-zygotic Isolation Prevents the development of fertile adults Hybrid inviability- zygote fails to develop Hybrid sterility- offspring are sterile & cannot produce offspring EX: Liger: cross between a male lion and a female tiger creates liger which is usually sterile EX: Mule: cross btwn donkey & horse. Tigon

Reproductive Isolation leads to SPECIATION Speciation: Process by which some members of a sexually reproducing population change so much that they can no longer produce fertile offspring with members of the original population.

Speciation Two Types: Allopatric Speciation (Geographic isolation) Physical barrier divides one population into two or more populations Mountain ranges, channels btwn islands, rivers, canyons, lava flows 2 different species evolve from same ancestral species EX: Kaibab squirrel & Abert squirrel separated by Grand Canyon Activity 23.2 Allopatric Speciation

Speciation Two Types: Sympatric Speciation Species evolves into a new species without a physical barrier Some insects and plants evolve this way Most likely due to mutation.

Patterns of Evolution Adaptive Radiation Many species evolve from a common ancestor Occurs as a result of formation of new habitat or other ecological opportunities Also called divergent evolution May follow mass extinctions EX: cichlid fish in Lake Victoria EX: Darwin’s finches

Patterns of Evolution Coevolution Species evolve in close relationships with other species Mutualism Ex: flowers & their insect pollinators Predator-prey Ex: cheetahs & antelope Ex: plant chemical defenses & insects

Patterns of Evolution Convergent evolution Unrelated species evolve similar traits even though they live in different parts of the world. Similarity in environment has led to evolution of similar traits. EX: Madagascar aye-aye and New Guinea striped opossum both have elongated middle fingers. Live separately but have same structure

Rates of Evolution Two Types: Gradualism Small, gradual steps Traits remain unchanged for millions of years Punctuated Equilibrium Abrupt transitions Seen in fossil record Rapid spurts of genetic change caused divergence quickly

What are some current trends in evolution? 1. Natural Selection Antibiotic resistance in bacteria Pesticide resistance in insects Industrial melanism- peppered moths changed due to pollution. Generally, organisms that are more general in their needs survive. A species that requires a specific food source or habitat will be less able to change. 2. Artificial Selection Genetically modified foods Selective breeding in dogs What are some current trends in evolution? Antibiotic Use & Evolution

HIV and drug resistance http://www.pbs.org/wgbh/evolution/library/10/4/l_104_10.html