Evolution and Zygotic Barriers (Part 5) Ms. Day AP Biology Chapter 24: The Origin of Life

How are new species created? Geographic isolation Reproductive barriers Change in chromosome numbers through mutation Adaptive radiation (example of divergent evolution) Speciation = formation of NEW species

Hello over there  A. harrisi A. leucurus Geographic Isolation

Speciation and geographic separation Speciation can occur in two ways: Allopatric speciation (means “other”) a genetic isolation WITH a geographical barrier; new group isolated from its parent population Sympatric speciation (means “together”) genetic isolation WITHOUT a geographical barrier; a reproductive barrier isolates population in SAME habitat

Allopatric speciation Sympatric speciation

http://www. pbs. org/wgbh/nova/evolution/evolution-action-salamanders http://www.pbs.org/wgbh/nova/evolution/evolution-action-salamanders.html

Reproductive Isolation biological factors (barriers) that stop 2 species from producing viable, fertile hybrids Two types of barriers Postzygotic “after the zygote” Zygote can NOT develope Prezygotic “before the zygote” Sperm and egg can not fuse

Pre-Zygotic Barriers

Habitat Isolation 2 species encounter each other rarely, or not at all, because they live in different habitats, even though not isolated by physical barriers

Temporal Isolation Species that breed at different times of the day, different seasons, or different years cannot mix their gametes Late Summer Late Winter

Behavioral Isolation Courtship rituals and other behaviors unique to a species are effective barriers http://wps.aw.com/bc_campbell_biology_7/26/6661/1705356.cw/index.html

Mechanical Isolation Morphological differences can prevent successful mating Related species may attempt to mate but CAN’T anatomically incompatible Sperm = transfer Mating organs don’t fit

Gametic Isolation Sperm of one species may not be able to fertilize eggs of another species Ex: specific molecules on egg coat adhere to specific molecules on sperm

Post-Zygotic Barriers

Reduced Hybrid Viability Genes of the different parent species may interact and impair the hybrid’s development Hybrids are very weak and/or underdeveloped Salamander hybrid shows incomplete development

Reduced Hybrid Fertility Even if hybrids may live and be strong, they may be sterile

Hybrid Breakdown Some F1 hybrids are fertile, but when they mate with another species or with either parent species, offspring of the next generation (F2) are weak or sterile Cultivated rice have different recessive mutant alleles F2 accumlates many of these alleles

Polyploidy Polyploidy is presence of EXTRA sets of chromosomes due to accidents during cell division ex: “nondisjunction” It has caused the evolution of some plant species More common in plants than in animals