1. Evolution and Zygotic Barriers
Ms. Day
Honors Biology
LECTURE #32

2. 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

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

4. 2 Types of 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

5.
Allopatric speciation
Sympatric speciation

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

7. 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

8. Pre-Zygotic Barriers

9. 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

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

11. Behavioral Isolation
Courtship rituals and other behaviors unique to a species are effective barriers

12. 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

13. 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

14. Post-Zygotic Barriers

15. 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

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

17. 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