Isolation and Reinforcement Mechanisms

Question 1

reinforcement

Answer 1

• prevents separated species from hybridizing
• genetic differences accumulate in isolated populations over time, reducing the probability that individuals can mate successfully
• if hybridization occurs, the hybrids will have a lower fitness and natural selection will result in reinforcement mechanisms and prevent hybridization

Question 2

reinforcement mechanisms

Answer 2

any trait that has evolved purely for the purpose of preventing hybridization
isolating trait or isolating mechanism

Question 3

postzygotic isolating mechanisms

Answer 3

reinforce separation between species
reduce the fitness of hybrid offspring
results in selection against hybrids, reinforcing prezygotic mechanisms
reinforcement mechanisms

Question 4

prezygotic isolating mechanisms

Answer 4

occur before fertilization
prevent hybridization from occurring
mechanical, temporal, habitat, behavioral, gametic
isolating mechanisms

Question 5

mechanical isolation

Answer 5

difference in size and shape of reproductive organs makes mating impossible

Question 6

temporal isolation

Answer 6

mating seasons do not line up
usually sympatric populations
ex: frog populations

Question 7

behavioral isolation

Answer 7

individuals reject or fail to recognize potential mating partners
breeding calls of male frogs quickly diverge between related species

Question 8

habitat isolation

Answer 8

when two closely related species evolve preferences for living or mating in different habitats, they never come into contact during mating periods

Question 9

gametic isolation

Answer 9

important in aquatic species
eggs of one species don’t have the appropriate chemical signals for sperm of another species
sperm cannot penetrate the egg
ex: sea urchins

Question 10

mate choice

Answer 10

mate choice of a species may be mediated by the behavior of another
whether two plant species hybridize depends on the food preference of their pollinators
ex: floral shape and birds’ beaks

Question 11

low hybrid zygote viability

Answer 11

zygotes fail to mature or have severe abnormalities

Question 12

low hybrid adult viability

Answer 12

offspring have lower survival rates

Question 13

hybrid infertility

Answer 13

hybrids are sterile

Question 14

hybrid zones

Answer 14

observed where prezygotic isolation mechanisms are absent
occur where two closely related species come into contact and mate
reinforcement is weak or absent

Question 15

narrow hybrid zones

Answer 15

• although isolation is incomplete, there is some mechanism preventing hybridization being viable
• selection against hybrids
• persists since both species combine to produce offspring

Question 16

broad hybrid zones

Answer 16

isolation is minimal
hybrids are not selected against
ex: warblers - only difference in genes is in color and feather pattern