Reproductive Barriers

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Reproductive Barriers

Prezygotic Barriers

Gametic Isolation

sperm or pollen may not be adapted to the environment of the female reproductive track

if the female immune system r ecognizes sperm as foreign and attacks it

red and purple sea urchins have different proteins on sperm and egg

sperm of one species cannot fertilize the egg of the other species

Temporal Isolation

two populations of plants may produce flowers in different seasons, making mating between populations impossible

drosophila persimilis breeds in early morning while drosophila persimilis breeds in the afternoon

eastern spotted skunks mate during the winter while western spotted skunks mate during the summer

species breed during different time of the day/year/season

Behavioral Isolation

species with complex courtship rituals usually echibit a stereotyped "give and take" between male and female before actual mating takes place

two different species of birds have different mating calls so they cannot recognize each other as mates

beetle mating displays show different spot patterns

mates cannot recognize each other because of different courtship rituals

Habitat Isolation

red legged frogs breed in fast moving, ephemeral streams. Bullfrogs breed in permanent ponds

the amazing partnership of the bucket orchids and orchid bee is so precise that if either one went extinct, the other would follow

Garter snakes live in water or land cannot mate although they live in the same geographic area

two species that live in the same area but different habitats encounter each other

Mechanical Behavioral

plant that is structured so a bee can pollinate it will not be compatible with a flower that relies on hummingbirds to spread its pollen

damsel flies of one species attempt to mate with females of another species but their genitalia are not compatible

an elephant penis cannot fit into a frog vagina

reproductive structure incompatibility

Postzygotic Barriers

Reduced Hybrid Viability

attempt to cross Norway rats and black rats have led to pups being born, but they die within hours

offspring die young when two species of salamanders mate - the offsprings to do make it to maturity

horse can be mated with zebras, but their offspring are sterile

hybrid is produced is produced but is sterile

Hydrid Breakdown

successive generations of hybrids suffer greatly lowered fertility -> sterility

two species of fish successfully interbreed, but their offspring does not live to maturity

hybrid does not survive

Reduced Hybrid Fertility

ligers are the result of a cross between a male lion and female tiger. Almost all known male offspring of these crosses have been infertile

mules are produced by mating a horse and a donkey, but mules are sterile and cannot breed

strains of cultived rice breakdown over generation

mating of hybrids results in sterile or weak offsprings