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Reproductive Barriers
Reproductive barriers are mechanisms that prevent species from mating and producing viable offspring. These barriers can be categorized into prezygotic and postzygotic types. Prezygotic barriers occur before fertilization and include mechanical isolation, where differences in reproductive structures prevent successful mating.
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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
