Reproductive Barriers

mating of hybrids results in sterile
or weak offsprings

strains of cultived rice
breakdown over generation

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

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

hybrid does not survive

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

successive generations of hybrids suffer greatly lowered fertility -> sterility

hybrid is produced is
produced but is sterile

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

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

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

reproductive structure incompatibility

an elephant penis cannot fit
into a frog vagina

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

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

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

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

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

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

mates cannot recognize each other because of different courtship rituals

beetle mating displays show
different spot patterns

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

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

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

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

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

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

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

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

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

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