Reproductive barriers             Pre-zygotic barriers prevent mating or egg fertilization if members of different species try to mate. Post-zygotic barriers zygotes may arise, but develop into inviable or infertile offspring

Prezygotic barriers a. Habitat isolation - rarely encounter each other b.  Behavioral isolation – courtship behaviours c.  Temporal isolation (different breeding seasons)    d.  Mechanical isolation – anatomical incompatibility e.  Gametic isolation – cannot fertilise

A Prezygotic isolation example Two closely related Mimulus flower species Different morphologies M. lewisii bumblebee pollination M. cardinalis hummingbird pollination

Courtship ritual as a behavioral barrier between species.

Anatomically unlikely!

Forget it!

Postzygotic barriers a. Reduced hybrid viability (aborts)   b.  Reduced hybrid fertility (eg donkey + horse = mule (sterile hybrid)          c.  Hybrid breakdown (future generations with reduced fertility)

Postzygotic – hybrid sterility mother horse, father donkey sterile mule mother donkey, father horse  sterile hinny

Postzygotic – hybrid inviability eg. sheep-goat embryos inviable

A summary of reproductive barriers between closely related species