Download Chapter 18.9

Reproductive Isolation
AP Biology
Spring 2011
 Species (Ernyst Mayr definition): interbreeding
individuals that produce viable, fertile offspring, and
do not interbreed with other individuals
 This may be an artificial designation, applicable at
only the local population level
 It would be hard to determine if geographically
isolated species would interbreed if they could
 This designation does help in determining when
evolutionary divergence, and speciation take place due
to some isolating mechanism
 Isolating mechanisms can work at several levels
 Before zygote formation (prezygotic)
 After zygotes form (postzygotic)
 Temporal Isolation: isolation due to the timing of an
organism’s reproductive cycle
 Mechanical isolation: isolation due to physical
incompatibility between mates or pollinators
 Behavioral Isolation: isolation caused that stops
gene flow.
 Ex. If female birds ignore mating dances of males from
related species, no interbreeding will occur
 Ecological Isolation: isolation that occurs when
related species become adapted to small changes in
microenvironments within a similar home range
 Gamete Incompatibility: a molecular difference
between species that blocks physical fertilization of
the egg
 Hybrid Inviability: fertilization occurs, but zygotes
fail to develop
 Hybrid Sterility: fertilization produces a viable
offspring that cannot produce