Reproductive+Barriers

Reproductive Barriers **Reproductive barriers** are biological factors that stip members of two species from producing fertile hybrids (see biological species concept).
 * **Prezygotic barriers** stop mating between species or the fertilizzation of ova if members of a different species attempt to mate.
 * If the sperm from the male overcomes a prezygotic barrier and fertilizes the egg, **postzygotic barriers** will usually brevent the zygote from developing into a viable fertile adult.

Types of prezygotic barriers include:
 * Habitat isolation
 * Temporal isolation
 * Behavioral isolation
 * Mechanical isolation
 * Gametic isolation


 * 1) **Habitat isolation** is when two species occupy the same general area, but rarely come in contact with each other, even though they may not be physically barricaded. Flies who live in single habitat may exist in different areas of the habitat, such as soil as apposed to water will not mate.
 * 2) **Temporal isolation** is a barrier that works because of how and when species mate during different times of the year or day. Two populations of plants may produce flowers in different seasons, making mating between the populations impossible.
 * 3) **Behavioral isolation** works as an effective barrier because of distinct mating habits each species has. species of crickets are morphologically identical, but can be distinguished by the fact that females will only respond to the mating songs of males of their own species and males of other species are ignored.
 * 4) **Mechanical isolation** also works because you can't fit a square peg in a round hole. Bush babies are divided into several species. Each species has distinctly shaped genitalia that, like locks and keys, only fit with the genitalia of its own species.
 * 5) **Gametic isolation** may happen when sperm from one species is biologically unable to fertilize an egg from another species. Gametic isolation is important in aquatic environments because many aquatic animals release their gametes into the water, where fertilization takes place.

Types of postzygotic barriers include:
 * Reduced hybrid viability
 * Reduced hybrid fertility
 * Hybrid breakdown


 * 1) **Reduced hybrid viability** is sucessful because the parents' genes may interact and heed the hybrid's development. Frogs in the genus //Rana// do not complete development when mated with each other.
 * 2) **Reduced hybrid fertility** will reduce the fertility of the offspring because of chromosomal differences in the parents. When donkeys and horses mate, they produce a mule. Mules cannot produce fertile offspring.
 * 3) **Hybrid breakdown** is when the offspring is viable and fertile, but if mated with an organism of the parent species, their offspring will in turn be feeble or sterile. Certain cotton species can produce fertile hybrids, but a breakdown occurs in the F2 generation when the F1 offspring mate with those of it's parental species



(1) Information from AP Edition Biology, Seventh Edition, Campbell and Reece (2) Examples from SparkNotes