Summarizing Formation of New Species

Summary

Speciation occurs along two main pathways: geographic separation (allopatric speciation) and through mechanisms that occur within a shared habitat (sympatric speciation). Both pathways isolate a population reproductively in some form. Mechanisms of reproductive isolation act as barriers between closely related species, enabling them to diverge and exist as genetically independent species. Prezygotic barriers block reproduction prior to formation of a zygote, whereas postzygotic barriers block reproduction after fertilization occurs.

For a new species to develop, something must cause a breach in the reproductive barriers. Sympatric speciation can occur through errors in meiosis that form gametes with extra chromosomes (polyploidy). Autopolyploidy occurs within a single species, whereas allopolyploidy occurs between closely related species.

Glossary

adaptive radiation

speciation when one species radiates out to form several other species

allopatric speciation

speciation that occurs via geographic separation

allopolyploid

polyploidy formed between two related, but separate species

aneuploidy

condition of a cell having an extra chromosome or missing a chromosome for its species

autopolyploid

polyploidy formed within a single species

behavioral isolation

type of reproductive isolation that occurs when a specific behavior or lack of one prevents reproduction from taking place

dispersal

allopatric speciation that occurs when a few members of a species move to a new geographical area

gametic barrier

prezygotic barrier occurring when closely related individuals of different species mate, but differences in their gamete cells (eggs and sperm) prevent fertilization from taking place

habitat isolation

reproductive isolation resulting when populations of a species move or are moved to a new habitat, taking up residence in a place that no longer overlaps with the other populations of the same species

hybrid

offspring of two closely related individuals, not of the same species

postzygotic barrier

reproductive isolation mechanism that occurs after zygote formation

prezygotic barrier

reproductive isolation mechanism that occurs before zygote formation

reproductive isolation

situation that occurs when a species is reproductively independent from other species; this may be brought about by behavior, location, or reproductive barriers

speciation

formation of a new species

species

group of populations that interbreed and produce fertile offspring

sympatric speciation

speciation that occurs in the same geographic space

temporal isolation

differences in breeding schedules that can act as a form of prezygotic barrier leading to reproductive isolation

vicariance

allopatric speciation that occurs when something in the environment separates organisms of the same species into separate groups