Pronunciation: I-so-la-ting ME-ka-niz’m

Etymology: Isolate is derived from the Latin for island (insula).

Isolating mechanisms are those factors that result in reproductive isolation between species. The isolation can be physical or temporal or by genomic incompatibility. Typically, physical and temporal barriers are considered to be pre-mating isolating mechanisms such as:

• geographic isolation (e.g. populations isolated by barriers like rivers or ocean if the populations occur on islands)
• temporal isolation (e.g. active at different time of day or reproductive at different times of the year)
• ecological isolation (e.g. preferred habitats are different)
• behavioral isolation (e.g. subtle differences in behavior like courtship rituals cause rejection by the female)
• mechanical isolation (e.g. structures necessary for copulation do not fit together)

Post-mating isolating mechanisms mainly are due to genomic incompatibility such as:

• gametic incompatibility (e.g. gametes cannot fuse or zygote does not form)
• zygotic mortality (e.g. zygote forms but cannot develop)
• hybrid inviability (e.g. zygotic success is very low)
• hybrid sterility (e.g. the hybrid develops but is sexually sterile)
• hybrid breakdown (e.g. first generation hybrids are fertile but become sterile in succeeding generations)

By Jack R. Holt. Last revised: 01/02/2009