← Evolutionary processes leading to speciation
5 Reproductive isolating mechanisms
Speciation needs gene flow between populations to stop.
Isolating mechanisms prevent interbreeding or prevent viable, fertile offspring.
Isolating mechanisms
| Type | Mechanism | Example |
|---|
| Pre-zygotic | Temporal: breed at different times | Two frog species breeding in different seasons |
| Pre-zygotic | Ecological/habitat: live in different habitats | One species in trees, another on the ground |
| Pre-zygotic | Behavioural: different courtship signals | Bird songs/displays that don’t attract each other |
| Pre-zygotic | Mechanical: incompatible reproductive structures | Flower shapes fitting different pollinators |
| Pre-zygotic | Gametic: gametes don’t fuse | Sperm & egg chemically incompatible |
| Post-zygotic | Hybrid inviability/sterility/breakdown | Mule (horse × donkey) is sterile |
ℹ
Pre- vs post-zygotic
Pre-zygotic mechanisms stop a zygote forming at all;
post-zygotic allow a zygote but it’s inviable, sterile, or its offspring are weak.
A fast check when naming an isolating mechanism
- Have I named the SPECIFIC type (temporal, ecological, behavioural, mechanical, gametic, or post-zygotic), not just "they can't interbreed"?
- Have I applied it to the actual organisms in the resource, rather than the generic textbook example?