What are the common reproductive barriers in sexual reproduction?

Common reproductive barriers in sexual reproduction include geographical, temporal, behavioural, mechanical, and genetic barriers.

Geographical barriers are perhaps the most straightforward. They occur when two populations are separated by physical barriers such as mountains, rivers, or stretches of water. This prevents them from coming into contact with each other and thus, from interbreeding. For example, a species of bird might be split into two populations by a mountain range, leading to the development of two distinct species over time.

Temporal barriers occur when two species reproduce at different times. This could be different times of the day, different seasons, or even different years. For instance, two species of flowers that are pollinated by the same type of insect might bloom at different times, preventing cross-pollination.

Behavioural barriers involve differences in mating behaviour. This could include different courtship rituals, mating calls, or other behaviours that attract mates. If two species have significantly different mating behaviours, they are unlikely to interbreed. For example, different species of frogs often have distinct mating calls, which attract females of their own species but not others.

Mechanical barriers occur when physical differences prevent successful mating. This could be due to differences in size, shape, or structure of reproductive organs. For example, in many species of insects, the male's reproductive organ is specifically shaped to fit with the female's of the same species, preventing mating with other species.

Finally, genetic barriers prevent interbreeding even if the above barriers are overcome. This could be due to differences in chromosome number or structure, which prevent successful fertilisation, or cause the resulting offspring to be sterile. For example, horses and donkeys can mate to produce a mule, but mules are usually sterile due to differences in chromosome number between their parents.