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A Thorough Understanding of Mechanical Isolation with Examples

Understanding Mechanical Isolation with Examples
If not for structural differences in reproductive organs of species, interbreeding would have resulted in several extinctions. We will shed light on mechanical isolation and provide a couple of examples of the same to make it easier for you to understand the concept.
BiologyWise Staff
Last Updated: Jan 27, 2018
Did You Know?
The birth of a sterile offspring does no good to the species. Rather, an increase in the number of sterile individuals hinders the population growth of the species.
Reproductive isolation is a biological mechanism that employs behavioral and physiological barriers to prevent interbreeding in closely related species. Interbreeding is not in the interest of the species, as the offspring resulting from it is most likely to be sterile (incapable of reproducing). The five different forms of reproductive isolation are mechanical isolation, gametic isolation, ecological isolation, temporal isolation, and behavioral isolation.
MECHANICAL ISOLATION EXPLAINED
In biology, two species are said to be mechanically isolated when differences in their reproductive organs prevent interbreeding and thus, prevent the birth of a sterile hybrid. In this case, even if the members of two different but closely related species attempt to copulate after successful courting, mating will not be successful.

This is different from behavioral isolation, where species are unable to copulate due to the difference in their courtship rituals. If the difference in courtship rituals is a behavioral barrier to reproduction, difference in genitalia will be a physiological barrier.

If we take it in the context of prezygotic and postzygotic barriers to reproduction, mechanical reproductive isolation will be a prezygotic barrier, as it 'prevents' mating in order to prevent the birth of hybrids.
MECHANICAL ISOLATION EXAMPLES
Bushbaby or galagos
Continental Africa is home to a group of small, arboreal primates called galagos or more commonly known as bushbabies. There are over 20 species in this group. Each of these species has distinctly shaped genitalia. The genitalia of a male bushbaby will only fit into the genitalia of a female belonging to the same species.
If two bushbabies belonging to different species try to mate, they won't be able to do so. Like we mentioned earlier, the difference in their genitalia will act as a physiological barrier.
Snail
In snails, reproductive parts will only align if the male and female belong to the same species. If they belong to two different species, their reproductive parts will not align, and as a result, these species will not be able to mate. For instance, a snail species with a flat disc-like shell will not be able to mate with a species having a tall conical shell even if the two have overlapping geographic range; courtesy, mechanical isolation.
Black Sage
Black Sage
White Sage
White Sage
Mechanical isolation is not just restricted to animals, but is also seen in plants. In fact, a textbook example of mechanical isolation in plants will be that of the two sage species, the black sage and white sage. Even though they grow in the same area, the chances of interbreeding between these two species are as good as none, as they are pollinated by different insects.
While the black sage is pollinated by honeybees, the white sage is pollinated by relatively larger carpenter bees. Carpenter bees are considerably large, so the moment they perch on black sage flowers, their petals close, and thus, these bees don't come in contact with the reproductive part of these flowers. On the other hand, honeybees are too small to reach the reproductive parts of the white sage.
In essence, mechanical isolation occurs when two closely related species are not able to mate. As with other forms of reproductive isolation, even mechanical isolation leads to speciation as the two species that are not able to mate, evolve separately.