Behavioral Isolation: Definition, Examples & Quiz

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Sarah Friedl

Sarah has a Master's degree in Zoology and a Bachelor's in Biology, and has taught college level Physical Science and Biology.

What prevents closely related species from reproducing? Behavioral isolation is an important evolutionary mechanism that helps members of the same species identify each other as proper mates.

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Definition

Of course you would not expect very dissimilar species like birds and fish to mate, but sometimes even very closely related species do not mate either. This is due to reproductive barriers, which are biological features of organisms that prevent species from reproducing and having offspring.

Two types of reproductive barriers exist: prezygotic barriers, which are those that prevent mating from even occurring, and postzygotic barriers, which are those that reduce the likelihood that an offspring will survive after mating has occurred.

One prezygotic reproductive barrier is behavioral isolation. Like the name implies, this is a reproductive barrier based on behavior, usually in the form of mating rituals and signals. Signals that attract mates to each other may be one of the most important factors in determining whether closely related species mate with each other or not.

Examples

We can see many examples of behavioral isolation in nature. For example, male fireflies of a variety of species signal to their female counterparts by flashing their lights in specific patterns. Females will only respond to the signals flashed by their own species, preventing them from mating with other closely related firefly species.

Many species have very elaborate courtship rituals to help indicate to each other that they are the correct ones to mate with. An example of this is the blue-footed booby. Male boobies perform a very elaborate dance that shows off his bright blue feet. This helps identify him to female boobies as a potential mate.

A blue-footed booby displaying his brightly colored feet
blue-footed booby mating

Visual signals are not the only ones that create behavioral barriers. Frog calls are very unique to each species in both pitch and pattern. These specific vocalizations create reproductive barriers for frogs that are not of the same species.

Bird songs are another non-visual way to identify members of the same species, and therefore proper mates. Not only are bird songs unique to each species, but most species have songs that are specifically for warnings, territory defense, and mating calls. This makes the reproductive barrier even stronger for closely related species.

Summary

Reproductive barriers prevent closely related species from mating, thus serving as an important mechanism for evolution. Behavioral isolation is one type of prezygotic barrier that prevents interbreeding between closely related species because there is no mate recognition between females and males of the different species. Special signals used to attract mates are unique to a species, and serve as one of the most important factors in whether mates find each other or not.

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