When two organisms typically do not interbreed with one another, they are considered different species. But what are the reproductive barriers that isolate one population from another? Hear the different songs of three lacewing flies in this interactive activity. These songs are an example of a reproductive barrier that can lead to speciation; the differences among the songs determine mate choice and result in reproductive isolation between the different populations. Also included is a table summarizing the different kinds of isolating mechanisms.

Credits: Lacewing audio song: Courtesy of Charles Henry. Lacewing Oscillograph: From Evolutionary Biology, by Douglas Futuyma. Copyright © 1998 Sinauer Associates, Inc. Reprinted with permission of the publisher.