Members of closely related species possess no physiological differences that would prevent them from interbreeding.
But closely related species are distinguished by subtle differences in the pulse rates of male crickets' simple courtship songs, a secondary sexual trait that plays a large role in mate attraction.
Among all species of Laupala, pulse rates of male courtship songs range from .5 to 4.2 pulses per second. Female crickets can detect these differences, says Mendelson, and they tend to hop towards the pulse rate of their own species and to reject songs sung at a different tempo.
Despite the fact that these crickets can interbreed (and produce fertile offspring, unlike when, say, a female horse and a male donkey produce an infertile mule), we consider them different species because they systematically do not breed. I recall reading about further experiments with similar crickets where scientists manipulated the pulse rates of one cricket species to be the same as the other. Mating occurred.
I think behavioral and genetic barriers are both considered factors that affect whether crickets "can" interbreed. I'm not sure if scientists would be consistent in applying that standard to humans, though.
From http://www.sciencedaily.com/releases/2005/02/050211082447.ht...:
Members of closely related species possess no physiological differences that would prevent them from interbreeding.
But closely related species are distinguished by subtle differences in the pulse rates of male crickets' simple courtship songs, a secondary sexual trait that plays a large role in mate attraction.
Among all species of Laupala, pulse rates of male courtship songs range from .5 to 4.2 pulses per second. Female crickets can detect these differences, says Mendelson, and they tend to hop towards the pulse rate of their own species and to reject songs sung at a different tempo.
Despite the fact that these crickets can interbreed (and produce fertile offspring, unlike when, say, a female horse and a male donkey produce an infertile mule), we consider them different species because they systematically do not breed. I recall reading about further experiments with similar crickets where scientists manipulated the pulse rates of one cricket species to be the same as the other. Mating occurred.