Passing on genes is the bottom line in the game of life. So if you hand off your DNA to infertile kids, your evolutionary score plummets. Not surprisingly, animals have evolved all sorts of ways to make sure they mate successfully. Perhaps the sweetest sounding approach is that of European flycatchers. Researchers have now shown that by creating musical innovation, these birds ensure that they'll woo the right lovers.
The pied and the collared flycatcher (Ficedula hypoleuca and F. albicollis) occur together in large parts of Europe. Because the two species share the same habitat, they sometimes interbreed--a grave mistake, as female hybrids are almost always sterile, says evolutionary biologist Jon Haavie of Uppsala University, Sweden. The mixed marriages come about when females are attracted to males of the other species, which may happen if young males have learned the wrong songs. In areas where both species occur, males of the pied flycatcher often copy sound bites of the males of the much more common collared flycatcher.
Other animals have avoided confusion by evolving more distinct courtship signals--certain banana flies develop different pheromones, for example, to prevent wooing other species they share their fruit with. To see whether the same would apply to a culturally transmitted signal like song, Haavie and his colleagues recorded flycatcher jingles in two hybrid zones in Sweden and the Czech Republic, and in areas elsewhere in Europe where either species occurs by itself. Sure enough, they found that in the hybrid zones, collared flycatcher males sing songs that have a higher pitch but a slower tempo than in the areas where their females are not distracted by the mixed tunes of pied males. "It was very weird," says Haavie, whose paper is published in the March issue of the Journal of Evolutionary Biology.
The researchers think the new collared flycatcher tunes spread when innovative males proved better at luring their females away from the pied flycatcher copycats. They also found that the tunes changed slowly: In their study site in Sweden, where the collared flycatcher arrived 150 years ago, the difference was less striking than in the Czech Republic, where the two species have been living together for thousands of years.
Behavioral biologist Hans Slabbekoorn of Leiden University, the Netherlands, is happy with the new study. Data on the evolutionary impact of learned traits are "very scarce and badly needed," he says.