When houseguests become parasites: Sympatric speciation in ants

Species are part of the common coinage of biology. Taxonomists name them, developmental biologists deconstruct them, physiologists compare them, ecologists count them, conservation biologists conserve them, and evolutionary biologists study their multiplication and extinction. It may be that only the individual is a more important biological unit than the species. It is thus no surprise that Darwin named his great work On the Origin of Species, nor is it a surprise that many evolutionary biologists today concentrate their efforts on understanding species formation, or speciation. Riitta Savolainen and Kari Vepsäläinen (1), in a study in this issue of PNAS, have contributed significantly to a long-standing debate in evolutionary biology, over whether geographic isolation is a necessary first step in speciation, in a study of social parasites in Myrmica ants (2). The resolution of this argument has important consequences beyond evolutionary biology. If species do not have to wait for the next geological event to speciate, then speciation could conceivably be very rapid. This, in turn, means that the process might be conducive to study in real time. We might expect to see speciation in response to humanity's incessant modification of the globe. Anthropogenic change might drive not only such well known adaptations as the evolution of insecticide, herbicide, and antibiotic resistance, but also, for example, speciation of herbivorous insects adapting to plants moved to new parts of the world.

To fully understand Savolainen and Vepsäläinen's results, some history is in order. In the 144 years since publication of On the Origin of Species, enormous progress has been made in illuminating the things we need to know to understand speciation (2). We now know a lot about geographic isolation and the biogeography of closely related species. We know the kinds of features that prevent mating between closely related species …