A central idea of evolution is that it is gradual. Evolution, not revolution. In genetic terms that means that evolution proceeds by an infinite number of mutations of infinitely small effect. Of course, we now know that the number of genes in a typical eukaryote is not infinitely large, but rather in the order of 25,000. Still, many adaptations probably do require multiple mutations, each of small effect. However, especially when selection is strong and reproductive isolation incomplete, evolutionary change through few major mutations each of large phenotypic effect might be possible. A promising system to test this hypothesis is pollinator-mediated speciation. If, for whatever reason, an established pollinator does not show up when its host is about to start flowering, the plant is under strong selective pressure to rapidly adapt to an alternative pollinator.
In RESPEC we used wild Petunia species that are adapted to different pollinators: bees, nocturnal hawkmoths and hummingbirds. We asked which genes needed to mutate to make a flower attractive to a hummingbird or a bee instead of a hawkmoth. We started with the simplest system, moth-pollinated to bee-pollinated, because these plants have very similar morphology and differ in so-called attraction traits, the color, UV absorption and scent of the flower. We identified four “major genes” that are responsible for most of the differences between the two species in visible color (1 gene), UV absorption (1 gene) and scent emission (2 genes). We started with the moth-pollinated plant and changed these four genes in such a way that they are functionally identical to their counterparts in the bee-pollinated plant. Then we tested whether moths and bees can tell the difference between this artificial mimic and the wild model plant. Our results indicate that they cannot.
People often ask why we are doing this. Is it because of the worldwide decline in bees? Could we change fruit trees to make them attractive to different pollinators? To be honest, I have my doubts about whether that is such a great idea. The motivation was really the challenge to work on something that had never been done and that was long thought to be impossible.
