Microevolution, or traits varying due to natural selection, is pretty settled in evolutionary science. But macroevolution – the evolution of new species – hasn’t been observed.
Doctor Sarah Bush, an evolutionary ecologist at the University of Utah, was able to see microevolutionary trends mirroring macroevolutionary patterns in her new study on natural selection in pigeon lice.
“Most species of lice are only found on a single species of bird," she said. "So, if you want to look at how lice adapt to different environments, it’s hard because if you try to move them to a different host species oftentimes they won’t make it. But pigeons are really cool because we have really light pigeons and really dark pigeons. So, we can move lice from one color pigeon to another colored pigeon. They’re all the same species but they have radically different environments from the perspective of the louse.”
Bush and her collaborators collected lice from pigeons in Salt Lake City. They used these lice to infect black pigeons, white pigeons and gray pigeons. Sixty generations of lice later…
“So, our starting stock of pigeons are really gray birds that you typically see. And so, the lice on those birds are pretty gray. When we put those lice on perfectly white birds those lice became very light over the course of the experiment. We also did the opposite and took lice from gray pigeons and put them on very black birds and those lice got much darker,” Bush said.
She was excited to see that the patterns of changes in lice color closely mimicked the range of colors seen in completely different species of pigeon lice. This means that the lice colors triggered by microevolution were similar to lice colors caused by macroevolution.
“The lightest species of louse is found on a very white pigeon in the South Pacific," Bush said. "At the end of the experiment, the lightest louse we had in this experiment was very similar to the color of lice on that white pigeon. The lice on the white pigeon and the lice on the pigeon we see around town diverged based on molecular techniques somewhere between 20 and 30 million years ago.”
Bush’s study can be found in the March 2019 edition of Evolution Letters.