KU Researchers' Paper Challenges Frequency of Adaptive Radiation
Many people are familiar with the Galapagos finches, and the evolutionary theory that differences in beak size led to the groups’ diversification. It’s one of the most popularly cited examples of a process known as adaptive radiation. Now, the frequency of that evolutionary process in nature is being challenged by a group of KU Biodiversity Institute graduate research students.
In a paper to be published in the journal Trends in Ecology and Evolution in January, the students argue why many instances of evolution previously believed to be caused by adaptive radiations are not truly “adaptive” but rather other types of evolutionary radiation altogether, or a blend of several forms.
“We read a lot of papers where something interesting biologically was going on, but it was being mischaracterized as adaptive, when truly there were other processes that were being ignored,” said graduate student Kaylee Herzog, one of the seven students who coauthored the paper.
Evolutionary radiation consists of several ways in which speciation, or the creation of new species from a single common ancestor, occurs. In early studies of evolutionary radiation, adaptive radiation was once thought to be the only way speciation could take place. This theory was proven false, after it became clear that many causes of radiation exist, oftentimes many in the same instance.
The group believes that geographic radiation in the finches could be the actual cause for changes in certain cases, or that both adaptive and geographic radiation play a role in some speciation. Geographic radiation is caused by two groups of the same species being physically separated and exposed to different environments. The high diversity of Galapagos finches is only one of several examples that the students say could be falsely attributed to adaptive radiation.
Graduate student Marianna Simoes says the paper’s concept was first initiated two years ago, when the graduate students began meeting for a macroevolutionary biology course at the University of Kansas. During the course, the students discussed types of radiation such as adaptive, exaptive, geographic, and climatic. While studying these processes, the group decided to make the occurrence of adaptive radiation the focus of their discussion group which followed the course the next semester.
In the discussion group, the students began to dig deeper into inconsistencies they found in the labeling of the processes of evolutionary radiation. The students found instances of possible false attributions to adaptive radiation in each of their specific fields of research, and brought these studies back to the group for discussion. They then teased out what they believe to be the true causes of speciation in these groups. While writing the paper, the students also named the process of pseudoradiation. This is the first time the process, which is related to but distinct from evolutionary radiation, have been summarized in one paper.
“We’ve found that adaptive radiation is not really the trigger for all of these speciations, so that’s where the rest of the different kinds of radiation come in,” graduate student Laura Breitkreuz said.
While the students maintain that adaptive radiation plays a big role in evolutionary radiation, they hope the paper will help point out the importance of recognizing other triggers that often occur.