Making a Species Using “Magic

By Aayush Purohit

Photo by Charles J. Sharp [CC-BY-SA 4.0]

It is truly remarkable to know that the planet we call home houses millions of different species, with speciation continuously adding to that amount. Speciation is the reason why the Earth houses such a wide variety of organisms, all sharing common features, while also having unique traits that set them apart from one another. The formation of new species does not happen in the blink of an eye, but rather takes centuries, or even millennia, before noticeable changes come about. Many different factors can account for speciation, ranging from environmental pressures to interactions with other organisms. Identifying and studying these factors can lead to understanding how certain species came to be and predicting what may happen to them in the future. Dr. Maria Servedio, a professor in the biology department at UNC-Chapel Hill, has spent more than 20 years working on understanding mechanisms of evolution, speciation, and sexual selection. She and her lab utilize mathematical models—specifically, population genetic models—to understand why organisms behave in certain ways and how those behaviors can lead to evolutionary patterns. Most of the models created by Dr. Servedio are made with the computing system Mathematica, which uses manually inputted parameters with mathematical equations to model evolutionary behavior in a species over future generations. An example of a recent model she constructed in 2020 looked at so-called “magic traits” in organisms. As they are aptly named, “magic traits” are rare traits which have diverged in their expression due to local adaptation, thus potentially determining mating behavior and resulting in non-random mating behavior.2 Dr. Servedio found through her modeling research that, contrary to popular belief, the mating trait, which determines mating preferences, has a much stronger effect on an ecological trait, which is related to the ecology of an organism, rather than the other way around. The mere presence of the mating trait is enough to cause local adaptation of ecological traits.2 Dr. Servedio

Dr. Maria Servedio

Figure 1. Example of a magic trait where butterfly wing colors have diverged and this trait affects choice in mate. Figure from article by C. D. Jiggins et al.

such as the divergence of butterly wing colors (see Figure 1). Another factor aiding in speciation can be geographical separation, as often times a population in a certain area will have completely different features from a population in another region. Due to this isolation, the populations may continue to diverge further and further apart as there is no gene flow between the two of them. Dr. Servedio’s research is centered around the interconnections between and various approaches to these concepts in evolutionary biology. “Unfortunately, the punch line for a lot of this work is that whether sexual selection helps or hurts speciation depends on geography, how it is working, and various other factors.”1 One of the difficulties with this area of research is that most models produced for predicting evolutionary behavior are forced to be overly simplified due to a lack of knowledge behind the actual genetics of factors such as mating preferences. Without that concrete evidence to back up mathematical models, they are not able to be as accurate as possible. On top of this issue is the fact that evolutionary mechanisms take very long periods of time to take hold, and collecting remarked that this was an intriguing generations. For example, snails show data on so many generations is tough, finding as even “having the mating trait evidence of phenotype matching in meaning that researchers may not at all increased local adaptation quite a relation to the patterning of their shells. really know enough about what the real lot, which was a direction people usually Snails that feature counterclockwise world should or will look like to make don’t think of with these magic traits.” spirals on their shells prefer—or are complex and precise models to predict One factor that has a great deal constrained—to mate with other snails outcomes. Dr. Servedio sees work on of importance in evolutionary biology with counterclockwise spirals, and vice the genetics of preference currently as and speciation is mate choice, which versa, serving as a barrier to speciation a “huge black box” and that in the near refers to an organism’s decision of who between the two populations.1 In certain future, research in the field will improve: to mate with. Studying mate choice, situations, phenotype matching can “We don’t have good data on which to which includes sexual selection, is very also be beneficial in bringing about base assumptions, so I would like to see important, since it can affect gene flow— speciation. For example, in a population the field get a much better sense of the the transfer of genetic that has a phenotype genetics of preferences in particular.”1 information— between different “‘Magic traits’ are rare traits of purple color due to a mixing of the genes With this kind of information, there is enormous potential for more complex populations, and thus which have diverged in coding for red and models to substantially improve our can impact speciation. their expression due to local blue color, individuals understanding of evolutionary processes Mate choice can adaptation, thus potentially selecting others who such as speciation. make speciation determining mating behavior are more distinctly red more difficult if it occurs through a and resulting in non-random or blue can result in the formation of two mechanism called mating behavior.” separate populations phenotype matching. from the initial one. Phenotype matching describes the As Dr. Servedio explains, “selection is tendency for organisms to seek out other directional in opposite directions so individuals that share similar phenotypes, there is more red in one population which then results in the passing of and more blue in another.” Numerous those specific traits to subsequent other examples can be seen in nature,

References

1. Interview with Maria Servedio, Ph.D. 02/08/21 2. Servedio, M. R., & Bürger, R. (2020). The effectiveness of pseudomagic traits in promoting divergence and enhancing local adaptation*. Evolution, 74(11), 2438-2450. doi:10.1111/evo.14056 3. Jiggins, C.D. et al. (2001). Reproductive isolation caused by colour pattern mimicry. Nature, 411, 302–305