Author Spotlight – Brett Seymoure and Timothy Thurman

30 03 2016

A Bird’s Eye View of Two Mimetic Tropical Butterflies: Coloration Matches Predator’s Sensitivity

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Heliconius sara, photo by Collin Whitsett

In many cases, experiments are designed in offices and during collaborative meetings, with specific questions and aims in mind. Sometimes, however, you are out in the rain forest diligently collecting data for your PI when your own curiosity gets the best of you. For Tim and I, this was exactly the case in May of 2014 when we were sent by our advisor at the Smithsonian Tropical Research Institute, Owen McMillan, to Ecuador to collect Heliconius butterflies. We were on the Eastern slope of the Andes attempting to catch Heliconius sara, a blue, yellow, and black butterfly that flies slowly and majestically, flashing its colors to warn predators of its toxicity. We caught a few H. sara, and then, when taking what had appeared to be an H. sara out of my net, I noticed that the body of the butterfly was quite different, with six legs, not the usual four on H. sara (which, as brush-footed butterflies, have two legs that have been modified into sensory appendages). These six-legged H. sara lookalikes were imposters, perhaps mimics of the unpalatable Heliconius model. This happened a few more times throughout the day, and we realized that if we were duped by these swallowtail imposters, perhaps birds were as well. We didn’t collect as many H. sara as we were hoping, but we decided to turn our unfortunate day of collecting into a curiosity-driven project, which serendipitously resulted in a manuscript in Journal of Zoology. Tim and I have not overlooked that other studies in Journal of Zoology have also been engendered by letting one’s curiosity taking the wheel during serendipitous walks in the forest (see post by Adrian Barnett). Perhaps, as a molecular biologist once told me, zoologists can’t seem to stay focused, or perhaps, we are opportunistic curiosity-driven investigators. Or perhaps both?

Brett Seymoure

Brett Seymoure

Our research project was not a bed of roses though. Once we had decided that we were going to compare the visual signals of the Heliconius sara with Mimoides pausanias, we needed to collect more individuals of both species to enable a strong understanding of the intraspecies variation. Of course, as we set out to catch a few more individuals of the swallowtail mimic, M. pausanias, they weren’t as common as they had been the previous day. It figures that when you aren’t looking for a rare mimic they seem to fly into your net, but when you go looking for them, they are nowhere to be found. We were able to catch one more during the last couple of days of the trip, and luckily for our study, the variation within species was much greater than the variation between species, an indicator of the mimetic association between these two species. One other difficulty that arose during our study was that Mimoides pausanias was a ghost of a species. Very few publications even make mention of the species and in most of those publications they use a different species name. In fact, for the first month of our study we were calling the species by an outdated name. Fortunately, with the help of excellent tropical entomologists, we were able to track down some information on the natural history of Mimoides pausanias.

Timothy Thurman

Timothy Thurman

Lastly, as Tim and I look back on this research, we realize how fortunate we were to have everything work out as it did. We had no idea that the most interesting finding would be that the two butterfly species are most mimetic in the eyes of their avian predators, flycatchers and jacamars. Depending on the species, birds either can see ultra-violet light (most songbirds and parrots), or as most birds, including flycatchers and jacamars, they cannot. It turns out that the two mimetic butterflies are closely matched in all wavelengths except for ultra-violet – rendering them close mimics in the eyes of their avian predators, but most likely not to each other as to cause themselves any confusion, as butterflies are able to see in the ultra-violet. As always, this study engendered more questions than answers and we hope to take another trip to Ecuador to discover more!

 

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