Why all the swallowtail butterflies?
You may have noticed that there have been a few different expeditions in the past few months focused on swallowtail butterflies. These specimens will be used for a larger project where we are planning to quantitatively look at the variation in wing morphology across and within swallowtail butterfly species. We have amassed approximately 1300 photos of swallowtail specimens from various museum and personal collections with the intention of having at least 10 males and 10 females from every Papilio species. Using morphometric analyses of landmarks on the dorsal and ventral wings, we will test the wing shape variation across species to see if there are correlations with sex, tropicality, geographic range size, and the number of congeners in the species’ range.
What do we mean by “landmarking”? This is an approach called “geometric morphometrics” where we select the same locations on a butterfly image in each image, and then we use some really neat tools that can find the best “fit” to a common “consensus”. For this project, we are using where veins in the butterfly wings meet the edge as our landmarks. Figure 1 shows an example of the ventral wing landmarks using this fitting method. The big black dots are the “consensus” landmarks and the variation around them in shown in the smaller grey ones. You can clearly see that some parts of the wing are much more variable than others. We know the orientation of the image below is a bit odd, but the variable landmark that is at the low point on the y-axis is near where the wing attaches to the body.
Now that all of the Notes from Nature swallowtail expeditions are complete, we will be working all summer to landmark these specimens and add more to our sample size for future analyses. If you are interested in the further ways we analyze morphological variation, give a holler and we can go into further detail. We will send along another update on this work later in summer, and thank you for helping us move forward with this research!
Figure 1. Plot for the x/y coordinates of the ventral wing landmarks for 27 Papilio specimens so far.
blog post by Laura Brenskelle