In this page are short summaries, explained in lay-terms, about some of my recent publications
August 2015 - Special feature on monarch butterfly populations - a collection of 7 scientific papers published in the Annals of the Entomological Society of America, organized by Dr. Davis
For many years, the status of the eastern monarch population in North America has been judged solely on the basis of the size of the overwintering colonies in Mexico, until now. This collection of papers contains information on monarchs outside of the wintering stage, including the spring, summer and fall.
Essentially, Dr. Davis coordinated a large group of researchers associated with a variety of citizen-science projects, and got them to examine their long-term data sets to look for evidence of patterns, and then submit their papers to a single journal. These papers were just published in a single issue of the journal, and collectively, they will no doubt have a profound impact on the monarch community.
April 2015 - Vasquez, D., A. Willoughby and A.K. Davis. Fighting while parasitized: can nematode infections affect the outcome of staged combat in beetles? PLoS One.
Imagine two olympic wrestlers competing in a title match, and one of them has a bad cold. Which one would win? It's easy to think of how the one with the cold would lose, because he(or she) would not be fighting at 100%. That was the essence of a project I supervised in summer 2014 using bess beetles as the study subjects, and the results of this work were recently published. Bess beetles are commonly infected with a small nematode parasite that lives in their bellies, and we (myself and a couple of sharp undergraduates) wanted to know if beetles with this parasite would not be able to defend themselfs in a fight. So we pitted random beetles against each other (shown to the right) and then figured out the winner, plus which one had parasites.
In the end we found evidence that parasitized beetles lose more matches, though it wasn't a huge difference, and their matches tend to have fewer aggressive moves (like the suplex shown right), so it seems the parasite does reduce their fighting ability a little.
August 2014 - Davis, A.K. Wing color variation is related to larval energy reserves in monarch butterflies (Danaus plexippus). Physiological Entomology. Online Early - DOI: 10.1111/phen.12069. PDF
While most people know that monarch wings are orange and black, there is actually some subtle variations in the shade of orange between individuals - some monarchs have more reddish color than others, and it turns out, this variation is important to monarchs. Prior work by myself and colleagues has shown that redder monarchs (at least males) have higher mating success than do paler monarchs, and that redder monarchs fly further. Up until now, it was not clear what gave the redder monarchs the advantage over paler ones in these behaviors.
This latest study examined a group of monarchs reared under identical conditions and looked at how much fat each monarch was 'born' with - that is, how much fat they had when they emerged from their pupal stage. When this information was compared to their wing colors, it became clear that the reddest monarchs tended to have more fat than the paler monarchs. Since fat is the universal supplier of energy, this means that redder monarchs have more energy, which is probably why they are able to outcompete paler monarchs in flying and mating. Both of these behaviors are energetically taxing, so having a built-in supply of energy would be advantageous!
April 2014 - Johnson, H., M.J. Solensky, D. Satterfield and A.K. Davis. 2014. Does skipping a meal matter to a butterfly's appearance? Effects of larval food stress on wing morphology and color in monarch butterflies. PLoS One 9(4): DOI: 10.1371/journal.pone.0093492
There has been considerable concern lately over the status of monarch butterfly populations in North America, and the availability of their larval food source - milkweeds. In this study, we tested what would happen if monarch larvae simply ran low on food near the end of the larval stage. In a controlled experiment, larvae were reared until their late stages, then we removed their food for either one day, or for two days. Then, we let the larvae finish their food and metamorphose into adults. We also had a control group, where larvae could eat as much as they wanted. When eveyone had become an adult, we measured their wings using a computer-based process (image analysis) that let us determine how orange their wings were, how big their wings were, and how their wings were shaped.
There were a variety of unexpected results from this project that we will be examining further in future experiments.For example, we found that skipping one meal (24hrs) led to a reduction in orange brightness, but skipping two meals (48hrs) did not! Importantly though, one of the clearest results was that running low on food led to smaller wings, by about 2%, compared to the control group. This may not seem like much, but we know from other studies that this amount is all that is needed to reduce migration success. So this project demonstrated that if the larval food supply of monarchs is limiting, it could affect their ability to migrate as adults.
March 2014 - Davis, A.K. 2014. Lifting capacity of horned passalus beetles during passive and stressed states. Journal of Insect Behavior. Online Early - DOI:10.1007/s10905-014-9444-6
This was one of the shortest projects I've ever worked on (it took me one afternoon), but it ended up being one of my all-time favorite publications. I have always been interested in what happens when organisms become stressed, both on the inside and out. Like me, most people have probably heard the urban legend about someone lifting a car off of an accident victim in the throws of panic. While this story is based on some facts (see the book Extreme Fear, by Jeff Wise), this scanario is difficult to test scientifically. In this project, I tried to emulate that scenario using a critter that I knew was exceptionally strong to begin with. The horned passalus beetle (pictured right) is a small insect (1-2 grams) that lives in rotting logs in the United States. It can pull up to 100 times its own weight! For the current project, I tested how much weight they could lift, by placing them under a force guage. I tested them without manipulation (meaning I left them alone while they lifted), and then I gently tapped on their shell, to simulate a stressful situation. I knew they became stressed when I did this because they started making alarm calls - which this beetle does by rubbing parts of its wings under its shell. The results of this project showed that this beetle is capable of lifting a heck of a lot more than it can pull - up to 500g! I was even more shocked to find that when they became stressed they immediately began lifting even more than that - about 87% more! So these super-strong beetles becaame super-ultra-mega-strong when they were stressed!