Name: Corinne Straube
Title of Research Project: The Metabolic Cost of Carrying a Sexually Selected Trait: Insights from
Male Fiddler Crabs
1.) Reflectively describe your literature research process. Tell us how you used library resources or services of any kind (from ILL to online databases to archives collections to meeting with your liaison librarian).
My study examined one facet of a body of work on a phenomenon in nature called sexual selection. This idea was first proposed by Charles Darwin, when he observed individuals in some species which bore exaggerated or colorful traits. These individuals seemed more likely to be predated on than others, which appeared to counter normal natural selection pressures. Darwin proposed that elaborate ornaments helped individuals that bore them attract mates better than others of the same sex. Since that initial hypothesis, many studies have been conducted worldwide to examine the details of sexual selection and the variety of effects it can have on mating success. My literature search therefore involved internet and print sources from many years and a wide variety of species found internationally.
Beginning with sources provided by my research adviser, I read about sexual selection studies using common fiddler crabs, the subject of my current study. Male fiddler crabs bear one large major claw that is used to attract females. I explored the energy costs to the males of exercising with this claw. I wanted to know more about work done with other species on sexual selection, so I used references from the studies I had, as well as an internet search, to find more electronic and print references using the library’s catalog. This yielded several new sources. I read about beetle horns, stalk-eyed fly eyes, elk horns, and swordtail fish tails, as well as models that tested theories on selection mechanisms. References from these papers led to more sources, all of which contributed to my knowledge of how sexual selection affects animals. Some costs of large ornaments are lethal, with increased predation and parasitism, while others are more subtle, increasing the swimming drag or decreasing maximum flying speeds so it is harder for the individual to feed or migrate. Still other studies showed no significant costs of exaggerated traits, contrary to hypotheses.
Besides providing background knowledge, my sources helped me design experiments. The basic experiment in the lab had been partially done by past summer research students; this itself was based on past studies which laid out methods for exercising the crabs and measuring oxygen and lactate levels while the crab walked. Additionally, my adviser and I used several sources to develop new experiments and explore new facets of the fiddler crab’s energy usage. After reading a paper about beetle horn size and flight speeds and distances, which used males with and without horns as well as females, we included females in our study to compare males for which the major claw was removed to females, which have no large claw. Another paper, which was not available through the library catalog, seemed promising to use in developing a racetrack which could test the maximum speed of crabs in each treatment group. I used interlibrary loan to request and acquire the article and design equipment for the experiment. My research, like many scientific studies, therefore relied heavily on previously published sources at all stages of the process.

2.) Tell us about a challenge you faced while doing literature research and how you overcame it.
One of the biggest challenges I faced was one that I had not anticipated: putting my data into context with data from other studies. An important part of the interpretation of results from a study is being able to compare them with data obtained by other research. Although I consulted a plethora of resources for the background, methods, and discussion sections of the research, there were a few key studies that had examined fiddler crab energetics with similar goals to those of my study. Some of these were written in the 1980s, others in the early 2000s, so there was a timespan that caused differences in the technology used. Furthermore, methods of data collection varied between studies. One part of my work was to examine anaerobic energy use by the crabs in the form of lactate. There are multiple ways to measure lactate, either from the whole body of the crab or through a blood sample, and these yield different results.
I cannot say that I’ve completely overcome this challenge; because of the differences in methodologies, whole body lactate and blood lactate concentrations will always be hard to compare perfectly. I did, however, manage to get a general sense of how well my work matched what was done in the past. Using standard estimates of how much of the crab’s mass is made up of its blood (about 30%) and references detailing how oxygen consumption and lactate levels translate to the more general measure of ATP usage in crabs, I was able to compare not only my study to other studies but also the various measurements in my study to each other. Through reference to past work, plus a lot of unit conversion and some chemistry calculations, I was able to get a pretty good sense of the different costs of exercise in the fiddler crabs. My results did not match up very well with those from a study done in 1984, which only became apparent when they were compared using equal units of measurement. One of my future goals with this, then, (because part of any study results is the new queries it raises) is to try and understand more clearly why this happened.
3.) How does your research contribute to the scholarly conversation in your field? What is the significance of your research, in layperson’s terms?
Sexually selected traits are elaborate ornaments common in the animal kingdom that are used by individuals of one sex to attract mates. Many studies have focused on various aspects of sexual selection and have uncovered information about the lethal costs of having a large, colorful tail or big antlers. My research focused on a less apparent side of carrying a large ornament: non-lethal energy costs. It may seem obvious that a bird or fish with lots of color might be spotted and eaten more easily by predators than its dull, camouflaged counterpart, but the costs of carrying a heavy or bulky ornament in the day to day life of the individual that bears it may be less clear-cut.
Male fiddler crabs, my study organisms, have a large major claw which makes up about 30% of the total body weight. These crabs use their claws to attract females and repel other males. My research looked at the energy costs of carrying this claw in sustained/routine and strenuous exercise to see if there was an increase in the aerobic (oxygen-fueled) or anaerobic (glycolysisfueled, lactate producing) exercise. I found that there is no difference in either of these parameters between crabs with and without their major claw during sustained exercise, but that clawed crabs had higher anaerobic energy costs when made to sprint for a long time. This is an interesting addition to the knowledge about sexually selected traits, because it suggests that

crabs have evolved some way of reducing the cost of carrying a claw during common, day-to-day walking. When made to do more strenuous exercise, however, a cost becomes clear.
My research thus contributes to knowledge about sexual selection, since high levels of exercise while carrying a claw incur higher energy demands than running without one. This may be significant in cases where crabs must flee predators over long distances. The results of my study also suggest the development of compensatory traits in fiddler crabs: these are traits, such as larger leg or shoulder muscles, which evolve in response to costly traits to make them easier to bear. Cases of compensatory traits are not as well described as sexual selection costs but may be important to explain how sexually selected traits have persisted despite their associated downsides. Further research on male fiddler crabs might help illuminate this mechanism and its effect on the species.