“Eat your veggies!” The importance of nutrition during the natal environment and its effect on adult sexually selected traits in the tortoise beetle Acromis sparsa

My name is Kalli Qutub and I am one of the students working in Professor Trillo’s lab. In Dr Trillo’s lab, we study a wide variety of sexually selected traits. These are traits that are used, generally by males, to attract, defend or fertilize females. We are especially interested in studying the interactions between primary sexual traits (e.g. testes or genitalia) and secondary sexual traits (e.g. long tail feathers in birds of paradise or antlers in ungulates) in a single organism. How do these traits develop? What trait is more useful for reproductive success?

For this summer research, the main question is: What happens if an organism has limited resources when developing? Would they be more likely to channel the resources to primary or secondary sexual traits or both?

To answer this question, I am using data that was previously collected by Dr. Trillo on the neotropical tortoise beetle  (Acromis sparsa) in Panama. These beetles feed, mate and oviposit on a single hostplant, Merremia umbellata (Convolvulaceae). They are also sexually dimorphic, with males having rigid elongated projections on their elytra and pronotum and females not having them at all. There is also a large amount of variation in the sizes of these projections for males, and some males possess really large projections whereas others lack them completely and resemble females. Males use these projections as weapons or claspers, to lift the opponent and toss him off the leaf surface during competitive encounters to access females. Males of this species also have really large genitalia and testes.

In an experiment, Dr. Trillo mated virgin A. sparsa females with males and split the broods in two. The first half of the brood was given as much food as they wanted (ad libitum), while the second half was given half of the amount of food. They were then allowed to grow and pupate into adulthood. Once they emerged, various parts of their morphology were photographed. My focus is to use these photographs to measure sexual traits, including their genitalia size, and elytral and pronotal weapon size. I make these measurements blind (meaning I do not know in advance which treatment they belong to), and once I finish, I will look at the effects on nutrient availability on the size of these sexual traits as well whether the amount of nutrition dictates the sexual trait that the energy gets put into. My hypothesis is that if nutrition is limited, the individual would choose to channel most of its energy either to primary sexual traits (testes or genitalia) or to the secondary sexual traits (elytral or pronotal weapons) rather than trying to split the energy evenly.

Most sexual traits are highly costly and understanding how organisms invest energy developing them when resources are not readily available is important because organisms are often faced with substandard natal environments. It would be interesting to see if the effects of nutrition on sexual traits we find in this species translate to other species or insects and maybe eventually look at larger animals to see whether the effects are similar. I believe that this experiment reveals an interesting perspective about sexual selection and the way individuals use the energy they gather during their natal environment.

A typical day in the lab for me involves me using a program called ImageJ, to take several measurements of the photographed morphologies of these beetles. Below are a couple examples of the measurements I need to take. I have mastered the use of Image J for just about any morphological measurement you could throw at me! It is also a relaxing process where I get to listen to my favorite music while I work. I plan to sit down with Dr. Trillo at the end of the summer to go through the statistical analysis of these measurements. I am very curious to see what happens in these beetles! Another interesting question I have been thinking about while measuring these beetles is: What about the females? Females do not usually have to have ornaments to attract males but use their elytra to defend larvae from predators, so it would be interesting to see what morphologies they choose to channel their energy towards.

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These three pictures show the tortoise beetle (Acromis sparsa) on its host plant (Merremia umbellata). In these pictures taken by Christian Ziegler, it is possible to see the beetles weapons on the male elytra and pronotum.

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This is a picture of an elytra that I have already measured. The white lines on the picture are both my guide lines (mainly on the outside of the elytra) and also my measurements (on top of the elytra). These measurements include the length, width and area of the projection and elytra itself. These are the measurements that I will be using in my statistical analysis.

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