Submitted to: Physiological Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2016
Publication Date: 6/29/2016
Citation: Srygley, R.B. 2016. Mormon crickets maximize nutrient intake at the expense of immunity. Physiological Entomology. 42(1):1-9. doi:10.1111/phen.12155.
Interpretive Summary: Malnourishment has major effects on movement and immunity of migrating Mormon crickets. Here we used a set of dietary choice experiments in the lab to investigate the abilities of immature and adult Mormon crickets to regulate their intake of carbohydrates (C) and proteins (P). A choice test was designed that would allow Mormon crickets to reach a single C:P intake target from four unique starting points. The Mormon crickets did not regulate C and P ingestion to reach a single intake target. Instead, they showed a strong preference for whichever diet was richest in C or P. When presented with a choice between a diet high in C and one high in P, the Mormon crickets chose them at random, further demonstrating equal preference for C and P. Four times more weight was gained from ingesting proteins than an equal amount of carbohydrates, and immunocompetence of nymphs was also dependent on protein consumption. In nature, Mormon crickets might consume an excess of one of the macronutrients because they can often find the other through active searching of their local habitat. However environmental change and interspecific or intraspecific competition can challenge their abilities to encounter required nutrients on a local scale, leading to their migratory behavior. A preference for the richest diet suggests that only protein needs to vary greatly in space and time for Mormon crickets to be highly variable in their nutritional deficiencies.
Technical Abstract: For insects, two of the most important dietary macronutrients are carbohydrates and protein, and many organisms regulate dietary intake of both. In the field, carbohydrate (C) to protein (P) intake of Mormon crickets is indicative of nutritional imbalance that has major effects on immunity to pathogens. Here I used a set of dietary choice experiments in the lab to investigate the preferences of Mormon cricket nymphs and adults for C and P. Diet pairs were selected that would allow Mormon crickets to reach a single intake target of C:P from four unique starting points. After the last pair of diets was removed on day 7, I assayed phenoloxidase and anti-bacterial activity. Both males and females at both the adult and nymphal stages showed a strong preference for the diet that was richest in macronutrients with equal preference for C or P. When given a choice of a high C diet and a high P diet, Mormon crickets selected both at random, balancing their daily intake of C and P. Weight gained was dependent on the mass of P consumed, with a conversion factor greater than four times that of the C consumed. As predicted, those Mormon cricket nymphs and adults that consumed more P had higher titers of total phenoloxidase, and lysozyme-like anti-bacterial activity was independent of dietary treatment. In nature, omnivores might consume an excess of one macronutrient because they can often find the other through active searching of their local habitat. However environmental change and interspecific or intraspecific competition can challenge an organism’s ability to encounter required nutrients on a local scale, contributing to long-distance migratory behaviors. A preference for the richest diet suggests that only the concentration of one macronutrient needs to vary in the environment for Mormon crickets to be highly variable in their nutritional deficiencies.