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Title: Weakness in the band: nutrient-mediated trade-offs between migration and immunity of Mormon crickets, Anabrus simplex

item Srygley, Robert

Submitted to: Animal Behaviour
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/3/2010
Publication Date: 2/1/2011
Citation: Srygley, R.B., Lorch, P.D. 2011. Weakness in the band: nutrient-mediated trade-offs between migration and immunity of Mormon crickets, Anabrus simplex. Animal Behaviour. 81(2): 395-400.

Interpretive Summary: Mormon crickets form migratory bands and march across rangeland in the western United States in search of nutrients. In contact with others in the migratory band, individual insects must defend themselves against contagious diseases. Because the Mormon crickets are nutrient-deprived and expending energy in migration, we predicted that their immune systems might also be compromised. In a band from Nevada which lacked carbohydrates in their diet, we found that insects fed carbohydrates did not migrate as far as those fed proteins. In addition, those fed carbohydrates increased their anti-bacterial activity. We propose that proteins which are typically active in transporting lipids to fuel migration are free when carbohydrates are plentiful. These proteins are known to assist in the destruction of bacteria. Insects fed carbohydrates were also more capable of encapsulating an invader relative to those fed proteins. There was an increase in prophenoloxidase but not in phenoloxidase. These enzymes are involved in wound repair and defense against fungi and other invaders. Our prior work showed that protein-deficiencies limited phenoloxidase activity, whereas this study showed that encapsulation and antibacterial activities are enhanced by dietary carbohydrates. Thus the need for either protein or carbohydrates may drive migration, but these dietary constituents affect very different aspects of immune defense.

Technical Abstract: MMormon crickets (Anabrus simplex) form large migratory bands that march over rangeland in the western United States in search of nutrients. Immune defense is particularly relevant to survival in migratory bands, but little is known about the role of nutrition in insect immunity, particularly in nature. We hypothesized that immune defenses are compromised in Mormon cricket bands due to nutrient limitations. Members of a migratory band in Nevada preferred carbohydrate diets over proteins. After feeding on the carbohydrate diet, migratory velocity was less and the ability to encapsulate foreign particles and lyse bacteria was greater than for Mormon crickets consuming protein. Less locomotory demand for lipids may result in greater anti-bacterial activity. Total phenoloxidase (PO) activity also increased following feeding on carbohydrates, whereas spontaneously active PO was not different between the two diets. These results were very different from those of a band in Utah that preferred the protein diet and had enhanced spontaneous PO activity after protein supplementation. Hemolymph of Mormon crickets from the Nevada band was sampled 18 h after the diet treatments, whereas that from the Utah band was drawn 4 h after treatment. Either the difference in immune measures was due to the difference in sampling time, or spontaneous PO activity was protein-limited whereas encapsulation and antibacterial activity required carbohydrates. Currencies for the generalized immunity of insects may differ, and constraints on immunity in a given environment depend on which macronutrients are in short supply.