Meeting Abstract
Whether immune challenges play a role in animal migration is poorly studied, particularly for insects. Mormon crickets Anabrus simplex engage in spectacular mass migrations where millions of insects group together and walk in a common direction. Anti-bacterial activity in these insects appears to be compromised by migratory activity. This trade-off is particularly evident when Mormon crickets do not consume sufficient carbohydrates in their diet. If migration compromises anti-bacterial activity, then challenged animals should migrate more slowly as the anti-bacterial immune system is elevated. In order to investigate the effect of immune activation per se, non-living surrogates of bacterial and fungal agents (lipopolysaccharide LPS and laminarin, respectively) were introduced into radiotagged Mormon crickets and the insects’ migratory activities and immune responses were measured. Mormon crickets always migrated more slowly when challenged with lipopolysaccharide or laminarin, and in two of the three cases, anti-bacterial activity was inversely proportional to migratory speed. Hence inducible defenses affected migratory activity of the insects. The induction of anti-bacterial activity might directly reduce migratory activity, because a lipid transport protein that is freed from its activity in locomotion can serve to enhance anti-bacterial immunity. Elevation of anti-bacterial activity by both laminarin and LPS suggests that activation of the Toll pathway is not specific to bacteria in Mormon crickets. In conclusion, migration was slowed with microbial-simulated challenges that induced anti-microbial activity.
