Increased aggression among <i>Asynarchus nigriculus</i> caddisfly larvae in a rapidly drying environment

Abstract

Global climate change will likely result in warmer, dryer environments and influence the behavior and development of a number of species. Asynarchus nigriculus is a species of caddisfly whose larval stage lives exclusively in temporary ponds where they develop synchronously and quickly before the ponds dry in the early summer. The cues used by this species to sense pond drying and accelerate development are unknown but may include increasing density due to shrinking pond area and decreasing water level. It has been shown that A. nigriculus engage in cannibalism to supplement their nutrient-poor diet of detritus with protein. I hypothesized that if decreasing water level and increased density are cues of impending pond drying, then caddisfly larvae will respond to those cues by engaging in more cannibalism in order to obtain more protein to develop faster and emerge before the pond dries. Field experiments were set up varying two cues of drying: water level and larval density, and also manipulating supplemental protein. Development time and larval behaviors were compared statistically among treatments. The results demonstrated that aggressive interactions among larvae, and escalations of aggressive behavior were highest in the drying treatment without protein supplementation, and the fewest number of larvae pupated in that treatment. Aggressions, escalations, as well as mobbing of one larva by others, also increased with increasing larval density. The frequency of cannibalism was low and inadequate for comparisons between treatments; however, the other aggressive behaviors are precursors to cannibalism. This species, like many, will need to respond to cues associated with a drying environment, and may need to alter its development to persist in the face of climate change. This study aids in the understanding of how aquatic invertebrates and other animals respond to ongoing environmental changes.

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