The Neurobehavioral Mechanisms of Ink as an Antipredation Strategy

Abstract

Inking is a chemical defense mechanism which has evolved independently in disparate taxa. The goal of this research was to investigate if the functional role of ink as an antipredator chemical deterrent has been conserved despite the divergent ancestry of three inking animal groups. I compared the ink from three unrelated taxa: California sea hares (Aplysia californica), common cuttlefish (Sepia officinalis) and pygmy sperm whales (Kogia breviceps). This research investigated the function of ink as a chemical deterrent by examining the chemical composition of ink, describing the chemosensory system of the predator affected by ink defenses, and quantifying the antipredator behavioral effects of ink. There was no single or cluster of amino acids which was consistently elevated across the three different inks. However, I recovered a large percentage of D-Amino acids which signal a connection to antimicrobial function and excretory pathways - the two evolutionary hypotheses for how ink arose. I also describe the microstructure for the olfactory system of sharks, common predators of inking organisms. I focus on bonnethead sharks and describe the distribution of sensory vs. nonsensory olfactory epithelium, mapped the pathway of the olfactory receptor axons through the olfactory lamellae, and investigated the lamellar morphological differences throughout the organ. I found that lamellae within the medial portion of the organ, which receives less water flow, had less sensory surface area and less secondary folds, leading to the hypothesis that these areas are less sensitive. Finally, I demonstrate that all three inks elicit a negative response on shark swimming behavior. When sharks came in contact with an ink cloud, they deviated from their swimming path, exhibiting aversion responses. This research investigated the three components of a chemically mediated predator defense: the chemical makeup of that defense, the morphology of the predator’s affected chemosensory system, and the behavioral effects of the interaction between the two.