Defense Mechanisms in Notaspid Snails: Acid Humor and Evasiveness

Abstract

Notaspid snails are known for their defensive skin secretion of sulfuric acid (pH 1–2) in response to noxious stimuli. We observed acid secretion and behavior in five notaspid species, and studied them in detail in Pleurobranchaea californica. All species secreted acid in response to skin abrasion or compression. Moreover, all species showed stereotypic avoidance behavior to acidified sea water less acidic (pH 2–3) then their own secretions. In Pleurobranchaea, secretion could also be stimulated by dilute solutions of taurine, 10−5-10−2moll−1. Secretion began at the stimulated region and spread slowly for about a minute following stimulation. Local contraction and transient edema of the skin were associated with acid secretion. In de-ganglionated preparations secretion could be caused by orthodromic stimulation of body wall nerves, by mechanical stimulation or by taurine. These data suggest that acid secretion is a positive feedback process modulated by inhibitory paths and coordinated by both central and peripheral nervous systems. A picture emerges of a defensive secretory response that provides an additional noxious stimulus initiating or potentiating avoidance behavior. The data also suggest a potential role for taurine release from injured tissue and the existence of specific nociceptive neural pathways regulating complex behavior. In addition to deterring extraspecific predation, acid secretion could regulate interactions between animals of the same species.

Defining Chemical Species in Complex Environments Using K-Edge X-ray Absorption Spectroscopy: Vanadium in Intact Blood Cells and Henze Solution from the TunicateAscidia ceratodes

“…However, the predatory Notaspid gastropod P. californica is strongly repelled by both acid and taurine. 58 Taurine may be the source of the intense aliphatic sulfonate signal we have detected in whole blood cells from A. ceratodes using sulfur K-edge XAS. [25][26][27] Definitive conclusions regarding chemical deterrance are also made problematic by the observation that the avoidance behavior of predatory snails following exposure to noxious chemicals is influenced by the hunger/satiation state of the snail.…”

“…The universal deterrance of predation by vanadium and acid is contradicted by the observation that several predatory gastropods including Fusitriton oregonensis , which is found on the Pacific north coast of North America, readily attack ascidians with vanadium- and acid-containing blood cells. , In addition, the defensive efficacy of vanadium and acid has been disputed on the basis of the observed clearance of acid- and vanadium-containing ascidian residents from noncryptic habitats. , Therefore the defensive utility of vanadium and acid to ascidians is problematic at best. However, the predatory Notaspid gastropod P. californica is strongly repelled by both acid and taurine . Taurine may be the source of the intense aliphatic sulfonate signal we have detected in whole blood cells from A. ceratodes using sulfur K-edge XAS. − Definitive conclusions regarding chemical deterrance are also made problematic by the observation that the avoidance behavior of predatory snails following exposure to noxious chemicals is influenced by the hunger/satiation state of the snail …”

“…This acid is apparently resident within intracellular vacuoles of the buccal gland tissues. In Notaspid snails, sulfuric acid to pH 1-2 is secreted from skin cells in a defensive response 58 that is apparently widespread among marine gastropods. 59 As an interesting aside, the apparently exclusive use of sulfuric acid among marine organisms which make acid, in the ubiquitous presence of chloride, appears to demand an explanation.…”

“…It is interesting to note that all five gastropods mentioned as specifically preying on ascidians which contain vanadium, and thus acid, i.e., Lamellaria, Cypraea, Velutina, Pleurobranchus , ,, and Fusitriton , are themselves known to deploy defensive and/or predation-assisting sulfuric acid. It may be that these predators have learned to recruit the defenses of their prey, as in the case of the nudibranch C. luteomarginata .…”

Neural division of labor: the gastropodBerghiadefends against attack using its PNS to retaliate and its CNS to erect a defensive screen

“…Research in the CNS of gastropods has elucidated fundamental, broadly conserved principles of neurophysiology, such as long-term potentiation and the cellular and molecular bases of both nonassociative and associative learning [10][11][12][13], central pattern generation [14], neuromodulation [15][16][17][18], and neuroeconomics [19][20][21][22]. Although investigations in these animals have additionally revealed specific contributions made by the PNS to several reflexes [23][24][25][26], the manners in which the CNS and PNS interact to generate more dynamic behaviors in these animals remains unexplored.…”