Olfaction and Chemical Sense

Olfaction and Chemical Sense

Overview Chemical Signals: oldest method of communication Detection of food was, and still is, the primary function of most chemical reception organs Unlike visual and acoustic communication, signal molecules have to move the entire distance between sender and receiver

I. Overview A. General Definition of Chemical Communication What is chemical communication? Definition = movement of individual chemical molecules from sender to receiver

I. Overview A. Production Chemicals used in communication and biological level of use (3 general levels): 1. Hormones: chemicals that regulate communication between organs 2. Neurotransmitters: chemicals that regulate communication between neurons

I. Overview A. Production Three categories of chemicals used in communication (and the 3 biological levels of use): 1. Hormones: chemicals that regulate communication between organs 2. Neurotransmitters: chemicals that regulate communication between neurons 3. Semiochemicals: chemical that mediate communication between organisms There are two general types of semiochemicals.. - Pheromones: chemicals that facilitate communication between conspecifics - Allomones: chemicals transmitted and detected between species

I. Overview B. Transmission Three Methods of Transmission: 1. Contact: receiver can move towards the molecule and pick it up 2. Diffusion: move naturally along a concentration gradient from high concentration to low concentration (requires time) 3. Current flow: air or water to carry molecules

I. Overview C. Reception Mechanisms of Reception: 1. Olfactory reception: smell detection of air or waterborne chemicals; often from a distance 2. Contact reception: taste Detection of chemicals from direct contact with source

II. Production of Chemical Signals Semiochemicals: chemicals that mediates communication between organisms. There are two general types of semiochemicals: A. Pheromones B. Allomones

II. Production of Chemical Signals 1. Pheromones: chemicals that regulate communication between conspecifics (animals of same species). characteristics: - diffusion rate inversely related to molecule size - small compounds are volatile (5-20 carbon atoms) - large compounds can persist (proteins and lipids) - can be metabolites of gonadal steroid hormones (e.g., goldfish)

II. Production of Chemical Signals Examples of Pheromones: Cockroach sex attractant Silkworm moth sex attractant Hamster mounting pheromone Termite alarm substance Honeybee queen substance Civet sex attractant

Function of Pheromones: - sexual attractant - aggregation - territory marking - social bonding (between groups, individual, colonies) - recruitment to food sources (social insects, e.g., ants and bees, commonly use scents to recruit conspecifics to food sources) - alarm signals, sometime called Schreckstoff (secretion from crushed tissue - fishes)

Is there evidence for pheromones and olfactory communication in humans? Yes. McClintock (1971) Menstrual synchrony and suppression. Nature 291:244-245. - showed that women in college dorms synchronized their menstrual cycles. Stern and McClintock (1998) Nature - isolated odorless compounds from the armpits of women during different phases of the menstrual cycle. - found compound (pheromone?) released during ovulation that lengthened the cycle of recipients. - compound released during follicular phase shorten cycle of recipients.

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II. Production of Chemical Signals 2. Allomones: chemicals that regulate communication between animals of different species, such as predators and prey or sympatric competitors. Function of allomones: - suppressant (inhibit competitors) - venom (poison prey) - escape (cephalopod ink) - attractants (carnivorous plants) - antipredator repellent (e.g., skunk, bombardier beetle)

An Investigation of Allomones: Chemical Shark Repellents USS Indianapolis natural shark repellent = Pardaxin Post WII early 1970s : discovery of the natural defense of the Red Sea Moses sole

Pardaxin and Surfactants Pardaxin was discovered to possess many surfactant like (detergent) properties. Red Sea Moses sole & Pardaxin Nelson & Smith discovered that SDS (sodium dodecyl sulfate) was the most effective surfactant chemical shark repellent Field tests using SDS Strong tests SDS on the Great White shark

Question: What makes SDS so effective? What is the structure-function relationship that makes SDS an effective chemical shark repellent? Does the carbon chain length and/or the counter-ion of the surfactant affect the shark repellent efficacy?

Test Subjects = Swell sharks Could not use large adult sharks or large vols of water due to the expensive nature of the test chemicals. Solution = use smaller sharks & miniaturize testing area Used juvenile swell sharks:

EC50 (ppm) Methods & Results: Used EC50s to determine the behavioral thresholds for: 1) minimum aversive response 2) strong aversive response EC50 represents the effective concentration at which 50% of the population shows a categorical response. No difference in behavioral thresholds between SDS and MDS. However. SDS was more effective than SOS & SDecS STDS & SODS were insoluble in seawater Sisneros and Nelson 2001

Fielding Testing

IMAX Filming: Search For the Great Sharks

Search For The Great Sharks

Ok, SDS/MDS are not effective chemical shark repellents. Are shark repellent surfactants allomones??? Is there still hope for an effective chemical shark repellent?? Remember Allomones facilitate chemical communication between predator and prey Evidence: - What about the tales of fishermen about sharks?? Anecdotal information about how sharks will avoid dead sharks - Study by Rasmussen & Schmidt (1992)

Shark Repellent Allomone? American Crocodile (Crocodylus acutus) Lemon shark (Negaprion brevirostris) Rasmussen & Schmidt (1992) suggested that sharks may be chemically aware of danger by sensing the bodily secretions from potential predators. American crocodile prey on juvenile lemon sharks in their natal puping ground in the FL keys. Rasmussen & Schmidt isolated 3 compounds that repel juvenile lemon sharks. Will this affect all sharks?? Potential shark repellent??

Shark Repellent Experiment