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The prevailing model of olfaction is that individual neurons express only one odorant receptor (OR). Goldman et al. challenge this view by finding that one olfactory receptor neuron (ORN) in [...]

Flowering plants communicate with their animal pollinators through a combination of olfactory, visual and gustatory signals. However, the evolution of odors as components of floral signals is poorly understood, due [...]

Hammerhead sharks (Family Sphyrnidae) are characterized by a unique head morphology in which the olfactory capsules of the cartilaginous neurocranium are laterally expanded. The enlarged olfactory capsules contain correspondingly large olfactory organs. It has been hypothesized that the widely spaced incurrent nares and large olfactory organs of sphyrnid sharks might confer directional localization of odors and enhanced olfactory sensitivity compared to their carcharhinid relatives. We tested these hypotheses by comparing the morphology of the peripheral olfactory system in all eight extant sphyrnid species as well as two carcharhinid species. The distinct prenarial grooves, characteristic of most sphyrnid species, channel water from along the anterior margin of the cephalofoil laterally into the incurrent nares. This effectively reduces the separation distance between left and right nares to a distance comparable to that of carcharhinid sharks. In addition, although sphyrnid sharks typically possess a greater number of olfactory lamellae than carcharhinid sharks, the dorso-ventrally compressed cephalofoil contrains the proportions of the lamellae such that the total lamellar surface area does not differ between comparably sized scalloped hammerhead and sandbar sharks. An electro-olfactogranl technique was employed to quantify the response of juvenile scalloped hammerhead sharks to a variety of proteogenic amino acids. Cysteine yielded the greatest response magnitude and dose-response curves indicated that this species is able to reliably detect concentrations less than 1 x [10.sup.-7] molar. These values are comparable with values for other elasmobranch fishes and, taken in conjunction with the morphological data, seem to indicate that sphymid sharks might not possess any extraordinary olfactory capabilities.

The sweet smell of success greeted Richard Axel and Linda Buck this week as the two U.S. neuroscientists were awarded the 2004 Nobel Prize in physiology or medicine for their [...]

Lobsters 'sniff' by flicking their antennular flagella. They discretely sample odors in the environment by rapidly closing the flagella, which permits water to flow through sensory hairs, and then slowly opening the flagella, which causes water to remain trapped in the sensory hairs. Panulirus argus is the model system in palinurid lobsters for studying chemoreception, but few studies have examined olfaction in other palinurid species. We conducted a comparative study of antennule morphology across 12 lobster genera in three families, including 13 species in the palinurid family. Using high speed video, kinematic analyses and morphometrics, we then compared antennule flicking in Palinurus elephas to published values for Panulirus argus. We found that Palinurus elephas flicks at rates an order of magnitude higher with flagella that are almost seven times shorter than those of Panulirus argus. When antennules were compared across lobsters, we found that Palinurus elephas is more typical of palinurid and other lobster families, whereas Panulirus species sample far larger areas of water per flick than any other lobster genus. Hence, while Panulirus argus is a highly informative model system in which to study chemoreception, the distinct anatomy and kinematics of their antennules suggests a unique strategy for detecting low odor concentrations in the environment.

Many crustaceans detect odors from distant sources by using chemosensory sensilla (aesthetascs) on their antennules. Stomatopods facilitate odorant access by flicking their antennules, thus increasing the relative velocity of the water and improving odor molecule access to their aesthetascs. In still water, the flick is asymmetric, with a rapid outstroke and a slow return stroke. Water (and odor) penetrate the array primarily during the rapid stroke. The flick asymmetry ensures that each flick samples a discrete volume of odor-containing water. The relative velocity has two components: the ambient water velocity and the velocity with which the stomatopods flick their antennules. To study the effect of ambient flow on flicking, specimens of Hemisquilla ensiguera californica were filmed in the field (Willow Cove, Catalina Island, CA) as they flicked in response to released odorant. Ambient flow near the antennules was measured simultaneously by filming the movement of particulate matter. In this wavy setting, water velocities at the level of the antennule ranged from -7 to +7 cm/s in the direction of the flick. Digitizing the video showed that in wavy flows, H. ensiguera altered their flicking velocity to preserve flick asymmetry. They also sometimes switched which stroke was fast and which stroke was slow, to increase the flick velocity of the rapid stroke. H. ensiguera were also filmed flicking in a laboratory flume while exposed to environmentally relevant water velocities. Analysis of high-speed video indicated that H. ensiguera respond to increased water velocity be changing both flicking velocity and flick length.

The unique head morphology of hammerhead sharks (Chondrichthyes, Sphyrnidae) has spawned a variety of adaptive hypotheses. Two hypotheses which have persisted without empirical evidence are the `expanded visual field' and the `stereo-olfaction' hypotheses. It has been suggested that the location of the eyes at the distal tips of the cephalofoil provide sphyrnid sharks with a larger visual field compared to similar-sized carcharhinid sharks. Comparative morphology and swimming behavior were employed to quantify the maximum visual field sampled by several sphyrnid shark species and a representative carcharhinid. Although the broadly spaced eyes of the sphyrnids may provide a greater lateral visual field under extremely turbid conditions, the cephalofoil head morphology produces a significantly greater blind spot directly anterior to the snout. This is at least partially offset by a greater yaw amplitude in the locomotion of the hammerheads. The stereo-olfaction hypothesis was tested by modeling the water volume that is sampled by sharks with different head morphologies. Although the nostrils of the sphyrnids are more widely spaced, a prenarial groove channels water from much of the anterior edge of the cephalofoil directly into the nostrils effectively decreasing the lateral separation distance. Therefore, the volume of water sampled is increased at the expense of spatial resolution - the hammerhead does sample a wider swath but it gains no advantage in localizing the scent source. Thus, neither hypothesis for the evolution of the sphyrnid cephalofoil is strongly supported.

The vomeronasal system is responsible for the detection of pheromones in mammals. These pheromones, which trigger off stereotyped behavioral responses that are unique to a species, are activated by genetically programmed neural pathways. Using gene targeting methods, it is shown that these pathways are made possible by the neural organization of vomeronasal system afferents. Results also indicate that the sensory neurons in the accessory olfactory bulb play a vital role in pheromone activation.