Olfaction: diverse species, conserved principles.

Nawroth et al. combine rat cardiomyocytes and silicone polymer to make a jellyfish replica that mimics the propulsive behavior of its live counterpart. The design principles guiding this feat may facilitate tissue engineering of muscular organs.

/pdf/a-tissue-engineered-jellyfish-with-biomimetic-propulsion-3f3snl6bko.pdf

A tissue-engineered jellyfish with biomimetic propulsion

Polychaetes are common in most marine habitats and dominate many infaunal communities. Functional guild classification based on taxonomic identity and morphology has linked community structure to ecological function. The functional guilds now include osmotrophic siboglinids as well as sipunculans, echiurans, and myzostomes, which molecular genetic analyses have placed within Annelida. Advances in understanding of encounter mechanisms explicitly relate motility to feeding mode. New analyses of burrowing mechanics explain the prevalence of bilateral symmetry and blur the boundary between surface and subsurface feeding. The dichotomy between microphagous deposit and suspension feeders and macrophagous carnivores, herbivores, and omnivores is further supported by divergent digestive strategies. Deposit feeding appears to be limited largely to worms longer than 1 cm, with juveniles and small worms in general restricted to ingesting highly digestible organic material and larger, rich food items, blurring the macrophage-microphage dichotomy that applies well to larger worms.

Diet of Worms Emended: An Update of Polychaete Feeding Guilds

The rhythmic motor activity of the vibrissae that rodents use for the tactile localization of objects provides a model system for understanding patterned motor activity in mammals. The muscles that drive this whisking are only partially fixed relative to bony attachments and thus shift their position along with the movement. As a means to characterize the pattern of muscular dynamics during different patterns of whisking, we recorded electromyogram (EMG) activity from the muscles that propel individual follicles, as well as EMG activity from a muscle group that moves the mystacial pad. The dominant pattern of whisking in our behavioral paradigm, referred to as exploratory whisking, consisted of large amplitude sweeps in the frequency range of 5-15 Hz. The frequency remained remarkably constant within a bout of whisking but changed values between bouts. The extrinsic musculature, which shifts the surface of the pad backwards, was found to be activated in approximate antiphase to that of the intrinsic muscles, which rotate individual vibrissae forward. Thus retraction of the vibrissae was driven by a backward shift in the attachment point of the follicles to the mystacial pad. In a less frequent pattern of whisking, referred to as foveal whisking, the vibrissae are thrust forward and palpate objects with low-amplitude movements that are in the higher frequency range of 15-25 Hz. Protraction of the vibrissae remains driven by the intrinsic muscles, while retraction in this pattern is largely passive. Interestingly, a mechanical argument suggests that activation of the extrinsic muscles during foveal whisking is not expected to affect the angle of the vibrissae. As a means to establish if the phasic control of the intrinsic versus extrinsic muscles depended on sensory feedback, we characterized whisking before and after bilateral transections of the infraorbital branch of the trigeminal sensory nerve. The loss of sensory feedback had no net effect on the antiphase relation between activation of the intrinsic versus extrinsic muscles over the full frequency range for exploratory whisking. These data point to the existence of a dual-phase central pattern generator that drives the vibrissae.

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Rhythmic whisking by rat: retraction as well as protraction of the vibrissae is under active muscular control.

1. The evolution of flowering plants has undoubtedly been influenced by a pollinator's ability to learn to associate floral signals with food. Here, we address the question of 'why' flowers produce scent by examining the ways in which olfactory learning by insect pollinators could influence how floral scent emission evolves in plant populations. 2. Being provided with a floral scent signal allows pollinators to learn to be specific in their foraging habits, which could, in turn, produce a selective advantage for plants if sexual reproduction is limited by the income of compatible gametes. Learning studies with honeybees predict that pollinator-mediated selection for floral scent production should favour signals which are distinctive and exhibit low variation within species because these signals are learned faster. Social bees quickly learn to associate scent with the presence of nectar, and their ability to do this is generally faster and more reliable than their ability to learn visual cues. 3. Pollinators rely on floral scent as a means of distinguishing honestly signalling flowers from deceptive ones. Furthermore, a pollinator's sensitivity to differences in nectar rewards can bias the way that it responds to floral scent. This mechanism may select for flowers that provide olfactory signals as an honest indicator of the presence of nectar or which select against the production of a detectable scent signal when no nectar is present. 4. We expect that an important yet commonly overlooked function of floral scent is an improvement in short-term pollinator specificity which provides an advantage to both pollinator and plant over the use of a visual signal alone. This, in turn, impacts the evolution of plant mating systems via its influence on the species-specific patterns of floral visitation by pollinators.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2435.2009.01627.x

The evolution of floral scent: the influence of olfactory learning by insect pollinators on the honest signalling of floral rewards

The first step in processing olfactory information, before neural filtering, is the physical capture of odor molecules from the surrounding fluid. Many animals capture odors from turbulent water currents or wind using antennae that bear chemosensory hairs. We used planar laser-induced fluorescence to reveal how lobster olfactory antennules hydrodynamically alter the spatiotemporal patterns of concentration in turbulent odor plumes. As antennules flick, water penetrates their chemosensory hair array during the fast downstroke, carrying fine-scale patterns of concentration into the receptor area. This spatial pattern, blurred by flow along the antennule during the downstroke, is retained during the slower return stroke and is not shed until the next flick.

https://science.sciencemag.org/content/sci/294/5548/1948.full.pdf

Lobster Sniffing: Antennule Design and Hydrodynamic Filtering of Information in an Odor Plume

Laboratory investigations of a turbulent scalar plume are performed to investigate the relationship between instantaneous scalar structure and the resulting mean scalar statistics. A planar laser-induced fluorescence technique is used to image two-dimensional instantaneous spatial plume structure at various locations and in three orthogonal planes. Long image sequences are used to calculate time-averaged scalar statistics (concentration mean, variance and intermittency), and the relationship between these statistics and the observed instantaneous scalar structure is discussed. We present both snapshots and animations of instantaneous scalar structure at various locations within the boundary layer. As with all boundary layer phenomena, the structural variation is greatest in the vertical direction (normal to the bed). The existence of a persistent, relatively uniform layer of dye within the viscous sublayer is identified. In this layer, instantaneous concentrations are moderate, but the persistence of the dye produces a relatively high mean concentration. Above this layer, stronger fluctuations and higher peak concentrations are present, but lower values of the intermittency produce lower mean concentrations. It is argued that a combination of three time-averaged statistics (mean, variance and intermittency) is required to deduce meaningful information about the nature of the instantaneous scalar structure.

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The relationship between mean and instantaneous structure in turbulent passive scalar plumes

Many marine animals track odor plumes to their source. Although studies of plume-tracking behavior have been performed in unidirectional flow, benthic animals such as crustaceans live in coastal habitats characterized by waves. We compared signal encounters by odor-plume-tracking stomatopods (mantis shrimp) in wave-affected and unidirectional flow in a flume. Stomatopods are small enough that we can study their natural behavior in a flume. They sample odors by flicking their antennules. A thin sheet of laser light illuminating an odor plume labeled with dye [planar laser induced fluorescence (PLIF) technique] permitted us to measure the instantaneous odor concentration encountered by the animal's chemosensory organs (antennules) while it tracked the plume. We simultaneously measured behavior and the high-resolution odor signal at the spatial and temporal scale of the animal. We found that the navigating animal encountered odor filaments more often in wave-affected flow than in unidirectional flow. Odor filaments along the animals' antennules were significantly wider and of higher concentration in waves than in unidirectional flow.

/pdf/fine-scale-patterns-of-odor-encounter-by-the-antennules-of-see4bokztu.pdf

Megan B. Wiley

Papers

Lobster Sniffing: Antennule Design and Hydrodynamic Filtering of Information in an Odor Plume

The relationship between mean and instantaneous structure in turbulent passive scalar plumes

Fine-scale patterns of odor encounter by the antennules of mantis shrimp tracking turbulent plumes in wave-affected and unidirectional flow