Peter John Fraser

Review: Depth, navigation and orientation in crabs: Angular acceleration, gravity and hydrostatic pressure sensing during path integration

This review shows how well the published work on the neural basis of balance and hydrostatic pressure reception in crabs agrees with the analyses and models of path integration. Fiddler crabs allow analyses at the level of behaviour. With considerable accuracy, they continuously show the direction to home with their body orientation and use idiothetic path integration to calculate a home vector from the internal measurements of their locomotion. All crabs have a well-developed vestibular system in the statocyst with horizontal and vertical canals which is used for angular acceleration sensing and depth reception. Large identified interneurones abstract the component of angular acceleration in one of the three orthogonal planes. These have properties consistent with a key role in path integration, combining vestibular and proprioceptor information with a central excitatory drive from the hemiellipsoid bodies. They have been monitored during walking, swimming and even in freefall for a 22 s period in parabolic flight. * Note: This review is part of the collection of reviews on Animal Orientation and Navigation in Marine, Maritime and Freshwater Habitats published in Volume 39(1) of the journal.

How morphology of semicircular canals affects transduction, as shown by response characteristics of statocyst interneurons in the crabCarcinus maenas (L.)

SummaryAction potentials in directional statocyst interneurons are measured during sinusoidal oscillation of the crabCarcinus around horizontal axes. Peak response of the interneurons precede peak position of the animal by 120 ° (Fig. 3). Optimum response of an interneuron occurs when the plane of oscillation of the crab coincides with the circumferential plane of the vertical canal of the statocyst providing input to the interneuron in question (Fig. 6). Directionality is explained in terms of unidirectional sensory receptors inCarcinus statocyst. Increased phase lead of response over peak position of the crab is explained in terms of reduced viscous damping in the ‘open’ statocyst.

Statocysts and Statocyst Control of Motor Pathways in Crayfish and Crabs

Statocysts are the organs of balance or equilibrium in crustacea. They have many structural features analogous with balance organs in vertebrate and Hensen (1863) considered them to have a hearing role and called them otocysts. Their function was first elucidated in crustacea with Delage (1887) showing that elimination of otocysts in Mysis and several other decapods caused “desorientation locomotrice” Kreidls iron filings experiment showed the equilibrium role more convincingly (Kreidl 1893). He introduced iron filings into the otocyst ofPalaemonetesin place of the normal sand grains during the moult (Prentiss 1901; Kinzig 1919; Panning 1924) and found he could influence the position of the prawn in space, with a magnet. He concluded that the otocyst had an equilibrium function and renamed it statocyst.

Effects of temperature on statocyst afferents of the crab Carcinus Maenas

Abstract 1. 1.|Statocyst afferents show decreased spontaneous firing frequencies, spike heights and conduction velocities to decreased temperature, with all activity failing at approx. 5°C. 2. 2.|On raising temperature, these parameters increase to between 20 and 30°C when an abrupt decrease in spike frequency is shown. There is a marked hysteresis in the response. High temperature effects are usually irreversible. 3. 3.|Temperature affects gain fairly evenly over the frequency range 1–100 Hz but there is a clear shift in peak frequency towards lower frequencies on decreasing temperature and towards higher frequencies on increasing temperature. Phase tends to change markedly at higher temperatures. 4. 4.|The response to a rapid step change in temperature is complicated with gain and phase having different time courses. 5. 5.|Arrhenius plots are curvilinear suggesting several processes may be involved.

Integration of hydrostatic pressure information by identified interneurones in the crab Carcinus maenas (L.); long term recordings

This paper was first presented at the RIN97 Conference held in Oxford under the auspices of the Animal Navigation Special Interest Groupe, April 1997. Migrating species may utilise hydrostatic pressure. In the aquatic environment, hydrostatic pressure changes much more rapidly than in air. In shallow water, tidal changes will impose larger percentage changes on organisms than those experienced in deep water. Small changes in pressure often cause locomotion (barokinesis) accompanied by orientation to light or gravity, often partially compensating for the equivalent depth change. Until recently, identification of hydrostatic pressure receptors without a gas phase has proved elusive, but it is now known that thread hair receptors in the statocyst of the shore crab Carcinus maenas respond to small changes in hydrostatic pressure. Using a tide machine, the responses of thread hairs to sinusoidally changing pressure cycles have been examined, and this paper reports progress monitoring this receptor and making long-term recordings from hydrostatic pressure sensitive pathways in the crabs nervous system.

Equilibrium Control by Statocyst Activated Interneurones

The statocyst of the crab is specialized for angular acceleration detection, with a fluid filled sack formed intohorizontal and vertical canals. Receptor hairs respond to fluid movements so that the statocyst mechanically abstracts componentsof angular acceleration in orthogonal planes. Equilibrium interneurones are multimodal interneurones which clearly code onedirection of angular acceleration in one of three orthogonal planes. The interneurones are active preceding and during walking and swimming. The output of the interneurones to a sinusoidal angular acceleration varies with temperature, and during the excited state which accompanies locomotion. The excited state may be simulated by perfusion of the cerebral artery with salinecontaining serotonin or octopamine. The set of equilibrium interneurones codes any direction of angular acceleration in terms of the relative activity in each cell. Although there are necessarily no connections between the cells, a form of multiplicative gain control exists, so that during a gain change, the activity levels of the separate cells change so as to preserve the coded direction.

Effects of temperature on tilt evoked swimming in the crabs Carcinus and Macropipus

Abstract 1. 1.|Integrated muscle activity, total number of limb beats and the maximum instantaneous limb beat frequency were measured in crabs during a standardized tilt regime at a series of different water temperatures between 10 and 25°C. 2. 2.|Total integrated activity and total number of limb beats showed a general increase for a decrease in temperature in all groups. Frequency of limb beat was always higher for Macropipus depurator than for Carcinus maenas , with M. depurator showing an increase and C. maenas a decrease in frequencies at extreme temperatures. 3. 3.|The temperature of acclimation of C. maenas affected the response of the crab in all parameters studied while all the results can be related to the size and normal environmental temperature range of the two species studied.

Maps and Compasses

The map and compass hypothesis suggests that a navigating animal uses a map to determine where it is relative to its goal and a compass to set a direction home. A sun compass, star compass, polarized light compass, inclination magnetic compass, polarity magnetic compass, wind compass, and moon compass have all been proposed for animals, and the use of some of these is discussed in this article. There is evidence for magnetic field-, olfactory-, and infrasound-based maps, but there are, still, gaps in our understanding particularly with regard to sensory thresholds and signal-to-noise ratios for slowly acting sensory modalities.

A systematic review of methods for specifying the target difference in randomised controlled trials (delta review).

Background Determining the sample size is a vital aspect of randomised control trial design; typically a (target) difference is specified. This provides reassurance that the study will be informative; i.e. should such a difference exist, it is likely to be detected with the required statistical precision. From both a scientific and ethical standpoint, selecting an appropriate target difference is of crucial importance; too large or small a study is arguable unethical, wasteful and potentially misleading. While a variety of methods have been proposed to specify a target difference, their relative merits are unclear.