(1/1866) Prey capture in the weakly electric fish Apteronotus albifrons: sensory acquisition strategies and electrosensory consequences.

Sensory systems are faced with the task of extracting behaviorally relevant information from complex sensory environments. In general, sensory acquisition involves two aspects: the control of peripheral sensory surfaces to improve signal reception and the subsequent neural filtering of incoming sensory signals to extract and enhance signals of interest. The electrosensory system of weakly electric fish provides a good model system for studying both these aspects of sensory acquisition. On the basis of infrared video recordings of black ghost knifefish (Apteronotus albifrons) feeding on small prey (Daphnia magna) in the dark, we reconstruct three-dimensional movement trajectories of the fish and prey. We combine the reconstructed trajectory information with models of peripheral electric image formation and primary electrosensory afferent response dynamics to estimate the spatiotemporal patterns of transdermal potential change and afferent activation that occur during prey-capture behavior. We characterize the behavioral strategies used by the fish, with emphasis on the functional importance of the dorsal edge in prey capture behavior, and we analyze the electrosensory consequences. In particular, we find that the high-pass filter characteristics of P-type afferent response dynamics can serve as a predictive filter for estimating the future position of the prey as the electrosensory image moves across the receptor array.  (+info)

(2/1866) Neuromuscular control of prey capture in frogs.

While retaining a feeding apparatus that is surprisingly conservative morphologically, frogs as a group exhibit great variability in the biomechanics of tongue protraction during prey capture, which in turn is related to differences in neuromuscular control. In this paper, I address the following three questions. (1) How do frog tongues differ biomechanically? (2) What anatomical and physiological differences are responsible? (3) How is biomechanics related to mechanisms of neuromuscular control? Frog species use three non-exclusive mechanisms to protract their tongues during feeding: (i) mechanical pulling, in which the tongue shortens as its muscles contract during protraction; (ii) inertial elongation, in which the tongue lengthens under inertial and muscular loading; and (iii) hydrostatic elongation, in which the tongue lengthens under constraints imposed by the constant volume of a muscular hydrostat. Major differences among these functional types include (i) the amount and orientation of collagen fibres associated with the tongue muscles and the mechanical properties that this connective tissue confers to the tongue as a whole; and (ii) the transfer of intertia from the opening jaws to the tongue, which probably involves a catch mechanism that increases the acceleration achieved during mouth opening. The mechanisms of tongue protraction differ in the types of neural mechanisms that are used to control tongue movements, particularly in the relative importance of feed-forward versus feedback control, in requirements for precise interjoint coordination, in the size and number of motor units, and in the afferent pathways that are involved in coordinating tongue and jaw movements. Evolution of biomechanics and neuromuscular control of frog tongues provides an example in which neuromuscular control is finely tuned to the biomechanical constraints and opportunities provided by differences in morphological design among species.  (+info)

(3/1866) Effects of size, motility and paralysation time of prey on the quantity of venom injected by the hunting spider Cupiennius salei.

Previous experimental studies have shown that neotropical wandering spiders (Cupiennius salei) inject more venom when attacking larger crickets. It has been postulated that this is a consequence of predator-prey interactions during envenomation, which increase in intensity with the size of a given prey species. The present study was designed to test this hypothesis using anaesthetized crickets of different sizes that were moved artificially. Cupiennius salei was found (1) to inject more venom the greater the intensity of the struggling movement of the crickets (prey size kept constant); (2) to inject more venom the longer the duration of the struggling movement of the crickets (prey size and intensity of movement kept constant); and (3) to inject equal amounts into crickets of different size (duration and intensity of movement kept constant). These results indicate that C. salei alters the amount of venom it releases according to the size and motility of its prey. Venom expenditure depends mainly on the extent of the interactions with the prey during the envenomation process, whereas prey size is of minor significance. The regulation of venom injection in concert with behavioural adaptations in response to various types of prey minimizes the energetic cost of venom production, thus increasing the profitability of a given prey item.  (+info)

(4/1866) Lunar cycles in diel prey migrations exert a stronger effect on the diving of juveniles than adult Galapagos fur seals.

In our study of the development of diving in Galapagos fur seals, we analysed changes in diving activity and body mass trends over the lunar cycle. Based on previously observed lunar cycles in colony attendance patterns, we hypothesized a greater impact of prey migrations of deep scattering layer organisms on younger fur seals. Using electronic dive recorders, we determined that seals dived less and deeper on moonlit nights than at new moon, and incurred body mass losses. These changes in foraging over the lunar cycle correlate with the suppression of the vertical migration of prey by lunar light. All effects were more pronounced in juveniles than adult females, with greater relative mass loss during full moon, which must (i) negatively affect long-term juvenile growth rates, (ii) lengthen periods of maternal dependence, and (iii) contribute to the lowest reproductive rate reported for seals. This underlines the importance of studying ontogeny in order to understand life histories, and for determining the susceptibility of animal populations to fluctuations in food availability.  (+info)

(5/1866) A trade-off between energy intake and exposure to parasites in oystercatchers feeding on a bivalve mollusc.

Models of animal dispersion between habitat patches that differ in resource density assume that animals maximize their fitness by maximizing the rate at which they consume resources. How valid is this assumption? Studies on wading birds have been central to the application of dispersion models to predator-prey systems. However, these birds do not always attempt to maximize their rate of energy intake, implying that maximization involves costs as well as benefits. Overwintering oystercatchers feeding on cockles in the Burry Inlet, South Wales, do not consume the larger more energetically profitable cockles even though consuming these prey would increase their rate of energy intake. This paper tests the hypothesis that maximizing energy intake involves a trade-off with exposure to helminth parasites. Cockles are important intermediate hosts for helminth parasites, for which oystercatchers are the definitive host. The helminth intensity of cockles increased significantly with cockle size. A functional response model was used to examine how size selection by the birds influenced energy intake and the ingestion rate of parasites. To maximize energy intake birds should selectively consume the larger size classes, but to minimize the ingestion rate of parasites they should consume the smallest size classes. In the wild, birds selectively consumed intermediate size classes, which could represent a compromise between these conflicting demands. The implications for animal dispersion models are discussed.  (+info)

(6/1866) Electrolocation-communication discharges of the fish Gymnotus carapo L. (Gymnotidae: Gymnotiformes) during behavioral sleep.

Technical problems have hampered the study of sleep in teleosts. The electrical discharges of Gymnotus carapo L. (Gymnotidae: Gymnotiformes) were monitored to evaluate their ease and reliability as parameters to study sleep. The discharges were detected by electrodes immersed in a glass aquarium and were recorded on a conventional polygraph. G. carapo showed conspicuous signs of behavioral sleep. During these periods, opercular beat rates were counted, electric discharges recorded, and the "sharp discharge increase" (SDI) of the orienting reflex was investigated. All 20 animals monitored maintained electrical discharges during behavioral sleep. The discharge frequencies during sleep (50.3 +/- 10.4 Hz) were not significantly different from those observed when the fish was awake and inactive (57.2 +/- 12.1 Hz) (Wilcoxon matched-pairs signed-ranks test, P>0.05). However, the SDI, which was prevalent in the awake fish, was not observed during periods of behavioral sleep. Additional observations showed that the species had cannibalistic habits. When presented with electrical discharges from a conspecific, the sleeping fish showed an initial decrease or pause in discharge frequency, while the awake fish did not have this response. We conclude that the electrical discharges of G. carapo were not conspicuous indicators of behavioral sleep. Discharges may have been maintained during sleep for sensory purposes, i.e., conspecific detection and avoidance of cannibalistic attacks.  (+info)

(7/1866) Accommodation in the cuttlefish (Sepia officinalis).

We have studied natural accommodation in the eye of six specimens of cuttlefish (Sepia officinalis) as they were fed with fish and shrimp. Using infrared photoretinoscopy, we observed (1) that the resting refractive state of the cuttlefish was emmetropic or slightly hyperopic, (2) that accommodation took place only a fraction of a second before a strike and (3) that accommodation focused selectively only in the frontal visual field while no change in refraction could be measured in the lateral field of view. Accommodation was bilateral and amounted to approximately 5 diopters (the reciprocal of the focal length expressed in meters). Simultaneously, the eyes converged. It appears that, as in most teleost fishes, accommodation in the cuttlefish involves a movement of the crystalline lens perpendicular to the axis of the eye. In histological sections, we observed the position and arrangement of the ciliary muscles, confirming earlier anatomical descriptions, and developed a model of how accommodation could be achieved.  (+info)

(8/1866) Role of prey-capture experience in the development of the escape response in the squid Loligo opalescens: a physiological correlate in an identified neuron.

Although extensively used for biophysical studies, the squid giant axon system remains largely unexplored in regard to in vivo function and modulation in any biologically relevant context. Here we show that successful establishment of the recruitment pattern for the giant axon in the escape response elicited by a brief electrical stimulus depends on prey-capture experience early in life. Juvenile squid fed only slow-moving, easy-to-capture prey items (Artemia salina) develop deficits in coordinating activity in the giant axon system with that of a parallel set of non-giant motor axons during escape responses. These deficits are absent in cohorts fed fast-moving, challenging prey items (copepods). These results suggest that the acquisition of inhibitory control over the giant axon system is experience-dependent and that both prey-capture and escape behavior depend on this control.  (+info)