Evaluation of the rate of basal oxygen consumption in the isolated frog skin and toad bladder.

In the study of active transport it is important to distinguish between oxygen consumption sustaining transepithelial transport and that responsible for other tissue functions (basal metabolism). Since amiloride blocks transepithelial active sodium transport and the associated oxygen consumption in the frog skin and toad bladder, we and others have employed this agent to evaluate the rate of basal metabolism. This technique has recently been criticized in a report that amiloride (and ouabain) increased oxygen consumption when no sodium was available for transport. We have been unable to corroborate these observations. With magnesium-Ringer as external bathing solutions, amiloride and ouabain failed to stimulate oxygen consumption. With sodium-Ringer as external bathing solution amiloride reduced oxygen consumption about 30%, to a level indistinguishable from that found on external substitution of magnesium-Ringer for sodium-Ringer. We conclude that the use of amiloride permits evaluation of the rate of basal metabolism with acceptable accuracy; a possible slight depressant effect of ouabain on basal metabolism remains to be investigated.     

A model of the visual localization of prey by frog and toad

In this paper we demonstrate how prey localization can be acheived rapidly and accurately by coupling prey-selection and lens-accommodation processes within a feedback loop. Information derived from prey selection supplies a setpoint for accomodation. In turn, adjustment of the lens modifies the visual input and can alter the prey selection process. The natural feedback of this goal-seeking system automatically corrects for the problem of ambiguity in binocular matching.Although it is of general interest as a depth algorithm, we tie the model to the known anatomy, physiology and behavior of frogs and toads. Instead of building a global depth-map we propose that the goal of catching a prey leads a frog or toad to select a particular region of its visual world for special scrutiny. We suggest that the first step of the prey-catching sequence is to adjust the accommodative state of the lenses and thus lock the visual apparatus on to a stimulus. We identify brain regions that could provide the neural substrates necessary to support the model's various functional stages and present experiments, with a computer simulation, that compare its functioning to animal behavior.     

Evaluation of the rate of basal oxygen consumption in the isolated frog skin and toad bladder

In the study of active transport it is important to distinguish between oxygen consumption sustaining transepithelial transport and that responsible for other tissue functions (basal metabolism). Since amiloride blocks transepithelial active sodium transport and the associated oxygen consumption in the frog skin and toad bladder, we and others have employed this agent to evaluate the rate of basal metabolism. This technique has recently been criticized in a report that amiloride (and ouabain) increased oxygen consumption when no sodium was available for transport. We have been unable to corroborate these observations.With magnesium-Ringer as external bathing solutions, amiloride and ouabain failed to stimulate oxygen consumption. With sodium-Ringer as external bathing solution amiloride reduced oxygen consumption about 30%, to a level indistinguishable from that found on external substitution of magnesium-Ringer for sodium-Ringer. We conclude that the use of amiloride permits evaluation of the rate of basal metabolism with acceptable accuracy; a possible slight depressant effect of ouabain on basal metabolism remains to be investigated.     

Diffusion of 133Xe through frog skins, toad bladders, and water boundary layers.

We have measured the total permeability coefficients P as a function of stirring frequency omega for 133Xe through frog skins and toad bladders. The permeability coefficients for the frog skins and toad bladders proper are, respectively, Pm = (3.9 +/- 0.8) X 10(-4) cm/s and (7.4 +/- 4.2) X 10(-4) cm/s. "Unstirred" water layer thickness delta is determined concurrently, from the frequency dependence of P(omega); the result for frog skin is delta = (0.060 +/- 0.016) square root of omega(rad/s) cm. The stirring frequency range is from omega = 7.5 rad/s (72 rpm) to 55 rad/s (530 rpm). The results support the conclusions that the principal barrier to Xe diffusion in these epithelia is inter- and intracellular water, and that the diffusion is passive and rapid. The experimental method may be straightforwardly adapted to the measurement of diffusion or counterdiffusion of any gamma-radioactive soluble or partly soluble solute through any flat membrane or through a solvent. We estimate the amount of total body-absorbed radioactivity due to environmental 133Xe to be 50 fCi for an ambient concentration of 2.6 pCi/m3 of air.     

Oocyte maturation and activation in the common frog and the clawed toad under the action of divalent cations]

Maturation of Rana temporaria and Xenopus laevis oocytes was induced by solutions containing Mn2+ and Co2+ ions. Completion of oocyte maturation was estimated by the following criteria: (1) appearance of the maturation promoting factor (MPF) in the oocyte cytoplasm and (2) oocyte capacity to activation and formation of male pronuclei from the injected sperm nuclei. X. laevis oocytes matured under the effect of Co2+ ions were shown to contain MPF. Oocytes of both species matured under the effect of either ions could not be activated by pricking with a needle and injected sperm nuclei didn't transform into pronuclei. R. temporaria oocytes matured under the effect of ions in late spring, when natural spawning takes place, showed spontaneous activation.     

Studies on the olfactory epithelium of the frog and the toad with the aid of light and electron microscopy

Summary Epithelial structures in the olfactory region of the frog and the toad have been examined with the aid of light and electronmicroscopy. The olfactory cells send out 6–12 extremely long cilia with a central fibrillar structure and a peripheral sheath. They are motile but only in a small degree as their peripheral ends are weaved together in a network which covers the epithelial surface. The sustentacular cells show a great number of small protoplasmic protrusions on their surface. Their importance is discussed.The cells of the glands of Bowman are also provided with small protoplasmic protrusions but they are smaller than those of the sustentacular cells and do not show their inner structures. In all three celltypes mitochondria were found containing systems of double-membranes and in the supporting cells and Bowman's cells intracellular cytoplasmic membranes were observed.     

Parental care and the ontogeny of predator-avoidance in two species of centrarchid fish

Stamps (1978) suggested that the type and extent of parental care can influence the behavioural ontogeny of the offspring. Largemouth bass (Micropterus salmoides) males guard the fry for up to a month after they leave the nest while rock bass (Ambloplites rupestris) males guard the fry only until they leave the nest. In laboratory experiments, naive largemouth fry displayed reduced predator-avoidance responses to large and small predators during their first 3 weeks of free-swimming. Rock bass fry, on the other hand, avoided predators throughout the study period. From 6 weeks (largemouth) and 5 weeks (rock bass) of age the fry showed a significantly greater response to the large predator than the small predator. The responses of laboratory-reared largemouth bass fry to the small predator changed from avoidance to association as the fry grew. The size of the fry relative to predator size was found to be important.     

Microelectrode study of K+ accumulation by tight epithelia: I. Baseline values of split frog skin and toad urinary bladder

Toad bladder and split frog skin were impaled with fine-tipped single- and double-barrelled K+-selective microelectrodes. In order to circumvent membrane damage induced by impaling toad bladder, a null point method was developed, involving elevations of mucosal potassium concentration. The results suggest that intracellular potassium activity of short-circuited toad bladder is approximately 82 mM, twice as large as earlier estimates. Far more stable and rigorously defined intracellular measurements were recorded from short-circuited split frog skins. The intracellular positions of the micropipette and microelectrode tips were verified by transient hyperpolarizations of the membrane potential with mucosal amiloride or by transient depolarizations with serosal barium or strophanthidin. Simultaneous impalement of distant cells with separate micropipettes demonstrated that both the baseline membrane potentials and the responses to depolarizing agents were similar, further documenting that frog skin is a functional syncytium. Measurements with double-barrelled microelectrodes and simultaneous single-barrelled microelectrodes and reference micropipettes suggest that the intracellular potassium activity is about 104 mM, lower than previously reported. Taken together with measurements of intracellular potassium concentration, this datum suggests that potassium is uniformly distributed within the epithelial cells.     

Sperm competition: defining the rules of engagement.

Genetic and cell biological analyses of sperm behavior in the female reproductive tract are providing important clues to the mechanisms of sperm competition, a form of sexual selection that is an important force that shapes reproductive behavior, physiology and morphology in a wide range of species.     

Multiple predator-avoidance behaviours of the freshwater snail Physella heterostropha pomila: responses vary with risk

• 1 We examined the predator‐avoidance behaviour, exhibited in response to chemical cues, of two populations of the snail Physella heterostropha pomila. Snails were subjected to four treatments simulating different degrees of predation risk: control water (low risk), or water from tanks containing nonforaging crayfish (intermediate risk), crushed conspecifics (high risk) or crayfish consuming conspecifics (high risk). Data were analysed using three‐way ANOVA models (population × predator chemicals × injured conspecific chemicals).
• 2 Physella increased its avoidance behaviour as risk increased. Crayfish cue elicited a significantly greater response than from controls. Cues from injured conspecifics elicited the strongest response.
• 3 Physella exhibited several types of avoidance behaviour, including burial into the substratum, moving to the water surface, and crawling out of the water. The type of cue present influenced response type. Cues from crayfish reduced burial and increased movement to the water surface or out of the water. Cues from injured‐conspecifics significantly increased crawling completely out of the water.
• 4 The two populations differed in the type and degree of response exhibited. One population exhibited significantly greater ‘reactivity’ (i.e. any avoidance behaviour) in response to foraging crayfish, and more burial and crawl‐out behaviours were exhibited in high‐risk treatments.

     

Transfer RNA splicing in Saccharomyces cerevisiae: defining the substrates.

The primary sequences of all the tRNA precursors which contain intervening sequences and which accumulate in the Saccharomyces cerevisiae rnal mutant are presented. A combination of DNA and RNA sequence analysis has led to elucidation of the primary sequence of four hitherto uncharacterized precursors. The location of the intervening sequence has in all cases been unambiguously determined by analysis of the intermediates in the splicing reaction. Secondary structures based upon the tRNA cloverleaf are shown for all the tRNA precursors and discussed with respect to common recognition by the yeast splicing endonuclease.     

Adaptive advantages of myrmecochory: the predator-avoidance hypothesis tested over a wide geographic range

The predator‐avoidance hypothesis states that once released from the parent plant, myrmecochorous seeds are rapidly taken by ants to their nests, where they are protected from predators. Previous studies conducted to test this hypothesis have frequently neglected two major aspects necessary for its verification: 1) the influence of processes acting after the seed release and 2) the spatial evenness of such processes. Thus, large‐scale variations in the mechanisms acting beyond seed release, and possibly influencing seed escape from predators, remain poorly documented. Here, we present the results of a post‐dispersal seed‐removal experiment on the myrmecochorous herb Helleborus foetidus, aimed at verifing the predator‐avoidance hypothesis by considering two key post‐release aspects of seed fate: seed destination (dispersed or nondispersed) and seed burial (buried or not buried). Experiments were performed in four different regions in the Iberian Peninsula. After three days of exposure of seeds to the main predator (fieldmice Apodemus sylvaticus), ca 30% of the seeds were removed. Seed destination affected the proportion of seeds escaping predation, but the sign, magnitude and statistical significance of the effect varied among the geographical regions. In the southern region (Cazorla), seeds dispersed in ant nests or intermediate destinations suffered scarcely any predation, but seeds under reproductive‐age plants experienced losses ca 50%. Conversely, in the northern region (Caurel), seeds in nests suffered significantly greater losses than seeds under plants or intermediate destinations, suggesting that nests were especially unsafe destinations. Seed burial had a strong impact on seed escape from predators, and its effect was highly consistent among geographical regions. In view of the consistency of its effect at different spatial scales, seed burial was a more general mechanism for predation avoidance than seed relocation to ant nests, which was habitat‐ and/or ant‐species‐dependent. Our results thus only partially support the predator‐avoidance hypothesis for the evolution of myrmecochory.