Larval Rana Catesbeiana Research Articles

Research Article: Foraging and prey handling behaviors of the generalist Thamnophis hammondii offered various prey types

Foraging success is critical to the survival of any predator. When encountering introduced prey species, predatory generalists often adapt more readily to the prey than do predatory specialists. The foraging and prey handling behaviors of Thamnophis hammondii offered three different prey types (Lepomis spp., larval Rana catesbeiana, and juvenile X. laevis) were examined. Durations of foraging and prey handling behaviors were analyzed to determine if these behaviors varied by snake gender, collection locality, or prey type. Differences in behavior type and duration as a function of gender or location were not detected. Snake behaviors varied between prey types, with differences in the duration of the following behaviors: time overland, cruising, margin wandering, midwater diving, prey-orienting underwater, and ingesting. Snakes successfully captured all prey types, with the highest attack and success rates when foraging for R. catesbeiana. The results indicate that T. hammondii exhibits a variable repertoire of foraging behaviors when presented various prey types. The generalist nature of this species may allow it to forage effectively for prey types that may be unavailable to other natricine snakes.

Functional morphology of feeding and gill irrigation in the anuran tadpole: electromyography and muscle function in larval Rana catesbeiana.

This study provides the first data on muscle activity patterns during active feeding in a larval anuran. Data regarding muscle function during gill irrigation and hyperexpiration are also provided. Electromyographic and kinematic data were recorded from six mandibular and hyoid muscles in unanesthetized, unrestrained larvae of Rana catesbeiana. Only three (hyoangularis, orbitohyoideus, anterior interhyoideus) of the six muscles examined are active during gill irrigation. Feeding cycles are characterized by the recruitment of three additional muscles: intermandibularis, suspensorioangularis, and levator mandibulae longus superficialis. The latter two contribute, respectively, to wide opening and forceful closing of the mouth during feeding. Hyperexpiration is characterized by a reversal of water flow anteriorly out of the mouth. This hydrodynamic change occurs due to modulation of the timing of firing of the anterior interhyoideus, as well as recruitment of the posterior interhyoideus, which is only active during hyperexpiration. Both regions of the interhyoideus, which are responsible for evacuation of the buccal cavity, are active during the opening phase of hyperexpiration. Kinematically, transitioning from gill irrigation to feeding involves both an overall shortening of the gape cycle and a shift in the relative length of opening phase vs. closing phase. Our results corroborate many of the findings of Gradwell ([1972] Can J Zool 50:501-521) regarding muscle function during gill irrigation and hyperexpiration. Furthermore, we demonstrate that in larval anurans the transition from gill irrigation to feeding involves modulation of gape cycle kinematics, changes in the level of activity of muscles, and recruitment of muscles that are not active during irrigation. In light of new data presented here, a review of muscle function in tadpoles is also provided.

Direct influence of melatonin on the thyroid and comparison with prolactin

Melatonin administered in vivo had previously been shown to inhibit thyroid cell proliferation and subsequent in vitro thyroxine (T(4)) secretion in anuran tadpoles. Melatonin in vitro also directly reduced the sensitivity of the thyroid to thyrotropin (TSH). The present work sought to determine whether melatonin directly affected baseline, unstimulated T(4) secretion, and to compare its effect with that of prolactin (PRL). Thyroids from larval Rana catesbeiana or adult Rana pipiens were incubated in control or melatonin (0.01 to 100 microg/ml) media. Melatonin directly inhibited T(4) secretion by thyroids from both tadpoles and frogs at all concentrations of melatonin used and at both prometamorphic and climax tadpole stages. PRL, used in vitro at 10 microg/ml, did not influence the response of the thyroid to TSH (0.2 microg/ml) in young tadpoles, or the baseline secretion of T(4) by thyroids at any stage of larval life except climax, when T(4) secretion was significantly decreased by the third day of culture. Thus although both melatonin and PRL have been shown to antagonize the action of T(4) in vitro, and to decrease metamorphic rate, melatonin is a much more effective thyroid gland inhibitor than PRL.

Jaw muscle development as evidence for embryonic repatterning in direct-developing frogs.

The Puerto Rican direct-developing frog Eleutherodactylus coqui (Leptodactylidae) displays a novel mode of jaw muscle development for anuran amphibians. Unlike metamorphosing species, several larval-specific features never form in E. coqui; embryonic muscle primordia initially assume an abbreviated, mid-metamorphic configuration that is soon remodelled to form the adult morphology before hatching. Also lacking are both the distinct population of larval myofibres and the conspicuous, larval-to-adult myofibre turnover that are characteristic of muscle development in metamorphosing species. These modifications are part of a comprehensive alteration in embryonic cranial patterning that has accompanied life history evolution in this highly speciose lineage. Embryonic 'repatterning' in Eleutherodactylus may reflect underlying developmental mechanisms that mediate the integrated evolution of complex structures. Such mechanisms may also facilitate, in organisms with a primitively complex life cycle, the evolutionary dissociation of embryonic, larval, and adult features.

Respiratory activity in the facial nucleus in an in vitro brainstem of tadpole, Rana catesbeiana.

1. In studies of the central neural control of breathing, little advantage has been taken of comparative approaches. We have developed an in vitro brainstem preparation using larval Rana catesbeiana which generates two rhythmic neural activities characteristic of lung and gill ventilation. Based on the pattern of the facial (VII) nerve activity both lung and gill rhythm-related respiratory cycles were divided into three distinct phases. The purpose of this study was to characterize and classify membrane potential trajectories of respiratory motoneurons in the VII nucleus at intermediate stages (XII-XVII) of development. 2. Seventy-five respiratory-modulated neurons were recorded intracellularly within the facial motor nucleus region. Their resting membrane potential was between -40 and -80 mV. Sixty of them were identified as VII motoneurons and fifteen were non-antidromically activated. Membrane potentials of fifty-six of the seventy-five neurons were modulated with both lung (5-27 mV) and gill rhythms (3-15 mV) and the remaining nineteen neurons had only a modulation with lung rhythmicity (6-23 mV). No cells with gill modulation alone were observed. 3. All of the cells modulated with lung rhythmicity had only phase-bound depolarizing or hyperpolarizing membrane potential swings which could be categorized into four distinct patterns. In contrast, of the fifty-six cells modulated with gill rhythmicity, thirty-two were phasically depolarized during distinct phases of the gill cycle (four patterns were distinguished), whereas the remaining twenty-four were phase spanning with two distinct patterns. The magnitudes of lung and gill modulations were proportionally related to each other in the cells modulated with both rhythms. 4. In all sixteen neurons studied, a reduction or a reversal of phasic inhibitory inputs during a portion of the lung or gill respiratory cycle was observed following a negative current or chloride ion (Cl-) injection. The phasic membrane resistance modulation in relation to the gill rhythm was analysed in six neurons and a relative decrease in the somatic membrane resistance (0.7-8.1 M omega) was detected during the periods of hyperpolarization. 5. We propose that, at these intermediate stages of development: (a) both gill and lung respiratory oscillations in motoneurons are generated by respiratory premotor neurons having only a few distinct activity patterns; (b) these patterns delineate distinct portions of the centrally generated respiratory cycles; and (c) phasic synaptic inhibition, mediated by Cl-, contributes to shaping the membrane potential trajectories of respiratory motoneurons.

Role of chloride-mediated inhibition in respiratory rhythmogenesis in an in vitro brainstem of tadpole, Rana catesbeiana.

1. The isolated brainstem of larval Rana catesbeiana maintained in vitro generates neural bursts that correspond to the lung and gill ventilatory activity generated in the intact specimen. To investigate the role of chloride channel-dependent inhibitory mechanisms mediated by GABA(A) and/or glycine receptors on fictive lung and gill ventilation, we superfused the isolated brainstems with agonists, antagonists (bicuculline and/or strychnine) or a chloride-free solution while recording multi-unit activity from the facial motor nucleus. 2. Superfusion with the agonists (GABA or glycine) produced differential effects on frequency, amplitude and duration of the neural bursts related to lung and gill ventilation. At a GABA or glycine concentration of 1.0 mM, fictive gill bursts were abolished while fictive lung bursts persisted, albeit with reduced amplitude and frequency. 3. At the lowest concentrations used (1.0-2.5 microM), the GABA(A) receptor antagonist bicuculline produced an increase in the frequency of lung bursts. At higher concentrations (5.0-2.0 microM) bicuculline produced non-specific excitatory effects. The glycine antagonist strychnine, at concentrations lower than 5.0 microM, caused a progressive decrease in the frequency and amplitude of the gill bursts and eventually abolished the rhythmic activity. At higher concentrations (7.5 microM), non-specific excitatory effects occurred. Superfusion with bicuculline (10 microM) and strychnine (5 microM) combined abolished the neural output for gill ventilation but increased the frequency, amplitude and duration of lung bursts. 4. Superfusion with Cl(-)-free solution also abolished the rhythmic neural bursts associated with gill ventilation, while it significantly increased the amplitude (228 +/- 51%; P < 0.05) (mean +/- S.E.M.) and duration of the lung bursts (3.5 +/- 0.1 to 35.3 +/- 3.7 s; P < 0.05) and improved the regularity of their occurrence. 5. We conclude that different neural systems generate rhythmic activity for lung and gill ventilation. Chloride-mediated inhibition may be essential for generation of neural bursts associated with gill ventilation. In contrast, the burst associated with lung ventilation can be generated in the absence of Cl(-)-mediated inhibition although the latter plays a role in shaping the normal lung burst.

Central arterial hemodynamics in larval bullfrogs (Rana catesbeiana): developmental and seasonal influences

Central arterial hemodynamics (blood pressure and velocity) as a function of ontogeny and season were determined in larval Rana catesbeiana (body mass 0.3-8.7 g, 20-22 degrees C). Ventricular systolic pressure increased from 1.8 mmHg at stage (St) II to 11.9 mmHg at St XIII, while ventricular diastolic pressures usually were less than 1.0 mmHg. In early stages (up to St V-VII) of fall/winter larvae, the pressure waveform in the conus arteriosus was often biphasic. The first peak was due to weak ventricular contraction (sometimes inadequate to eject blood into the arterial tree), and a stronger second peak resulted from conal contraction. In these young fall/winter larvae, the conus--not the ventricle--was the major circulatory pump. Older larvae (greater than St X) showed "adultlike" central hemodynamics, with the ventricle ejecting blood through the conus into the central arterial circulation. Systolic blood pressure was considerably higher in young spring/summer (April-June) larvae, and the ventricle rather than the conus was the main circulatory pump at all stages, in contrast to fall/winter larvae. Thus both season and development have profound influences on the central hemodynamics of bullfrog larvae.

Effects of Parentage and Competitor Phenology on the Growth of Larval Hyla Chrysoscelis

Larvae of four sibships (a 2 x 2 factorial cross) of Hyla chrysoscelis were raised in three competition regimens. These were competitors (larval Rana catesbeiana) absent, competitors introduced simultaneously with Hyla, and competitors introduced 11 d after Hyla. Hyla body mass at day 41 of growth was influenced by level of competition, timing of competitor introduction, and effects of male and female parent. Rana introduced simultaneously with Hyla reduced Hyla mass at day 41 more than did Rana introduced 11 d later. Female parentage affected body mass at day 41 additively. The effects of male parentage depended on the timing of competitor introduction: when Rana were introduced simultaneously with Hyla, offspring of male 2 were larger at day 41 than offspring of male 1. When Rana were introduced 11 d after Hyla, offspring of male 1 were larger at day 41 than offspring of male 2. This interaction between the effects of male parentage and timing of competitor introduction suggests that some genotypes may exhibit tradeoffs between maximum growth rate and competitive ability, and that phenological variation may lead to selection among genotypes in the natural population.

Lactate Production, Tissue Distribution, and Elimination following Exhaustive Exercise in Larval and Adult Bullfrogs Rana catesbeiana

The time course following exhaustive exercise of changes in lactate in blood, muscle, skin, kidney, urine, and branchial exhaled water in larval Rana catesbeiana, and in blood and muscle of adult R. catesbeiana, has been investigated. Tissue concentrations of pyruvate, lactate dehydrogenase (LDH) activity, and whole-animal V̇o2 and V̇co2 were also measured. Resting levels of blood and muscle lactate in tadpoles were not significantly different from those of adults. Muscle lactate concentrations, determined immediately following exhaustive exercise, were the same in tadpoles and adults and increased six times above resting levels in both forms. Blood lactate in adults was maximal within 1 min following exercise in adults but did not peak for 30 min in tadpoles. Blood lactate in tadpoles and adults returned to resting values 4 and 6 h, respectively, following exercise. The major difference between tadpoles and adults was thus the time course of blood lactate changes during recovery from exhaustive exercise. In tadpoles, 7% of total lactate produced during exercise was eliminated via the gills (80% of eliminated lactate), skin (13%), and urine (6%). Prevention of gill ventilation (responsible for less than one-half of total oxygen uptake) resulted in a 140% increase in blood and muscle lactate concentration during the first 2 h after exercise. Gill lactate elimination probably is important to acid-base regulation by tadpoles during recovery from exercise. The LDH activity in both larvae and adults can be summarized as follows: muscle ≫ kidney > liver ≫ heart ∼ lung. Muscle concentrations of pyruvic acid decreased following exercise in tadpoles and adults, even though blood pyruvate increased two times and remained elevated for more than 2 h. Pyruvate concentration of kidney and of whole-body homogenates of tadpoles increased two times and five times, respectively, immediately following exhaustive exercise. Low pyruvate and high LDH activity, conditions favoring reconversion of lactate to pyruvate, were thus most evident within the muscle itself. The rapid decrease in muscle lactate following exercise, which was not paralleled by an increase in blood lactate, suggests that reconversion of lactate to pyruvate may occur in muscle. Oxygen uptake remained significantly elevated after exercise for 10 h in tadpoles and 4 h in adults, partially reflecting O₂ consumed in the metabolism of lactate produced during the exercise bout. The respiratory quotient in both stages remained depressed for several hours after exercise, possibly because of acid-base imbalances incurred during and after exercise.

Nystatin studies of the skin of larval Rana catesbeiana.

Transport and electrical characteristics of the isolated skin of larval Rana catesbeiana were analyzed using ion substitution and nystatin. When the inner (IBS) and outer (OBS) bathing solutions contained Na Ringer solution the electrical potential (TEP), short-circuit current (SCC), and resistance (R2) were 23.5 +/- 7.0 mV, 2.8 +/- 0.7 microA . cm-2, and 8.00 +/- 0.74 k omega. cm2, respectively (n = 4). When K was substituted for Na in the OBS these values were not changed significantly. When nystatin (120 U.cm-3), a drug that increases the permeability of membranes to small cations, was added to the OBS (Na Ringer) there was a striking increase in the TEP to 52.8 +/- 3.1 mV, SCC to 14.8 +/- 2.0 microA . cm-2, and drop in R2 to 3.75 +/- 0.52 k omega . cm2. The response to nystatin was similar with Na or K Ringer solution in the OBS (Na Ringer in the IBS). With Na Ringer in the OBS and IBS, the increase in SCC induced by low doses of nystatin equaled net Na flux measured isotopically. Plots of transepithelial conductance against SCC after nystatin were linear and provided estimates of shunt resistance (R*sh = 14.6 +/- 1.3 k omega . cm2) and electromotive driving force for ions (E*A = 76 +/- 3 mV). Similar curves were obtained with K Ringer in the OBS. In the presence of nystatin, characteristics of the basolateral membrane were evaluated. It displayed selective permeability to K relative to Na or Tris.

Electrical and transport characteristics of skin of larval Rana catesbeiana

Carefully dissected, mounted, and bathed with Ringer solution, the larval bullfrog skin has a resistance of about 9,000 omega.cm2 and a stable transepithelial electrical potential of about 20 mV (inside +). A short-circuit current of about 2 microA.cm-2 is generated that is comparable in magnitude to the net inward flux of Na+. At open circuit the flux ratio equation for Na+ is not satisfied. Larval skin is less sensitive to ouabain, amiloride, and ADH than adult skin. The current-voltage (C-V) relationship across the preparation is not linear; there are distinct breaks in both the hyperpolarizing and hypopolarizing regions. The former break, at about +130 mV, corresponds with a break observed in adult skin that corresponds with ENa. The shunt resistance (RS) and active pathway resistance (RA) were estimated by C-V curve analysis and by ion substitution. The two methods yielded comparable values with RS about 11 k omega.cm2 and RA about 62 k omega.cm2. It is suggested that transport is limited by the number of entry sites for sodium at the apical border of transport cells.

Lymphoid changes during antibody synthesis in larval Rana catesbeiana.

AbstractThymectomy, splenectomy and/or lymphadenctomy affect antibody synthesis to a soluble antigen, hemocyanin, in bullfrog larvae. Tadpoles were divided into seven groups and these into three subgroups: Experimentals— A: operated and immunized by hemocyanin or allografts; Controls—B: operated but non‐immunized; Controls—C: one group unoperated and immunized. With regard to the spleen, good correlation between antibody titer and degree of splenic regeneration was observed. Structurally, the white pulp contained numerous small lymphocytes but in the red pulp, the number of blast cells and lymphocytes increased. The spleen may be the main organ involved in larval antibody synthesis. The lymph glands seem secondary; lymphadenectomized larvae showed no regeneration of lymph glands and antibody titers were lower than in sham‐operated controls. Compensatory hypertrophy of the remaining gland in unilaterally lymphadenectomized larvae was absent. With regard to cell types, lymph glands showed a picture similar to active nodules, i.e., the core of the cords consisted of blast cells and larger lymphocytes surrounded by layers of small lymphocytes. Thymic regeneration occurred in all tadpoles and, of much interest, titers were always highest in this previously thymectomized group. Observations on thymectomized tadpoles suggest a thymus stimulating effect on certain peripheral lymphoid organs, notably the spleen. The thymus in frog larvae may be important in antibody synthesis during later stages when the capacity to develop cellular immunity has already matured.

Adenosinetriphosphatase activity in gills of larval Rana catesbeiana.

Adenosinetriphosphatase activity in gills of larval Rana catesbeiana.

Lymphomyeloid organs of amphibia. II. Vasculature in larval and adult Rana catesbeiana.

AbstractThere were no lymphatic vessels and lymph nodes demonstrable in adult and larval Rana catesbeiana by a method that adequately demonstrated the same in mammals. Although the parenchymal arrangement in the lymphomyeloid organs is not exactly the same as in mammalian hemal nodes, nonetheless the vascular patterns of the lymph glands and jugular bodies are prima facie evidence that they function as blood‐filtering organs among other probable functions. The vascular pattern of the lymph gland is that of a rete mirabile, particularly a venous portal system, inasmuch as the afferent and efferent vessels are venous in character and interposed between them is a labyrinth of sinusoids. This is not the case, though, in the adult organs. The vascular pattern of the jugular bodies is very much like the spleen, viz., artery‐capillary‐sinusoid‐vein sequence. It is doubtful, however, if the propericardial and procoracoid bodies ever filter blood, because the smallest blood vessels in them are capillary in type Because of the absence of a well‐defined capsule in some parts of the propericardial body, similarly to lymphoid follicles, especially in the mammalian gastrointestinal tract, it is probable that it filters tissue fluid. The last two organs are apparently mainly blood cell‐forming organs. It is inferred from the vascular connections of the larval and the adult lymphomyeloid organs that they are not genetically related. This aspect was analyzed from earlier developmental data, but actual follow‐up of the larval organs to the adult stage is still in progress.