The reaction of tadpoles of the common toad (Bufo bufo L.) to chemical signals from individuals of their own and other species

In behavioral experiments, toad tadpoles-recipients chose between two parts of test aquarium with chemical signals of donor tadpoles of the same or different (Rana esculenta) species. The youngest studied tadpoles (43-45 stages) preferred the part of the aquarium with chemical cues from sibs as compared to non-sibs. No reliable difference in "non-sibs: water" system was observed. In "tadpoles of the same species: tadpoles of the other species" system, recipient tadpoles chose "their" part of the aquarium. Hence, toad tadpoles revealed a trend to aggregate with their sibs and avoid R. esculenta toads in the presence of certain chemical cues and in the absence of visual signals.     

Behavioral reactions of Bufo bufo L. tadpoles to chemical excretion of adult toads and changes during larval development

The reactions of toad (Bufo bufo L.) tadpoles to chemical excretes of adults were studied. In double-choice test aquarium tadpoles demonstrated avoidance reactions (swimming away from the place of stimulus delivering, reduction time of spent in stimulus part of aquarium and reduction of movement activity). Efficiency of stimulus reduced when its concentration decreased. The thresholds of tadpoles sensitivity estimated according to the reduction of time spent in stimulus part of aquarium decreased in onthogeny: they were near 500 x 10(-5) g hour/l at 36-39 developmental stages and 500 x 10(-4) g.hour/l at 40-41 stages.     

Sublethal effect of a weak intermittent magnetic field on the development of Xenopus laevis (Daudin) tadpoles

In three repeated experiments with three different litters of Xenopus laevis (Daudin) tadpoles, three cohorts were reared in an aquarium under the "saw-tooth" magnetic field produced by a television set. Their maturation times are compared with those of three corresponding control cohorts grown in an unexposed aquarium. In the exposed aquarium, the magnetic field amplitude was less than 25 T and the frequency in the extremely-low-frequency and very-low-frequency wavebands. Neither the exposed nor the unexposed cohorts suffered significant mortality and malformations. However, the exposed tadpoles took about 5 days more than the unexposed ones to reach metamorphosis. The differences in mean maturation times between the exposed and control cohorts were extremely significant (P < 0.001). The results show that a biological population can suffer a sublethal effect when exposed to the magnetic field of a TV set for a long time in the course of juvenile life stages, and that this effect can consist of a delay in reaching the adult stage.     

Effects of Sibship and the Presence of Multiple Predators on the Behavior of Green Frog (Rana clamitans) Tadpoles

In nature, prey are exposed to multiple predators simultaneously. We examined the effects of the cues of two potential predators, mosquitofish and odonate larvae, individually and in combination on the behavior of green frog (Rana clamitans) tadpoles. In addition to examining the behavioral response of green frog tadpoles to multiple predators, we examined variation in behavior among tadpoles from different egg masses (i.e. different sibships). Sibships differed in activity level and there was a significant predator cue by sibship interaction. Two sibships were relatively more active in the control and odonate predator cue treatments but showed reduced activity in treatments containing mosquitofish cues, whereas the remaining sibships showed consistently low levels of activity in all predator cue treatments, including the control. The use of the vegetated side of the aquarium did not differ between tadpoles exposed to the different predator cues. Sibship had no effect on tadpoles’ use of the vegetated side of the aquarium, and there was no interaction between sibship and predator cue. Our results suggest that green frogs did not respond to simultaneous exposure to multiple predator cues any differently than they did to exposure to individual predator cues. More importantly, our results suggest variation, possibly genetically based, in behavioral responses of tadpoles to predators, and thus selection on these behaviors is possible. Of particular interest is that there was variation in behavioral responses to a non‐native predator (Gambusia affinis), suggesting an evolutionary response to an invasive predator is possible.     

Ontogeny of corticotropin-releasing factor effects on locomotion and foraging in the Western spadefoot toad (Spea hammondii)

We investigated the effects of corticotropin-releasing factor (CRF) and corticosterone (CORT) on foraging and locomotion in Western spadefoot toad (Spea hammondii) tadpoles and juveniles to assess the behavioral functions of these hormones throughout development. We administered intracerebroventricular injections of ovine CRF or CRF receptor antagonist alphahelical CRF((9-41)) to tadpoles and juveniles, and observed behavior within 1.5 h after injection. In both premetamorphic (Gosner stage 33) and prometamorphic (Gosner stages 35-37) tadpoles, CRF injections increased locomotion and decreased foraging. Injections of alphahelical CRF((9-41)) reduced locomotion but did not affect foraging in premetamorphic tadpoles, but dramatically increased foraging in prometamorphic tadpoles compared to both placebo and uninjected controls. Similarly, alphahelical CRF((9-41)) injections stimulated food intake and prey-catching behavior in juveniles. These results suggest that in later-staged amphibians, endogenous CRF secretion modulates feeding by exerting a suppressive effect on appetite. By contrast to the inhibitory effect of CRF, 3-h exposure to CORT (500 nM added to the aquarium water) stimulated foraging in prometamorphic tadpoles. These tadpoles also exhibited a CORT-mediated increase in foraging 6 h after CRF injection, which was associated with elevated whole-body CORT content and blocked by glucocorticoid receptor (GR) antagonist (RU486) injections. Thus, exogenous CRF influences locomotion and foraging in both pre- and prometamorphic tadpoles, but endogenous CRF secretion in relatively unstressed animals does not affect foraging until prometamorphic stages. Furthermore, the opposing actions of CRF and CORT on foraging suggest that they are important regulators of energy balance and food intake in amphibians throughout development.     

Predaceous diving beetle, Dytiscus sharpi sharpi (Coleoptera: Dytiscidae) larvae avoid cannibalism by recognizing prey

Larvae of diving beetles such as the various Dytiscus species (Coleoptera: Dytiscidae) are carnivorous and usually prey on other aquatic animals. Cannibalism among larvae of Dytiscus sharpi sharpi (Wehncke) was observed to begin when they were starved for more than two days under artificial breeding conditions. However, the 2-day starved larvae did not show cannibalism in the presence of intact, motionless, frozen tadpoles, or frozen shrimps. The beetle larvae attacked and captured intact tadpoles faster (15 sec) than other motionless and frozen tadpoles (120 sec), indicating that prey movement was an important factor in stimulating feeding behavior in larvae. Prey density does not have an effect on larval cannibalism. In cases in which preys are present at lower densities than that of larvae, a group of beetle larvae frequently fed on single prey. This feeding behavior, therefore, provides direct evidence of self-other recognition at the species level. Using two traps in one aquarium that allows the larvae to detect only prey smell, one containing tadpoles and another empty, the beetle larvae were attracted to the trap with tadpoles at high frequency, but not to the empty trap. In another experiment, the beetle larvae were not attracted to the trap containing a beetle larva. These results suggest that the larvae of D. sharpi sharpi are capable of recognizing prey scent, which enables the promotion of foraging behavior and the prevention of cannibalism.     

The Ability of Three Species of Tadpoles to Differentiate among Potential Fish Predators

The ability of prey to respond to novel predator cues may depend on the generality or specificity of the response to predator cues. We used laboratory behavioral experiments to examine the ability of tadpoles of three species of anurans (American toad, Bufo americanus ; bullfrog, Rana catesbeiana ; and green frog, R. clamitans ) to respond to the presence of two native potential predators (bluegill, Lepomis macrochirus ; and largemouth bass, Micropterus salmoides ) and one non-native potential predator (goldfish, Carassius auratus ). We also examined the effect of tadpole size on the behavioral responses of American toads and green frogs to predator cues. All three species of tadpoles responded to the presence of predator cues, although the specific responses varied among species. American toads and green frogs reduced activity in the presence of at least some fish cues, but bullfrog tadpoles did not change their activity. Bullfrogs decreased use of vegetation in the presence of some predator cues, whereas American toads and green frogs did not. American toads only responded to the presence of bluegill cues but not the other fish predator cues, whereas bullfrogs and green frogs responded more generally to the fish predators. In both American toads and green frogs, tadpole size affected behavior. For American toads, activity increased, as did the use of the vegetated side of the aquarium, in larger tadpoles. Not only did size affect American toad behavior, but it also influenced the responses of the tadpoles to predator cues. For green frogs, activity decreased in larger tadpoles. Our results suggest that behavioral responses of tadpoles to predator cues can be influenced by both the identity of the predator and the prey, as well as the size of the potential prey.     

A model for the crowding effect in the growth of tadpoles

Crowded tadpoles in a limited volume grow to divide into two groups, a normally growing group and a stunted group, even if there are a plenty of food. This phenomenon was found to be interpreted by a model involving a mutual inhibition of the growth among individuals. It was assumed that the growth curve of an individual was modelled by a Gompertz growth equation. Through mathematical analysis and computer simulation of the model, it was shown that the average growth rate of the group was a decreasing function of the population density and that the group segregated into two subgroups, a normally growing group and a stunted group in a certain range of density. A theoretical prospect that the population of normally growing group is proportionate to the volume of the aquarium was obtained.     

Maternally derived chemical defences are an effective deterrent against some predators of poison frog tadpoles (Oophaga pumilio)

Parents defend their young in many ways, including provisioning chemical defences. Recent work in a poison frog system offers the first example of an animal that provisions its young with alkaloids after hatching or birth rather than before. But it is not yet known whether maternally derived alkaloids are an effective defence against offspring predators. We identified the predators of Oophaga pumilio tadpoles and conducted laboratory and field choice tests to determine whether predators are deterred by alkaloids in tadpoles. We found that snakes, spiders and beetle larvae are common predators of O. pumilio tadpoles. Snakes were not deterred by alkaloids in tadpoles. However, spiders were less likely to consume mother-fed O. pumilio tadpoles than either alkaloid-free tadpoles of the red-eyed treefrog, Agalychnis callidryas, or alkaloid-free O. pumilio tadpoles that had been hand-fed with A. callidryas eggs. Thus, maternally derived alkaloids reduce the risk of predation for tadpoles, but only against some predators.     

Cultivating Lithoglyphopsis aperta Temcharoen, a new snail host for Schistosoma japonicum, Mekong strain.

Lithoglyphopsis aperta Temcharoen, a new intermediate host for Schistosoma japonicum, Mekong strain, was cultivated successfully through the F2 generation with the use of a petri dish aquarium provided with mud and alga. The incubation period of eggs was about 4 weeks; the young grew to maturity in 16 to 20 weeks; egg-laying followed about 6 to 8 weeks later, the cycle taking roughly 6 months. The husked eggs were deposited exclusively at the edge and wall of the aquarium. Eggs were hemispherical and with the husks were between 0.37 and 0.43 mm in diameter. The newly hatched young were only 0.24 mm in shell length and the full-grown snails were 3.11 to 3.36 mm long. Logarithmic growth began between the 12th and 14th weeks.     

Isolation of salmonellae and other potential pathogens from the freshwater aquarium snail Ampullaria.

The freshwater aquarium snail (Ampullaria spp.) was demonstrated to carry as many as 10(8) viable mesophilic bacteria per g of meat plus shell. Some 16 genera of bacteria were identified, with gram negatives predominating. Enrichment culture techniques enabled the isolation of salmonellae from 24 to 42 lots of 200 g each. The salmonellae comprised eight different serotypes, including Salmonella newport, Salmonella saint-paul, and Salmonella infantis. This association of salmonellae with snails may contribute to cases of human salmonellosis, since other aquarium species have already been shown to contribute to many such cases. The snails were also found to commonly harbor Pseudomonas aeruginosa and, occasionally, Edwardsiella tarda.     

Spatially heterogeneous selection in nature favors phenotypic plasticity in anuran larvae

Theory holds that adaptive phenotypic plasticity evolves under spatial or temporal variation in natural selection. I tested this prediction in a classic system of predator‐induced plasticity: frog tadpoles (Rana temporaria) reacting to predaceous aquatic insects. An outdoor mesocosm experiment manipulating exposure to Aeshna dragonfly larvae revealed plasticity in most characters: growth, development, behavior, and external morphology. I measured selection by placing 1927 tadpoles into enclosures within natural ponds; photographs permitted identification of the survivors six to nine days later. Fitness was defined as a linear combination of growth, development, and survival that correlates with survival to age 2 in another anuran species. In enclosures with many predators, selection‐favored character values similar to those induced by exposure to Aeshna in mesocosms. The shift in selection along the predation gradient was strongest for characters that exhibited high predator‐induced plasticity. A field survey of 50 ponds revealed that predator density changes over a spatial scale relevant for movement of individual adults and larvae: 17% of variation in predation risk was among ponds separated by tens to thousands of meters and 81% was among sites ≤10 m apart within ponds. These results on heterogeneity in the selection regime confirm a key tenant of the standard model for the evolution of plasticity.     

The "third eye"-- a new concept of trans-differentiation of pineal gland into median eye in amphibian tadpoles of Bufo melanostictus

Median third eye was found to develop from transplanted pineal gland of external gill stage tadpoles in the recipient 5 toe stage tadpoles of Bufo melanostictus. Pineal gland along with a bit part of brain tissue of the donor external gill stage tadpole was cut out and transplanted into a pit made between two lateral eyes of 5 toe stage recipient tadpoles. Half of the operated tadpoles were treated with vitamin A (15 IU/ml.) for 15 days. Median "third eye" was found to develop in the both untreated and vitamin A treated tadpoles. However, vitamin A increased the percentage of the development of median eyes. Morphological and histological study revealed that newly transformed median eyes were similar to that of normal functional eyes. A stalk like structure developed which connects the median eye to the brain. The median third eye could not develop when pineal gland of 5 toe stage mature tadpole was transplanted into the tadpole of the same age.     

Vitamin A-Mediated Homeotic Transformation of Tail to Limbs, Limb Suppression and Abnormal Tail Regeneration in the Indian Jumping Frog Polypedates maculatus

In this study the effects of vitamin A on tadpoles of Polypedates maculatus with an amputated tail were investigated. After amputation of half the tail at the hindlimb-bud stage, tadpoles were exposed to vitamin A (palmitate) 10 IU/ml solution for 24 hr (Group I), 48 hr (II), 72 hr (III), 96 hr (IV), 120 hr (V) or 144 hr (VI). Vitamin A was deleterious to survival of the tadpoles since 10, 30 and 30% tadpoles died from Group IV, V and VI, respectively before the emergence of forelimbs. Regeneration of the tail was abnormal in 91.7% of the tadpoles. Vitamin A induced homeotic transformation of the amputated tail to hindlimbs in 11.6% of the animals. Normal limb development was suppressed partially or completely in 48.3% tadpoles. These results indicate that in addition to traumatic effects, vitamin A can lead to homeotic transformation of the tail into hindlimbs and can also interfere with normal development of limbs.     

Resistance to shell breaking in two intertidal snails

The ability of shells to withstand shell breaking forces has been examined in two intertidal prosobranchs, Nucella lapillus and Littorina littorea , using four methods: measuring shell strength on a compressive testing machine, measuring the shell to body mass ratio, measuring the shell thickness and measuring the ability of crabs to break shells in aquarium experiments. Nucella lapillus consistently showed a relationship between shell vulnerability and environmental variables: the shells were easier to break at sites where rock and boulder movement was the least. Although some between-site differences were found in L. littorea shells, these were less than in N. lapillus and did not relate to environment variables: the shells were easier to break at sites where exposure to wave action was the least. Although some between-site differences were found in L. littorea shells , these were less than in N. lapillus and did not relate to environmental factors. However, both species appear to grow into a size refuge in which they are secure from predation by shore crabs at the sites where these crabs are commonest.     

黑斑侧褶蛙蝌蚪断尾后的补偿生长和发育研究

动物在经历不利的生长条件或环境后往往出现补偿生长。研究了黑斑侧褶蛙(Pelophylax nigromaculatus)蝌蚪经历来自食蚊鱼(Gambusia affinis)捕食造成断尾损伤后的补偿生长模式、断尾损失对蝌蚪游泳能力以及变态时间与大小的影响。结果表明,经历捕食压力后,全尾组和1/3断尾组蝌蚪的体长显著大于1/2断尾组蝌蚪的体长,全尾组和1/3断尾组之间的蝌蚪体长差异不显著;第19天时,1/2断尾组蝌蚪经过补偿生长后体长显著大于全尾组蝌蚪,1/3断尾组与全尾组和1/2断尾组之间的蝌蚪体长差异均不显著;三个实验组之间蝌蚪尾长差异不显著;全尾组蝌蚪的疾游速显著大于1/2断尾组蝌蚪的疾游速,1/3断尾组蝌蚪的疾游速与全尾组和1/2断尾组之间差异不显著,表明严重断尾对蝌蚪疾游速产生了消极影响。三个实验组蝌蚪的变态时间和变态前后形态差异均不显著。黑斑侧褶蛙蝌蚪能够在变态前调整生长轨迹补偿早期捕食风险造成的生长损失,断尾损失并不影响变态时间与大小,断尾超过一半的蝌蚪经过补偿生长后仍要付出一定的运动代价。     

Oxidative stress during vitamin A-induced abnormal tail regeneration in the tadpoles of Polypedates maculatus

Vitamin A and its derivatives inhibit normal tail regeneration in amphibians. The most remarkable effect is the development of limbs at the cut end of the tail in anurans. Prior to ectopic limb development, there is an abnormal tail regeneration in the treated tadpoles. The purpose of the present study was to compare oxidative stress condition in the regenerated tail of normal and vitamin A (10I U/ml, 72 h) treated tadpoles. The present findings show a hyper-oxidative stress condition in the regenerated tail of the vitamin A-treated tadpoles of the Indian jumping frog, Polypedates maculatus (Anura: Rhacophoridae).     

Background to work on retinoids and amphibian limb regeneration: Studies on anuran tadpoles—a retrospect

Studies on the effects of exogenous vitamin A palminate on limb development and regeneration in anuran tadpoles carried out since late 1960s at the author’s laboratory are reviewed and discussed. Most significant was the initial discovery that vitamin A causes regeneration of complete or nearly complete limbs instead of only the missing distal part, thus altering the P-D pattern of regeneration—a phenomenon now called proximalization. Often more than one such regenerates develop per stump. Vitamin A produces proximalizing effect on regeneration cells during their dedifferentiation and blastema formation but inhibits regeneration if given once redifferentiation begins. Shank-level blastemas from treated tadpoles grafted into orbits of previously treated/untreated host tadpoles formed complete limbs. Proximalizing effect is proportionate to vitamin A concentration, duration of treatment, amputational level and stage of tadpoles. Vitamin A produces this effect also if given only prior to amputation. Its influence persists after cessation of treatment, declining with time. Proximalizing effect is correlated with natural ability in limbs to regenerate. Vitamin A improves regenerative ability and can induce it to some extent in non-regenerating limbs. Vitamin A excess retards limb development and produces stage dependent teratogenic defects. Further development of only that limb region is prevented in which differentiation is beginning when vitamin A is given. Short treatment of tadpoles beginning with limbs at spatula/paddle stage inhibited foot development in the unoperated limbs hut promoted regeneration of complete limbs from the contra-lateral amputated limbs. These dual effects were due to cells of the former differentiating and of the latter dedifferentiating when exposed to vitamin A palmitate.     

Nitrate removal in aquariums by immobilized pseudomonas

Biological denitrification of nitrate to nitrogen gas was examined in a freshwater and a marine aquarium. Nitrate removal in the aquarium water was accomplished with denitrifiers immobilized in a freeze-dried, alginate-starch matrix. Starch served as a bacterial carbon source and cellular matrix-strengthening filler. Freeze-dried beads were placed in canisters through which nitrate-rich aquarium water was recirculated. The freshwater aquarium (100 L) contained goldfish (Carassius auratus) at a total biomass of 390 g, whereas cichlids (Oreochromis mossambicus) were kept at a similar stocking density in the marine aquarium. Denitrification resulted in low ambient nitrate concentrations in both aquariums. The specific nitrate removal rate of the freshwater beads was significantly higher (50 microg of NO(3)-N/bead/day) than that of seawater beads (5 microg of NO(3)-N/bead/day). Differences in ambient nitrate concentrations between both aquariums and diffusion limitation of nitrate to the active denitrification sites within the beads might explain these observed differences.     

Further notes on the natural history of the South American pepper frog, Leptodactylus labyrinthicus (Spix, 1824) (Anura, Leptodactylidae)

Leptodactylus labyrinthicus tadpoles reach a large size in the nest through consumption of trophic eggs. We previously suggested that the trophic eggs are laid just after amplexus has finished, but our new data do not support this hypothesis. We also present further details on the natural history of the species with regard to breeding activity, spawning site, retreats and the ability of tadpoles in preying upon fully-growth heterospecific tadpoles. We also show that the tadpoles are mainly nocturnal and take diurnal refuges. We collected the data in Brazil in three localities within the Cerrado Biome. We examined burrows used by L. labyrinthicus males, verified if females still contained mature eggs just after released from amplexus, and tested the ability of tadpoles in preying fully-growth heterospecific tadpoles. Field observations and experiments were conducted on tadpole activity time, hiding behaviour and level of susceptibility to predation by the bird leaf-scrapers in four sheltering situations. Reproduction could start before the first rains; this may be advantageous by allowing the tadpoles to exploit eggs of other frogs. We found one floating nest built in a temporary pool. The nest of the species is normally circumscribed in an excavated basin beside the water body. Adult males were found during the day with their head-out of the entrance of underwater burrows, which were perforations through dense root mats beside calling/spawning sites. Probably, these burrows in permanently water-filled soil are actively excavated by males. Females released all their eggs during the amplexus, so trophic eggs are not produced by the currently-accepted mechanism. Fully-grown heterospecific tadpoles were not preyed upon by L. labyrinthicus tadpoles, which can prey only slow-moving newly hatched ones. Field tadpoles took shelter under mud/dead leaves during daylight and became exposed on the bottom at night. Free-ranging leaf-scrapers removed dead leaves from a pool with their beaks and preyed upon tadpoles. In the experiments, the tadpoles sheltered under gravel/leaves during daylight, but they were exposed at night. Leaf-scrapers ate all exposed tadpoles, but no tadpole of the gravel/leaves trays was consumed. Hence the nocturnal habits and use of diurnal refuges may protect the tadpoles from visual predators, such as the leaf-scrapers.