Rana Sphenocephala Research Articles

The Maintenance of Phenotypic Plasticity as a Signal Detection Problem

The Maintenance of Phenotypic Plasticity as a Signal Detection Problem

Adaptive, Chemically Mediated Fright Response in Tadpoles of the Southern Leopard Frog, Rana utricularia

breeding success (e.g., Smith, 1987; Berven, 1988). However, foraging may also lead to increased susceptibility to predation. Selective pressures therefore may exist for larvae to balance conflicts between maximizing food intake and minimizing exposure to predators. Furthermore, defenses appropriate for certain predators may be maladaptive for others. For example, reducing movement may decrease detection by visually or pressure-oriented predators (Skelly, 1994), whereas fleeing may be more appropriate for tactile-oriented predators. One way that amphibian larvae may detect predators is through chemical cues given off by predators or injured conspecifics (Petranka et al., 1987; Kats et al., 1988; Lefcort and Eiger, 1993). For example, Kats (1988) found that salamander larvae, (Ambystoma texanum), increased refuge use when exposed to chemical cues from a predacious fish. Similarly, boreal toad larvae (Bufo boreas) avoided areas where giant water bugs (Lethocerus americanus) had recently fed on tadpole conspecifics. Aquatic vertebrates often alter their behavior when exposed to such chemicals, especially in murky water where visual cues are less useful (e.g., von Frisch, 1941; Magurran, 1989; Chivers and Smith, 1993). Rather than reacting to background levels of all potential predators, some tadpoles only respond to predators that have fed on conspecifics. Tadpoles of Rana aurora exhibit a fright response (i.e., they reduce their activity levels) only when exposed to chemical cues from predatory newts (Taricha granulosa) that have fed on R. aurora tadpoles or to an extract of crushed tadpoles (Wilson and Lefcort, 1993). The tadpoles may be reacting to metabolites and undigested parts of prey in the predator's urine and feces.

Responses of amphibian populations to water and soil factors in experimentally-treated aquatic macrocosms

Survival of anuran embryos and tadpoles is reduced in acidic (pH<5.0) waters under laboratory conditions. However, field data on the presence-absence of amphibian species and acidity are equivocal. This study attempts to reconcile some of this discrepancy by using macrocosms to examine the interaction of soil type and water acidification on free-ranging tadpole populations. Tadpoles were caught with activity traps in 24 aquatic macrocosms experimentally treated with H2SO4 and Al2(SO4)3 and lined with either comparatively high metal, low organic matter clay soils or lower metal, higher organic matter loams. Northern cricket frog (Acris crepitans) tadpole abundance was less in acidified macrocosms than in circumneutral ones (p<0.05) and less in those with loam soils than in macrocosms with clay soils (p<0.04). Gray treefrog (Hyla versicolor) abundance was affected by an interaction between soil and acidification (p<0.07) in that treatment effects were only observed in macrocosms with clay soils (p<0.01). No differences were observed among treatments for green frog (Rana clamitans) or southern leopard frog (R. utricularia) tadpoles. The study shows that soil type may interact with water conditions to affect amphibian populations in acidified waters.

Competition, pH, and the Ecology of Larval Hyla Andersonii

I investigated the effects of an abiotic factor, pH, and a biotic factor, interspecific competition, on breeding success in a low—pH tolerant anuran, Hyla andersonii. I tested whether low pH would indirectly facilitate H. andersonii by lessening the impact of competition from two less acid—tolerant species. I also tested whether the competitive effect of an allotopic, closely related species (Hyla versicolor) would be greater than that of a syntopic, more distantly related species (Rana sphenocephala). I exposed H. andersonii tadpoles to two levels of pH (3.9, ambient) and three levels of competition (H. versicolor, R. sphenocephala, and none). Reduced pH had no direct effect on any of the species and did not influence the outcome of interspecific competition. from R. sphenocephala decreased survival and mass of H. andersonii, whereas competition from H. versicolor only decreased mass, without affecting survival of H. andersonii. These results suggest that some other correlate of low pH in natural ponds limits H. andersonii to acidic ponds. Further, the assumptions that co—occurrence or level of relatedness can be used as a gauge of competitive strength are shown to be unreliable.

Prostaglandin regulation of H+ secretion in amphibian epithelia

The role of prostaglandins in regulating H+ excretion in amphibian epithelia was investigated. The abdominal skin of the southern leopard frog Rana pipiens and the urinary bladder of the toad Bufo marinus were used to measure proton excretion across their mucosal surface. Prostaglandin F2 alpha (PGF2 alpha) produced a dose-dependent inhibition of H+ excretion across the frog skin. Frogs pretreated with ibuprofen (30 mg.kg-1.day-1 for 3 days) showed an enhanced proton excretion similar to that observed when frogs are placed in chronic metabolic acidosis. The number of mitochondria-rich cells, the cells responsible for proton excretion, was also increased in frog skins after chronic metabolic acidosis or ibuprofen treatment. Mezerein and the phorbol ester 4 beta-phorbol 12-myristate 13-acetate (4 beta-PMA), activators of protein kinase C (PCK), decreased H+ excretion in frog skin, whereas the inactive phorbol 4 alpha-PMA was without an effect. The inhibition of proton excretion was similar to that observed with PGF2 alpha and suggested that the effects of PGF2 alpha and activation of PKC were mediated through a common pathway. Frogs pretreated with ibuprofen not only had an enhanced proton excretion rate but also had a decrease in cytosolic PKC activity. In another amphibian tissue, the toad urinary bladder, PGE2 inhibited proton excretion at low doses but enhanced H+ excretion at higher doses. Toads maintained under chronic metabolic acidosis had enhanced proton excretion rates and also had a threefold increase in cellular PGE2 concentration, which was consistent with the observation that PGE2 enhanced proton excretion at high doses.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptive changes of H + secreting cells in the epidermis of the leopard frog RANA PIPIENS

1. Mitochondria-rich (MR) cells in the integument of the southern leopard frog, Rana pipiens, berlandieri, were stained with AgNO 3 under a variety of environmental and metabolic treatment conditions known to increase H + excretion rates across the skin. In this tissue AgNO 3 proved to be a good stain for discriminating the MR cell populations from the granular cells. 2. High salinity adapted southern frogs showed no change in the MR cell population. The inability of the MR cell number to significantly increase suggested that the increased H + excretion rates previously seen in these animals were not due to increased MR cell proliferation. 3. The MR cell population was found to increase in the NaNO 3 adapted frogs, demonstrating the contribution of altered extracellular Cl − concentrations on the regulation of MR cell density. 4. Animals that were placed in chronic metabolic acidosis or pre-treated with ibuprofen demonstrated an increased MR cell population. The current observations are consistent with previous findings that these treatment regimes increase H + excretion, suggesting that one of the cellular adaptive mechanisms responsible for increasing H + excretion involves increasing the MR cell density. 5. The results further suggest that prostaglandins may play a role in regulating H + excretion in MR cells, and that either changes in intracellular pH or prostaglandin formation regulates cell proliferation.

A Comparative Study of Heating Rates in Arboreal and Nonarboreal Frogs

Heating rates and time constants of heating were determined for similarly sized green tree frogs, Hyla cinerea, and southern leopard frogs, Rana sphenocephala exposed to step changes in ambient temperature from 15 to 30?C. Whereas the initial body temperatures were not significantly different (15?C), equilibration body temperatures were significantly higher in H. cinerea (26.6?C) than in R. sphenocephala (18.1?C). Rates of temperature change were 2.5 x higher in H. cinerea and are explained by the presence of reduced cutaneous evaporative heat loss in this species. The thermal time constant is inappropriate for interspecific comparisons of heating in anurans. lo , ol. 23, No. 2, pp. 141-145, 1989 ciet for the Study of Amphibians and Reptiles of eating Rates in a oreal Frogs During the nearly twenty years since reduced cutaneous evaporative water loss (CWL) was first reported in an arboreal frog (Loveridge, 1970), some degree of waterproofing has been found to be present among species belonging to at least nine tree frog genera (see Wygoda, 1988b). Because anuran hydroand thermoregulation are closely linked (Tracy, 1976; Bundy and Tracy, 1977; Beuchet et al., 1984), profound differences in thermoregulatory strategies are expected to be present between these frogs and non-waterproof frogs. However, little is known of the thermal consequences of CWL reduction because, with few exceptions (McClanahan et al., 1978; Wygoda, 1984, 1988a, b; Shoemaker et al., 1987), simultaneous water loss and body temperature measurements have not been performed. It is known that body temperatures (Tbs) of waterproof arboreal frogs approximate air temperature (Ta) up to around 40?C (Shoemaker et al., 1987), but remain constant when Ta is further increased (McClanahan et al., 1978; Shoemaker et al., 1987). TbS of non-thermally stressed moderately waterproof arboreal frogs are intermediate between Ta and the Tb of nonwaterproof frogs (Wygoda, 1984) and are less coupled to relative humidity (RH) changes than are those of non-waterproof frogs (Wygoda, 1988b). In addition to providing elevated Tbs, rel., 1987), simultaneous water loss and body e perature measurements have not b e perormed. It is known that body temperatures (Tbs) f waterproof arbo eal frogs approximate air e perature (Ta) up to around 40?C (Shoemaker t al., 1987), but remain constant whe Ta is 141 This content downloaded from 40.77.167.54 on Thu, 06 Oct 2016 04:20:27 UTC All use subject to http://about.jstor.org/terms

Role of sodium on H + excretion in the integument of the leopard frog Rana pipiens

1. 1. The northern leopard frog, Rana pipiens, pipiens, in contrast to the southern leopard frog, Rana pipiens, berlandieri, did not demonstrate any significant H + excretion across its integument even during a challenge of chronic metabolic acidosis. Likewise, no increase in the number of H + secreting mitochondria-rich cells were observed in the northern frogs. 2. 2. Under normal acid-base conditions in the southern frogs, H + excretion was found to be dependent on mucosal sodium concentrations, whereas during chronic metabolic acidosis, H + excretion was independent of mucosal sodium concentrations, but was amiloride sensitive. 3. 3. High salinity adapted southern frogs, under normal and acidotic conditions, had enhanced H4 + excretion rates as compared to the control non-salt adapted frogs. 4. 4. Blood analyses demonstrated that significant acid-base changes were the result of systemic acidosis and not due to salt adaptations. Blood Na + and K + concentrations were also efficiently maintained during salt adaptations or chronic metabolic acidosis. 5. 5. The results suggest that H + excretion in epithelia can be influenced by the sodium transport state of the cell and the systemic acid-base profile. Models are proposed explaining these relationships.

Selection of Egg Deposition Sites: A Seasonal Shift in the Southern Leopard Frog, Rana sphenocephala

Selection of Egg Deposition Sites: A Seasonal Shift in the Southern Leopard Frog, Rana sphenocephala

Priority Effects in Experimental Pond Communities: Responses of Hyla to Bufo and Rana

The timing of hatching of two early spring breeding frogs, Rana sphenocephala and Bufo americanus, was controlled in a 3 x 3 factorial experiment (each species introduced early, introduced late, or not present) in a randomized block design replicated three times in an array of 27 experimental ponds. After nearly all Bufo had metamorphosed and left the ponds, but before Rana began metamorphosis, 500 hatchlings of a summer—breeding species, Hyla chrysoscelis, were added to each of the 27 ponds and to 3 more ponds that had recently been filled. Hyla had a higher survival rate, shorter mean larval period, and larger mean size at metamorphosis in the newly filled ponds than in any other treatment. The older ponds without either spring species were the next best habitat. These “old” controls were used to assay the effects of the spring—breeding species on Hyla. Bufo had a significantly adverse effect on Hyla even though the two species were not contemporaneous, this was interpreted as being due to an impact by Bufo on the trophic structure of the ponds, an impact that persisted throughout the summer. Rana had an even stronger negative effect on Hyla than did Bufo. The 2 x 2 subset of treatments consisting of Hyla with early or late Rana and early or late Bufo was analyzed separately. The combination of late Rana and late Bufo had the strongest adverse effect on Hyla and the other three combinations were about equal in their effects. These experiments demonstrate the advantages to anurans of ovipositing soon after pond filling and of colonizing ponds that have not been used previously in the season by other species. The detection of historical effect reveals that our experimental communities were not governed by stationary first—order Markov processes and that perturbations had persistent effects on their trajectories. Our results suggest that optimal seasonal patterns for reproduction exist in animals with complex life cycles that exploit temporary habitats.

Priority Effects in Experimental Pond Communities: Competition between Bufo and Rana

The effect of order to hatching on the outcome of larval competition between two species of frogs breeding in 27 artificial ponds was studied. There were nine different treatments, each replicated three times: all combinations of various introductions of Bufo americanus hatchlings (none added, 500 added on day 0, or 500 added on day 6) and various introductions of Rana sphenocephala hatchlings (none added, 100 added on day 0, or 100 added on day 6). Response variables were the body size at metamorphosis, the length of the larval period of each individual, and the number of survivors of each species in each experimental pond. Bufo individuals and populations did best when alone. Also, they did better when introduced on day 6 rather than day 0. This may have been because the standing crop of food was greater in the communities that were 6 d older. When present with Rana, Bufo did better if added before Rana and worse if added after Rana, as compared to when both species were added at the same time. These results are consistent with a mechanism of size—specific competition. Rana also did best when alone and when introduced late rather than early. Rana did better when added after Bufo and worse when added before Bufo as compared to when both species were introduced at the same time. These results are not consistent with simple size—specific competition. When the species were together, both species did best when Bufo was added early and Rana was added late. These results suggest that optimal oviposition behavior is problematical for female frogs: the time that will be best depends on whether or not another species will be present at the time of hatching.

Ontogeny of Temperature Selection in Larval Amphibians

Ontogenetic shifts in final temperature preferenda were examined in larvae of four amphibian species. The mean thermal preference of all species increased with developmental stage and peaked at or shortly before metamorphic climax. Two ontogenetic patterns of thermal selection were observed. Pseudacris triseriata and Rana sphenocephala showed weak thermal preferences during the early to mid larval period, but strong preferences thereafter. In contrast, Bufo americanus and Ambystoma texanum showed strong thermal preferences during all developmental stages. Ontogenetic shifts in preferred temperature may promote segregation of size classes within breeding habitats, thus reducing competition or cannibalism. Use of warmer microhabitats with age accelerates development at the end of the larval period when larvae become increasingly susceptible to habitat deterioration and predation. Developmental constraints may limit the effectiveness of thermoregulation in early developmental stages of certain species.

Inhibition of neurotoxic esterase and acetylcholinesterase by organophosphorus compounds in selected ectothermic vertebrates

The sensitivity of brain acetylcholinesterase and neurotoxic esterase to inhibition by several organophosphorus compounds was studied in selected ectothermic vertebrates. These enzymes are associated with organophosphorus compound acute and delayed toxicity, respectively. In addition, the susceptibility of several of these species to delayed neurotoxicity induced by organophosphorus compounds was studied. Larvae of the gray treefrog, Southern leopard frog, and narrow-mouthed toad were exposed dermally to tri- o-tolyl phosphate or phenyl saliginen cyclic phosphate (PSCP); no symptoms of delayed neurotoxicity were observed in any of these animals up to 2 weeks after metamorphosis. No symptoms of delayed neurotoxicity were seen in juvenile bullfrogs exposed to multiple ip doses of PSCP. The specific activity of neurotoxic esterase was highest in the larval bullfrog, with juvenile channel catfish and adult mosquitofish demonstrating intermediate levels. The larval Southern leopard frog, adult Northern leopard frog, juvenile green treefrog, and adult marine toad exhibited extremely low activities. The specific activity of acetylcholinesterase was highest in the juvenile channel catfish. Neurotoxic esterase in the larval bullfrog was more sensitive to organophosphate inhibition than that in either fish. PSCP was a more potent neurotoxic esterase inhibitor than leptophos-oxon. The juvenile channel catfish had the acetylcholinesterase most sensitive to organophosphate inhibition. Under the conditions tested, no evidence of in vivo sensitivity to the organophosphate-induced delayed neurotoxicity phenomenon was observed.

Taste responses to amino acids in the southern leopard frog, Rana sphenocephala

1. 1. Integrated taste recorclings of the glossopharyngeal (IX) nerve innervating the tongue of the southern leopard frog were studied in response to various amino acids and quinine hydrochloride. 2. 2. Amino acids and quinine hydrochloride elicited primarily phasic taste responses. 3. 3. Acidic ( l-aspartic and l-glutamic) and basic ( l-lysine and l-arginine) amino acids, adjusted to pH8, were effective taste stimuli. 4. 4. All glossopharyngeal nerve twigs that responded to amino acid stimuli also responded to quinine; however, not all quinine-sensitive IX nerve bundles were responsive to amino acids. 5. 5. Electrophysiological thresholds for amino acids were estimated to be 2.5–10 mM, whereas threshold for quinine hydrochloride averaged approximately 10 μM.

Anuran Responses to Salamander Predation

A previous experiment by P. J. Morin demonstrated that the newt, Notophthalmus viridescens (Amphibia: salamandridae) preyed on the species of tadpole that was the competitive dominant in communities of six species of anurans without newts. We studied the mechanism producing this result by combining three densities of the predator with three densities of prey in replicated artificial ponds. Pond communities were established in 27 tanks 1.52 m in diameter and 0.62 m deep. Because the late arrival of rains delayed the start of the planned experiment, 300 hatchlings of the toad Bufo woodhousei fowleri were added to all tanks to control algal populations. To these standardized communities we added all nine combinations of three densities of adult newts (0, 4, or 8 in an equal sex ratio) and three densities of larvae of the frogs Rana sphenocephala (Ranidae), Bufo terrestris (Bufonidae), and Scaphiopus holbrooki (Pelobatidae), in constant relative abundance. These nine treatments were randomly located in each of three blocks. The nine tanks without adult newts (three replicates of three densities of tadpoles: 50 Rana + 100 Bufo americanus + 100 Scaphiopus, 100 + 200 + 200, and 200 + 400 + 400) were used to assay competition within the tadpole guild. In the absence of predators, the anurans had density-dependent survival, lengths of larval period, and sizes at metamorphosis. There was evidence of competition among as well as within species. Rana sphenocephala had wintering tadpoles only in the highest density populations (Figure 1). Overwintering tadpoles were also observed in crowded natural populations with little predation.

Salamander Predation and the Structure of Experimental Communities: Anuran Responses

Replicated pond communities were established in 27 tanks 1.52 m in diameter and 0.62 m deep. The communities included a sample from a pooled mixture of zooplankton from nine small ponds, 20 stems of the aquatic perennial Myriophyllum heterophyllum, and 300 hatchlings of the toad Bufo woodhousei fowleri. All nine combinations of three densities of a predator (0, 4, or 8 adult Notophthalmus viridescens in an equal sex ratio) and three densities of prey (larvae of the frogs: Rana sphenocephala, Bufo terrestris, and Scaphiopus holbrooki, in constant relative abundance) were randomly represented in each of three blocks arranged in a Graeco—Latin square design. In the absence of predators, the anurans had density—dependent survival, lengths of larval period, and sizes at metamorphosis. There was evidence of competition among, as well as within, species. Rana sphenocephala had wintering tadpoles only in the highest—density populations. In this system community structure is affected by a gape—limited predator, Notophthalmus, that acts early in the anuran larval period, probably before competition occurs. In the presence of Notophthalmus all anurans had low survival, large mean size at metamorphosis, and short mean larval period. The survivors of predation probably have enhanced success as terrestrial juveniles compared to the survivors of competition in communities where there is a low risk of predation.

Predation, Competition, and the Composition of Larval Anuran Guilds

Experimental manipulations of densities of the predatory salamanders Notophthalmus viridescens dorsalis and Ambystoma tigrinum significantly altered relative abundances of six species of larval anurans in 22 artificial—pond communities. One competitively inferior anuran, Hyla crucifer, was virtually excluded from predator—free control communities but survived best and occurred at greater relative abundances in communities containing high densities of Notophthalmus. A second competitively inferior species, Hyla gratiosa, survived best at intermediate intensities of predation. Each of four competitively superior species (Scaphiopus holbrooki, Rana sphenocephala, Bufo terrestris, and Hyla chrysocelis) exhibited inverse relationships between relative abundance and Notophthalmus density. Ambystoma eliminated the entire anuran guild from tank communities and had a much greater per capita impact on anuran guild composition than did Notophthalmus. In most anuran species, maximum and mean mass at metamorphosis were positively correlated with predator density, suggesting an inverse relationship between intensities of predation and competition among tadpoles. Low growth rates of most anuran species in the absence of predators were correlated with high abundances of superior competitors. These results indicate that predators mediated interspecific competition among larval anurans. Intermediate values of Notophthalmus density maximized the total production of anuran metamorph biomass. Biomass of metamorphs of each species varied in a species—specific manner with predation. The propensity of Rana sphenocephala for overwintering as tadpoles following a season of growth was also related to predator density. Laboratory feeding experiments demonstrated that at least two competitively superior anurans, Scaphiopus holbrooki and Bufo terrestris, were especially vulnerable to predation by salamanders. This suggested that Notophthalmus may preferentially remove competitively superior anurans from pond communities, allowing competitively inferior anurans to persist and to complete development successfully at moderate to high predator densities.

Morphological Differentiation and Adaptation of the Larvae of Rana berlandieri and Rana sphenocephala (Rana pipiens Complex) in Sympatry

Syntopic larvae of Rana berlandieri and Rana sphenocephala, both of the Rana pipiens complex, were analyzed for morphological differentiation using multivariate techniques. Field-collected and laboratory-reared larvae of both species were compared for 12 morphometric characters. R. berlandieri larvae differ from R. sphenocephala larvae in having a more fusiform body shape, greater tail musculature development, a longer tail, relatively narrow dorsal and ventral tail fins, a shorter gastrointestinal tract length, fewer oral papillae on the lower labium, and a smaller ratio of interocular distance/ internareal distance. The number of oral papillae, however, is phenotypically plastic and probably varies with diet or mode of feeding. Pigmentation differences include tail blotching in R. berlandieri vs relatively uniform melanophore distribution in the tail fin of R. sphenocephala. Most of the morphological differentiation can be explained on the basis of larval habitat and dietary differences between these two species. R. berlandieri larvae are stream-adapted and probably more benthivorous than are the pond-adapted, planktivorous R. sphenocephala larvae. HE obscure morphological differentiation of adults among the various species of the Rana pipiens complex once resulted in taxonomic instability within this group (Pace, 1974). Only recently have most of the United States species of the R. pipiens complex been adequately defined; most of the Central American species are yet to be described or allocated to a specific taxon. Tadpoles of even the bestknown species within this group often cannot be identified with published information (Wassersug, 1976), which has led to further taxonomic confusion (Tucker, 1976). To date, the only leopard frog larvae that have been characterized morphologically in the literature are R. blairi and R. pipiens (Korky, 1978). Hillis (1981) reported breeding habitat distinctions between Rana berlandieri and Rana sphenocephala (=R. utricularia sensu Pace, 1974) in central Texas. R. berlandieri naturally breeds primarily in streams, whereas R. sphenocephala typically breeds in non-flowing water. Therefore, the larvae of these two species should show differential morphological adaptations to their respective habitats. In areas where syntopic breeding does occur, R. berlandieri usually breeds in the fall or early winter and R. sphenocephala breeds in late winter or early spring. Because of temporal differences of food-type availability in the larval habitat there may be differences in the diets of the larvae of these two species; these differences could be reflected in the morphological structures associated with feeding in the two species. This study was undertaken to find a means of distinguishing the larvae of R. berlandieri from the larvae of R. sphenocephala and to test the above predictions regarding adaptation to habitat and diet in these two species.

Comparative analysis of amphibian somite morphogenesis: cell rearrangement patterns during rosette formation and myoblast fusion

Detailed SEM observations of the changes in cellular morphology, arrangements, and contacts that occur during the process of somite formation were made in two species of urodele amphibians, Ambystoma mexicanum and Pleurodeles waltlii, and one species of anuran amphibian, Rana sphenocephala. After fixation, embryos were fractured transversely, horizontally, and parasagittally, and the intrasomitic cellular arrangement pattern was examined with the SEM. It was found that Ambystoma and Pleurodeles embryos followed exactly the same development sequence in rosette formation and myoblast fusion. Rana somites did not, however, appear to form rosettes. Those myotomal cells underwent fusion immediately after a few segmentations occurred. Patterns of cellular rearrangement were also described during urodele rosette formation at the time of somite segmentation and during myoblast fusion. Extensive changes in cell shape and orientation appeared to occur during those processes. When cells changed their orientation, they often exhibited a triangular configuration. Probable roles of these triangular-shaped cells in rosette formation and myoblast fusion are discussed. During the initial period of myoblast or myotomal cell fusion, cells first send out specialized cell processes and then establish their cell-cell contacts. The establishment of such contacts eventually leads to tight membrane appositions and fusion. Since myoblast fusion appeared to occur between two cells which were tandemly arranged in a rosette, the origin of multi-nuclearity in the fused cells is discussed. Finally, comparative analyses of the pattern of somite formation and subsequent muscle development were made between different species of amphibians. The possibility is discussed that patterns of somitogenesis may provide useful indicators for determining how different families of amphibians evolved.

Acute toxicities of toxaphene and endrin to larvae of seven species of amphibians

Seven species of amphibian larvae were exposed to toxaphene and endrin in a continuous-flow dosing system to determine differences in sensitivity to the two compounds. EC 50 and LC 50 estimates varied from those for Rana sphenocephala by no more than one order of magnitude when calculated on the basis of intended concentrations. Removal of pesticides from water by the test animals was significant and it makes interpretation of results difficult. Continuous-flow toxicity tests conflict with the adaptations of amphibian larvae for static water; use of such tests for amphibians requires further evaluation.