Observations on the life history and descriptions of coccidia (Apicomplexa) from the western chorus frog,Pseudacris triseriata triseriata,from eastern Nebraska

Two hundred and twenty-four anurans of 6 species (47 adults and 16 tadpoles of Rana blairi, 35 R. catesbeiana, 31 Hyla chrysoscelis, 30 adults and 46 tadpoles of Pseudacris triseriata triseriata, 11 Bufo woodhousii, and 8 Acris crepitans) from Pawnee Lake, Lancaster County, Nebraska, were surveyed for coccidian parasites during March 2001 to May 2002. Of these, 23 of 30 (77%) adults and 4 of 46 (9%) tadpoles of P. t. triseriata shed oocysts of Isospora cogginsi n. sp. Oocysts of I. cogginsi were ovoid, 19.3 x 15.1 (18-23 x 11-20) microm, with a thin, smooth, colorless, single-layered wall, with no micropyle or oocyst residuum. Sporocysts were ovoid, 13.3 x 9.9 (11-15 x 9-13) microm, with a thin, colorless, smooth wall, and Stieda body absent. Sporocyst residuum was present, 5.5 x 5.3 (4-7 x 4-7) microm, consisting of numerous granules. Histological examination of frogs and tadpoles infected with the new species revealed endogenous stages including mature meronts, developing microgamonts, mature microgametes, mature macrogamonts, and young unsporulated oocysts located in the cytoplasm of the epithelial cells of the small intestine. Concurrently, 2 adult P. t. triseriata shed oocysts of Eimeria streckeri. Oocysts of E. streckeri were spherical, 15.7 x 15.4 (14-17 x 14-19) microm, with a thin, smooth, single-layered, colorless wall with an oocyst residuum composed of numerous granules surrounding a large vacuolated area, with a previously undescribed globularlike body present within the vacuole, and no micropyle. Sporocysts were ovoid, 9.1 x 6.1 (7-10 x 5-7) microm, with a thin, colorless, smooth wall with a Stieda body and sporocyst residuum. Our results are the first to document infection of adult and tadpole stages of frogs of the same species with the same species of coccidian, indicating that adult frogs may contaminate breeding ponds with oocysts during their breeding season and infect tadpoles directly by the ingestion of sporulated oocysts.     

Time course for cryoprotectant synthesis in the freeze-tolerant chorus frog, Pseudacris triseriata

Increases in liver glycogen phosphorylase activity, along with inhibition of glycogen synthetase and phosphofructokinase-1, are associated with elevated cryoprotectant (glucose) levels during freezing in some freeze-tolerant anurans. In contrast, freeze-tolerant chorus frogs, Pseudacris triseriata, accumulate glucose during freezing but exhibit no increase in phosphorylase activity following 24-h freezing bouts. In the present study, chorus frogs were frozen for 5- and 30-min and 2- and 24-h durations. After freezing, glucose, glycogen, and glycogen phosphorylase and synthetase activities were measured in leg muscle and liver to determine if enzyme activities varied over shorter freezing durations, along with glucose accumulation. Liver and muscle glucose levels rose significantly (5-12-fold) during freezing. Glycogen showed no significant temporal variation in liver, but in muscle, glycogen was significantly elevated after 24 h of freezing relative to 5 and 30 min-frozen treatments. Hepatic phosphorylase a and total phosphorylase activities, as well as the percent of the enzyme in the active form, showed no significant temporal variation following freezing. Muscle phosphorylase a activity and percent active form increased significantly after 24 h of freezing, suggesting some enhancement of enzyme function following freezing in muscle. However, the significance of this enhanced activity is uncertain because of the concurrent increase in muscle glycogen with freezing. Neither glucose 6-phosphate independent (I) nor total glycogen synthetase activities were reduced in liver or muscle during freezing. Thus, chorus frogs displayed typical cryoprotectant accumulation compared with other freeze-tolerant anurans, but freezing did not significantly alter activities of hepatic enzymes associated with glycogen metabolism.     

Phylogenetic relationships of the North American chorus frogs (Pseudacris: Hylidae)

We examined phylogenetic relationships of the North American chorus frogs (Pseudacris: Hylidae) from 38 populations using 2.4 kb of 12S and 16S mtDNA to elucidate species relationships and examine congruence of previous phylogenetic hypotheses. Parsimony, maximum likelihood, and Bayesian phylogenies are consistent and reveal four strongly supported clades within Pseudacris: (1). A West Coast Clade containing regilla and cadaverina, (2). a Fat Frog Clade including ornata, streckeri, and illinoensis, (3). a Crucifer Clade consisting of crucifer and ocularis, and (4). a Trilling Frog Clade containing all other Pseudacris. Explicit hypothesis testing using parametric bootstrapping indicates that previous phylogenetic hypotheses are rejected by our sequence dataset. Within the Trilling Frog Clade, brimleyi and brachyphona form the sister group to the Nigrita Clade: nigrita, feriarum, triseriata, kalmi, clarkii, and maculata. The Nigrita Clade shows geographic division into three clades: (1). populations of maculata and triseriata west of the Mississippi River and Canadian populations, (2). southeastern US populations of feriarum and nigrita, and (3). northeastern US populations of feriarum, kalmi, and triseriata. We find that subspecific epithets for crucifer (crucifer and bartramiana) and nigrita (nigrita and verrucosa) are uninformative, therefore we discourage recognition of these subspecies. Pseudacris regilla, cadaverina, ocularis, and crucifer are maintained in Pseudacris.     

Heart rate response to gentle handling of frog and lizard

Heart rate was counted telemetrically in lizards (Iguana iguana) and frogs (Rana catesbeiana and Rana pipiens) to estimate their response to gentle 1-min handling. The animals were kept at steady body temperatures of ca. 28 degrees C (lizards), and 24 degrees C (frogs). Handling increased the heart rate of lizards from ca. 70 to 110 beats per min immediately during and after handling and this tachycardia decreased in ca. 10 min. Similar handling did not modify significantly the frogs' heart rates. Although the absence of a response to mild stress is not synonymous with the absence of emotion, the absence of handling-tachycardia in frogs and its presence in lizards (as well as in mammals and birds), together with the emotional fever in mammals, birds, and reptiles, but not frogs or fish as reported in the literature, might suggest that 'emotional' response to stress emerged in phylogeny between amphibians and reptiles.     

小气候对东北林蛙生长发育和繁殖的影响

于2009年5月—2010年5月,通过分组实验,研究了在大棚增温环境和围栏常温模拟林下环境条件下东北林蛙(Rana dybowskii)的生长发育情况。结果表明:与围栏常温模拟林下条件相比,大棚圈舍内平均气温、地温和湿度显著升高,有效积温增加;林蛙发育历期缩短,性成熟提前,二龄雌蛙性成熟比例增加,大棚圈舍的雌蛙的繁殖率为93.1%,围栏圈舍雌蛙的繁殖率为76.0%;在大棚中林蛙生长速度加快,饲养的一、二龄林蛙体重分别达到(6.30±2.62)g和(36.55±11.79)g,较围栏中体重提高了85.5%和56.6%;在大棚里林蛙出蛰时间、进食时间提前,停食时间、入蛰时间延后,生长期间延长,每窝平均产卵量增加,林蛙体重与产卵量呈显著的正相关(r=0.921,P<0.01)。     

The growth–mortality tradeoff: evidence from anuran larvae and consequences for species distributions

A tradeoff affecting the ability to grow under high versus low resource levels has been commonly hypothesized to influence species distributions across resource gradients in a wide variety of taxa. This influence is dependent on individual growth being proportional to traits that affect demographic processes such as mortality. However, data on how individual growth scales with demographic performance are rare. We conducted a mesocosm experiment, and re-analyzed data from a similarly designed field experiment, to examine the relationship between growth and mortality in two tadpole species that segregate across a resource gradient. Overall, environmental conditions leading to faster growth also lead to lower mortality rates. However, species differed in this relationship. Leopard frogs achieved faster growth than wood frogs, but their absolute mortality was greater and increased steeply as growth decreased. Conversely, absolute mortality of wood frogs was lower and less strongly dependent on growth. These interspecific differences suggest a second tradeoff, that between maximizing growth rates or minimizing mortality, with potentially important demographic consequences. Leopard frogs grow faster than wood frogs in productive ponds, but are excluded from unproductive ponds dominated by wood frogs due to accelerating mortality rates with declining realized growth. A review of the literature suggests that in diverse taxa, including plants, microcrustaceans and drosophilids, patterns in mortality are consistent with this tradeoff indicating that the mechanism we demonstrate could be a link between individual performance and demographic rates influencing species distributions in other systems.     

Generation of albino Xenopus tropicalis using zinc‐finger nucleases

To generate albino lines of Xenopus tropicalis, we injected fertilized eggs with mRNAs encoding zinc‐finger nucleases (ZFNs) targeting the tyrosinase coding region. Surprisingly, vitiligo was observed on the skin of F0 frogs that had been injected with ZFN mRNAs, indicating that both tyrosinase genes in the genome were disrupted in all melanocytes within the vitiligo patches. Mutation analysis using genomic DNA from the skin revealed that two mosaic F0 frogs underwent spatially complex tyrosinase gene mutations. The data implies that the ZFN‐induced tyrosinase gene ablations occurred randomly over space and time throughout the entire body, possibly until the young tadpole stage, and that melanocyte precursors lacking functional tyrosinase proliferated and formed vitiligo patches. Several albino X. tropicalis, which are compound heterozygotes for biallelic tyrosinase mutations, were obtained by mating the mosaic F0 frogs. To our knowledge, this is the first report of the albino vertebrates generated by the targeted gene knockout.     

Vertebral development and amphibian evolution

Amphibians provide an unparalleled opportunity to integrate studies of development and evolution through the investigation of the fossil record of larval stages. The pattern of vertebral development in modern frogs strongly resembles that of Paleozoic labyrinthodonts in the great delay in the ossification of the vertebrae, with the centra forming much later than the neural arches. Slow ossification of the trunk vertebrae in frogs and the absence of ossification in the tail facilitate the rapid loss of the tail during metamorphosis, and may reflect retention of the pattern in their specific Paleozoic ancestors. Salamanders and caecilians ossify their centra at a much earlier stage than frogs, which resembles the condition in Paleozoic lepospondyls. The clearly distinct patterns and rates of vertebral development may indicate phylogenetic separation between the ultimate ancestors of frogs and those of salamanders and caecilians within the early radiation of ancestral tetrapods. This divergence may date from the Lower Carboniferous. Comparison with the molecular regulation of vertebral development described in modern mammals and birds suggests that the rapid chondrification of the centra in salamanders relative to that of frogs may result from the earlier migration of sclerotomal cells expressing Pax1 to the area surrounding the notochord.     

A new Kupffer cell receptor mediating plasma clearance of carcinoembryonic antigen by the rat.

Previous studies were unable to identify Z-protein in elasmobranch liver with bromosulphophthalein as ligand. By using 8-anilinonaphthalene-1-sulphonate and Rose Bengal as ligands, however, we demonstrated in hepatic cytosol from Platyrhinoides triseriata an organic-anion-binding protein with gel-filtration characteristics identical with those of rat Z-protein. By comparison with pooled rat Z-protein, Pl. triseriata Z-protein had slightly lower affinity for 8-anilinonaphthalene-1-sulphonate and Rose Bengal, greatly decreased binding affinity for bromosulphophthalein and no binding activity for oleic acid or squalene. The Pl. triseriata Z-protein binding site was less hydrophobic than that of rat Z-protein. This observation may explain the differences in binding characteristics between the Z-proteins of these species.     

The relationship between size,budding rate,and growth efficiency in three species of hydra

Three species of the fresh water carnivore hydra, H. littoralis, H. pseudoligactis, and C. viridissima present a graduation in size with the first species the largest and albino Chlorohydra the smallest. When presented with a daily overabundance of food (artemia), considerable variation in food intake and gross efficiency of growth (proportion of food energy consumed that is turned into new protoplasm or buds) existed among the species. The degree of association between size of species and food intake was highly significant. However, budding efficiency among the species was found to be independent of food intake (when the effects of species size were eliminated) and of species size (when the effects of food intake were removed). However, species with high (low) efficiencies have significantly higher (lower) reproductive rates. A lowering of the temperature from 25° to 15° C. increased the size of the species, increased food intake, but decreased reproductive rate. In all species except H. pseudoligactis a corresponding increase in the production of bud energy with no change in efficiency also occurred. On the other hand, lowering of the temperature for H. pseudoligactis significantly lowered reproductive efficiency but had no effect on the total calorific output of buds. This species, in constrast to the others, appears to have a compensatory ability to adjust its efficiency to maintain a high calorific output when temperature increases. It was also found that albino Chlorohydra have budding efficiencies of around 35 percent which are not influenced by changes in food intake or light. Normal green hydras, however, have efficiencies which range from 40 to 62 percent above their albino counterparts when fed once a day and once every two days in light respectively. It it concluded first, that the symbiotic algae in the gastrodermals cells of green hydra contribute quantitatively in the order of the above amounts to the growth process in this species, and second, that green hydras have the ablity to increase their growth efficiency when food intake is reduced thus reducing the drop in calorific but output that normally occurs in the albino (control) form.     

Delayed effects of larval predation risk and food quality on anuran juvenile performance

Metamorphosis can disrupt the correlation structure between juvenile and adult traits, thus allowing relatively independent evolution in contrasting environments. We used a multiple experimental approach to investigate how diet quality and larval predation risk affected the rates of growth and development in painted frogs (Discoglossus galganoi), and how these changes influence post-metamorphic performance. A high-energy diet entailed growth advantages only if predation risk did not constrain energy acquisition, whereas diet quality affected primarily the extension of the larval period. Predation risk influenced juvenile shape, most likely via the effects on growth and differentiation rates. Juvenile frogs emerging from predator environments had shorter legs and longer bodies than those from the nonpredator tanks. However, these morphological changes did not translate into differences in relative jumping performance. Neither size-adjusted lipid storage nor fluctuating asymmetry was significantly influenced by food quality or predation risk. Our data suggest that the post-metamorphic costs of predator avoidance during the larval phase are mostly a consequence of small size at metamorphosis.     

A spontaneous albino mutant of Ceratocystis resinifera results from a point mutation in the polyketide synthase gene, PKS1

We characterized a spontaneous albino mutant of Ceratocystis resinifera. Compared with the wild-type progenitor strain, the albino mutant had a reduced linear growth on culture medium, but its growth on lodgepole pine sapwood was unaffected. The albino mutant did not produce any coloured pigment on agar media or wood. However, upon exposure to exogenous scytalone, an intermediate metabolite of the melanin pathway, the production of a brownish melanin was restored. This suggests that the albino phenotype resulted from a mutation affecting the melanin synthesis pathway, upstream of the scytalone synthesis step. Melanin production was restored in the mutant by transforming it with a wild-type copy of the Ceratocystis resinifera polyketide synthase gene, PKS1. The complemented transformants produced melanin, indicating that the PKS1 gene was defective in the albino mutant. Sequence analysis revealed that the PKS1 allele found in the albino contained a single point mutation that resulted in an amino acid change from serine to proline at the 3' end of the beta-ketoacyl synthase motif.     

Interactions Between Competition and Predation Shape Early Growth and Survival of Two Neotropical Hylid Tadpoles

Experimental studies in temperate regions have revealed that competition and predation interact to shape aquatic communities. Predators typically reduce the effect of competition on growth and competitors provide alternative prey subjects, which may also alter predation. Here, we examine the independent and combined effects of competition and predation on the survival and growth of hatchling tadpoles of two widespread co‐occurring Neotropical hylid frogs (Agalychnis callidryas and Dendropsophus ebraccatus). Using 400 L mesocosms, we used a 2 × 3 factorial substitutive design, which crossed tadpole species composition with the presence or absence of a free‐roaming predator (Anax amazili dragonfly larva). Dragonflies were effective predators of both species, but had larger effects on A. callidryas survival. Both species had similar growth rates when alone, whereas A. callidryas grew 30 percent faster than D. ebraccatus when they co‐occurred, suggesting interspecific rather than intraspecific competition had relatively stronger effects on D. ebraccatus growth, while the opposite was true for A. callidryas. Predator presence dramatically reduced growth rates of both species and erased this asymmetry. Results suggest that the effects of predator induction (i.e., nonconsumptive effects) on growth were larger than both consumptive and competitive effects. Our study demonstrates that predators have strong effects on both survival and growth of prey, highlighting the potential importance of predators in shaping prey populations and tropical aquatic food web interactions. Abstract in Spanish is available at http://www.blackwell‐synergy.com/loi/btp .     

Local adaptation for enhanced salt tolerance reduces non‐adaptive plasticity caused by osmotic stress

Organisms often respond to environmental change via phenotypic plasticity, in which an individual modulates its phenotype according to the environment. Highly variable or changing environments can exceed physiological limits and generate maladapted plastic phenotypes, which is termed nonadaptive plasticity. In some cases, selection may reduce the negative or disruptive impacts of environmental stress and produce locally adapted populations. Salt is an increasingly prevalent contaminant of freshwater systems and can induce nonadaptive plastic phenotypes for freshwater organisms like amphibians. Hyla cinerea is a frog species with populations inhabiting brackish, coastal habitats, so we use this species to test whether coastal populations are locally adapted to tolerate saltwater by determining how salt exposure during the embryonic and larval stages alters mortality and plastic developmental and metamorphic phenotypes of coastal and inland populations. Coastal frogs have higher survival, faster growth rates, and metamorphose sooner than inland frogs across salinities. Coastal frogs also metamorphose smaller (likely a consequence of earlier metamorphosis) yet maintain constant size, while higher salinities reduce metamorphic size for inland frogs. Coastal frogs evolved to minimize nonadaptive and disruptive impacts of saltwater during larval development and accelerate the larval period to reduce time spent in a stressful environment.     

Metabolic depression induced by urea in organs of the wood frog, Rana sylvatica: effects of season and temperature

It has long been suspected that urea accumulation plays a key role in the induction or maintenance of metabolic suppression during extended dormancy in animals from diverse taxa. However, little evidence supporting that hypothesis in living systems exists. We measured aerobic metabolism of isolated organs from the wood frog (Rana sylvatica) in the presence or absence of elevated urea at various temperatures using frogs acclimatized to different seasons. The depressive effect of urea on metabolism was not consistent across organs, seasons, or temperatures. None of the organs from summer frogs, which were tested at 20 degrees C, or from winter frogs tested at 4 degrees C were affected by urea treatment. However, liver, stomach, and heart from spring frogs tested at 4 degrees C had significantly lower metabolic rates when treated with urea as compared with control samples. Additionally, when organs from winter frogs were tested at 10 degrees C, metabolism was significantly decreased in urea-treated liver and stomach by approximately 15% and in urea-treated skeletal muscle by approximately 50%. Our results suggest that the presence of urea depresses the metabolism of living organs, and thereby reduces energy expenditure, but its effect varies with temperature and seasonal acclimatization. The impact of our findings may be wide ranging owing to the number of diverse organisms that accumulate urea during dormancy. J. Exp. Zool. 309A:111-116, 2008. (c) 2008 Wiley-Liss, Inc.     

Density dependence in the terrestrial life history stage of two anurans

Populations of species with complex life cycles have the potential to be regulated at multiple life history stages. However, research tends to focus on single stage density-dependence, which can lead to inaccurate conclusions about population regulation and subsequently hinder conservation efforts. In amphibians, many studies have demonstrated strong effects of larval density and have often assumed that populations are regulated at this life history stage. However, studies examining density regulation in the terrestrial stages are rare, and the functional relationships between terrestrial density and vital rates in amphibians are unknown. We determined the effects of population density on survival, growth and reproductive development in the terrestrial stage of two amphibians by raising juvenile wood frogs (Rana sylvatica) and American toads (Bufo americanus) at six densities in terrestrial enclosures. Density had strong negative effects on survival, growth and reproductive development in both species. We fitted a priori recruitment functions to describe the relationship between initial density and the density of survivors after one year, and determined the functional relationship between initial density and mass after one year. Animals raised at the lowest densities experienced growth and survival rates that were over twice as great as those raised at the highest density. All female wood frogs in the lowest density treatment showed signs of reproductive development, compared to only 6% in the highest density treatment. Female American toads reached minimum reproductive size only at low densities, and male wood frogs and American toads reached maturity only in the three lowest density treatments. Our results demonstrate that in the complex life cycle of amphibians, density in the terrestrial stage can reduce growth, survival and reproductive development and may play an important role in amphibian population regulation. We discuss the implications of these results for population regulation in complex life cycles and for amphibian conservation.     

Pond canopy cover: a resource gradient for anuran larvae

1. The gradient in pond canopy cover strongly influences freshwater species distributions. This study tested the effects of canopy cover on the performance of two species of larval anurans, a canopy cover generalist (Rana sylvatica, the wood frog) and an open‐canopy specialist (R. pipiens, the leopard frog), and tested which factors co‐varying with canopy cover mediate these effects. 2. A field transplant experiment demonstrated that canopy cover had negative performance effects on both species. However, leopard frogs, which grow faster than wood frogs in open‐canopy ponds, were more strongly affected by closed‐canopy pond conditions. 3. Closed‐canopy ponds had lower temperature, dissolved oxygen (DO), and food nutritional quality as indicated by carbon‐to‐nitrogen ratio (C : N) analysis of field‐sampled food types, and of gut contents of transplanted larvae. 4. Laboratory experiments demonstrated that higher temperature and food quality but not DO substantially increased larval growth. However, only food quality increased growth rates of leopard frogs more than wood frogs. 5. The strong correlation of growth rates to gut content C : N in the field, and the similarity of growth curves as a function of resource quality in the field and laboratory, strongly suggest that resources are of primary importance in mediating intraspecific, and especially interspecific differences in performance across the canopy cover gradient.     

Competition and the distribution of spring peeper larvae

Studies of tadpole distributions have shown that despite overlapping affinities for semipermanent and permanent ponds, distributions of the spring peeper (Pseudacris crucifer) and the green frog (Rana clamitans) tend to be nonoverlapping. Because spring peepers are believed to be poor competitors, I hypothesized that competition from green frog larvae limits the distribution of spring peeper larvae. I stocked field enclosures with a constant density of spring peeper larvae, and one of four densities of green frog larvae (a target-neighbor design). Increased green frog density had a small effect on metamorphic size and no effects on survivorship, larval period or growth rates of spring peepers. In contrast to these small interspecific effects, green frogs had a large effect on their own performance. Intraspecific competition resulted in a 50% decline in growth rate and an 11% decline in metamorphic size. These results suggest that the species are segregated in resource use, or that compared with green frogs, spring peepers are better able to cope with depressed resource densities. In either case, this field experiment provides no evidence that interspecific competition from green frogs limits distributions of spring peepers. Other factors such as predation and breeding site choice by adults may contribute to the absence of spring peeper larvae from many semipermanent and permanent ponds.     

Effects of an invasive species on refuge‐site selection by native fauna: The impact of cane toads on native frogs in the Australian tropics

Invasive species can induce shifts in habitat use by native taxa: either by modifying habitat availability, or by repelling or attracting native species to the vicinity of the invader. The ongoing invasion of cane toads (Rhinella marina) through tropical Australia might affect native frogs by affecting refuge‐site availability, because both frogs and toads frequently shelter by day in burrows. Our laboratory and field studies in the wet‐dry tropics show that native frogs of at least three species (Litoria tornieri, Litoria nasuta and Litoria dahlii) preferentially aggregate with conspecifics, and with (some) other species of native frogs. However, the frogs rarely aggregated with cane toads either in outdoor arenas or in standardized experimental burrows that we monitored in the field. The native frogs that we tested either avoided burrows containing cane toads (or cane toad scent) or else ignored the stimulus (i.e. treated such a burrow in the same way as they did an empty burrow). Native frogs selected a highly non‐random suite of burrows as diurnal retreat sites, whereas cane toads were less selective. Hence, even in the absence of toads, frogs do not use many of the burrows that are suitable for toads. The invasion of cane toads through tropical Australia is unlikely to have had a major impact on retreat‐site availability for native frogs.