Do tadpoles affect leaf decomposition in neotropical streams?

1. Of the relatively few studies that have examined consequences of amphibian declines on stream ecosystems, virtually all have focused on changes in algae (or algal‐based food webs) and little is known about the potential effects of tadpoles on leaf decomposition. We compared leaf litter decomposition dynamics in two neotropical streams: one with an intact community of tadpoles (with frogs) and one where tadpoles were absent (frogless) as a result of a fungal pathogen that had driven amphibians locally extinct. The stream with tadpoles contained a diverse assemblage (23 species) of larval anurans, and we identified five species of glass frog (Centrolenidae) tadpoles that were patchily distributed but commonly associated with leaf detritus and organic sediments in pools. The latter reached total densities of 0–318 tadpoles m^?2. 2. We experimentally excluded tadpoles from single‐species leaf packs incubated over a 40‐day period in streams with and without frogs. We predicted that decomposition rates would be higher in control (allowing access of tadpoles) treatments in the study stream with frogs than in the frogless stream and, in the stream with frogs, in the control than in the tadpole exclusion treatment. 3. In the stream with frogs, Centrolene prosoblepon and Cochranella albomaculata tadpoles were patchily distributed in leaf packs (0.0–33.3 m^?2). In contrast to our predictions, leaf mass loss and temperature‐corrected leaf decomposition rates in control treatments were almost identical in our stream with frogs (41.01% AFDM lost, k_{degree day} = ?0.028 day^?1) and in the frogless stream (41.81% AFDM lost, k_{degree day} = ?0.027 day^?1) and between control and tadpole exclusion treatments within each stream. Similarly, there were no significant differences in leaf pack bacterial biomass, microbial respiration rates or macroinvertebrate abundance between treatments or streams. Invertebrate assemblages on leaf packs were similar between treatments (SIMI = 0.97) and streams (SIMI = 0.95) and were dominated by larval Chironomidae, Simuliidae (Diptera) and larval Anchytarsus spp. (Coleoptera). 4. In contrast to dramatic effects of grazing tadpoles on algal communities observed previously, tadpoles had no major effects on decomposition. While centrolenid tadpoles were common in the stream with frogs, their patchy distribution in both experimental and natural leaf packs suggests that their effects on detrital dynamics and microbes are probably more localised than those of grazing tadpoles on algae.     

Changes in Stream Primary Producer Communities Resulting from Large-Scale Catastrophic Amphibian Declines: Can Small-Scale Experiments Predict Effects of Tadpole Loss?

Global declines of amphibian populations are well documented, yet effects of these declines on freshwater ecosystem structure and function are poorly understood. Here we examine responses of algal primary producers to tadpole extirpation over differing spatial and temporal scales. We experimentally excluded tadpoles from artificial substrata within localized areas (0.25 m²) of two streams. One stream had an intact community of frogs (frog stream), and the other had recently experienced a catastrophic decline (frogless stream), leaving virtually no tadpoles. In the frog stream, there were significantly greater levels of chlorophyll a (+111%, P = 0.009), ash-free dry mass (AFDM) (+163%, P = 0.02), inorganic sediments (+114%, P = 0.001), and higher mean algal cell biovolume in tadpole exclusion treatments than in the tadpole access treatments. Correspondingly, overall AFDM-specific net primary production (NPP) increased by 38% (P = 0.001) and chlorophyll a-specific NPP increased by 29% (P = 0.001) in tadpole access treatments compared to tadpole exclusion treatments. Areal-specific NPP did not differ between treatments. There were no significant differences in chlorophyll a, AFDM, inorganic sediments, algal cell biovolume, or biomass-specific NPP between treatments in the frogless stream. Fifteen months after our experiments, a massive amphibian decline associated with a fungal pathogen occurred in the frog stream, resulting in the extirpation of over 90% of tadpoles. This extirpation was followed by significant increases in levels of chlorophyll a (269%, P = 0.001), AFDM (+220%, P < 0.001), and inorganic sediments (+140%, P = 0.001). Reach-scale NPP increased from −1587 to −810 mg DO m⁻² d⁻¹. Additionally, algal community composition shifted from a dominance of small adnate diatoms (pre-decline) to a dominance of large upright algal species (post-decline). Our experimental results, combined with algal monitoring at the reach scale, indicate that over the course of our study catastrophic amphibian losses have significant effects on stream ecosystem structure and function. Ecosystem-level impacts of tadpole extirpations were more dramatic than results from our small-scale, short-term experiments, which predicted the direction of change in response variables but underestimated the magnitude. However, the long-term stream ecosystem responses remain unknown. Author Contributions: S.C., C.M.P., M.R.W., K.R.L., and S.K. designed the study, S.C., C.M.P., R.B., M.R.W., K.R.L., and A.D.H. performed research, S.C., C.M.P., R.J.B., M.R.W., and A.D.H. analyzed data. S.C., C.M.P., and R.J.B. wrote the paper.     

Disease-Driven Amphibian Declines Alter Ecosystem Processes in a Tropical Stream

Predicting the ecological consequences of declining biodiversity is an urgent challenge, particularly in freshwater habitats where species declines and losses are among the highest. Small-scale experiments suggest potential ecosystem responses to losses of species, but definitive conclusions require verification at larger scales. We measured ecosystem metabolism and used whole-ecosystem stable isotope tracer additions to quantify nitrogen cycling in a tropical headwater stream before and after the sudden loss of amphibians to the fungal pathogen Batrachochytrium dendrobatidis. Tadpoles are normally dominant grazers in such streams, where greater than 18 species may co-occur and densities often exceed 50 individuals m^?2. Loss of 98% of tadpole biomass corresponded with greater than 2× increases in algae and fine detritus biomass in the stream and a greater than 50% reduction in nitrogen uptake rate. Nitrogen turnover rates in suspended and deposited organic sediments were also significantly lower after the decline. As a consequence, the stream cycled nitrogen less rapidly, and downstream exports of particulate N were reduced. Whole stream respiration was significantly lower following the decline, indicating less biological activity in the stream sediments. Contrary to our predictions, biomass of grazing invertebrates, or any invertebrate functional groups, did not increase over 2 years following loss of tadpoles. Thus, reductions in ecosystem processes linked to the amphibian decline were not compensated for by other, functionally redundant consumers. Declining animal biodiversity has ecosystem-level consequences that may not be offset by ecological redundancy, even in biologically diverse regions such as the Neotropics.     

Plant—herbivore interactions in streams near Mount St Helens

1. In four separate field experiments near Mount St Helens (Washington, U.S.A.) during 1986, the grazing effects of two large benthic herbivores, tadpoles of the tailed frog Ascaphus truei and larvae of the caddisfly Dicosmoecus gilvipes, were investigated using streamside channels and in-stream manipulations. In the experimental channels, abundances of periphyton and small benthic invertebrates declined significantly with increasing density of these larger herbivores. 2. In eleven small, high-gradient streams affected to varying degrees by the May 1980 eruption, in-stream platforms were used to reduce grazing by A, truei tadpoles on tile substrates. Single platforms erected in each tributary and compared to grazed controls revealed only minor grazing effects, and no significant differences among streams varying in disturbance intensity (and, consequently, tadpole density). However, results probably were confounded by high variability among streams in factors other than tadpole abundance. 3. Grazing effects were further examined in two unshaded streams with different tadpole densities, using five platforms per stream. In the stream with five tadpoles m^?2, grazing reduced periphyton biomass by 98% and chlorophyll a by 82%. In the stream lacking tadpoles, no significant grazing effects were revealed. Low algal abundance on both platforms and controls, and high invertebrate density in that stream (c. 30000m^?2) suggests that grazing by small, vagile invertebrates was approximately equivalent to that of tadpoles. 4. The influence of large benthic herbivores on algal and invertebrate communities in streams of Mount St Helens can be important, but reponses vary spatially in relation to stream disturbance history, local environmental factors, and herbivore distributional patterns and abundance.     

Trophic roles of tadpoles in tropical Australian streams

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Distribution and reproductive strategies of Gyrinicola batrachiensis (Oxyuroidea: Pharyngodonidae) in larvae of eight species of amphibians from Nebraska

In total, 462 tadpoles and salamander larvae of 8 species were examined for the presence of Gyrinicola batrachiensis from 5 locations in Nebraska. Infection by G. batrachiensis occurred in tadpoles of Rana blairi , Rana catesbeiana, Rana pipiens, and Bufo woodhousii. Tadpoles of Hyla chrysoscelis , Spea bombifrons, and Pseudacris maculata and larvae of Ambystoma mavortium were not infected with G. batrachiensis. Population structure, defined as prevalence, mean abundance, and mean intensity of G. batrachiensis, varied among tadpoles of different amphibian species and was determined by collection locality, developmental period of tadpole hosts, amphibian species co-occurrence, and different reproductive strategies of G. batrachiensis , or a combination. Gyrinicola batrachiensis observed in all ranid tadpoles and B. woodhousii tadpoles from where bufonids were the only anuran species present, confirmed to the didelphic haplodiploidy and monodelphic parthenogenetic reproductive strategies, respectively. However, tadpoles of B. woodhousii that co-occurred with tadpoles of R. pipiens at Cedar Creek were inconsistent with these predictions and contained both male and didelphic female nematodes, but at a low mean intensity (1.61 ± 0.70). Didelphic female nematodes from B. woodhousii tadpoles at Cedar Creek only produced thick-shelled eggs, whereas nematodes in R. pipiens tadpoles had a high mean intensity (14.88 ± 23.83) from this location and contained both thick-shelled and thin-shelled eggs in their respective uteri. More importantly, adult female nematodes from tadpoles of R. pipiens and B. woodhousii from Cedar Creek were morphologically more similar to each other than to female nematodes recovered from tadpoles of other anuran species, other locations, or both. These data suggest that when strains of G. batrachiensis are shared by tadpoles of different amphibian species that differ in developmental period, the nematodes have an intermediate reproductive strategy in amphibian species, with tadpoles having short development.     

Invasive Plant and Experimental Venue Affect Tadpole Performance

Introductions of non-native predators and competitors appear to contribute to worldwide amphibian declines; however, potential negative impacts of invasive plants on habitat quality and amphibian populations have not been examined. Loss of diversity and alterations in ecosystem function associated with plant invasions may disrupt food webs, potentially leading to further declines of already threatened amphibian populations. We used a combination of small bins, mesocosms, and field experiments to examine the impacts of Eurasian purple loosestrife (Lythrum salicaria) replacing native cattails (Typha latifolia) in North American freshwater wetlands on survival, developmental rate, and diet (freshwater algae) of American toad (Bufo americanus) tadpoles. Tadpoles developed slower in L. salicaria compared to tadpoles developing in T. latifolia. This effect was consistent across experimental venues, although mesocosms showed this effect only in the second year of our study. Survival and development rates were always more variable in purple loosestrife than in cattail. In bins, tadpoles showed significantly reduced survival when raised in purple loosestrife extract and addition of leaf litter exacerbated this negative effect. Tadpole survival rates in mesocosms and field cages were not significantly different between plant species, most likely an effect of high variability among replicates. We suspect a combination of direct toxicity of high tannin concentrations in L. salicaria leaves and their indirect negative impacts on aquatic food webs are responsible for these results. Tadpole gut analyses revealed differences in algal communities among venues and between L. salicaria and T. latifolia suggesting that alterations in tadpole food quality and quantity contribute to the observed reduced tadpole performance. The replacement of native wetland plant species by L. salicaria does not represent a simple exchange of ecological equivalents and the function of invaded habitats for native species has clearly changed. While we were investigating only a single amphibian species, our results suggest that the impact of L. salicaria on ecosystem processes and aquatic food webs may be more general and likely to negatively affect other wetland species. The threats non-indigenous plants represent for amphibian populations and food webs may be underestimated, and warrant further investigation.     

Environmental variables associated with the distribution and occupancy of habitat specialist tadpoles in naturally acidic,oligotrophic waterbodies

Environmental factors play an integral role, either directly or indirectly, in structuring faunal assemblages. Water chemistry, predation, hydroperiod and competition influence tadpole assemblages within waterbodies. We surveyed aquatic predators, habitat refugia, water height and water chemistry variables (pH, salinity and turbidity) at 37 waterbodies over an intensive 22‐day field survey to determine which environmental factors influence the relative abundance and occupancy of two habitat specialist anuran tadpole species in naturally acidic, oligotrophic waterbodies within eastern Australian wallum communities. The majority of tadpoles found were of Litoria olongburensis (wallum sedge frog) and Crinia tinnula (wallum froglet) species, both habitat specialists that are associated with wallum waterbodies and listed as Vulnerable under the IUCN Red List. Tadpoles of two other species (Litoria fallax (eastern sedge frog), and Litoria cooloolensis (cooloola sedge frog)) were recorded from two waterbodies. Tadpoles of Litoria gracilenta (graceful treefrog) were recorded from one waterbody. Relative abundance and occupancy of L. olongburensis tadpoles were associated with pH and water depth. Additionally, L. olongburensis tadpole relative abundance was negatively associated with turbidity. Waterbody occupancy by C. tinnula tadpoles was negatively associated with predatory fish and water depth and positively associated with turbidity. Variables associated with relative abundance of C. tinnula tadpoles were inconclusive and further survey work is required to identify these environmental factors. Our results show that the ecology of specialist and non‐specialist tadpole species associated with ‘unique’ (e.g. wallum) waterbodies is complex and species specific, with specialist species likely dominating unique habitats.     

“KIN RECOGNITION” AMONG SPADEFOOT TOAD TADPOLES: A SIDE-EFFECT OF HABITAT SELECTION?

Many animals modify their behavior toward unfamiliar conspecifics as a function of their genetic relatedness. A fundamental problem of any kin recognition study is determining what is being recognized and why. For anuran tadpoles, the predominant view is that associating with relatives is kin-selected because these relatives may thereby accrue benefits through increased growth or predation avoidance. An alternative view is that kin associations are simply a side-effect of habitat selection and thus do not represent attempts to identify kin per se. In the laboratory, spadefoot toad tadpoles (Scaphiopus multiplicatus) preferentially associated with unfamiliar siblings over unfamiliar nonsiblings, as do other anurans. However, same age tadpoles also were more likely to orient toward unfamiliar nonsiblings reared on the same food (familiar food) than toward unfamiliar siblings that were reared on unfamiliar food. These results, together with the results of previous tadpole kin recognition studies, suggest that tadpoles orient toward cues learned early in ontogeny, regardless of the cues' source. Tadpoles that preferentially associated with cues learned from their environment at birth would tend to be philopatric. Censuses of 14 natural ponds revealed that tadpole density remained greatest near oviposition sites until four days before metamorphosis. Tadpole philopatry may be advantageous: tadpoles restricted to their natal site had greater growth and survivorship than did their siblings restricted to randomly selected sites elsewhere within the same pond. Thus kin affiliative tendency observed in the laboratory in this and perhaps other species of anurans may be a byproduct of habitat selection. Since kin discrimination in animals is most commonly assayed as orientation toward kin, it follows that many examples of “kin recognition” may not represent true attempts to identify kin as such, but rather may reflect some other recognition system that is under entirely different selective pressures.     

Potential functional redundancy and resource facilitation between tadpoles and insect grazers in tropical headwater streams

1. We quantified production and consumption of stream‐dwelling tadpoles and insect grazers in a headwater stream in the Panamanian uplands for 2 years to assess their effects on basal resources and energy fluxes. At the onset of our study, this region had healthy, diverse amphibian populations, but a catastrophic disease‐driven decline began in September 2004, which greatly reduced amphibian populations. 2. Insect grazer production was 348 mg ash‐free dry mass (AFDM) m^?2 year^?1 during the first year of the study and increased slightly to 402 mg AFDM m^?2 year^?1 during the second year. 3. Prior to amphibian declines, resource consumption by grazers (tadpoles and insects) was estimated at 2.9 g AFDM m^?2 year^?1 of algal primary production, which was nearly twice the estimated amount available. Insect grazers alone accounted for c. 81% of total primary consumption. During the initial stages of the declines, consumption remained at c. 2.9 g AFDM m^?2 year^?1, but only 35% of the available resource was being consumed and insect grazers accounted for c. 94% of total consumption. 4. Production and resource consumption of some insect grazers increased during the second year, as tadpoles declined, indicating a potential for functional redundancy in this system. However, other insect grazer taxa declined or did not respond to tadpole losses, suggesting a potential for facilitation between tadpoles and some insects; differential responses among taxa resulted in the lack of a response by insect grazers as a whole. 5. Our results suggest that before massive population declines, tadpoles exerted strong top‐down control on algal production and interacted in a variety of ways with other primary consumers. 6. As amphibian populations continue to decline around the globe, changes in the structure and function of freshwater habitats should be expected. Although our study was focused on tropical headwater streams, our results suggest that these losses of consumer diversity could influence other aquatic systems as well and may even reach to adjacent terrestrial environments.     

Ontogenetic dietary shifts in European common frog (Rana temporaria) revealed by stable isotopes

During migrations and ontogeny amphibians change their habitat and feeding, and thus are important in linking terrestrial and aquatic ecosystems. We measured δ ¹³C and δ ¹⁵N values of early stages (egg, embryo, tadpole) and toes of adult frogs Rana temporaria, collected from a small wetland in Lithuania. We compared the isotopic composition of these tissues with potential food sources, excrements of tadpoles, and filled intestinal tracts. We found that δ ¹³C values in R. temporaria tadpoles were markedly depleted in comparison to adults, eggs or embryos, demonstrating a terrestrial to aquatic shift in energy sources. After the onset of feeding, tadpoles approached isotopic equilibrium with available food (algae and litter). Tadpoles had higher δ ¹⁵N than both algae and litter, differing by 3.6 and 2.4‰, respectively, and similar δ ¹³C to these sources. However, tadpole excrements and body tissue diverged, with mean δ ¹³C values of excrements (−30.3 ± 1.6‰ SD) more similar to litter (−31.7 ± 1.2‰ SD) and body tissue δ ¹³C (−34.8 ± 0.7‰ SD) more similar to algae (−34.2 ± 4.1‰ SD). This suggests that algal resources are critical in early life stages of this anuran, particularly at stages characterized by high growth and low development (stages: 25–35).     

Revisiting “what do tadpoles really eat?” A 10‐year perspective

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Dietary protein restriction impairs growth,immunity, and disease resistance in southern leopard frog tadpoles

The immune system is a necessary, but potentially costly, defense against infectious diseases. When nutrition is limited, immune activity may consume a significant amount of an organism’s energy budget. Levels of dietary protein affect immune system function; high levels can enhance disease resistance. We exposed southern leopard frog [Lithobates sphenocephalus (=Rana sphenocephala)] tadpoles to high and low protein diets crossed with the presence or absence of the pathogenic amphibian chytrid fungus (Batrachochytrium dendrobatidis; Bd) and quantified: (1) tadpole resistance to Bd; (2) tadpole skin-swelling in response to phytohaemagglutinin (PHA) injection (a measure of the T cell-mediated response of the immune system); (3) bacterial killing ability (BKA) of tadpole blood (a measure of the complement-mediated cytotoxicity of the innate immune system); and (4) tadpole growth and development. Tadpoles raised on a low-protein diet were smaller and less developed than tadpoles on a high-protein diet. When controlled for developmental stage, tadpoles raised on a low-protein diet had reduced PHA and BKA responses relative to tadpoles on a high-protein diet, but these immune responses were independent of Bd exposure. High dietary protein significantly increased resistance to Bd. Our results support the general hypothesis that host condition can strongly affect disease resistance; in particular, fluctuations in dietary protein availability may change how diseases affect populations in the field.     

Locomotion in Amphibian Larvae (or "Why Aren't Tadpoles Built Like Fishes?")

SYNOPSIS. A variety of morphological features that affect locomotiondistinguish larvae of the three living amphibian orders fromfishes and their larvae. The oddest amphibian larvae are anurantadpoles. With their globose bodies, concealed forelimbs, abruptlycompressed and terminally tapered tails, tadpoles not only differradically from fishes but they—unlike caecilians or salamanders—alsodiffer radically from their adults. Tadpoles typically haveless axial musculature and much simpler myotomes than fishes.Surprisingly, in terms of mechanical (propeller) efficiencyand maximum sprint speeds, tadpoles still perform as well asmany teleosts of comparable sizes. From a consideration of hydromechanics,no amphibian larvae appear to be designed for sustained swimmingat high speeds. High maneuverability, rather than sustainablespeed, are important for amphibian larval survival.Two key featuresof tadpoles are the absence of caudal vertebrae and unexposedpectoral appendages. With only a notochord to serve as a skeleton,the tadpole tail is extremely flexible. Because of this exceptionalflexibility, tadpoles can fold their tails up against the bodyand turn rapidly with virtually no displacement of their centerof mass. Caudal flexibility can be regulated by muscle activityin the tadpole to effect turning. Lateral appendages are notneeded for this movement and are free to develop directly intotheir adult morphology; the anterior ones develop under coverof an opercular fold where they do not contribute to drag. Acase is presented, based on the ecology of metamorphosis, thatanuran transformation should be as brief as possible. With nobone to resorb, metamorphosis of the anuran caudal appendagecan, indeed, be very rapid.The basic kinematics of constantvelocity straightforward swimming for tadpoles and salamanderlarvae is reviewed, as well as the kinematics and electromyographyof starting, stopping, and turning in tadpoles. An attempt ismade to relate swimming kinematics to the characteristic morphologiesof amphibian larvae. Swimming speed in Rana, Bufo and Aynbystomalarvae, which swim only intermittently, is modulated by changingtail beat frequency. However, Xenopus, which swims constantlyby sculling with its tail, regulates swimming speed (at lowto intermediate velocities) by varying the length of the propulsivewave in its tail. Xenopus and Rana differ in the morphologyof their notochord, spinal cord, spinal nerves, and spinal motorpool distribution within the spinal cord. These differencesmay underlie the different way these larvae regulate swimming.They may also reflect their phylogenetic history.     

Activity of Sphaerotheca breviceps tadpoles in response to chemical cues of the predaceous tadpoles Hoplobatrachus tigerinus

Tadpoles of Sphaerotheca breviceps raised in the laboratory from the egg stage, and hence lacking prior experience of a predator or its odors, were tested to examine their responses to a predator’s (tadpoles of Hoplobatrachus tigerinus) water-borne chemical cues. The stimulus solution was obtained following 24 h of rearing tadpoles of H. tigerinus (one tadpole per 200 mL water) that were not fed during this period. Upon exposure to the stimulus solution the activity of S. breviceps tadpoles decreased by about 90% within 5 min. Their resting period increased significantly over baseline activity, whereas the swimming period, distance traversed, and swimming spurts declined. However, whenever a test tadpole moved, its swimming velocity was high in response to stimulus solution. The antipredatory responses declined with increase in time of storage of the stimulus solution, indicating decay of the predator’s chemical cues. The findings suggest that (1) antipredator defense strategies of S. breviceps do not require prior experience of predators, (2) the predator’s chemical cues are labile in nature, and (3) the response of prey tadpoles to such cues is similar to reported behavior of anuran tadpoles in response to real predators and alarm cues.     

The effects of cannibalism on Amazonian poison frog egg and tadpole deposition and survivorship in Heliconia axil pools

This study investigated the influence of cannibalism on egg and larval mortality, and on the deposition strategies of adults, in a tropical anuran breeding in very small leaf axil pools. Patterns of egg and tadpole deposition and mortality in the Amazonian poison frog, Dendrobates ventrimaculatus, were monitored in rainforest near Pompeya in Sucumbios Province, Ecuador. Oviposition and tadpole deposition typically ocurred in leaf axils of Heliconia plants. Pools typically received more than one oviposition. Egg survivorship was low, and significantly lower when eggs were deposited in pools with large tadpoles, indicating that cannibalism is an important source of mortality. Tadpole survivorship was also associated with the presence of other tadpoles: most pools ended with only one surviving tadpole, regardless of the number of tadpoles deposited in the pool. Egg deposition was signifcantly less likely for pools that had a tadpole in them, suggesting that adults can detect the presence of tadpoles and avoid ovipositing in pools that contain them. This hypothesis was tested with a series of pool choice experiments, which revealed that D. ventrimaculatus avoid placing either eggs or tadpoles into a pool which contains a large tadpole. Several hypotheses which could explain multiple deposition in this species are discussed. Received: 14 September 1998 / Accepted: 25 January 1999     

Histology and microscopic anatomy of the thyroid gland during the larval development of Pseudis platensis (Anura,Hylidae)

Several hormones regulate anuran larval development, most notably thyroid hormones (THs). In anurans, metamorphosis fails when the thyroid gland is absent or inactivated, resulting in giant tadpoles. Larval gigantism occurs naturally in neotropical frogs of the genus Pseudis as a result of a prolonged larval period. Its thyroid function is poorly investigated and the focus of this study. We describe qualitative and quantitative variations in larval development for field-captured specimens of Pseudis platensis and compare those to the development of two sympatric species, Phyllomedusa sauvagii and Pithecopus azureus, which have small tadpoles and a shorter larval period. We describe morphological changes in the thyroid glands of larval and adult specimens. In contrast to other species with similar ecological requirements, P. platensis exhibits distinct glandular activity. During premetamorphosis, there was little or no thyroid activity, a period in which the tadpole reached 70% of its maximum size. Development and degree of activity of the thyroid gland determine the duration of the early stages of the larval period. Thyroid gland histology in tadpoles appears to correlate with the TH activity, and in turn with the diversity in anuran life history transitions.     

峨眉髭蟾在重庆的分布——蝌蚪在无尾类分类和多样性调查中的应用一例

2008年5月在重庆市酉阳县采集到7号体尾背部具有"Y"形斑纹的蝌蚪,对其形态特征和口部结构予以描述,经与峨眉髭蟾Vibrissaphora boringii和崇安髭蟾瑶山亚种V. liui yaoshanensis蝌蚪比较,确定其为峨眉髭蟾,为重庆市新纪录.现作为应用蝌蚪进行无尾两栖动物分类鉴定和多样性调查实例予以报道.     

Alternative life cycle strategies of Megalodiscus temperatus in tadpoles and metamorphosed anurans

Megalodiscus temperatus (Stafford, 1905) is a common paramphistome trematode of North American amphibians with a two host life cycle and has been reported to infect frogs and rarely tadpoles. In this study we document the alternative life cycle strategy of M. temperatus in tadpoles and metamorphosed anurans. We show through field work and experimental infections that M. temperatus can establish in both anuran life stages and worms become gravid and release eggs in both tadpoles and metamorphosed frogs. However, worms exhibit differences in route of infection, development, egg production, and diet in tadpoles and metamorphosed anurans. These alternative life history strategies of M. temperatus suggest different selective pressures on the development and reproductive success of these worms in tadpoles and metamorphosed anurans, and we discuss the evolutionary avenues for and constraints on amphibian trematode life cycles presented by these two different anuran life stages.     

Effects of omnivorous shrimp in a montane tropical stream: sediment removal,disturbance of sessile invertebrates and enhancement of understory algal biomass

Freshwater shrimp dominate the faunal biomass of many headwater tropical streams: however, their role in community organization is unclear. Enclosure/exclosure experiments in a montane Puerto Rican stream examined direct and indirect effects of two dominant taxa of atyid (Atyidae) shrimp, Atya lanipes Holthuis and Xiphocaris elongata Guerin-Meneville. Both shrimp taxa caused significant reductions in sediment cover on rock substrata, reducing sedimentation and enhancing algal biovolume on clay tiles in cages. When tiles incubated in shrimp exclosures for 2 wks were placed outside of cages, atyid shrimp removed 100% of the sediment cover within a 30 min observation period. Atyid shrimp appear to play an important role in stream recovery after high discharge events by rapidly removing sediments and detritus deposited on benthic substrata in pools. We evaluated the mechanism by which A. lanipes influences algae and benthic insects by comparing patterns of algal biomass, taxonomic composition, and insect abundance between shrimp-exclusion and shrimp-presence treatments both with and without manual sediment removal. The shrimp exclusion treatment without manual sediment removal bad significantly lower algal biomass and greater sedimentation than all other treatments. The treatment in which shrimp were excluded but sediment was manually removed, however, accrued almost the same algal biovolume as the shrimp enclosure treatment, supporting the hypothesis that sediment removal enhances the biovolume of understory algal taxa. Algal community composition was similar between stream bottom bedrock exposed to natural densities of shrimp and all experimental treatments for both Atya and Xiphocaris: a diatom community strongly dominated (78–95%) by the adnate taxon, Achnanthes lanceolata Breb ex. Kutz. Atyid shrimp are important in determining the distribution and abundance of benthic insects through both direct and indirect effects. Sessile, retreat-building chironomid larvae (Chironomidae: Diptera) are negatively affected by both A. lanipes and X. elongata, through direct removal by foraging activities and/or indirectly through depression of sediment resources available to larvae for the construction of retreats. In constrast, the mobile grazer, Cloeodes maculipes (Baetidae: Ephemeroptera) was not adversely affected and atyid shrimp have the potential to exert positive indirect effects on this taxon by facilitating its exploitation of algal resources and/or through enhancement of understory algal food resources through sediment removal.