Ontogeny of the appendicularian <Emphasis Type="Italic">Oikopleura dioica</Emphasis> (Tunicata,Chordata) reveals characters similar to ascidian larvae with sessile adults

Appendicularians have always occupied a central role in considerations of tunicate and chordate evolution. Two hypotheses have been proposed – one holds that appendicularia represents the sister taxon to the remaining tunicates, the other suggests that appendicularians were derived from an ascidian-like ancestor. In the present study I report results from electron microscopic investigation of larval tunicates including the first electron microscopic investigation of the tail of the early ontogenetic appendicularian “Streckform” and discuss their phylogenetic implications. The early “Streckform” of Oikopleura dioica Fol, 1872 is invested with an extracellular covering that consists of an inner electron-light layer and an electron-dense outermost layer. In addition, the extracellular covering forms fin blades. Because these traits are shown to be similar to the tunic of different ascidian larvae, the extracellular covering in early appendicularian embryos is suggested to be homologous to the larval tunic of ascidian larvae. Overall, the tail of early developmental stages of appendicularians consists of a mosaic of apomorphic and plesiomorphic features. The straight, continuous endodermal strand was inherited from a common chordate ancestor whereas the finlets of larvae, consisting of extracellular material, were inherited from a common tunicate ancestor. The horizontal orientation of the tail as a whole was inherited from the last common ancestor of appendicularians and aplousobranch ascidians, and the discovered floating extension at the posterior tip of the tail is unique to the holoplanktonic Oikopleura dioica. These findings support the hypothesis that Appendicularia is derived from a sessile, ascidian-like ancestor.     

Environmentally relevant cadmium concentrations affect development and induce apoptosis of <Emphasis Type="Italic">Paracentrotus lividus</Emphasis> larvae cultured in vitro

Sea urchin embryos and larvae represent suitable model systems on where to investigate the effects of heavy metals on development and cell viability. Here, we tested the toxic effects of low (10⁻¹² M), medium (10⁻⁹ M), and high (10⁻⁶ M) cadmium chloride concentrations, mimicking unpolluted, moderately and highly polluted seawaters, respectively, on Paracentrotus lividus sea urchins offspring. Larvae were continuously treated from fertilization and inspected at time intervals comprised between 10 and 30 days of development. Delays and/or morphological abnormalities were firstly evident in larvae treated for 15 days with high cadmium (10⁻⁶ M) and for 25 days with medium cadmium (10⁻⁹ M). Major defects consisted in the reduction and lack of arms and skeleton elongation. No obvious differences with respect to controls were observed in embryos/larvae exposed to low cadmium (10⁻¹² M), even after 30 days of exposure. Using in situ terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay (TUNEL) assay on larvae whole mounts, we detected apoptosis after 10 days of treatment with 10⁻⁶ and 10⁻⁹ M CdCl_2, when no morphological abnormalities were recognizable yet. Supernumerary apoptotic cells were found in arm buds, ciliary bands, and apex. In conclusion, echinoderm embryos and larvae represent candidates of choice for the study of stress and defense mechanisms activated by cadmium exposure.     

Sublethal Effects of Nitrite on Eastern Tiger Salamander (<Emphasis Type="Italic">Ambystoma tigrinum tigrinum</Emphasis>) and Wood Frog (<Emphasis Type="Italic">Rana sylvatica</Emphasis>) Embryos and Larvae: Implications for Field Populations

Ephemeral pools, which can have high animal biomass and low dissolved oxygen, may be prone to nitrite accumulation. As such, it is important to understand how exposure to nitrite might affect development and growth of amphibians that breed in these ephemeral pools. Wood frog (Rana sylvatica) and eastern tiger salamander (Ambystoma tigrinum tigrinum) embryos and tadpoles and young larvae were exposed to elevated concentrations of nitrite derived from sodium nitrite: 0, 0.3, 0.6, 1.2, 2.1, 4.6, and 6.1 mg l⁻¹ NO₂–N. Increasing nitrite exposure slowed embryonic and larval development in both the eastern tiger salamander and the wood frog, reduced growth in tiger salamander embryos and larvae, and delayed metamorphosis in the wood frog. At concentrations less than 2 mg l⁻¹ NO₂–N nitrite delayed hatching, and at concentrations above 2 mg l⁻¹ time to hatching decreased causing more individuals to hatch at less developed stages. Nitrite also increased asynchrony in tiger salamander hatching. The sublethal effects of nitrite on amphibian development, growth and hatching could have serious repercussions on amphibian fitness in ephemeral environments. Potential increases in mortality on field populations caused by sublethal effects of nitrite are discussed.     

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.     

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).     

Identification of a cytoskeletal protein localized in the myoplasm of ascidian eggs: localization is modified during anural development

The myoplasm of ascidian eggs is a localized cytoskeletal domain that is segregated to presumptive larval tail muscle cells during embryonic development. We have identified a cytoskeletal protein recognized by a vertebrate neurofilament monoclonal antibody (NN18) which is concentrated in the myoplasm in eggs and embryos of a variety of ascidian species. The NN18 antigen is localized in the periphery of unfertilized eggs, segregates with the myoplasm after fertilization, and enters the larval tail muscle cells during embryonic development. Western blots of one-dimensional and two-dimensional gels showed that the major component recognized by NN18 antibody is a 58 x 10(3) Mr protein (p58), which exists in at least three different isoforms. The enrichment of p58 in the Triton X-100-insoluble fraction of eggs and its reticular staining pattern in eggs and embryos suggests that it is a cytoskeletal protein. In subsequent experiments, p58 was used as a marker to determine whether changes in the myoplasm occur in eggs of anural ascidian species, i.e. those exhibiting a life cycle lacking tadpole larvae with differentiated muscle cells. Although p58 was localized in the myoplasm in eggs of four urodele ascidian species that develop into swimming tadpole larvae, this protein was distributed uniformly in eggs of three anural ascidian species. The eggs of two of these anural species contained the actin lamina, another component of the myoplasm, whereas the third anural species lacked the actin lamina. There was no detectible localization of p58 after fertilization or segregation into muscle lineage cells during cleavage of anural eggs. NN18 antigen was uniformly distributed in pre-vitellogenic oocytes and then localized in the perinuclear zone during vitellogenesis of urodele and anural ascidians. Subsequently, NN18 antigen was concentrated in the peripheral cytoplasm of post-vitellogenic oocytes and mature eggs of urodele, but not anural, ascidians. It is concluded that the myoplasm of ascidian eggs contains an intermediate filament-like cytoskeletal network which is missing in anural species that have modified or eliminated the tadpole larva.     

Anatomy of the trunk mesoderm in tunicates: homology considerations and phylogenetic interpretation

The tadpole stage of tunicates has played a pivotal role in understanding chordate evolution. While the organization of the mesoderm has been given high importance in comparative anatomical studies of Bilateria, this morphological character remains largely unexplored in tunicate tadpoles. For larvae of the phlebobranch ascidian Ciona intestinalis, the presence of two mesodermal pockets had been claimed, raising the possibility that paired coelomes are present in the larval ascidian. Using computer assisted 3D-reconstructions based on complete series of 1 μm-sections analyzed by light microscopy complemented by TEM-investigation of selected regions a comparative anatomical study of tadpole stages from four major tunicate clades, Aplousobranchiata, Phlebobranchiata, Stolidobranchiata, and Appendicularia is presented. In the aplousobranch Clavelina lepadiformis numerous mesodermal cells are found throughout the entire trunk plus the unpaired ventral rudiment of the pericardium. In the phlebobranch Ascidia interrupta, massive mesodermal components occur in the posterior trunk, whereas more anteriorly situated mesoderm consists of loose streaks of cells or isolated cells. This is also the case in the stolidobranch ascidians Herdmania momus and Styela plicata. In the stolidobranch Molgula occidentalis and the appendicularian Oikopleura dioica the anterior trunk is entirely devoid of mesodermal cells. TEM-investigation revealed that all mesodermal structures in the trunk of tunicate tadpoles were mesenchymal with the exception of a ventral portion of the mesoderm in C. lepadiformis, which probably corresponds to the developing pericardium, and the differentiated pericardium of the juvenile O. dioica. Thus no evidence for paired coelomic cavities in Tunicata was found. Outgroup comparison suggests that the reduction of paired coelomic cavities is an apomorphic trait of Tunicata. Within Tunicata a stepwise evolutionary reduction of the anterior larval mesenchyme is documented.     

Settlement behaviour of larvae of the Stripey Snapper, <Emphasis Type="Italic">Lutjanus carponotatus</Emphasis> (Teleostei: Lutjanidae)

Larval behaviour is important to dispersal and settlement, but is seldom quantified. Behavioural capabilities of larval Lutjanus carponotatus in both offshore pelagic and reef environments at Lizard Island, Great Barrier Reef were observed in situ to determine if they were sufficient to influence dispersal. Offshore, larvae swam with higher directional precision and faster on the windward side of the island (28 cm.s⁻¹) than on the leeward side (16 cm s⁻¹). Most larvae swam directionally. Mean swimming directions were southerly in the windward area and northerly in the leeward area. Larvae avoided the surface and remained mostly between 3–15 m. Larvae released near reefs were 2–3 times faster swimming away from reefs (19 cm s⁻¹) than swimming toward or over them (6–8 cm s⁻¹). Speed swimming away was similar to that offshore. Of 41 larvae released near reefs, 73% reached the reef, 59% settled, and 13% of those reaching the reef were eaten. Larvae settled onto hard and soft coral (58%), topographic reef features (29%) and sand and rubble (13%). Settlement depth averaged 5.5 m (2–8 m). Before settling larvae spent up to 800 s over the reef (mean 231 s) and swam up to 53 m (mean 14 m). About half of the larvae interacted with reef residents including predatory attacks and aggressive approaches by residents and aggressive approaches by settling larvae. Settlement behaviour of L. carponotatus was more similar to a serranid than to pomacentrids. Settlement-stage larvae of L. carponotatus are behaviourally capable, and have a complex settlement behaviour.     

Toxicity of Diazinon 60 EC for embryos and larvae of tench, <Emphasis Type="Italic">Tinca tinca</Emphasis> (L.)

The effects of Diazinon 60 EC (organophosphate insecticide, active substance diazinon) on mortality, growth rate, early ontogenetic rate, and occurrence of malformations was studied in embryos and larvae of tench, Tinca tinca (L.). The exposure of fish to 0, 10, 100, 1,000, and 3,000 μg dm⁻³ of Diazinon 60 EC was initiated 24 h after fertilization of eggs and concluded 32 days later. At the highest concentration tested (3,000 μg dm⁻³), total mortality was observed within the first 15 days of exposure. A concentration of 1,000 μg dm⁻³ caused high incidence of malformations, decrease in growth rate and ontogenetic development slowed down. A concentration of 100 μg dm⁻³ mildly decreased growth rate, but at 10 μg dm⁻³ no changes compared to the control were observed. Thus, Diazion 60 EC at the concentration of 10 μg dm⁻³ is not dangerous for the embryos and larvae of tench.     

Vertical transmission of photosymbionts in the colonial ascidian Didemnum molle: the larval tunic prevents symbionts from attaching to the anterior part of larvae

Morphological processes in the vertical transmission of photosymbionts were investigated in the Prochloron-bearing ascidian Didemnum molle. Prochloron cells were found exclusively in the common cloacal cavity of the colony, attached mainly to the tunic lining of the cavity wall. Oocytes were found in the abdominal region of each zooid, but no Prochloron cells were associated with this stage. During embryogenesis, embryos moved into the tunic core of the colony and were always separated from Prochloron cells in the cloacal cavity by the tunic matrix, until they hatched out from the tunic core. In swimming larvae, Prochloron cells covered the surface of the posterior half of the larval trunk, whereas a thin larval tunic layer covered the anterior half, where no Prochloron cells were found. The tunic of the posterior half of the larval trunk had many folds that enfolded the Prochloron cells and may be adhesive in order to acquire Prochloron cells from the mother colony. The thin larval tunic layer is probably not adhesive and protects the anterior half of the trunk from interference by Prochloron cells with sensory receptors and adhesive organs.     

Thermal sensitivity of scope for activity in Pagothenia borchgrevinki, a cryopelagic Antarctic nototheniid fish

The thermal sensitivity of scope for activity was studied in the Antarctic nototheniid fish Pagothenia borchgrevinki. The scope for activity of P. borchgrevinki at 0°C was 189 mg O₂ kg⁻¹ h⁻¹ (factorial scope 6.8) which is similar to that of temperate and tropical species at their environmental temperatures, providing no evidence for metabolic cold adaptation of maximum activity. The scope for activity increased to a maximum value of 266 mg O₂ kg⁻¹ h⁻¹ (factorial scope 8.3) at 3°C and then decreased from 3 to 6°C. The thermal sensitivity of critical swimming speed was also investigated and followed a similar pattern to aerobic scope for activity, suggesting oxygen limitation of aerobic performance. Oxygen consumption rates and ventilation frequencies were monitored for 24 h after the swimming challenge and the recovery of both parameters to resting levels was rapid and independent of temperature.     

Loss of test cells leads to the formation of new tunic surface cells and abnormal metamorphosis in larvae of Ciona intestinalis (Chordata, Ascidiacea)

The larvae of the ascidian Ciona intestinalis from which the chorion with the test cells and follicle cells were removed developed normally without the test cells until the early tailbud stage. A number of round-shaped cells morphologically similar to the test cells but with different lectin affinities and autofluorescence, then appeared on the neck region of the demembranated embryos. The new cells had three different types: round, particulate, and granular, and these cells increased in number after the late tailbud stage. The morphology of the adhesive papillae, tunic layers and epidermis of the demembranated larvae was similar to that of control larvae; however, the affinity to lectins was different in the swimming period. Control larvae attached to the substratum after the swimming period, resorbed the tail completely and underwent rotation of the visceral organs. Conversely, rotation occurred before completion of tail resorption in the demembranated larvae. Furthermore, the metamorphic events progressed more slowly in the demembranated larvae. These results suggest that the test cells play important roles in normal development and morphogenesis of ascidian larvae. Received: 4 December 1998 / Accepted: 9 April 1999     

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.     

Risk of predation and behavioural response in three anuran species: influence of tadpole size and predator type

Many species alter their activity, microhabitat use, morphology and life history in response to predators. Predation risk is related to predator size and palatability of prey among others factors. We analyzed the predation risk of three species of tadpoles that occur in norwestern Patagonia, Argentina: Pleurodema thaul, Pleurodema bufoninum and Rhinella spinulosa. We sampled aquatic insect predators in 18 ponds to determine predator–tadpole assemblage in the study area. In laboratory conditions, we analysed the predation rate imposed by each predator on each tadpole species at different tadpole sizes. Finally, we tested whether tadpoles alter their activity in the presence of chemical and visual cues from predators. Small P. thaul and P. bufoninum tadpoles were the most vulnerable prey species, while small R. spinulosa tadpoles were only consumed by water bugs. Dragonflies and water bugs were the most dangerous tadpole predators. Small P. thaul tadpoles reduced their activity when they were exposed to all predators, while large tadpoles only reduced the activity in the presence of large predators (dragonfly larvae and water bugs). Small P. bufoninum tadpoles reduced the activity when they were exposed to beetle larvae and dragonfly larvae, while large tadpoles only reduced activity when they were exposed to larger predators (water bugs and dragonfly larvae). R. spinulosa tadpoles were the less sensitive to presence of predators, only larger tadpoles responded significantly to dragonfly larvae by reducing their activity. We conclude that behavioural responses of these anuran species were predator-specific and related to the risk imposed by each predator.     

Energy flow and subsidies associated with the complex life cycle of ambystomatid salamanders in ponds and adjacent forest in southern Illinois

Breeding adults and metamorphosing larval amphibians transfer energy between freshwater and terrestrial ecosystems during seasonal migrations and emergences, although rarely has this been quantified. We intensively sampled ambystomatid salamander assemblages (Ambystoma opacum,A. maculatum, and A. tigrinum) in five forested ponds in southern Illinois to quantify energy flow associated with egg deposition, larval production, and emergence of metamorphosed larvae. Oviposition by female salamanders added 7.0–761.4 g ash-free dry mass (AFDM) year⁻¹ to ponds (up to 5.5 g AFDM m⁻² year⁻¹). Larval production ranged from 0.4 to 7.4 g AFDM m⁻² year⁻¹ among populations in three ponds that did not dry during larval development, with as much as 7.9 g AFDM m⁻² year⁻¹ produced by an entire assemblage. Mean larval biomass during cohort production intervals in these three ponds ranged from 0.1 to 2.3 g AFDM m⁻² and annual P/B (production/biomass) ranged from 4 to 21 for individual taxa. Emergent biomass averaged 10% (range=2–35%) of larval production; larval mortality within ponds accounted for the difference. Hydroperiod and intraguild predation limited larval production in some ponds, but emerging metamorphs exported an average of 70.0±33.9 g AFDM year⁻¹ (range=21.0–135.2 g AFDM year⁻¹) from ponds to surrounding forest. For the three ponds where larvae survived to metamorphosis, salamander assemblages provided an average net flux of 349.5±140.8 g AFDM year⁻¹ into pond habitats. Among all ponds, net flux into ponds was highest for the largest pond and decreased for smaller ponds with higher perimeter to surface area ratios (r ² =0.94, P<0.05, n=5). These results are important in understanding the multiple functional roles of salamanders and the impact of amphibian population declines on ecosystems. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

The Antarctic notothenioid fish <Emphasis Type="Italic">Pagothenia borchgrevinki</Emphasis> is thermally flexible: acclimation changes oxygen consumption

Antarctic marine organisms are considered to have extremely limited ability to respond to environmental temperature change. However, here we show that the Antarctic notothenioid fish Pagothenia borchgrevinki is an exception to this theory. P. borchgrevinki was able to acclimate its resting metabolic rate and resting ventilation frequency after a 5°C rise in temperature. Acute exposure to 4°C resulted in an elevation in metabolic rate (57.8 ± 4.79 mg O₂ kg⁻¹ h⁻¹) and resting ventilation rate (40.38 ± 1.61 breaths min⁻¹) compared with fish at −1°C (metabolic rate 34.45 ± 3.12 mg O₂ kg⁻¹ h⁻¹; ventilation rate 29.88 ± 3.72 breaths min⁻¹). However, after a 1-month acclimation period, there was no significant difference in the metabolic rate (cold fish 29.52 ± 3.01; warm fish 31.13 ± 2.30 mg O₂ kg⁻¹ h⁻¹), or the resting ventilation rate (cold fish 28.75 ± 0.98; warm fish 34.25 ± 2.28 breaths min⁻¹) of cold and warm acclimated fish. Acclimation changes to the rate of oxygen consumption following exhaustive exercise were complex. The pattern of oxygen consumption during recovery from exhaustive exercise was not significantly different in either cold or warm acclimated fish.     

Novel Antifouling and Antimicrobial Compound from a Marine-Derived Fungus Ampelomyces sp.

In this study, using a bioassay-guided isolation and purification procedure, we obtained 3-chloro-2,5-dihydroxybenzyl alcohol from a marine-derived Ampelomyces species that effectively inhibited larval settlement of the tubeworm Hydroides elegans and of cyprids of the barnacle Balanus amphitrite. The inhibitive effect on larval settlement was nontoxic and the EC₅₀ of 3-chloro-2,5-dihydroxybenzyl alcohol ranged from 3.19 μg ml⁻¹ to 3.81 μg ml⁻¹ while the LC₅₀ was 266.68 μg ml⁻¹ for B. amphitrite cyprids; EC₅₀ ranged from 0.67 μg ml⁻¹ to 0.78 μg ml⁻¹, and LC₅₀ was 2.64 μg ml⁻¹ for competent larvae of H. elegans, indicating that inhibitive effect of this compound was nontoxic. At a concentration of 50 μg per disc, this compound showed strong inhibitive effects on the growth of 13 out of 15 marine bacterial species tested in disc diffusion bioassay. Overall, the high inhibitory activities against bacteria and larval settlement as well as the non- or low-toxic nature of this compound to the barnacle and polychaete larvae suggest this compound could be a potent antifoulant and/or antibiotic.     

Embryonic and larval defensive responses of agile frog (Rana dalmatina) to alien crayfish

Red swamp crayfish Procambarus clarkii, a widespread invasive alien crayfish, represents a serious threat for several freshwater species, including amphibians, which are declining at a global scale. As a shared coevolutionary history is the main factor determining the emergence of antipredator responses, Anuran tadpoles may not be able to cope effectively with this introduced predator. We performed two experiments to assess agile frog's (Rana dalmatina) defensive responses to both P. clarkii and native dragonfly larvae (Anax imperator). First, we conditioned embryos (collected from two ponds 30 km away from each other) with predators’ chemical cues to explore possible variation in hatching time caused by predation risk. In the second experiment, to evaluate how predators’ diet affects tadpole behavior, we conditioned tadpoles for a 5‐week period with cues from tadpole‐fed and gammarid‐fed predators and recorded behavioral and morphological responses. Embryos did not alter hatching time in the presence of any predator cue, while tadpoles from both populations strongly reduced activity and visibility when raised in the presence of tadpole‐fed dragonfly larvae. Morphological changes were less straightforward and were induced only in one population, for which broader tails and a slight increase in body size of tadpoles exposed to tadpole‐fed predators were observed. The lack of defensive responses in crayfish‐exposed tadpoles suggests that the spreading of this invasive species in agricultural lowlands of northern Italy may represent a further threat to their conservation.     

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     

Relationship Between Medium Salinity, Body Density, Buoyancy and Swimming in Artemia franciscana Larvae: Constraints on Water Column Use?

Body density measurements were carried out on larval Artemia franciscana that had been held for 24 h at either 33 or 100‰ after hatching. Body density was low (1.0308–1.0342 g ml⁻¹) by comparison with marine crustacean zooplankters or benthic freshwater crustaceans, and very stable, being only 0.3% higher in 100‰ than in 33‰. Vertical and horizontal swimming in 2nd instar larvae was studied at 8.5, 17, 34, 50, 100, 150 and 250‰ at 23 °C. At 8.5–50‰ downwards swimming was always significantly faster than upwards swimming, but in 100‰ downwards swimming was much slower than upwards swimming, indicating substantial positive buoyancy. At 150 and 250‰ downwards swimming was impossible. Horizontal swimming speed was unaffected by salinity over the range 8.5–100‰, but could not be studied at 150 and 250‰ as larvae could not leave the surface film. An asymptotic relationship between salinity and viscosity was found over the range 8.5–250‰. Calculations indicate a rise from 1.197 to 1.513 cp between 8.5 and 100‰, but this does not significantly impede horizontal locomotion. It appears that water column use by early stage Artemia larvae, that use a pair of 2nd antennae for rowing-type locomotion, is constrained by the increasing positive buoyancy associated with living at salinities above that corresponding to neutral buoyancy (approximately 48‰).