Morphology and metamorphosis of Eupsophus calcaratus tadpoles (Anura: Leptodactylidae)

Eupsophus calcaratus, a leptodactyloid frog from the austral Andean forests of Argentina and Chile, has endotrophic, nidicolous tadpoles. We studied a metamorphic series from Stages 31 to 46 of Gosner's developmental table (1960). Other than the scarce pigmentation, proportionately large eyes, and massive developing hindlimbs, the remaining external characters are similar to those of generalized, exotrophic larvae. At the same time, internal morphology does not reveal any character state attributable to the endotrophic-nidicolous way of life; conversely, structures such as the hyobranchial skeleton and the mandibular cartilages are similar to those of exotrophic-macrophagous tadpoles. The metamorphic process is characterized by the delayed development of diverse structures (e.g., ethmoid region, palatoquadrate, and hyobranchial apparatus), and the retention of some larval characters (e.g., parietal fenestrae, overall absence of ossification) with the absence of development of some "juvenile" characters (e.g., adult otic process, several bones) in metamorphosed individuals. These heterochronic processes and truncation of larval development are related to a shorter larval life (when compared to other species of the austral Andean region) and to the small size at metamorphosis.     

Living in fast‐flowing water: Morphology of the gastromyzophorous tadpole of the bufonid Rhinella quechua (R. veraguensis group)

We describe the bufonid gastromyzophorous tadpoles of Rhinella quechua from montane forest streams in Bolivia. Specimens were cleared and stained, and the external morphology, buccopharyngeal structures, and the musculoskeletal system were studied. These tadpoles show a combination of some traits common in Rhinella larvae (e.g., emarginate oral disc with large ventral gap in the marginal papillae, labial tooth row formula 2/3, prenarial ridge, two infralabial papillae, quadratoorbital commissure present, larval otic process absent, mm. mandibulolabialis superior, interhyoideus posterior, and diaphragmatopraecordialis absent, m. subarcualis rectus I composed of three slips), some traits apparently exclusive for the described species of the R. veraguensis group (e.g., second anterior labial tooth row complete, lingual papillae absent, adrostral cartilages present), and some traits that are shared with other gastromyzophorous tadpoles (e.g., enlarged oral disc, short and wide articular process of the palatoquadrate, several muscles inserting on the abdominal sucker). In the context of the substantial taxonomic and nomenclatural changes that the former genus Bufo has undergone, and despite the conspicuous morphological differences related to the presence of an abdominal sucker, the larval morphology of R. quechua supports including it in the genus Rhinella and placing it close to species of the R. veraguensis assemblage. J. Morphol., 2009. © 2009 Wiley‐Liss, Inc.     

The Reproductive Biology and Larvae of the First Tadpole-Bearing Frog,Limnonectes larvaepartus

Most of the reproductive modes of frogs include an exotrophic tadpole, but a number of taxa have some form of endotrophic development that lacks a feeding tadpole stage. The dicroglossid frog genus Limnonectes ranges from China south into Indonesia. The breeding biologies of the approximately 60 described species display an unusual diversity that range from exotrophic tadpoles to endotrophic development in terrestrial nests. There have been mentions of oviductal production of typical, exotrophic tadpoles in an undescribed species of Limnonectes from Sulawesi, Indonesia. Here we examine newly collected specimens of this species, now described as L. larvaepartus and present the first substantial report on this unique breeding mode. Typical exotrophic tadpoles that are retained to an advanced developmental stage in the oviducts of a female frog are birthed into slow-flowing streams or small, non-flowing pools adjacent to the streams.     

The hyal and ventral branchial muscles in caecilian and salamander larvae: Homologies and evolution

Amphibians (Lissamphibia) are characterized by a bi‐phasic life‐cycle that comprises an aquatic larval stage and metamorphosis to the adult. The ancestral aquatic feeding behavior of amphibian larvae is suction feeding. The negative pressure that is needed for ingestion of prey is created by depression of the hyobranchial apparatus as a result of hyobranchial muscle action. Understanding the homologies of hyobranchial muscles in amphibian larvae is a crucial step in understanding the evolution of this important character complex. However, the literature mostly focuses on the adult musculature and terms used for hyal and ventral branchial muscles in different amphibians often do not reflect homologies across lissamphibian orders. Here we describe the hyal and ventral branchial musculature in larvae of caecilians (Gymnophiona) and salamanders (Caudata), including juveniles of two permanently aquatic salamander species. Based on previous alternative terminology schemes, we propose a terminology for the hyal and ventral branchial muscles that reflects the homologies of muscles and that is suited for studies on hyobranchial muscle evolution in amphibians. We present a discussion of the hyal and ventral branchial muscles in larvae of the most recent common ancestor of amphibians (i.e. the ground plan of Lissamphibia). Based on our terminology, the hyal and ventral branchial musculature of caecilians and salamanders comprises the following muscles: m. depressor mandibulae, m. depressor mandibulae posterior, m. hyomandibularis, m. branchiohyoideus externus, m. interhyoideus, m. interhyoideus posterior, m. subarcualis rectus I, m. subarcualis obliquus II, m. subarcualis obliquus III, m. subarcualis rectus II‐IV, and m. transversus ventralis IV. Except for the m. branchiohyoideus externus, all muscles considered herein can be assigned to the ground plan of the Lissamphibia with certainty. The m. branchiohyoideus externus is either apomorphic for the Batrachia (frogs + salamanders) or salamander larvae depending on whether or not a homologous muscle is present in frog tadpoles. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.     

The energetics of endotrophic development in the frog Geocrinia vitellina (Anura: Myobatrachinae).

The energetics of endotrophic development, where the nutrition required to complete metamorphosis is provided solely by yolk, has seldom been quantified. The energy cost of development to metamorphosis of the endotrophic Australian frog Geocrinia vitellina was measured using bomb calorimetry and closed-system respirometry. Dry yolk had an energy density of 26.4 J x mg(-1), and an average 2.8-mm-diameter ovum contained 144 J. Incubation at 15 degrees C produced a froglet of 5.8 mm snout-vent length, containing 88 J in 87 d, with 11% of residual yolk in the gut, which is markedly less than the 50% recorded in another endotroph, Eleutherodactylus coqui. Geocrinia vitellina lost 56 J of metabolic energy during development to metamorphosis at 15 degrees C, and the total production efficiency was 61.0%. A review of published egg energy densities found a mean for amphibians of 25.1 kJ x g(-1), significantly lower than the mean of 27.1 kJ x g(-1) for reptiles. Moreover, available amphibian data suggest that endotrophic species have high yolk energy densities and low mass-specific rates of oxygen consumption relative to exotrophic species (with feeding larvae); consequently, large ovum size may not necessarily be prerequisite for endotrophic development.     

Biochemical compounds’ dynamics during larval development of the carpet-shell clam <Emphasis Type="Italic">Ruditapes decussatus</Emphasis> (Linnaeus, 1758): effects of mono-specific diets and starvation

Successful larval growth and development of bivalves depend on energy derived from internal (endotrophic phase) and external (exotrophic phase) sources. The present paper studies survival, growth and biochemical changes in the early developmental stages (from egg to pediveliger) of the clam Ruditapes decussatus in order to characterize the nutritional requirements and the transition from the endotrophic to the exotrophic phase. Three different feeding regimes were applied: starvation and two mono-specific microalgal diets (Isochrysis aff galbana and Chaetoceros calcitrans). A comparison between fed and unfed larvae highlighted the importance of egg lipid reserves, especially neutral lipids, during a brief endotrophic phase of embryonic development (first 2 days after fertilization). Egg reserves, however, may energetically contribute to the maintenance of larvae beyond the embryonic development. In fed larvae, the endotrophic phase is followed by a mixotrophic phase extending to days 5–8 after fertilization and a subsequent exotrophic phase. Metamorphosis starts around day 20. The intense embryonic activities are supported by energy derived from lipids, mainly from neutral lipids, and the metamorphic activities are supported by energy derived essentially from proteins accumulated during the planktonic phase and depend on the nutritional value of diets. The diet of I. aff galbana proves to be more adequate to R. decussatus larval rearing. The results provide useful information for the successful production of R. decussatus aquaculture.     

Profile of Digestive Enzymes Activity During Early Development of Featherback <Emphasis Type="Italic">Chitala chitala</Emphasis> (Hamilton, 1822)

The ontogenetic development of the key digestive enzymes of featherback Chitala chitala was assayed during the early development. Amylase, lipase, trypsin and chymotrypsin activities were detected on 1 days after hatch (DAH), (during endotrophic stage) but pepsin activity was detected on 12 DAH (exotrophic phase) correlated with the improvement of gastric secretion at the beginning of flexion stage. The gradual shift of alkaline protease activity (trypsin and chymotrypsin) to more efficient acidic digestion indicated a change in the digestive physiology as a result of metamorphosis acquiring the juvenile characteristic during the postflexion or extrophic phase. The initial high level of amylase (i.e. from 1 DAH to 9 DAH) during endotrophic and endoexotrophic feeding stage could be better explained as a result of programmed gene expression. But a constant decrease in activity after the 12 DAH i.e. on the onset of flexion and exotrophic stage of featherback fish in the present study may be possibly due to the developmental changes in the gut morphology and increased protein level in the tissue. These fluctuations of the enzymatic activities in featherback larvae reflect the ability of the fish to adapt with the diet during ontogenetic shift. This information can lead to the possibility of developing an age specific formulated feed for intensive farming of this new candidate species.     

From competent larva to exotrophic juvenile: a morphofunctional study of the perimetamorphic period of Paracentrotus lividus (Echinodermata, Echinoida)

 The perimetamorphic period in Paracentrotus lividus lasts for 8–12 days. It starts from the acquisition of larval competence, includes the change in form (metamorphosis) and the endotrophic postlarval life, and stops with the appearance of the exotrophic juvenile. All major postlarval appendages already occur in competent larvae being either grouped into the echinoid rudiment (terminal plates, early spines and primary podia) or scattered within the larval integument (genital plates and sessile pedicellariae). Competent larvae show particular behaviour which brings them close to the substratum. The latter is tested by primary podia protruding through the vestibular aperture of the larva. Primary podia are sensory–secretory appendages that are deprived ampullae. They are able to adhere to the substratum in order to allow evagination of the echinoid rudiment (i.e. metamorphosis) and substatum adhesion of the postlarva. Particular spines are borne by the postlarva; these are multifid non-mobile appendages forming a kind of protective armour. Like those of the larva, all characteristic structures of the postlarva (primary podia, multified spines and sessile pedicellariae) are transitory and regress either at the end of postlarval life (primary podia) or during early juvenile life (multifid spines and sessile pedicellariae). Other appendages that develop during postlarval life (i.e. podia with ampulla, point-tipped spines and sphaeridiae) are similar to those borne by the adults and become functional when the individual enters its juvenile life. Thus, the perimetamorphic period appears to be a fully fledged period in the life-cycle of P. lividus, and presumably in the life-cycle of any other sea-urchin species. Accepted: 7 October 1997     

Morphogenesis and phenotypic divergence in two developmental morphs of Streblospio benedicti (Annelida,Spionidae)

Abstract. The morphology of marine invertebrate larvae is strongly correlated with egg size and larval feeding mode. Planktotrophic larvae typically have suites of morphological traits that support a planktonic, feeding life style, while lecithotrophic larvae often have larger, yolkier bodies, and in some cases, a reduced expression of larval traits. Poecilogonous species provide interesting cases for the analysis of early morphogenesis, as two morphs of larvae are produced by a single species. We compared morphogenesis in planktotrophic and lecithotrophic morphs of the poecilogonous annelid Streblospio benedicti from the trochophore stage through metamorphosis, using observations of individuals that were observed alive, with scanning electron microscopy, or in serial sections. Offspring of alternate developmental morphs of this species are well known to have divergent morphologies in terms of size, yolk content, and the presence of larval bristles. We found that some phenotypic differences between morphs occur as traits that are present in only one morph (e.g., larval bristles, bacillary cells on the prostomium and pygidium), but that much of the phenotypic divergence is based on heterochronic changes in the differentiation of shared traits (e.g., gut and coelom). Tissue and organ development are compared in both morphs in terms of their structure and ontogenetic change throughout early development and metamorphosis.     

Configurations of the rectus abdominis muscle of anuran tadpoles

Configurations of the rectus abdominis in tadpoles of 60 anuran species in 13 families were examined. This muscle is present by Gosner stage 25 and does not change until late in metamorphosis. The anterior terminus of the r. abdominis usually is a straight, transverse front or fan-shaped array only loosely associated with the rectus cervicis. In some suspension feeders (Rhinophrynus, Xenopus, but not microhylids), macrophagous suction feeders (Lepidobatrachus) and bromeliad inhabitants (Hyla bromeliacia) the r. abdominis is contigous with the r. cervicis which continues anterolaterally and dorsally from the wall of the spiracular cavity. Suctorial forms (Scutiger), those that live in confined spaces (burrowers, Centrolenella; bromeliad inhabitants, Hyla bromeliacia), and the taxa that have the r. cervicis and r. abdominis contiguous all have closed myosepta; the myosepta of other taxa; except for ones with large tadpoles (e.g., Rana catesbeiana), have large gaps between at least anterior myotomes. These initial data suggest that the configurations of the r. abdominis have responded to selection based on ecomorphological function and convergence among lineages are noted. © 1992 Wiley-Liss, Inc.     

Metamorphosis of cranial design in tiger salamanders (Ambystoma tigrinum): A morphometric analysis of ontogenetic change

While ontogenetic analyses of skull development have contributed to our understanding of phylogenetic patterns in vertebrates, there are few studies of taxa that undergo a relatively discrete and rapid change in morphology during development (metamorphosis). Morphological changes occurring in the head at metamorphosis in tiger salamanders (Ambystoma tigrinum) were quantified by a morphometric analysis of cranial osteology and myology to document patterns of change during metamorphosis. We employed a cross-sectional analysis using a sample of larvae just prior to metamorphosis and a sample of transformed individuals just after metamorphosis, as well as larvae undergoing metamorphosis. There were no differences in external size of the head among the larval and transformed samples. The hyobranchial apparatus showed many dramatic changes at metamorphosis, including shortening of ceratobranchial 1 and the basibranchial. The subarcualis rectus muscle increased greatly in length at metamorphosis, as did hypobranchial length and internasal distance. A truss analysis of dorsal skull shape showed that at metamorphosis the snout becomes wider, the maxillary and squamosal triangles rotate posteromedially, and the neurocranium shortens (while maintaining its width), resulting in an overall decrease in skull length at metamorphosis. These morphometric differences are interpreted in light of recent data on the functional morphology of feeding in salamanders. Morphological reorganization of the hyobranchial apparatus and shape changes in the skull are related to the acquisition of a novel terrestrial feeding mode (tongue projection) at metamorphosis. Metamorphic changes (both internal and external) that can be used to judge metamorphic condition are discussed.     

Metamorphosis of the feeding mechanism in tiger salamanders (Ambystoma tigrinum): the ontogeny of cranial muscle mass

Most previous research on metamorphosis of the musculoskeletal system in vertebrates has focused on the transformation of the skeleton. In this paper we focus on the transformation of the muscles of the head during metamorphosis in tiger salamanders ( Ambystoma tigrinum ) in order (1) to provide new data on changes in myology during ontogeny, and (2) to aid in interpreting previous data on the metamorphosis of function in the head of salamanders.
The physiological cross-sectional area of nine head muscles was calculated by measuring fibre angles, fibre lengths, and muscle mass in two samples of tiger salamanders obtained just before and just after metamorphosis. The major mouth-opening muscles (rectus cervicis and depressor mandibulae) exhibit a significant decrease in estimated maximum tetanic tension (MTT) across metamorphosis of about 36%. The jaw-closing muscles (adductor mandibulae internus and externus) and the head-lifting muscles (epaxials) also decrease in MTT but not significantly. The muscles associated with tongue projection during feeding on land (the subarcualis rectus I, geniohyoideus, interhyoideus and intermandibularis) all show a slight increase in MTT at metamorphosis.
Metamorphic transformation of feeding behaviour in Ambystoma tigrinum involves changes in performance, the design of skeletal elements, changes in muscle force-generating capability, and changes in hydrodynamic design from unidirectional flow in larvae to bidirectional flow during aquatic feeding after metamorphosis. Although muscle activity patterns during aquatic feeding do not change across metamorphosis, tongue-based terrestrial feeding involves a suite of novel muscle activity patterns, morphological characters acquired at metamorphosis, and a metamorphic increase in the masses of muscles important in tongue projection.     

Energetics of metamorphic climax in the pickerel frog (Lithobates palustris)

Anuran metamorphosis, the transition from aquatic larvae to terrestrial juveniles, is accompanied by significant morphological, physiological, and behavioral changes. Timing of metamorphosis and final size, which can influence adult fitness, may depend on sufficient energy accumulated during the larval period to support metamorphosis. However, only two species of anurans have been examined for energetic costs of metamorphosis, Rana tigrina and Anaxyrus terrestris. Based on these species, it has been hypothesized that differences in energy expenditure are related to duration of metamorphosis. To compare energetic costs of metamorphosis among species and examine this hypothesis, we quantified the total energy required for metamorphosis of Lithobates palustris tadpoles by measuring oxygen consumption rates over the duration of metamorphic climax using closed-circuit respirometry. Total energy costs for L. palustris were positively related to tadpole mass and duration of metamorphic climax. However, larger tadpoles completed metamorphosis more efficiently because they used proportionally less total energy for metamorphic climax than smaller counterparts. Costs were intermediate to R. tigrina, a larger species with similar metamorphic duration, and A. terrestris, a smaller species with shorter metamorphic climax. The results supported the hypothesis that amphibian species with more slowly developing tadpoles, such as ranids, require more absolute energy for metamorphosis in comparison to more rapidly developing species like bufonids.     

A study of the assimilation of fluorescent pigments of microalgae Isochrysis galbana by the early larval stages of turbot and herring

The appearance of large supranuclear vacuoles in the enterocytes of 1- and 4-days post-hatch larvae of turbot and herring, respectively, revealed by the pinocytotic uptake of a fluorescent marker (FITCdextran), indicates a potential for the absorption of dissolved nutrients by the endotrophic stages of marine fish larvae. Ingestion of algal cells by turbot larvae was observed soon after hatching, but low level pinocytotic absorption of algal material was first seen during the second day. More extensive lysis of algal cells and pinocytotic absorption occurred 24 h later. Although lysis of I. galbana was shown to occur at low external osmolarities, it is unlikely that sufficiently low osmolarities present in the hind gut of turbot larvae explained the observed rupture of algae. Other mechanisms for digestion are discussed. In newly hatched herring larvae, algal cells were unable to pass beyond the constriction in the mid-gut caused by the yolk sac. When algal cells were eventually seen to pass into the hind gut, there was no evidence of algal digestion or absorption throughout the remaining endotrophic and early exotrophic stages of herring larvae, although pinocytosis was observed to occur mid-way through the endotrophic stage.     

Digestive plasticity in tadpoles of the Chilean giant frog (Caudiverbera caudiverbera): factorial effects of diet and temperature

Anuran metamorphosis is one of the most spectacular processes in nature. Metamorphosis entails morphological transformations and extensive changes in feeding habits, such as transforming from an herbivore to a carnivore. This phenomenon is especially sensitive to environmental cues. We studied the phenotypic plasticity of intestinal morphology and enzyme activity in tadpoles of the Chilean giant frog Caudiverbera caudiverbera. We tested the effects of diet and temperature using a factorial design, which included a control of nontreated individuals. There was no significant effect of diet treatment (i.e., low- vs. high-quality diet) on any of the measured variables, including external morphology. We found significant effects of temperature on morphological traits. Temperature treatment also had significant effects on aminopeptidase-N and maltase activity. Both enzymes exhibited complex interactions with temperature along the intestine. Gut size varied significantly among temperatures, with intestines from warm-treated individuals smaller than the intestines from control and cold-treated tadpoles. Our findings suggest that phenotypic plasticity of intestinal morphology and physiology exists in larvae of this species, at least in response to temperature. However, we did not detect clear effects of diet or temperature on the timing of metamorphosis.     

Reversibility of predator‐induced plasticity and its effect at a life‐history switch point

In natural systems, organisms are frequently exposed to spatial and temporal variation in predation risk. Prey organisms are known to develop a wide array of plastic defences to avoid being eaten. If inducible plastic defences are costly, prey living under fluctuating predation risk should be strongly selected to develop reversible plastic traits and adjust their defences to the current predation risk. Here, we studied the induction and reversibility of antipredator defences in common frog Rana temporaria tadpoles when confronted with a temporal switch in predation risk by dragonfly larvae. We examined the behaviour and morphology of tadpoles in experimental treatments where predators were added or withdrawn at mid larval development, and compared these to treatments with constant absence or presence of predators. As previous studies have overlooked the effects that developing reversible anti‐predator responses could have later in life (e.g. at life history switch points), we also estimated the impact that changes in antipredator responses had on the timing of and size at metamorphosis. In the presence of predators, tadpoles reduced their activity and developed wider bodies, and shorter and wider tails. When predators were removed tadpoles switched their behaviour within one hour to match that found in the constant environments. The morphology matched that in the constant environments in one week after treatment reversal. All these responses were highly symmetrical. Short time lags and symmetrical responses for the induction/reversal of defences suggest that a strategy with fast switches between phenotypes could be favoured in order to maximise growth opportunities even at the potential cost of phenotypic mismatches. We found no costs of developing reversible responses to predators in terms of life‐history traits, but a general cost of the induction of the defences for all the individuals experiencing predation risk during some part of the larval development (delayed metamorphosis). More studies examining the reversibility of plastic defences, including other type of costs (e.g. physiological), are needed to better understand the adaptive value of these flexible strategies.     

Adaptive features of life history for space experiments seen in Rana tagoi tadpoles]

We propose to use the physiological responses of tadpoles in space to study the effects of gravity at the organismal level. The tadpoles we propose for study, Rana tagoi, have naturally transparent abdominal walls, permitting viscera, such as heart and intestine, to be easily observed. Rana tagoi is a mountainous species that lays eggs in water, typically at crevasses in rocky substrates. Its eggs are rich in yolk, and tadpoles can grow without being fed (except own feces). However, they will eat when presented food. Coprophagy in these tadpoles can be clearly seen when small amount of food is fed. Abdominal wall remains transparent until metamorphosis. Intestinal and cardiac activity are clearly visible and can be documented by video without any invasive procedures. Because of the limited requirements on the digestive system in this species, their intestine does not elongate much when the tadpoles grow up. Even in this species, periodical contractions occur in the intestine throughout the larval period. Space experiments using R. tagoi tadpoles are promising in terms of scientific merit and technical feasibility. With this species it is possible to study the effects of gravity on visceral physiology and metamorphosis. Rana tagoi tadpoles would be a good model for space experiments where only the basic minimum capability of life support function (e.g., temperature and oxygen control), could be provided.     

Cannibalistic Interactions Resulting from Indiscriminate Predatory Behavior in Tadpoles of Poison Frogs (Anura: Dendrobatidae)1

Poison frogs in the genus Dendrobates have very small clutch sizes (2–6 eggs among species for which there are data) and typically transport their tadpoles singly to small phytotelmata, such as bromeliad tanks, leaf axils, fallen fruit capsules, and treeholes. Tadpoles of many species are predaceous, consuming larvae of insects that use the same microhabitat for breeding, such as giant damselflies and mosquitoes. Previous studies and observations on the behavior of poison frog tadpoles led us to question whether tadpoles might be cannibalistic. We studied a population of Dendrobates castaneoticus in lowland rainforest in Pará, Brazil; additional data were collected on Dendrobates auratus in Nicaragua. At the study site in Brazil, we established a grid of 40 Brazil nut capsules, the microhabitat used by D. castaneoticus for tadpole deposition. Of 42 tadpoles deposited during the 55 days of the study, 20 were killed or died; 16 of these were presumably killed by conspecific tadpoles. Growth rate and time to metamorphosis was higher among tadpoles that consumed three or more tadpoles or relatively large larvae of the mosquito Trichoprosopon digitatum, a colonist of newly opened Brazil nut capsules. We propose that selection has favored the development of predatory behavior in poison frog tadpoles primarily as a mechanism to eliminate predators from the small phytotelmata in which they develop and that cannibalism is a secondary outcome of this behavior. Predatory behavior also provides tadpoles with a source of food, which is frequently limited in these microhabitats. Additional studies of the biology of tadpoles of other species of Dendrobates are needed to determine the evolution of predatory and cannibalistic behavior in the clade.