Sequence of ontogenetic development and atrophy of the oral apparatus of six anuran tadpoles

Unravelling drivers on the morphological diversification of the terminal phalanx in hyloid frogs

The anuran locomotor system integrates traits that are influenced by phylogenetic, ecological, and development constraints. Given their significance to locomotion, we studied terminal phalange morphology in the Hyloidea group. We aim to deduce if morphological variability stems from phylogenetic, ecological, or life-cycle constraints. We explore the influence of size on variation and assess if evolutionary rates and shape disparities differ among the groups under consideration. Finally, we optimized phalangeal morphology within the phylogenetic framework to delineate evolutionary trends. We included 424 specimens of 128 species representing 17 families of Hyloidea and two of non-hyloid anurans. Configuration of the terminal phalanx was quantified using geometric morphometrics and characterized through qualitative traits. We established four categories based on microhabitats and locomotor abilities. Our life-cycle categorization distinguishes species by their consistent or changing microhabitat across larval and adult stages. The results show a complex scenario, where certain clades occupy distinct regions of morphospace, but there is also a relationship between phalangeal shape, microhabitats, and locomotor abilities. However, both the phylogenetic signal and the relationship with microhabitats and locomotor abilities are not particularly robust. Species inhabiting arboreal microhabitats develop convergent traits to thrive in this niche, such as rounded proximal epiphysis and the claw-shaped phalanx. Morphological disparity was higher in walkers, which also includes arboreal species, prompting further questions on the demands of locomotion in vertical substrates.

Assessment of multiple biomarkers in Lithobates catesbeianus (Anura: Ranidae) tadpoles exposed to zinc oxide nanoparticles and zinc chloride: integrating morphological and behavioral approaches to ecotoxicology

The ecotoxicological risk to vertebrates posed by zinc oxide nanoparticles (ZnO NPs) is still poorly understood, especially in animals with a biphasic life cycle, which have aquatic and terrestrial phases, such as amphibians. In the present study, we investigated whether acute exposure (7 days) to ZnO NPs and zinc chloride (ZnCl₂) at three environmentally relevant concentrations (0.1, 1.0, and 10 mg L^-1) induces changes in the morphology, chondrocranium, and behavior of the tadpoles of Lithobates catesbeianus (Anura: Ranidae). Tadpoles exposed to both forms of Zn did not undergo any morphological or behavioral changes at the lowest concentrations (0.1 and 1.0 mg L^-1). However, the animals exposed to the highest concentration (10 mg L^-1) lacked oral disc structures, were smaller in size, had a longer tail, and presented changes in the position and coiling of the intestine and malformations of the chondrocranium in comparison with the control group. This indicates that ZnO NPs and ZnCl₂ altered the development of the tadpoles, causing delays in their metamorphosis and even reducing individual fitness. The tadpoles exposed to both forms of Zn at 10 mg L^-1 also had reduced mobility, especially in the presence of conspecifics. Based on these findings, we emphasize the importance of studying morphological, skeletal, and behavioral biomarkers to evaluate the toxic effects of metal-based nanoparticles in amphibians.

The missing piece of the puzzle: larval morphology of Xenohyla truncata (Anura: Hylidae: Dendropsophini) and its implication to the evolution of Dendropsophini tadpoles

Dendropsophini is a highly diverse clade with a controversial phylogenetic and taxonomic history. Different generic arrangements have been proposed and the monophyly of several clades supported or rejected. Previous evidence suggested that larval morphology could play an important role in our understanding of the evolution and diversification of Dendropsophini, although data are missing for most lineages, including the sister group of Dendropsophus, Xenohyla. Herein we describe the internal morphology of the tadpoles of X. truncata and compare our results with available information for members of Dendropsophini and closely related lineages. We propose that the presence of a fan-like papilla in the buccopharyngeal cavity, a single element suprarostral, and a triangular process at the base of the muscular process are synapomorphies for Dendropsophini; moreover, the presence of a divided m. subarcualis rectus II–IV seems to be a synapomorphy for Pseudini and, the nasal sac insertion of the m. levator lateralis could be a synapomorphy of Dendropsophini + Pseudini.

Finding a pathway through the rocks: the role of development on the evolution of quasi-terrestriality and the origin of endotrophism in cycloramphids (Anura)

Anurans have served as models in evolutionary studies on reproduction and development. Several generalizations have emerged but it is unclear whether they represent the diversity of the entire group. We studied the development of two species of the Neotropical family Cycloramphidae. Frogs in this family have peculiar spawning sites and developmental biologies. Whereas some cycloramphid tadpoles are exotrophic, quasi-terrestrial and thrive in films of water that flow over rocky outcrops, others are endotrophic, terrestrial and complete their development outside the eggs laid on the forest floor, under logs or in crevices. Cycloramphid tadpoles have aspects of their morphology distinct from those of pond and stream dwellers; they hatch in more advanced stages of development and have typical tadpole structures, either in a modified form or absent. Herein we present a study of the tadpoles of C. lithomimeticus and T. miliaris, in order to document and discuss alterations in the ontogeny of several larval structures. These changes seem to be associated with adaptations to life in the peculiar habitats where the tadpoles thrive. We infer that the observations we present are explained by development being associated with aspects of terrestrialization and endotrophism.

Evolution and development of parrot pseudoteeth

Parrot embryos carry peculiar appendages at their developing beak that have been described as pseudoteeth. To better characterize the pattern of development responsible for the emergence of these dental appendages, we examined parrot embryos combining conventional histology and microtomography approaches. Using immunohistochemistry, we observed the epithelial and mesenchymal expression of several proteins involved in tooth development in mammals. Parrot pseudoteeth arose by epithelial and mesenchymal evagination, and their early development was similar to the ontogeny of scales and feathers. There was no enamel tissue, and the evaginations were surrounded by the rhamphotheca. In adults, the rhamphotheca covers entirely the appendages, now represented by bone evaginations, which were more numerous in the lower than in the upper beak, being similar to the osseous teeth of the fossil Pelagornithidae. These embryonic pseudoteeth resembled reptile's first-generation teeth and dental appendages of chicken talpid² mutants. Proteins involved in mammalian odontogenesis, such as SHH, BMP4, PITX2, and PAX9, were found to be generally expressed in beak epithelium and mesenchyme during parrot pseudoteeth development, with clusters of high-level expression in the pseudoteeth rudiments. This suggests that a similar, highly conserved gene expression program gives rise to the appearance of odontode derivatives in numerous species, despite their divergent developmental paths. These results provide new insights into the development and evolution of odontode-derived structures in vertebrates.

The phylogeny of Dendropsophini (Anura: Hylidae: Hylinae)

The relationships of the hyline tribe Dendropsophini remain poorly studied, with most published analyses dealing with few of the species groups of Dendropsophus. In order to test the monophyly of Dendropsophini, its genera, and the species groups currently recognized in Dendropsophus, we performed a total evidence phylogenetic analysis. The molecular dataset included sequences of three mitochondrial and five nuclear genes from 210 terminals, including 12 outgroup species, the two species of Xenohyla, and 93 of the 108 recognized species of Dendropsophus. The phenomic dataset includes 46 terminals, one per species (34 Dendropsophus, one Xenohyla, and 11 outgroup species). Our results corroborate the monophyly of Dendropsophini and the reciprocal monophyly of Dendropsophus and Xenohyla. Some species groups of Dendropsophus are paraphyletic (the D. microcephalus, D. minimus, and D. parviceps groups, and the D. rubicundulus clade). On the basis of our results, we recognize nine species groups; for three of them (D. leucophyllatus, D. microcephalus, and D. parviceps groups) we recognize some nominal clades to highlight specific morphology or relationships and facilitate species taxonomy. We further discuss the evolution of oviposition site selection, where our results show multiple instances of independent evolution of terrestrial egg clutches during the evolutionary history of Dendropsophus.

Anatomical features of the phytotelma dwelling, egg-eating, fanged tadpoles of Rhacophorus vampyrus (Anura: Rhacophoridae)

Tadpoles of the Vampire tree frog Rhacophorus vampyrus differ substantially from other rhacophorid tadpoles, by having profound modifications in external morphology. The morphological peculiarities of this species likely correlate with their arboreal microhabitat and strict oophagous diet. In this work, we examine buccal and musculoskeletal anatomy and compare them to other rhacophorid and egg-eating larvae. The shape and arrangement of cartilages of the lower jaw are unique among tadpoles, and the lack of a palatoquadrate suspensorium is only known in the distantly related macrophagous tadpoles of the dicroglossid Occidozyga baluensis. The cranial musculature is massive, and the morphology of several mandibular, hyoid, and abdominal muscles could be related to the ingestion and transit of large eggs. In the buccal cavity, conspicuous aspects are the absence of ridges and papillae, and the development of a unique glandular zone in the buccal floor. Finally, observations of the skeletal support of keratinized mouthparts allow us to present a topography-based hypothesis of homology of the conspicuous fangs of these tadpoles.

Chemical composition of food induces plasticity in digestive morphology in larvae of Rana temporaria

Food conditions are changing due to anthropogenic activities and natural sources and thus, many species are exposed to new challenges. Animals might cope with altered quantitative and qualitative composition [i.e. variable protein, nitrogen (N) and energy content] of food by exhibiting trophic and digestive plasticity. We examined experimentally whether tadpoles of the common frog (Rana temporaria) exhibit phenotypic plasticity of the oral apparatus and intestinal morphology when raised on a diet of either low (i.e. Spirulina algae) or high protein, N and energy content (i.e. Daphnia pulex). Whereas intestinal morphology was highly plastic, oral morphology did not respond plastically to different chemical compositions of food. Tadpoles that were fed food with low protein and N content and low-energy density developed significantly longer guts and a larger larval stomachs than tadpoles raised on high protein, N and an energetically dense diet, and developed a different intestinal surface morphology. Body sizes of the treatment groups were similar, indicating that tadpoles fully compensated for low protein, N and energy diet by developing longer intestines. The ability of a species, R. temporaria, to respond plastically to environmental variation indicates that this species might have the potential to cope with new conditions during climate change.

Embryonic ontogeny of three species of Horned Frogs, with a review of early development in Ceratophryidae

Horned Frogs of the family Ceratophryidae are conspicuous anurans represented by three endemic South American genera. Most ceratophryids inhabit semiarid environments, but three species of Ceratophrys occupy tropical or temperate humid areas. Several morphological and behavioral characters of larvae and adults are conserved across the family. Based on examination of specimens and accounts in the literature, the embryonic development of C. ornata, C. cranwelli, and the monotypic genus Chacophrys are described and compared with that of species of Lepidobatrachus. Ceratophryid embryos share a suite of morphological features and heterochronic shifts during development. Most features, such as gill structure, ciliation, early hatching, and precocious differentiation of the gut and hind limbs, are shared by all the species regardless the differences in the habitats that occupy. This is consistent with previous observations of some adult characters, and likely supports the hypothesis of an early diversification of ceratophryids in semiarid environments. Other embryonic features, such as the morphology and ontogeny of the oral disc and digestive tract, are correlated with larval feeding habits and vary within the family. The evolutionary and ecological significance of some conserved characters (e.g., gastrulation pattern, Type-A adhesive glands) and other taxon-specific features (e.g., nasal appendix) remain to be explored in the group.

Early ontogeny and sequence heterochronies in Leiuperinae frogs (Anura: Leptodactylidae)

The study of early development in Neotropical Leiuperinae frogs (Anura, Leptodactylidae) has been addressed by several works in recent times. However, a comparative developmental approach under a phylogenetic context was not available. Herein we analyzed the morphological and ontogenetic diversity of embryos belonging to 22 species of the three largest genera in Leiuperinae. We find that in most cases, variations fit with the phylogeny at the inter- and intrageneric levels. Embryo kyphosis and whitish color are synapomorphies for the clade grouping Physalaemus and Engystomops. The presence of a third lower tooth row on the oral disc is plesiomorphic for Leiuperinae, only changing in derived clades. The configurations and developmental trajectories of the lower lip are exceptionally diverse. The developmental sequences optimized on the phylogenetic tree recover an early differentiated first lower tooth row a synapomorphy of Pseudopaludicola and Physalaemus, and an early differentiated second row as synapomorphy of Pleurodema. On the other hand, few features are highly conserved in the subfamily, such as the adhesive glands universally present in a type-C configuration. Our results also suggest that the morphology and ontogeny of embryos is in some cases associated to the environment where they develop. A large body size, poorly developed transient respiratory structures, large yolk provision and delayed development of the digestive tract occur convergently in embryos inhabiting cold, oxygenated environments. Embryos that develop in warmer water bodies in xeric environments show more complex and persistent transient respiratory structures and an early onset of hind limbs development. Our survey highlights that morphology and early development of anurans can be a valuable source of information for phylogenetic studies, and provide fundamental bases to explore and discuss how evolutionary changes can be shaped by environmental conditions.

Ontogenetic development of the oral apparatus and oropharyngeal cavity in bullfrog tadpoles (Lithobates catesbeianus, Shaw 1802)

OBJECTIVE

The present study aimed to describe the morphology of oral apparatus and oral cavity of bullfrog tadpoles during their development and metamorphosis.

DESIGN

The oral apparatus and oropharyngeal cavity of tadpoles from hatching up to metamorphosis stage was dissected for further analysis. These structures were fixed in Karnovsky solution, afterwards in osmium tetroxide and metalized in palladium gold and electron-micrographed using the scanning electron microscope.

RESULTS

The development of oral apparatus started with the formation and keratinization of the jaw sheaths and labial teeth followed by the formation of marginal and sub-marginal papillae. Degeneration of oral apparatus and formation of mouth was observed during metamorphosis. From stage-42 (metamorphic climax) to stage-43, the jaw sheath and labial tooth rows were disappeared progressively while the size and number of labial papillae were decreased. At stage-44, mouth formation started with the development of anterior and posterior labium though the labial papillae were still present. At stage-45 and 46, mouth was already formed, being very similar to the adult and characterized by the progressive increase in size.

CONCLUSION

The sequence of events that happen during the development of oral apparatus of Lithobates catesbeianus Shaw, 1802 tadpoles follows the same pattern as occur in other anuran species but metamorphic atrophy of the oral apparatus follows the sequence of morphogenesis.

Unraveling the relative contribution of inter- and intrapopulation functional variability in wild populations of a tadpole species

Functional traits are increasingly recognized as an integrative approach by ecologists to quantify a key facet of biodiversity. And these traits are primarily expressed as species means in previous studies, based on the assumption that the effects of intraspecific variability can be overridden by interspecific variability when studying functional ecology at the community level. However, given that intraspecific variability could also have important effects on community dynamics and ecosystem functioning, empirical studies are needed to investigate the importance of intraspecific variability in functional traits. In this study, 256 Scutiger boulengeri tadpole individuals from four different populations are used to quantify the functional difference between populations within a species, and the relative contribution of inter‐ and intrapopulation variability in functional traits. Our results demonstrate that these four populations differ significantly in functional attributes (i.e., functional position, functional richness, and low functional overlap), indicating that individuals from different populations within a species should be explicitly accounted for in functional studies. We also find similar relative contribution of inter‐ (~56%) and intrapopulation (~44%) variation to the total variability between individuals, providing evidence that individuals within populations should also be incorporated in functional studies. Overall, our results support the recent claims that intraspecific variability cannot be ignored, as well as the general idea of “individual level” research in functional ecology.

Morphological and microstructural changes of the oral apparatus in two Anuran tadpoles, in regard to pH

Scanning Electron Microscopy (SEM) and Light Microscopy (LM) of the oral apparatus of Polypedates teraiensis and Hylarana leptoglossa tadpoles revealed a number of morphological and microstructural alterations in the labial tooth rows, jaw sheaths and marginal papillae on exposure to acidic and alkaline pH. These morphological and microstructural alterations observed in the oral apparatus of the tadpole are discussed in the light of available literature. The significance of the study with reference to adverse effects of acidic as well as alkaline pH on oral apparatus of the tadpole is also discussed.

A novel sample preparation method that enables nucleic acid analysis from ultrathin sections

The ability to isolate and perform nucleic acid analyses of individual cells is critical to studying the development of various cell types and structures. We present a novel biological sample preparation method developed for laser capture microdissection-assisted nucleic acid analysis of ultrathin cell/tissue sections. We used cells of the mitotic bed of the tadpole teeth of Lithobates sphenocephalus (Southern Leopard Frog). Cells from the mitotic beds at the base of the developing teeth series were isolated and embedded in the methacrylate resin, Technovit® 9100®. Intact cells of the mitotic beds were thin sectioned and examined by bright-field and transmission electron microscopy. The cytological and ultrastructural anatomy of the immature and progressively more mature tooth primordia appeared well preserved and intact. A developmental series of tooth primordia were isolated by laser capture microdissection (LCM). Processing of these cells for RNA showed that intact RNA could be isolated. The study demonstrates that Technovit® 9100® can be used as an embedding medium for extremely small tissues and from individual cells, a prerequisite step to LCM and nucleic acid analyses. A relatively small amount of sample material was needed for the analysis, which makes this technique ideal for cell-specific analyses when the desired cells are limited in quantity.

Body length of Hylodes cf. ornatus and Lithobates catesbeianus tadpoles, depigmentation of mouthparts, and presence of Batrachochytrium dendrobatidis are related

A fungal pathogen Batrachochytrium dendrobatidis (Bd), which can cause morbidity and death of anurans, has affected amphibian populations on a worldwide basis. Availability of pure cultures of Bd isolates is essential for experimental studies to understand the ecology of this pathogen. We evaluated the relationships of body length of Hylodes cf. ornatus and Lithobates catesbeianus tadpoles to depigmentation of mouthparts and determined if dekeratinization indicated an infection by Batrachochytrium dendrobatidis. A strong association existed for both species, one from South America (Brazil: São Paulo) and one from North America (USA: Maine). We believe it prudent not to kill adult amphibians if avoidable, thus obtaining tissue for isolating Bd from tadpoles is reasonable because infected specimens of some species can be selectively collected based on depigmentation of mouthparts.

Coloration of Anuran Tadpoles (Amphibia): Development, Dynamics, Function, and Hypotheses

Colorations of anuran tadpoles surely function in many of the same ways that have been ascribed to color and pattern in other animals, but the paucity of data forces one to look to other groups to generate hypotheses. Such an action often occurs because of the difficulty of defining specific fitness parameters to larval forms. The commonly muted colorations of tadpoles are typically considered to function only in some form of crypsis, but we discuss other functions in the particular context of behavioral ecology and changes induced by various kinds of coinhabitants. We review the development, terminology, diversity, and functions of coloration in tadpoles and then pose various questions for future research. We strongly support a broad-based perspective that calls for an integration of several fields of research.