Giant Tadpoles Research Articles

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.

Thyroid hormones in the skeletogenesis and accessory sources of endogenous hormones in Xenopus laevis (Amphibia; Anura) ontogeny: Experimental evidence.

Skeletal development was studied in normal and goitrogen-treated Xenopus laevis tadpoles reared under thyroid hormone (TH) deficiency. Early stages of skeletal development proceed similarly in both groups. Later stages are retarded or completely arrested in goitrogen-treated tadpoles. After goitrogen-treated tadpoles were transferred into pure water or into a medium containing both goitrogen and exogenous TH, tadpoles resumed development. Consequently, late stages of skeletogenesis are TH-dependent and TH-induced. Athyroid X. laevis "giant tadpoles" described in literature differ from goitrogen-arrested tadpoles in that they have features which require TH to appear. The appearance of TH-depended features in giant tadpoles indicates the occurrence of the additional sources of TH other than thyroid gland.

Heterochrony in Growth and Development in Anurans from the Chaco of South America

Heterochrony refers to those permutations in timing of differentiation events, and those changes in rates of growth and development through which morphological changes and novelties originate during phyletic evolution. This research analyzes morphological variation during the ontogeny of 18 different anuran species that inhabit semi-arid environments of the Chaco in South America. I use field data, collection samples, and anatomical methods to compare larval growth, and sequences of ontogenetic events. Most species present a similar pattern of larval development, with a size at metamorphosis related to the duration of larval period, and disappearance and transformations of larval features that occur in a short period between forelimb emergence and tail loss. Among these 18 species, Pseudis paradoxa has giant tadpole and long larval development that are the results of deviations of rates of growth. In this species events of differentiation that usually occur at postmetamorphic stages have an offset when tail is still present. Tadpoles of Lepidobatrachus spp. reach large sizes at metamorphosis by accelerate developmental rates and exhibit an early onset of metamorphic features. The uniqueness of the ontogeny of Lepidobatrachus indicates that evolution of anuran larval development may occasionally involve mid-metamorphic morphologies conserving a free feeding tadpole and reduction of the morphological-ecological differences between tadpoles and adults.

The Synthetic Gestagen Levonorgestrel Impairs Metamorphosis in Xenopuslaevis by Disruption of the Thyroid System

Synthetic gestagens, including levonorgestrel (LNG), are active compounds in contraceptives, and several studies report their occurrence in surface waters. However, information about endocrine-disrupting effects in nontarget organisms is scarce. The present study investigated effects of LNG exposure on thyroid hormone-dependent metamorphosis of Xenopus laevis. Premetamorphic X. laevis tadpoles at Nieuwkoop and Faber (NF) stage 48 were exposed in a flow-through culture system to four LNG concentrations (10(-11), 10(-10), 10(-9), and 10(-8)M) over the period of metamorphosis. At NF 58 and 66, tadpoles were examined sex specifically. Developmental time and organismal responses were recorded and correlated with molecular and histopathological endpoints. Exposure to 10(-8)M LNG caused an inhibition of metamorphosis resulting in developmental arrest at early climax stages as giant tadpoles or tailed frogs. In brain-pituitary tissue of NF 58 tadpoles, gene expression of thyroid-stimulating hormone (β-subunit; TSHβ), TH receptor β (TRβ), and deiodinase type 3 (D3) was not changed. Instead, prolactin (PRL) messenger RNA (mRNA) was significantly increased by 10(-9)M LNG in females and by 10(-8)M LNG in both sexes. In NF 66 tadpoles, mRNA levels of TSHβ mRNA were significantly increased in the 10(-9) and 10(-8)M LNG treatment groups indicating a hypothyroid state. No changes of TRβ, D3, and PRL gene expression were detected. Histopathological evaluation of thyroid gland sections revealed no typical sign of hypothyroidism but rather an inactivated appearance of the thyroid. In conclusion, our data demonstrate for the first time a completely new aspect of thyroid system disruption caused by synthetic gestagens in developing amphibians.

The ontogeny of Pseudis platensis (Anura, Hylidae): Heterochrony and the effects of larval development on postmetamorphic life

Recent studies have described the giant tadpole, delayed metamorphic transformations, and absence of postmetamorphic growth of the skeleton of Pseudis Platensis. These features address questions about derived patterns of life cycles and the role of the heterochrony during the metamorphosis in anurans. Using anatomical methods, we provide new data on the development of reproductive, digestive and integument systems, and age inference obtained from ontogenetic series of Pseudis platensis. Our results indicate that at the end of metamorphosis, the adult skin is completely differentiated, including the calcified dermal layer; the testis has seminiferous tubules with spermatogonia, spermatocytes, and spermatids; ovarian sacs present previtellogenic ova; and the adult digestive tract is fully formed. The froglets differ from adults only in being unable to reproduce. The entire life cycle of P. platensis can occur in 4 years. In the first year, larval development, growth to adult size, and gonad differentiation are completed. Long larval development rather than size of the tadpoles seems to be involved in the absence of juvenile stages.

Giant Tadpole and Delayed Metamorphosis of Pseudis platensis Gallardo, 1961 (Anura, Hylidae)

Pseudis platensis, like Pseudis paradoxa, is a Neotropical aquatic frog with a giant tadpole. Despite being one of the few anuran species whose larvae grow larger than adults, knowledge of its larval development is limited to prometamorphic stages. This study describes qualitative and quantitative variation through P. platensis larval development, including descriptions of various traits (lateral line, oral disc, vent tube, limbs) and their transformations during metamorphosis. We found similarities with the development of other anurans at larval stages up to the end of prometamorphosis but not with their metamorphic stages. For this species, we described key features to characterize 13 ontogenetic stages as follows: four for prometamorphic larval morphologies, eight stages covering metamorphic changes, and one defining the posmetamorphic adult stage. At the end of prometamorphosis, tadpole body size in P. platensis is similar to adult size, but the tail shows extra development. Unlike most anurans, the disappearance of two larval traits (i.e., vent tube and tail) is delayed until later in metamorphosis. Larval development of P. platensis exhibits unique features not reported for other anurans and offers a model to study developmental and evolutionary aspects of anuran metamorphosis.

Heterochrony during skeletal development of Pseudis platensis (anura, hylidae) and the early offset of skeleton development and growth

The aquatic frog Pseudis platensis has a giant tadpole, long developmental time, and dissociated metamorphic events that include later offset of larval somatic morphologies. Moreover, when the tadpole metamorphoses, the young frog is nearly the size of an adult, suggesting that this species has low rates of postmetamorphic growth. Herein, we study the development of the skeleton during larval development up to the end of metamorphosis, which is denoted by the complete lost of the tail in P. platensis. Our study revealed heterochronic differences in skeletal development compared with that of most anurans; these involve the complete differentiation of skull bones and the extensive ossification of the postcranial skeleton before completion of metamorphosis. The skull of metamorphosing P. platensis has an ossified sphenethmoid and a fully formed plectral apparatus, thus differing with regard to the pattern observed in most anurans in which both developmental events take place during the postmetamorphic life. Despite the fact that the iliosacral articulation and the urostyle are present at the end of metamorphosis as in most anurans, ossification/calcification of carpus, tarsus, and limb epihyses during metamorphosis of P. platensis suggests that the postcranial skeleton lacks postmetamorphic growth. This study also includes a discussion of the pattern of development of the plectral apparatus, which allows us to propose a new hypothesis regarding pars externa plectri homology.

Developmental disturbances in Rana esculenta tadpoles and metamorphs

Rana esculenta progeny from experimental crosses (using R. esculenta from natural lineages and F1 Ram ridihztncia x Rnrlo lessonarr), reared in artificial ponds and in cages immersed in natural breeding ponds, showed three different types of malformations reflecting developmental disturbances, each affecting few individuals overall. Giant tadpoles arrested development at the foot-paddle stage, independent from a size at metamorphosisitime to metamorphosis trade-off that may be under selection. The fused nostrils/eyeless syndrome probably reflects a disturbed gastrulation. The observed polymely, affecting the hind limbs, may result from infectious agents in pond water used to inoculate the tanks. Although known parentage and distribution among rearing tanks for each of the three malformations exclude a simple genetic basis and a direct influence of particular human-caused factors, it is not possible to further discriminate among genetic, biotically-induced, and non-biotically induced environmental causes of the developmental disturbances and their interactions. Direct experimental approaches will be needed to disentangle these possibilities and to assess their relative contributions to the observed decline of amphibian populations.

Tissue sensitivity to thyroid hormone in athyroid Xenopus laevis larvae.

Tadpoles that spontaneously arrest development and remain as larvae occur occasionally in Xenopus laevis populations. These non-metamorphosing tadpoles continue to grow, and they develop into grossly deformed giant individuals which come as close as any anurans to being truly neotenic. Giant X. laevis tadpoles that fail to metamorphose lack thyroid glands. In this study, the hypothesis that the tissues of these tadpoles nevertheless remain thyroid hormone sensitive was tested, by exposing isolated tadpole tail tips to exogenous thyroid hormone in tissue culture. The tail tips from giant tadpoles significantly shrank in response to the thyroid hormone treatment, showing that their tissue was still capable of metamorphosis. However, the amount of shrinkage was less than that observed in tail tissue from normal tadpoles. It was hypothesized that complete induction of metamorphosis may not be possible in the giant tadpoles due to a disproportionate growth and development of tissues and organs.

Diet of the giant tadpole Pseudis paradoxa platensis (Anura, Pseudidae) from Argentina

97 Pseudis paradoxa platensis is restricted to areas along the Paraguay and Parana Rivers, from Paraguay, Bolivia and Mato Grosso (Brazil) to northeast of Argentina (Cei 1980). In Argentina, this subspecies has been found in Formosa, Chaco, Corrientes, Misiones and Santa Fe provinces (Frost 1985, Gallardo and Varela de Olmedo 1992). The adults are very aquatic, occurring in semipermanent and permanent ponds (Dixon et al. 1995, Dure and Kehr 2001). In Argentina breeding occurs between November and March. Tadpoles of P. paradoxa platensis reach lengths up to 168 mm (Bokermann 1967, Emerson 1988). Studies on the biology of this giant tadpole in nature are extremely scarce. This study describes the tadpole diet of P. paradoxa platensis and presents some behavior data. Tadpoles were collected in a semipermanent pond located 30 km from the city of Corrientes (27o25’S 58o44’W, Province of Corrientes, Argentina) during the summer season (December, January and February). The area corresponds to the Oriental Chaquena phytogeographical region (Carnevali 1994, Burkart et al. 1999). Climatically, this area has a mean annual rainfall of 1100 mm and a mean annual temperature of 20o C. The pond area was Diet of the giant tadpole Pseudis paradoxa platensis (Anura, Pseudidae) from Argentina

Function of thyroid hormone receptors during amphibian development.

Thyroid hormone (T3) plays important roles during vertebrate development (). In humans, T3 is detected in the embryonic plasma by 6 mo and rises to high levels around birth (). During this postembryonic period, extensive tissue remodeling and organogenesis take place. T3 deficiency during human development leads to developmental defects, such as mental retardation, short stature, and in the most severe form, cretinism (,). Likewise, T3 is also critical for amphibian development. It is the controlling agent of anuran metamorphosis, a process that transforms a tadpole into a tailless frog (,). Blocking synthesis of endogenous T3 leads to the formation of giant tadpoles that cannot metamorphose, while addition of exogenous T3 to premetamorphic tadpoles causes precocious metamorphosis. Importantly, most, if not all, organs are genetically predetermined to undergo specific changes, and these changes are organ autonomous. Thus, T3 appears to act directly on individual metamorphosing organs. Such properties have made anuran metamorphosis one of the best-studied postembryonic developmental process at morphological, cellular, and biochemical levels and paved the way for current molecular investigations of the underlying mechanisms.

Mr. Ealy Fishbeck Knits Some Yarns on his Porch in Fly, Ohio

In Chaucerian rhythms and sometimes more than comic mock-seriousness Richard Hague presents Mr. EaIy Fishback, an Appalachian yarnspinner from Fly, Ohio. MR. EALY FISHBECK KNITS SOME YARNS ON HIS PORCH IN FLY, OHIO Now I think I told you boys about the Hoopsnake and the Head Fly—them's common things, to make the people from the city wince and quiver when they come down here from Akron in their flivver. But today I think I'll tell about the rarer beasts, that you have to live here fifty years, at least, to even hear of, let alone lay eyes on. Of course, it's true that most of them is gonemuseum people used to come here by the trainloads and put everything in jars—by God, even minnows, toads. Got all their learning out of some big book they read in college for the courses that they took, and never used their own eyes or their common sense. 32 Most of them I seen couldn't cross a bob-wire fence without nearly snagging both their seeds, and they lost their fancy tackle in the weeds. No sir, I never steered them up the Fishing Bottom Creek nor told them what I'd heard about that week the big blue thing mauled every hog along the banks, then disappeared one morning, like the fog. I never sent them down to hear the tale about that giant tadpole Hobie Becker carried in a pail all the way to Morgantown aboard the train, or how he watched them experts dig a socket in its brain and sent electric through it till it whistled higher than a steamboat. No sir, they'd of called me liar. So I let them pickle everything they seen and thought was rare, but really wasn't worth a bean, and when they left, they'd cleared most common creatures out, so that the good ones left, the ones I'll tell about, had room to grow in, like the big bass in the run that all the small bass have been caught from. Now this first is quite a thing: a snail that's neither female, nor a male. It's kind of in between, and it'll wander into houses in the dark. It kind of makes you ponder, how it rattles like a pounded heap of unjust a little thing, of shell, and snot, and skin. Or how about your Ham-Hock Sparrow, heavy as a ballpeen hammer's head, but hollow-winged and quicker than an arrow? Why, if it hits your shack, you're dead. And then the Buzzsaw Fly, that runs its wings on chain with noisy ratchets. Feeds on farmer's forearms and the sweaty handles of old hatchets. Or how about the Fence-Post Toad, that hoots just like a barn owl in the dark? Once I parked and watched one, down the road. It hides in high grass, and it eats them owls, you see, and while I watched it, wolfed down three. 33 à ? m. \ 1 * i. À à M y I 4 f Ä f W i t ? Lífy?f Si« That's why I keep that fence-line mowed. Now let me finish with a list of others of some interest: there's the Murder Worm, or Thunder-In-The-Cellar; there's the Pig-Leg Warbler, and the Snake-In-Vest; there's the Night Hog, or Haunt-Sow, and the Three-Fanged Meddler, and then the big night bird called Killrest. Finally, down Moss Run, I once heard Walter Short tell the story of the mermaid that he killed a week before he'd got his first beans hilled. This is, to my knowledge, boys, most the earliest report of mermaids in these parts, though later, men of sport will net them in great numbers, from the Big Muskingum. Yessir, by the dozens, so help me God and Kingdom Come. —Richard Hague 34 ...

Concerning the effect of prostate feeding on tadpoles

Gudernatsch was the first to call attention to the remarkable influence of the feeding of thyroid and thymus glands on frogs'rarvae. That observer noted that the thyroid causes a dwarfing or shrinkage of the growth and size of tadpoles, and at the same time very rapidly hastens their metamorphosis into frogs, while the thymus, on the other hand, causes giant tadpoles but inhibits their metamorphosis. Gudernatsch and other observers have also studied the effect of feeding of other organs and glands on the development of frogs'rarvae. As far as the present author has been able to ascertain, however, no experiments concerning the feeding of prostate gland to tadpoles are on record. The present author, in connection with a physiological and pharmacological study of prostatic extracts, conducted a series of experiments in feeding tadpoles with desiccated prostatic substance (Armour). The results are so interesting that it is deemed desirable to make a preliminary announcement on the subject in this place.Prostat...