Extreme tadpoles: The morphology of fossorial megophyrid larva, Leptobrachella mjobergi

Biozentrum Grindel und Zoologisches Museum, Martin-Luther-King-Platz 3, Hamburg, Germany.
Zoology (Impact Factor: 1.67). 02/2006; 109(1):26-42. DOI: 10.1016/j.zool.2005.09.008
Source: PubMed


The bizarre larvae of Leptobrachella mjobergi are fossorial and live in the gravel beds of small streams. These tadpoles are vermiform in body shape. Here we present details on their skeleton and musculature, particularly of the head. The entire cranium and its associated musculature are reconstructed in three dimensions from serial histological sections. The hyobranchial apparatus is highly reduced. The head of the L. mjobergi larva is more mobile than in other anuran species. This mobility can largely be ascribed to the exclusion of the notochord from the cranial base and an articulation of the foramen magnum floor with the atlas of the tadpole. The articulation is unique among anuran species, but design parallels can be drawn to salamanders and the articulation between atlas and axis in mammals. In L. mjobergi, the atlas forms an anterior dens that articulates with the basal plate in an accessory, third occipital articular face. The muscle arrangements deviate from the patterns found in other tadpoles: For instance, epaxial and ventral trunk muscles reach far forward onto the skull. The post-cranial skeleton of L. mjobergi is considerably longer than that of other anurans: it comprises a total of 35 vertebrae, including more than 20 post-sacral perichordal centra. Despite a number of features in cranial and axial morphology of L. mjobergi, which appear to be adaptations to its fossorial mode of life, the species clearly shares other features with its megophryid and pelobatid relatives.

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    • "Having multiple periods of development and growth suggests more opportunity for phylogenetic diversification. Indeed, amphibian PA elements show pronounced interspecific differences in PA skeletal shape that arise during metamorphosis as well as embryogenesis (Smith, 1920; Wilder, 1925; Wassersug & Hoff, 1982; Ruibal & Thomas, 1988; Haas et al. 2006, 2014; Ziermann et al. 2013). Further, the embryonic repatterning of certain larval elements and the metamorphic appearance of a new adult element have been identified as key innovations in salamander evolution (Wake, 1982; Alberch & Gale, 1986; Alberch, 1987). "
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    ABSTRACT: Understanding skeletal diversification involves knowing not only how skeletal rudiments are shaped embryonically, but also how skeletal shape changes throughout life. The pharyngeal arch (PA) skeleton of metamorphosing amphibians persists largely as cartilage and undergoes two phases of development (embryogenesis and metamorphosis) and two phases of growth (larval and post-metamorphic). Though embryogenesis and metamorphosis produce species-specific features of PA cartilage shape, the extents to which shape and size change during growth and metamorphosis remain unaddressed. This study uses allometric equations and thin-plate spline, relative warp and elliptic Fourier analyses to describe shape and size trajectories for the ventral PA cartilages of the frog Xenopus laevis in tadpole and frog growth and metamorphosis. Cartilage sizes scale negatively with body size in both growth phases and cartilage shapes scale isometrically or close to it. This implies that most species-specific aspects of cartilage shape arise in embryogenesis and metamorphosis. Contributions from growth are limited to minor changes in lower jaw (LJ) curvature that produce relative gape narrowing and widening in tadpoles and frogs, respectively, and most cartilages becoming relatively thinner. Metamorphosis involves previously unreported decreases in cartilage size as well as changes in cartilage shape. The LJ becomes slightly longer, narrower and more curved, and the adult ceratohyal emerges from deep within the resorbing tadpole ceratohyal. This contrast in shape and size changes suggests a fundamental difference in the underlying cellular pathways. The observation that variation in PA cartilage shape decreases with tadpole growth supports the hypothesis that isometric growth is required for the metamorphic remodeling of PA cartilages. It also supports the existence of shape-regulating mechanisms that are specific to PA cartilages and that resist local adaptation and phenotypic plasticity.
    No preview · Article · Apr 2015 · Journal of Anatomy
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    • "The presence of keratodonts in the larger Leptolalax tadpoles indicates to some extent a substrate-scraping mode of food intake, while keratodonts are lacking completely in Leptobrachella. In their morphological description of L. mjobergi, Haas et al. (2006) discussed the unique features of the feeding apparatus of this species and speculated that the cup–like oral disc without keratodonts is inconsistent with a substrate–scraping mode of feeding. Leptobrachella brevicrus, Leptolalax dringi and Megophrys dringi are to be regarded as currently considered rare species so far known only from their type localities in the borders of the Gunung Mulu National Park or from a few other sites of northern Borneo (Stuart et al. 2008). "
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    ABSTRACT: The megophryid frogs Leptobrachella brevicrus, Leptolalax dringi and Megophrys dringi are species exclusively known from highly localised areas in isolated mountain ranges on Borneo. The tadpoles and adults in this study were collected at the shared type locality for the three species in Gunung Mulu National Park, Sarawak, Malaysia (Borneo). The species identities of larvae were determined via comparison to syntopic adults using DNA barcoding techniques based on partial 16S rRNA mitochondrial gene sequences. The genetic data supported the status of the three taxa as valid species. Descriptions of colouration in life and after preservation, external morphological features, morphometric measurements and ecological notes in comparison to congeneric species are supplied. The tadpoles of L. brevicrus and L. dringi show similar adaptations to a fossorial lifestyle. These include an elongated, vermiform body, a relatively long tail and small eyes. Both were found in the gravel beds of a small mountain stream. In contrast, the larvae of M. dringi are adapted to occupying and feeding at the surface of pools within the stream.
    Full-text · Article · Jul 2014 · Zootaxa
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    • "We present field-based observations and anatomical evidence to address the questions related to the extent of carnivory in this species and the anatomical features that relate to this feeding mode. Examination of structurally and ecologically extremely aberrant tadpoles (see Haas et al. 2006) has the potential to change our perception of tadpole morphospace (Roelants et al. 2011) and lets us better understand the diversification processes in anuran evolution. "
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    ABSTRACT: Tadpoles of Occidozyga species have been reported to be carnivorous, feeding on insects and other tadpoles. We present photographic evidence for the previously undocumented larval feeding behavior in O. baluensis. Furthermore, we present a detailed anatomical description of the skull, cranial musculature, and gross gut morphology based on three-dimensional reconstructions from serial sections and mu CT imagery. The cranial anatomy of larval O. baluensis is highly derived in many characters, with respect to taxa outside the genus Occidozyga, most notably the palatoquadrate and hyobranchial apparatus, that play a major role in tadpole feeding. A large larval stomach was present in the specimens examined, indicative of a macrophagous carnivorous mode of feeding. Because of the relatively small oral orifice, relatively large-sized food items found in the larval stomach, and the tunnel-like arrangement of structures that form the buccal cavity, we hypothesize that suction feeding utilizing strong negative pressure is employed by this species. Furthermore, we propose that force, rather than speed, is the main characteristic of their feeding. The unique features of the study species substantially expand the known morphospace for tadpoles, particularly among the Acosmanura (Pelobatoidea, Pelodytoidea, and Neobatrachia). Except for Microhylidae, acosmanurans previously described possess limited innovative larval morphologies. Larval carnivory has evolved convergently several times in distant anuran clades and shows structural, behavioral, and functional differences in the known examples.
    Full-text · Article · Mar 2014 · Zoomorphology
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