Morphology of the prometamorphic larva of the spadefoot toad, Scaphiopus intermontanus (Anura: Pelobatidae), with an emphasis on the lateral line system and mouthparts

Abstract

We provide a detailed description of the larval morphology of the Great Basin spadefoot toad (Scaphiopus intermontanus), a species with documented morphological variability in larval structures associated with feeding. We based our findings on laboratory-raised individuals fed a herbivorous diet. We characterized the morphology of the prometamorphic larva (limited to developmental stages 37 and 38) and then related our findings to the larval ecology of the species. Based on its morphology, such as slightly depressed body, dorsally positioned eyes, anteroventrally oriented oral disc, intermediate tail fin height and slightly attenuated tail tip, relative lack of ventral neuromasts (compared to Xenopus laevis), and pigmentation banding patterns, and habits, such as selection of breeding sites by adults and larval foraging behavior, S. intermontanus can be characterized best as belonging to a (lentic-) benthic guild of anuran larvae. Nevertheless, the larvae are capable of occupying a broader array of ecological niches. Because we characterized individuals raised on a herbivorous diet, our morphological descriptions apply only to the herbivorous S. intermontanus larva (and perhaps to those larvae that are dietary generalists and may feed carnivorously only infrequently). Our findings can serve as a baseline for future morphological and developmental comparisons with the carnivorous morphological variant of this species.

The Development ofDermatonotus muelleri(Anura: Microhylidae: Gastrophryninae)

“…The period between stages 41 and 46 corresponds to metamorphic climax and at a maximum, lasts 3 days. By stage 37, tadpoles have attained their metamorphic snout-vent size; this seems to distinguish larvae of D. muelleri from other Type-IV tadpoles in which the snout-vent size increases until the forelimbs emerge (Hall et al, 1997;Quinzio et al, 2006;Fabrezi, 2011). Larval somatic growth and metamorphic development seem to parallel each other in most anurans; thus, one might expect that any negative external factor (e.g., diet, temperature, competence, and predation) might affect the rate of development and modify somatic growth or vice versa (Wilbur and Collins, 1973).…”

“…The consequence of basing larval descriptions on standard tables is the assumption that developmental events (e.g., toe differentiation, forelimb emergence, and tail loss) are equivalent stages of tadpole development across all taxa and that these events are not subject to species-specific patterns of developmental timing. Studies assessing morphological variation of tadpole development provide detailed information for individual species (Hall and Larsen, 1998;Hall et al, 1997Hall et al, , 2002 or report the effects of heterochrony on larval growth, such as delayed loss of larval features and early differentiation of adult-like traits (e.g., Downie et al, 2004;Fabrezi and Quinzio, 2008;Fabrezi et al, , 2010. These studies demonstrate the richness of information derived from the analyses of the entire larval development-including timing of development-to understand anuran diversity and the reciprocal influences between larval and adult body plans.…”

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

“…As soon as both forelimbs emerge, mouth parts disappear rapidly in the following sequence: teeth rows, followed by jaw sheaths, and finally the soft mouth parts (e.g. tooth ridges and labial ridges) and marginal papillae (Hall et al 2002;). Exceptions are found in microhylids and in Lepidobatrachus spp.…”

The ontogeny of the lateral line system in Telmatobius atacamensis (Anura, Telmatobiidae)

“…The asymmetry of the left lateral ventral line in T . atacamensis must occur at early developmental stages, and represents a deviation from the bilateral symmetry that characterizes the paired structures of the system in all the other anuran larvae analyzed so far (Lannoo, 1987; Chou & Lin, ; Hall, Larsen, & Fitzner, ; Quinzio, Fabrezi, & Faivovich, ; Fabrezi & Quinzio, ; Fabrezi et al, , ; Quinzio & Fabrezi, ). Studies exploring the early development of the lateral line system could help to elucidate morphogenetic aspects of this remarkable asymmetry.…”

“…The topography of the larval mechanosensory receptors shows interspecific variation in the arrangement, extension, and relationship among the lateral lines of neuromasts of about 70 species (e.g., Lannoo, 1987;Hall, Larsen & Fitzner, 2002;Fabrezi & Quinzio, 2008;Fabrezi, Quinzio, & Goldberg, 2009;Fabrezi, Quinzio, Goldberg & De Sá, 2012;Quinzio & Fabrezi, 2014). These studies have allowed us to characterize the topography of the lateral lines into distinct patterns (Quinzio & Fabrezi, 2014) that correspond to the larval types established by Orton (1953).…”