The tadpole of the Lake Oku clawed frog Xenopus longipes (Anura; Pipidae).

Xenopus longipes Loumont and Kobel, 1991 is an aquatic polyploid frog endemic to the high altitude crater lake, Lake Oku in North West region, Cameroon (Loumont & Kobel 1991). The tadpole of X. longipes is currently undescribed. So far, only dead tadpoles have been found at Lake Oku during regular monitoring since 2008 (Doherty-Bone et al. 2013), with specimens too decomposed to make adequate descriptions. Captive breeding provides one opportunity to obtain fresh specimens for description.

Reversal to air-driven sound production revealed by a molecular phylogeny of tongueless frogs, family Pipidae.

BACKGROUND: Evolutionary novelties often appear by conferring completely new functions to pre-existing structures or by innovating the mechanism through which a particular function is performed. Sound production plays a central role in the behavior of frogs, which use their calls to delimit territories and attract mates. Therefore, frogs have evolved complex vocal structures capable of producing a wide variety of advertising sounds. It is generally acknowledged that most frogs call by moving an air column from the lungs through the glottis with the remarkable exception of the family Pipidae, whose members share a highly specialized sound production mechanism independent of air movement. RESULTS: Here, we performed behavioral observations in the poorly known African pipid genus Pseudhymenochirus and document that the sound production in this aquatic frog is almost certainly air-driven. However, morphological comparisons revealed an indisputable pipid nature of Pseudhymenochirus larynx. To place this paradoxical pattern into an evolutionary framework, we reconstructed robust molecular phylogenies of pipids based on complete mitochondrial genomes and nine nuclear protein-coding genes that coincided in placing Pseudhymenochirus nested among other pipids. CONCLUSIONS: We conclude that although Pseudhymenochirus probably has evolved a reversal to the ancestral non-pipid condition of air-driven sound production, the mechanism through which it occurs is an evolutionary innovation based on the derived larynx of pipids. This strengthens the idea that evolutionary solutions to functional problems often emerge based on previous structures, and for this reason, innovations largely depend on possibilities and constraints predefined by the particular history of each lineage.

The evolution of jumping in frogs: morphological evidence for the basal anuran locomotor condition and the radiation of locomotor systems in crown group anurans.

Our understanding of the evolution of frog locomotion follows from the work of Emerson in which anurans are proposed to possess one of three different iliosacral configurations: 1) a lateral-bending system found in walking and hopping frogs; 2) a fore-aft sliding mechanism found in several locomotor modes; and 3) a sagittal-hinge-type pelvis posited to be related to long-distance jumping performance. The most basal living (Ascaphus) and fossil (Prosalirus) frogs are described as sagittal-hinge pelvic types, and it has been proposed that long-distance jumping with a sagittal-hinge pelvis arose early in frog evolution. We revisited osteological traits of the pelvic region to conduct a phylogenetic analysis of the relationships between pelvic systems and locomotor modes in frogs. Using two of Emerson's diagnostic traits from the sacrum and ilium and two new traits from the urostyle, we resampled the taxa originally studied by Emerson and key paleotaxa and conducted an analysis of ancestral-character state evolution in relation to locomotor mode. We present a new pattern for the evolution of pelvic systems and locomotor modes in frogs. Character analysis shows that the lateral-bender, walker/hopper condition is both basal and generally conserved across the Anura. Long-distance jumping frogs do not appear until well within the Neobatrachia. The sagittal-hinge morphology is correlated with long-distance jumping in terrestrial frogs; however, it evolved convergently multiple times in crown group anurans with the same four pelvic traits described herein. Arboreal jumping has appeared in multiple crown lineages as well, but with divergent patterns of evolution involving each of the three pelvic types. The fore-aft slider morph appears independently in three different locomotor modes and, thus, is a more complex system than previously thought. Finally, it appears that the advent of a bicondylar sacro-urostylic articulation was originally related to providing axial rigidity to lateral-bending behaviors rather than sagittal bending.

Morphology of skin incubation in Pipa carvalhoi (Anura: Pipidae).

South American Pipidae show a unique reproductive mode, in which the fertilized eggs develop in temporarily formed brood chambers of the dorsal skin after eggs have been deposited on the back of the female. We studied the skin incubation of Pipa carvalhoi using light microscopy and scanning electron microscopy. The skin consists of a stratified epithelium with a one-layered stratum corneum, and the dermis. The dermis of the dorsal skin of nonreproductive and reproductive females lacks a distinct stratum compactum, which is typical for most anuran skins. The entire dermis shows irregularly arranged collagen bundles like a stratum spongiosum. Before egg laying, the skin swells, primarily by thickening and further by loosening of the middle zone of the dermis. In the epidermis, large furrows develop that are the prospective sites of egg nidation. The epidermis, which forms a brood chamber around the developing egg becomes bi-layered and very thin and lacks a stratum corneum. Further, the dermis loosens and becomes heavily vascularized. Egg carrying females do not have mature oocytes in their ovaries indicating a slow down or interruption of egg maturation during this period. Similarities with the brood pouch of marsupial frogs are discussed.

The evolution of development: two portraits of skull ossification in pipoid frogs.

Development creates morphology, and the study of developmental processes has repeatedly shed light on patterns of morphological evolution. However, development itself evolves as well, often concomitantly with changes in life history or in morphology. In this paper, two approaches are used to examine the evolution of skull development in pipoid frogs. Pipoids have highly unusual morphologies and life histories compared to other frogs, and their development also proves to be remarkable. First, a phylogenetic examination of skull bone ossification sequences reveals that jaw ossification occurs significantly earlier in pipoids than in other frogs; this represents a reversal to the primitive vertebrate condition. Early jaw ossification in pipoids is hypothesized to result from the absence of certain larval specializations possessed by other frogs, combined with unusual larval feeding behaviors. Second, thin-plate spline morphometric studies of ontogenetic shape change reveal important differences between pipoid skull development and that of other frogs. In the course of frog evolution, there has been a shift away from salamander-like patterns of ontogenetic shape change. The pipoids represent the culmination of this trend, and their morphologies are highly derived in numerous respects. This study represents the first detailed examination of the evolution of skull development in a diverse vertebrate clade within a phylogenetic framework. It is also the first study to examine ossification sequences across vertebrates, and the first to use thin-plate spline morphometrics to quantitatively describe ontogenetic trajectories.

Ontogeny of the bizarre: an osteological description of Pipa pipa (Anura: pipidae), with an account of skeletal development in the species.

The adult osteology of the direct-developing pipid frog, Pipa pipa, is described based on cleared-and-stained and dry skeletal specimens. Observations on skeletal development are based on cleared-and-stained embryos and young removed from the backs of preserved females. Osteologically, P.pipa is distinguished from its congeners and other pipid anurans by its large size and peculiar skull, which is extremely depressed and hyperossified. Skulls of the smallest individuals are not significantly different from those of other basal anurans at a similar stage of development; comparisons are made with Bombina orientalis, Discoglossus sardus, Spea bombifrons, Rhinophrynus dorsalis, and Xenopus laevis. The general sequence of chondrification and ossification resembles that of X.laevis; however, there is evidence that the mandible forms earlier in Pipa than in Xenopus. The major allometric transformations that result in the morphologically bizarre skull of adult P.pipa commence after the embryo has resorbed its tail, an event interpreted as marking the end of metamorphic climax in this taxon. In addition, ontogenetic comparisons reveal that the sacrum forms differently in Discoglossus sardus,Silurana tropicalis, and P.pipa. The development of the sphenethmoid region of the skull is the same in P.pipa and X.laevis, and distinctly different from the development of this region of the skull in other non-pipid basal anurans and neobatrachians for which ontogenetic descriptions exist.

Differential labelling of primary olfactory system subcomponents by SBA (lectin) and NADPH-d histochemistry in the frog Pipa.

SBA and NADPH-d histochemistries allow identification of functionally distinct components of the amphibian primary olfactory system. In Pipa, a secondarily aquatic frog, combination of both methodologies, using alternate sets of histological sections, reveals that, apart from Jacobson's organ, this species has a "water-nose" and an "air-nose". The epithelia occupy separate chambers of the olfactory organ and give rise to olfactory nerve fiber bundles that are identified by the dual staining procedure.