External Morphology, Chondrocranium, Cranial Muscles, and Buccopharyngeal Features of Tadpoles of Pleurodema thaul (Anura: Leiuperidae): a Comparison with P. bufoninum

A hundred-year-old mystery-the reproductive mode and larval morphology of the enigmatic frog genus Allophryne (Amphibia; Anura; Allophrynidae)

Frogs of the Allophrynidae are an enigmatic family from South America. To date, published information is lacking regarding this group's reproductive biology and larval morphology. Here, we provide the first detailed description of the reproductive mode, developmental mode, and tadpole morphology for Allophryne ruthveni. We developed a captive breeding and rearing protocol for this species and then conducted a series of observations to describe aspects of its reproductive biology. In captivity, this species exhibits aquatic oviposition, where single eggs are laid ungrouped within a simple jelly capsule and are scattered free in the water column before sinking to develop on benthic substrates. We did not observe parental care nor any parental interactions with eggs post-fertilization. Tadpoles are characterized by an oval body, anteroventral oral disc, a labial tooth row formula of 2(2)/3, and a dextral vent tube. The buccopharyngeal cavity is marked by the presence of two pairs of infralabial papilla and four lingual papillae. Cranial morphology is characterized by the presence of the commissura quadratoorbital. This species possesses an additional slip of the m. rectus cervicis and of the m. levator arcuum branchialium III. We discuss our results in comparison with glassfrogs (Centrolenidae).

Larval morphology of Amazonia foam-nesting frogs of the genus Engystomops (Anura: Leptodactylidae: Leiuperinae)

The highly differentiated anuran larvae make them an interesting and complementary source of information to understand anuran evolution. Among neotropical foam-nesting frogs, the available information on tadpole morphology for the subfamily Leiuperinae remains largely incomplete and variably reported among genera; in the monophyletic genus Engystomops it is still incipient. Herein, we summarize available information on larval morphology for five of the nine known species of Engystomops, three of them for the first time, reporting external morphology, buccopharyngeal cavity, and skeleton. The tadpoles of the genus have an overall generalized morphology and many traits are conserved across species. Nevertheless, many characters are systematically informative and some are diagnostic for some species, as the paravertebral gland in E. petersi and the dorsally directed spiracle in E. puyango. Other characters provide support for some subclades within the genus. Moreover, some traits, such as the direction of the vent tube, supports the close relationship between Engystomops and Physalaemus, whereas other support the existence of these two as distinct genera, such as the overall shape of the lateral ridge papillae and the presence of a processus pseudopterygoideus. This article is protected by copyright. All rights reserved.

The remarkable larval anatomy of Proceratophrys minuta Napoli, Cruz, Abreu and Del-Grande, 2011 (Amphibia: Anura: Odontophrynidae)

The free living larvae of anurans (i.e., tadpoles) are a key element in the evolution and diversification of this group, and as such, their morphology is an important element to understand the phylogenetic relationships of frogs. However, the lack of data on larval morphology prevents us from fully understanding larval evolution in several lineages. The Neotropical genus Proceratophrys currently comprises 39 species, but descriptions of the internal morphology of larvae in this group are rare and restricted to few aspects of their buccopharyngeal cavity, chondrocranium, and muscles. In the present study, I describe the internal anatomy of the tadpole of P. minuta and report a new remarkable myological character state for the species. Given the rarity of this material, the description of this species' buccopharyngeal and musculo-skeletal elements is based on two tadpoles in developmental stages 30 and 31. Several new apomorphic character states are described: (a) the presence of a conical papilla in the interior of the nostril; (b) a row of five short, conical papilla preceding the tall, postnarial papilla; and (c) the m. mandibulolabialis inserting in the gular skin. This latter feature is a remarkable, newly discovered character state that had never been reported in the literature before and is probably related to a particular feeding habit of the tadpoles of this species. The function of the m. mandibulolabialis in P. minuta is unknown.

Tadpole of the Amazonia frog Edalorhina perezi (Anura: Leptodactylidae) with description of oral internal and chondrocranial morphology

The genus Edalorhina consists of two species of small forest-floor frogs inhabiting the Amazon basin. The tadpole of Edalorhina perezi, the most widely distributed species, was previously described based on a single and early stage (Gosner 25) individual. Herein, we provide a description of the tadpole in Gosner stages 35-36 including internal morphology data (i.e., buccopharyngeal cavity and larval skeleton) based on samples from two populations from Ecuador. Edalorhina shares a generalized morphology with most members of its closely related taxa; however, it is distinguished from the other species by having an almost terminal oral disc. The presence of a dextral vent tube is considered a synapomorphy for the clade consisting of Edalorhina, Engystomops, and Physalaemus. Within this clade, the combination of two lingual papillae, a filiform median ridge, and the lack of buccal roof papillae are diagnostic of E. perezi and putative autapomorphies of Edalorhina. Chondrocranial anatomy provides characteristics, that is, presence of and uniquely shaped processus pseudopterygoideus and cartilago suprarostralis with corpora and alae joined by dorsal and ventral connections that readily differentiates the genus from other Leiuperinae.

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.