Caecilita Wake & Donnelly, 2010 (Amphibia: Gymnophiona) is not lungless: implications for taxonomy and for understanding the evolution of lunglessness 

Abstract

According to current understanding, five lineages of amphibians, but no other tetrapods, are secondarily lungless and are believed to rely exclusively on cutaneous gas exchange. One explanation of the evolutionary loss of lungs interprets lunglessness as an adaptation to reduce buoyancy in fast-flowing aquatic environments, reasoning that excessive buoyancy in such an environment would cause organisms being swept away. While not uncontroversial, this hypothesis provides a plausible potential explanation of the evolution of lunglessness in four of the five lungless amphibian lineages. The exception is the most recently reported lungless lineage, the newly described Guyanan caecilian genus and species Caecilita iwokramae Wake & Donnelly, 2010, which is inconsistent with the reduced disadvantageous buoyancy hypothesis by virtue of it seemingly being terrestrial and having a terrestrial ancestry. Re-examination of the previously only known specimen of C. iwokramae and of recently collected additional material reveal that this species possesses a reasonably welldeveloped right lung and is a species of the pre-existing caecilian genus Microcaecilia Taylor, 1968. We therefore place Caecilita in the synonymy of Microcaecilia, and re-evaluate the plausibility of the reduced disadvantageous buoyancy hypothesis as a general explanation of the evolution of lunglessness.

Morphological evolution and modularity of the caecilian skull

“…Together, these analyses contribute clear quantitative support for the qualitative documentation and interpretation of the extremely divergent cranial morphology of A. eiselti [66, 71]. As the largest lungless tetrapod and only known lungless caecilian [66, 72], the constraint of respiratory buccal pumping has been lifted, and this release (along with a reduction of constraints associated with fossoriality) is reflected in cranial morphology, with a uniquely large gape and cheek architecture [66, 73]. Atretochoana eiselti is a member of a clade including the three obligate aquatic typhlonectid species in our dataset, and the significant increase in the rate of cranial module shape evolution along the stem of this lineage suggests that this ecological transition promoted a faster rate of cranial evolution (although the signal for this is caused to a substantial degree by A. eiselti ).…”

Phylogenetic relationships of the largest lungless tetrapod (Gymnophiona, Atretochoana) and the evolution of lunglessness in caecilians

“…Potomotyphlus has partially sealed choanal valves with very small and concealed openings into the buccal cavity, while Atretochoana is unique among tetrapods in having the choanae completely sealed (Wilkinson et al . ).…”

“…Atretochoana presents the most derived condition for this character, being the only caecilian known to lack these pulmonary vascular elements (Wilkinson et al . ).…”

“…Atretochoana is the only caecilian that lacks lungs (Wilkinson et al . ). Acronyms of collections are as follows: CZDP = Coleção Zoológica Delta do Parnaíba, Parnaíba, Piauí, Brazil; MCP = Museu de Ciências e Tecnologia da PUCRS, Porto Alegre, Rio Grande do Sul, Brazil; MPEG = Coleção Herpetológica Osvaldo Rodrigues da Cunha, Museu Paraense Emílio Goeldi, Belém, Pará, Brazil; MUSM = Museo de Historia Natural, Universidad Nacional Mayor de San Marcos, Lima, Peru; SMNS = Staatliches Museum für Naturkunde, Schloss Rosenstein, Stuttgart, Germany; UFC = Departamento de Biologia, Universidade Federal do Ceará, Fortaleza, Ceará, Brazil; UFRGS = Universidade Federal do Rio Grande do Sul, Porto Alegre, Rio Grande do Sul.…”

A new species of Indian caecilian highlights challenges for species delimitation within Gegeneophis Peters, 1879 (Amphibia: Gymnophiona: Indotyphlidae)

“…Research since 1999 has resulted in many new species descriptions of Gegeneophis (Agarwal et al 2013;Bhatta et al 2007a, b;Bhatta & Srinivasa 2004;Giri et al 2003Giri et al , 2004Giri et al , 2011Kotharambath et al 2012a;Pillai & Ravichandran 1999;Ravichandran et al 2003). This descriptive work, together with the removal of the northeast Indian forms (Kamei et al 2012) and a new synonymy (Gower et al 2013), has seen Gegeneophis become the fourth most speciose of the 32 currently recognised (Wilkinson et al 2011(Wilkinson et al , 2013a(Wilkinson et al , 2014aKamei et al 2012;Nishikawa et al 2012) caecilian genera globally. As currently conceived (Wilkinson et al 2011;Gower et al 2013;Agarwal et al 2013), the endemic Indian genus Gegeneophis comprises 11 species that are the only caecilians in peninsular India that have the eye covered by bone.…”