Dramatic Dietary Shift Maintains Sequestered Toxins in Chemically Defended Snakes

Unlike other snakes, most species of Rhabdophis possess glands in their dorsal skin, sometimes limited to the neck, known as nucho-dorsal and nuchal glands, respectively. Those glands contain powerful cardiotonic steroids known as bufadienolides, which can be deployed as a defense against predators. Bufadienolides otherwise occur only in toads (Bufonidae) and some fireflies (Lampyrinae), which are known or believed to synthesize the toxins. The ancestral diet of Rhabdophis consists of anuran amphibians, and we have shown previously that the bufadienolide toxins of frog-eating species are sequestered from toads consumed as prey. However, one derived clade, the Rhabdophis nuchalis Group, has shifted its primary diet from frogs to earthworms. Here we confirm that the worm-eating snakes possess bufadienolides in their nucho-dorsal glands, although the worms themselves lack such toxins. In addition, we show that the bufadienolides of R. nuchalis Group species are obtained primarily from fireflies. Although few snakes feed on insects, we document through feeding experiments, chemosensory preference tests, and gut contents that lampyrine firefly larvae are regularly consumed by these snakes. Furthermore, members of the R. nuchalis Group contain compounds that resemble the distinctive bufadienolides of fireflies, but not those of toads, in stereochemistry, glycosylation, acetylation, and molecular weight. Thus, the evolutionary shift in primary prey among members of the R. nuchalis Group has been accompanied by a dramatic shift in the source of the species’ sequestered defensive toxins

Correction: The Acoustic Properties of Low Intensity Vocalizations Match Hearing Sensitivity in the Webbed-Toed Gecko, Gekko subpalmatus.

[This corrects the article DOI: 10.1371/journal.pone.0146677.]

A new perspective on the reduction of cephalic scales in fossorial legless skinks (Squamata, Scincidae)

In this study, we provide an extended multilocus phylogenetic analysis combining mitochondrial and nuclear DNA of a group of fossorial and miniaturized legless lizards (genus Paracontias) from Madagascar, including the description of two species new to science, P. ampijoroensis sp. nov. and P. mahamavo sp. nov. Our analyses revealed the existence of two distinct, parapatric and diagnosable clades within the genus: (i) the ‘kankana clade’ (including P. kankana and the two newly described species), located in the north (but absent from the extreme northern tip) of the island and characterized by a pattern of cephalic scales very unusual for Malagasy Scincinae, with large loreal scales extending to and meeting each other at dorsal midline, and (ii) the ‘brocchii clade’ (including all other studied species), endemic to the north of Madagascar and characterized by small loreal scales separated from each other by the rostral and the frontonasal scale. By combining phylogenetic results with morphological traits observed among species, we develop novel hypotheses on the simplification of the cephalic scalation pattern within this genus, a trend frequently encountered among various lineages of legless squamates that convergently adapted to a burrowing lifestyle. Additionally, a user-friendly graphical identification key for species of Paracontias is provided and made available as supplementary information

Audiogram and power spectra of vocalizations for <i>Gekko subpalmatus</i>(±SE).

<p>Audiogram and power spectra of vocalizations for <i>Gekko subpalmatus</i>(±SE).</p

Representative ABR waveforms for a single gecko showing multiple waveform peaks within the first 5–10 ms in response to 3 kHz tone bursts ranging from 35 to 70 dB SPL.

<p>Representative ABR waveforms for a single gecko showing multiple waveform peaks within the first 5–10 ms in response to 3 kHz tone bursts ranging from 35 to 70 dB SPL.</p

ABR latency of <i>Gekko subpalmatus</i> for tones of different frequencies at 70 dB SPL(±SE.

<p>ABR latency of <i>Gekko subpalmatus</i> for tones of different frequencies at 70 dB SPL(±SE.</p

Response waveforms from 0.4 kHz to 1.5 kHz reveal a well-defined frequency following response (FFR) that masked late response peaks.

<p>Response waveforms from 0.4 kHz to 1.5 kHz reveal a well-defined frequency following response (FFR) that masked late response peaks.</p