Evolution of nuchal glands, unusual defensive organs of Asian natricine snakes (Serpentes: Colubridae), inferred from a molecular phylogeny

A large body of evidence indicates that evolutionary innovations of novel organs have facilitated the subsequent diversification of species. Investigation of the evolutionary history of such organs should provide important clues for understanding the basis for species diversification. An Asian natricine snake, Rhabdophis tigrinus, possesses a series of unusual organs, called nuchal glands, which contain cardiotonic steroid toxins known as bufadienolides. Rhabdophis tigrinus sequesters bufadienolides from its toad prey and stores them in the nuchal glands as a defensive mechanism. Among more than 3,500 species of snakes, only 17 Asian natricine species are known to possess nuchal glands or their homologues. These 17 species belong to three nominal genera, Balanophis, Macropisthodon, and Rhabdophis. In Macropisthodon and Rhabdophis, however, species without nuchal glands also exist. To infer the evolutionary history of the nuchal glands, we investigated the molecular phylogenetic relationships among Asian natricine species with and without nuchal glands, based on variations in partial sequences of Mt-CYB, Cmos, and RAG1 (total 2,767 bp). Results show that all species with nuchal glands belong to a single clade (NGC). Therefore, we infer that the common ancestor of this clade possessed nuchal glands with no independent origins of the glands within the members. Our results also imply that some species have secondarily lost the glands. Given the estimated divergence time of related species, the ancestor of the nuchal gland clade emerged 19.18 mya. Our study shows that nuchal glands are fruitful subjects for exploring the evolution of novel organs. In addition, our analysis indicates that reevaluation of the taxonomic status of the genera Balanophis and Macropisthodon is required. We propose to assign all species belonging to the NGC to the genus Rhabdophis, pending further study.

Size of recurrent laryngeal nerve as a new risk factor for postoperative vocal cord paralysis

Recurrent laryngeal nerve paralysis (RLNP) is a frequent and serious complication following esophageal cancer surgery. Therefore, this study aims to evaluate the correlation between recurrent laryngeal nerve (RLN) size and RLNP. This was a retrospective study of esophageal cancer patients who underwent thoracoscopic esophagectomy from January 2012 to December 2014. Eighty-four patients were included in the primary analysis. Diameter of the RLN was measured using the digital video recording of surgical procedures by the ratio between scissor and RLN. For evaluation of vocal cord paralysis or paresis, indirect laryngoscopy was performed. Because RLNP more frequently occurs on the left side than the right, we evaluated the correlation between size of the left RLN and left RLNP. The median size of the left RLN was 1.51 mm. We found that the incidence of postoperative left RLNP (Clavien-Dindo classification ≥1) was significantly higher (71% vs. 24%; P < 0.001) in thin RLNs (≤1.5 mm) than in thick RLNs (>1.5 mm). Thin RLN (P < 0.001), female sex (P = 0.025), and being overweight (P = 0.034) were identified as significant independent risk factors for postoperative RLNP. RLNP more easily occurred when the RLN was thin. It is difficult to confirm occurrence of postoperative RLNP before and at extubation. Therefore, it is helpful to know its risk factors including size of RLN.

Meta-analysis of the impact of postoperative complications on survival after oesophagectomy for cancer

Background

Oesophagectomy has a high risk of postoperative morbidity. The impact of postoperative complications on overall survival of oesophageal cancer remains unclear. This meta‐analysis addressed the impact of complications on long‐term survival following oesophagectomy.

Methods

A search of PubMed and Cochrane Library databases was undertaken for systematic review of papers published between January 1995 and August 2016 that analysed the relation between postoperative complications and long‐term survival. In the meta‐analysis, data were pooled. The main outcome was overall survival (OS). Secondary endpoints included disease‐free (DFS) and cancer‐specific (CSS) survival.

Results

A total of 357 citations was reviewed; 21 studies comprising 11 368 patients were included in the analyses. Overall, postoperative complications were associated with significantly decreased 5‐year OS (hazard ratio (HR) 1·16, 95 per cent c.i. 1·06 to 1·26; P = 0·001) and 5‐year CSS (HR 1·27, 1·09 to 1·47; P = 0·002). Pulmonary complications were associated with decreased 5‐year OS (HR 1·37, 1·16 to 1·62; P < 0·001), CSS (HR 1·60, 1·35 to 1·89; P < 0·001) and 5‐year DFS (HR 1·16, 1·00 to 1·33; P = 0·05). Patients with anastomotic leakage had significantly decreased 5‐year OS (HR 1·20, 1·10 to 1·30; P < 0·001), 5‐year CSS (HR 1·81, 1·11 to 2·95; P = 0·02) and 5‐year DFS (HR 1·13, 1·02 to 1·25; P = 0·01).

Conclusion

Postoperative complications after oesophagectomy, including pulmonary complications and anastomotic leakage, decreased long‐term survival.

Toxin-resistant isoforms of Na+/K+-ATPase in snakes do not closely track dietary specialization on toads

Toads are chemically defended by bufadienolides, a class of cardiotonic steroids that exert toxic effects by binding to and disabling the Na⁺/K⁺-ATPases of cell membranes. Some predators, including a number of snakes, have evolved resistance to the toxic effects of bufadienolides and prey regularly on toads. Resistance in snakes to the acute effects of these toxins is conferred by at least two amino acid substitutions in the cardiotonic steroid binding pocket of the Na⁺/K⁺-ATPase. We surveyed 100 species of snakes from a broad phylogenetic range for the presence or absence of resistance-conferring mutations. We found that such mutations occur in a much wider range of taxa than previously believed. Although all sequenced species known to consume toads exhibited the resistance mutations, many of the species possessing the mutations do not feed on toads, much less specialize on that food source. This suggests that either there is little performance cost associated with these mutations or they provide an unknown benefit. Furthermore, the distribution of the mutation among major clades of advanced snakes suggests that the origin of the mutation reflects evolutionary retention more than dietary constraint.

Methods for invasive species control are transferable across invaded areas

Cane Toads (Rhinella marina) are invasive pests in many parts of the world, including the Japanese island of Ishigaki. Extensive research in Australia has identified promising new methods for control, but also has shown that toads exhibit geographic variation in many traits (suggesting that methods developed in one location may not work in another). Can the approaches developed in Australia play a useful role for controlling this invasive species in Japan? Our experimental trials on Ishigaki Island suggest that these new methods can be successfully applied to Japan. First, Cane Toad embryos exposed to chemical cues of conspecific tadpoles exhibited a reduction in viability (subsequent growth and development). This response appears to be species-specific, with native frog embryos not being affected by exposure to cues from toad tadpoles, and Cane Toad embryos not being affected by exposure to cues from native frog tadpoles. Second, Cane Toad tadpoles were attracted to traps containing water from conspecific eggs, and toxin from adult conspecifics. Third, adult Cane Toads were attracted to acoustic cues of calling males, with sex differences in rates of attraction to specific versions of a synthetic call (males were attracted to choruses whereas females were attracted to low-frequency calls). Our results suggest that the methods developed by Australian researchers are applicable to controlling invasive Cane Toads in Japan.