Unlike other snakes, most species ofRhabdophispossess 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 ofRhabdophisconsists 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, theRhabdophis nuchalisGroup, 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 ofR. nuchalisGroup 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 theR. nuchalisGroup 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 theR. nuchalisGroup has been accompanied by a dramatic shift in the source of the species’ sequestered defensive toxins.

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.

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Many animals are equipped with specialized defensive systems that function in a coordinated manner involving morphological structure, physiological processes and behaviour. Nucho-dorsal glands, unusual organs known in a few Asian natricine snakes, are believed to function in avoidance of predation, based on the defensive function of similar organs in a related Japanese species that sequesters prey toxins and stores them in the glands. We examined the arrangement of the nucho-dorsal glands of Rhabdophis nuchalis, R. pentasupralabialis and Macropisthodon plumbicolor and tested behavioural responses to tapping stimulation to investigate the spatial distribution of glands on the body and related defensive displays respectively. We confirmed the presence of glands that extend from the neck along the length of the body in all three species. The spatial arrangement of the glands was similar between the two Rhabdophis species, but it differed substantially in M. plumbicolor. In M. plumbicolor, there were two uninterrupted rows of glands throughout the full length of the body, whereas in the two Rhabdophis species, the position and size of the glands differed between the neck and trunk regions, with the two series separated by a spatial gap. In spite of these structural differences, M. plumbicolor and R. pentasupralabialis exhibited a similar defensive display, which we refer to as body lift, in response to a tapping stimulus on the body. Our study shows detailed morphological features of the nucho-dorsal glands and a novel display that are consistent with the presumed predator deterrent function of the glands, which have evolved as a unique defensive system in this lineage of snakes.

Information on lichen flora in Sri Lanka is scarce. Therefore a study was carried out to investigate lichens growing on a tree species common to all five eco regions (Montane, Wet, Intermediate, Arid and Dry zone) of Sri Lanka. The common tree species found in all regions was Artocarpus heterophyllus Lam. (jak). Lichen flora found on bark of jak trees between 1.5 m and 2 rn above the