Hirohiko Takeuchi

Assessing species boundaries and the phylogenetic position of the rare Szechwan ratsnake, Euprepiophis perlaceus (Serpentes: Colubridae), using coalescent-based methods

Delimiting species and clarifying phylogenetic relationships are the main goals of systematics. For species with questionable taxonomic status, species delimitation approaches using multi-species coalescent models with multiple loci are recommended if morphological data are unavailable or unhelpful. Moreover, these methods will also reduce subjectivity based on genetic distance or requirement of monophyletic genetic lineages. We determine the validity and phylogenetic position of a rare and long controversial species of Chinese reptile, the Szechwan ratsnake (Euprepiophis perlaceus), using multi-locus data from multiple individuals and coalescent-based approaches. Species were first delimited using Bayesian Phylogenetics & Phylogeography (BP&P), Brownie and Bayes Factor model comparison approaches, while relationships among species were estimated using species tree inference in (*)BEAST. Results indicate that Euprepiophis perlaceus is a distinct species sister to Euprepiophis mandarinus. Despite gene tree discrepancy, the coalescent model-based approaches used here demonstrate the taxonomic validity and the phylogenetic position of Euprepiophis perlaceus. These approaches objectively test the validity of questionable species diagnoses based on morphological characters and determine their phylogenetic position.

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.

Extremely Low Genetic Diversity in the Japanese Population of Zootoca vivipara (Squamata: Lacertidae) Revealed by Mitochondrial DNA

Abstract: Genetic diversity in the Japanese population of Zootoca vivipara was investigated using partial sequences of mitochondrial cytochrome b (706 bp) gene for 24 individuals from three sites. The phylogenetic status of the Japanese population was also examined using data from the current and previous studies. Only one haplotype was recognized in the Japanese population, which was different by only one nucleotide from the Russian and Belarusian populations. Individuals from disparate regions (>7000 km apart) quite rarely share such closely related haplotypes. From the results of the current and previous studies, members of the continental population seem to have invaded Hokkaido via the land bridge during the latest Pleistocene glaciation.

Antipredator Displays and Prey Chemical Preference of an Asian Natricine Snake, Macropisthodon rudis(Squamata: Colubridae)

Abstract: Several Asian natricine snakes are known to possess special organs called nuchal glands. Extensive studies on the nuchal glands of Rhabdophis tigrinus have shown that the glands contain cardiac steroidal toxins known as bufadienolides, which are sequestered from its toad prey and are stored in the nuchal glands as defensive substances. In addition, several species of snakes with nuchal glands exhibit unique behaviors to enhance the effects of the glands (nuchal gland-related behaviors). Macropisthodon rudis is the only species that does not have the nuchal glands in the genus. We investigated its antipredator displays and chemical preference for toads to gain insight into the evolution of the nuchal glands. The results showed that M. rudis does not exhibit the nuchal gland-related behaviors such as neck arching, neck butting, and dorsal-facing posture. Additionally, this species showed high preference for toad chemicals. These results support a previous hypothesis that preference for toads predates the evolution of the nuchal glands and that the unique antipredator behaviors have evolved to enhance the defensive efficiency of the glands.

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.

A new species of the genus Rhabdophis Fitzinger, 1843 (Squamata: Colubridae) from Guangdong Province, southern China

A new species, Rhabdophis guangdongensis sp. nov., is described from the Guangdong Province, China. It can be easily distinguished from other known congeners by cyt b and c-mos sequences, and by the following combination of morphological characters: body size small; head distinct from the neck; 20 maxillary teeth, the three most posterior teeth strongly enlarged, and not separated by diastemata from other teeth; six supralabials, the third and fourth touching the eye; seven infralabials, the first four in contact with anterior chin shields; dorsal scales in 15 rows throughout the body, weakly keeled, the outer row smooth; 126 ventrals; 39 paired subcaudals; anal scale divided; 44 pairs of narrow dorsolateral black cross-bars on body and 15 pairs on tail; body and tail with two dorsolateral longitudinal brownish-red lines, respectively with a series of white spots in cross-bars. The description of this new species brings the total number of described species of this genus to 21 and represents the tenth known Rhabdophis species in China.

Taxonomic Validity and Phylogeography of the East Eurasian Natricine Snake, Rhabdophis lateralis (Berthold, 1859) (Serpentes: Colubridae), as Inferred from Mitochondrial DNA Sequence Data

Abstract: We investigated the phylogenetic status and pattern of geographic variation in Rhabdophis lateralis on the basis of samples from across continental China, southeastern Russia, and the Korean Peninsula. The results confirmed the monophyly of the species and also revealed its extremely low genetic divergence. The population genetic analyses suggested that such low intraspecific divergence may reflect recent rapid population growth from a small ancestral population, extensive gene flow, or both. We conclude that R. lateralis is a good species, as suggested by our previous study, which analyzed fewer continental samples from a more limited range.

Biotic Resistance to an Alien Amphibian: Larval Competition between Japanese Frogs and Invasive Cane Toads.

Understanding negative effects of native species on introduced taxa may suggest novel ways to control the invasive species by enhancing such effects. Previous studies have reported that the larvae of invasive cane toads (Rhinella marina) are suppressed by competition with the larvae of native anurans in Australia, but not in North America. We conducted laboratory trials to measure the effect of exposure to the larvae of Japanese frogs (Microhyla ornata, Fejervarya sakishimensis, Rhacophorus owstoni) on rates of survival, growth and development of cane toad tadpoles in Ishigaki Island, in southern Japan. Survival rates were not affected by native species, but competition with Dicroglossids and Rhacophorids (but not Microhylids) strongly reduced rates of growth and development in the tadpoles of cane toads. Dicroglossid tadpoles also reduced the body condition to toad tadpoles in addition to effects on SVL and mass. Encouraging populations of native frogs in toad-invaded areas of Japan thus may help to reduce the numbers of invasive cane toads.