Fluorescent cacao oil: A material suited for highlighting blood vessel in macro-scale dissection.

This study describes a novel method to highlight vascular networks in animal tissue during macro-scale dissection using cacao oil and ultraviolet (UV) fluorescent dye. This is a three-step method: 1) injecting warmed cacao oil containing oil-based UV fluorescent dye ("fluorescent cacao oil" or FCO) into the blood vessels of a dead animal; 2) lowering the temperature to solidify the FCO in blood vessels; and 3) illuminating blood vessels with UV light when the specimen is dissected. This method uses the unique properties of cacao oil, which is solid at room temperature but becomes liquid at 40°C. Such a relatively low melting temperature meets two conflicting demands, i.e., maintaining low viscosity for better flow into the blood vessels and preventing damage of animal tissue by heat. This method is:•Practical, as blood vessel is strongly highlighted using handy UV light during dissection; therefore, a specific medical equipment is not required•Inexpensive, as FCO is made by mixing two commercially available produces (cacao oil and UV fluorescent dye)•Stable, as FCO-injected tissue can be fixed and preserved semi-permanently in formalin. The fluorescent ability of FCO is not affected by this process.

Morphology, Diet, and Reproduction of Coastal Hydrophis Sea Snakes (Elapidae: Hydrophiinae) at Their Northern Distribution Limit.

The Ryukyu Archipelago represents the northern distribution limit for hydrophiine sea snakes, the largest group of marine reptiles. Ryukyuan sea snakes may have developed distinct local adaptations in morphology and ecology, but they have been poorly studied. We examined preserved specimens of 111 Hydrophismelanocephalusand 61 Hydrophis ornatusfrom the Ryukyu Archipelago to obtain data on morphology, diet, and reproduction. Sexual size dimorphism was detected in H. melanocephalus (mean ± standard deviation of adult snout-vent length: SVL, females 1062 ± 141 mm vs. males 959 ± 96 mm) but not in H. ornatus. Female H. melanocephalus had larger head widths and shorter tail lengths relative to SVL compared to males. Relative girth was low in neonates of both species (1.0-1.3), but increased in adults to about 1.7-2.6 in H. melanocephalus and 1.3-1.8 in female H. ornatus. Stomach contents of H. melanocephalus consisted of ophichthid and congrid eels, a sand diver, and gobies, whereas in H. ornatus, gobies and a goat fish were found. Litter size of three reproductive H. melanocephalus ranged from five to seven, and parturition seems to occur from August to October. Litter size of six H. ornatus ranged from two to seven, and was correlated with maternal SVL. Parturition in H. ornatus probably occurs around November. Different selective forces related to locomotion, feeding and predation risk, which influence the pregnant mother and neonates, may have resulted in having few, long but slender offspring that show positive allometric growth in hind-body girth.

Population history and genomic admixture of sea snakes of the genus Laticauda in the West Pacific.

Speciation in the open ocean has long been studied, but it remains largely elusive what factors promote or inhibit speciation in such an open environment. Marine amniotes, which evolved from terrestrial ancestors, provide valuable opportunities for studying speciation in the ocean because of their evident aquatic origins. Sea snakes are phylogenetically related to terrestrial elapid snakes and consist of two monophyletic groups (Hydrophiini and Laticaudini). These two groups migrated from land to water almost at the same time, but species diversities are remarkably different: there are approx. 60 species in 16 genera described for hydrophiins, whereas only eight species in the genus Laticauda are described for laticaudins. Here, we provide a high-quality reference genome assembly of a laticaudin L. colubrina with a scaffold N50 value of 40 Mbp, and focused on laticaudins to consider why they have seldom speciated. We performed whole-genome shotgun sequencing of several species of laticaudins sampled in their southmost (Vanuatu) and northmost (Ryukyu) habitats. Demographic histories of Vanuatu and Ryukyu populations suggest that populations of broadly distributed major species are geographically structured. Each species is genetically clearly distinguished, but there is a considerable amount of gene flow between two sibling species distributed sympatrically in Vanuatu. In addition, inter-species genomic admixture is ubiquitously observed among laticaudins even between phylogenetically distant species. Broad distribution of major species combined with such genetic mixability might have prevented laticaudins from genetic isolation and speciation.

Complete mitochondrial genome of the Ijima's Sea Snake (Emydocephalus ijimae) (Squamata, Elapidae).

In this study, we provide the first report of the complete mitochondrial genome of Emydocephalus ijimae. The mitogenome length is 18,259 bp and includes 13 protein-coding genes, two rRNA genes, 22 tRNA genes, and three non-coding regions. The sequence presented could be very useful for further phylogenetic and evolutionary study.

How Snakes Find Prey Underwater: Sea Snakes Use Visual and Chemical Cues for Foraging.

Fully aquatic adaptation generally leads amniotes to change sensory modalities drastically. Terrestrial snakes rely heavily on chemical cues to locate and recognize prey, but little is known about how sea snakes find prey fishes underwater. Sea snakes of the genus Hydrophis are fish-eating marine elapids which adapted from land to water approximately 5-10 million years ago. Here, using two species of captive Hydrophis snakes, we show that they can recognize and discriminate their preferred fish species solely by using olfactory cues. However, they locate places where their preferred fishes may hide without relying on chemical cues. These findings indicate that Hydrophis snakes find prey in water as follows: they use visual cues to locate a place where their prey fishes are likely to hide, and then use chemical cues to find and attack prey. As is the case for other aquatic amniotes, snakes also modified their sensory modalities upon becoming aquatic.