Sequestered toxins and diet shift in snakes
Rhabdophis pentasupralabialis feeding on a larval firefly under captive conditions. Image courtesy of Masaya Fukuda (Kyoto University, Kyoto, Japan).
The Japanese colubrid snake Rhabdophis tigrinus, which typically feeds on frogs and poisonous toads, accumulates potent toxins called bufadienolides in its neck glands. The toxins are derived from the toads and can perturb heart function in the snake’s predators. One group of Rhabdophis snakes, called the Rhabdophis nuchalis Group, however, has evolved to feed primarily on nontoxic earthworms, rather than frogs and toads, but nonetheless harbors bufadienolide toxins. To uncover the source of the snakes’ toxins, Tatsuya Yoshida, Rinako Ujiie, et al. (pp. 5964–5969) performed a series of laboratory feeding preference tests and analyzed bufadienolides in gland fluids from R. nuchalis Group members. Analysis revealed that the snakes’ bufadienolides closely resembled those produced by fireflies of the family Lampyridae. Feeding tests confirmed the snakes’ predilection not only for earthworms but also for the fireflies, whose larvae were also detected in the snakes’ guts. The findings suggest that an evolutionary shift in the snakes’ primary diet—from frogs to earthworms—was accompanied by an expansion of dietary range and a compensatory shift in the source of the snakes’ sequestered toxins. According to the authors, the study demonstrates the species’ ability to retain a prey-derived defense mechanism despite a drastic shift in diet from vertebrate to invertebrate prey. — P.N.
Algal darkening of Greenland Ice Sheet
Extremophile glacier algae darken and increase melting of the GrIS.
Processes that darken the Greenland Ice Sheet (GrIS) accelerate surface melt, but the potential for microalgae to drive such darkening is unclear. To determine how specialized glacier algae are able to thrive on and darken the GrIS, Christopher Williamson et al. (pp. 5694–5705) analyzed samples of algal blooms that grew on the GrIS surface between July and August 2016. By analyzing the algae’s biooptical properties, the authors determined that secondary phenolic pigmentation allows the algae to survive under the extreme surface ice conditions of intense light and low temperatures. The authors also found that the pigments absorb damaging UV-A and UV-B light, providing shading to the underlying, low-light–adapted chloroplasts, while simultaneously capturing energy that can be used to produce meltwater around the algal cells. By measuring pigment profiles of algal assemblages and modeling algal biomass within GrIS surface ice throughout the 2016 ablation season, the authors determined that the presence of glacier algae in surface ice drives widespread darkening of the southwestern GrIS during summer melt months. The findings suggest that the mechanisms needed for algal survival in the extreme environment of the GrIS also drive the ice sheet’s darkening, contributing to its melt, according to the authors. — M.S.
Swamp wallabies’ reproductive strategy
Female swamp wallaby in Victoria, Australia. Image courtesy of Geoff Shaw (University of Melbourne, Melbourne, Australia).
In kangaroos and wallabies, young are born immature and complete development during an extended period of lactation. Females, which possess two uteri that are alternately used for conception, normally ovulate and mate after giving birth. Suckling of the newborn in the pouch triggers signals that arrest the development of the new embryo until the newborn leaves the pouch. Brandon Menzies et al. (pp. 5938–5942) report an extraordinary form of reproduction in the swamp wallaby (Wallabia bicolor), which ovulates, mates, and conceives anew while still actively pregnant—a phenomenon previously reported only in the European brown hare, among mammals. Mature female swamp wallabies were sourced from the wild in Victoria, Australia, and held in a facility. Experiments on 10 individuals, some of which were scanned using high-resolution ultrasound through pregnancy, revealed that swamp wallabies ovulate and mate 1–2 days before giving birth and conceive a new embryo during active pregnancy. The finding indicates that gestation length in swamp wallabies exceeds the length of the estrous cycle. Because they become pregnant before giving birth, swamp wallabies may be continuously pregnant throughout their reproductive lives, according to the authors. — P.N.
Avian influenza and live poultry trade in China
Bar-headed geese (Anser indicus) wintering in the Yarlung Tsangpo River basin, Tibet, China.
The highly pathogenic avian influenza virus (HP AIV) H5N1 has spread to more than 60 countries since its identification in 1996, with an estimated 50–60% fatality rate in humans. Most H5N1 cases are linked to exposure to live poultry, which are thought to play a key role in transmission. Qiqi Yang et al. (pp. 5949–5954) compared the structure of live poultry trade networks in China with genome sequences of H5N1 and two related AIV lineages from domestic poultry to estimate the role of poultry trading in virus transmission. Movement of virus lineages tended to occur between nearby provinces, suggesting a geographically continuous process of virus transmission. The intensity of poultry trade between provinces was a significant predictor of virus spread. The authors identified five regional live poultry trade communities (LPTCs) within China and used viral genome sequences to reconstruct the evolutionary history of each viral lineage. Clades within each lineage tended to coincide with specific LPTCs, and movement between LPTCs was often associated with major evolutionary divergences. Lineage transmission was much more likely to occur within LPTCs than between LPTCs. The results suggest a strong association between virus transmission and the live poultry trade network in China and could inform prevention and control efforts, according to the authors. — B.D.