Embryonic colors in water striders
Embryos of L. franciscanus showing ocular and extraocular color patterns.
Color in the animal kingdom serves crucial functions, including protection against UV, heat regulation, camouflage, and mate signaling. However, the origin and role of embryonic color in animals are poorly understood. Aidamalia Vargas-Lowman et al. (pp. 19046–19054) examined coloration in the embryos of 34 species of water striders, a group of crimson-eyed semiaquatic bugs whose embryos—but not adults—sport a range of varied color patterns. From pale yellow to deep red, the embryonic colors, which are produced in zygotes, are readily visible through the transparent sheath enclosing eggs glued to surfaces, suggesting that the colors serve as a signal to ward off aquatic predators and parasitic wasps. Phylogenetic analysis revealed that water striders use the pteridine biosynthesis pathway, a biochemical process that generates red visual pigment in the eyes, to produce colors in the legs and antennae of embryos, with extraocular yellow being ancestral and extraocular red emerging as a derived trait at least 6 different times in the group. Despite the vibrant color palette of water strider embryos, the underlying biosynthetic pathway appears to have been largely preserved over 200 million years of evolution. Using liquid chromatography and mass spectrometry, the authors detected the red pigment erythropterin and yellow pigment xanthopterin in the embryos of the water striders Limnogonus franciscanus and Limnoporus dissortis. According to the authors, the findings provide a model to examine how biochemical pathways are repurposed during evolution and to identify the ecological forces that shape such repurposing. — P.N.
Anthropogenic disturbances, climate change, and mammalian extinction
Although human activity and global warming are thought to be responsible for the rapid extinction of mammalian species, long-term data on the links are sparse. Xinru Wan, Guangshun Jiang, Chuan Yan, et al. (pp. 19001–19008) analyzed more than 9,000 historical records dating from 905 BCE to 2006 CE of the distribution of 11 mammalian species found in China, and examined how the mammals’ population sizes were associated with climate change-related stress, represented by air temperature, and anthropogenic stress, represented by cropland coverage and human population density. Both extreme climate change and intensified human disturbances were associated with increased local extinction. Since 1644 CE, all species’ survival rates decreased by 36–100%, whereas cropland coverage, human population density, and average summer temperatures rapidly increased. Global cooling prior to 1911 CE and global warming since 1911 CE were both positively associated with increased local extinction. Compared with small- and medium-sized mammals, large mammals, such as elephants, pandas, and rhinos, had earlier and larger population declines. The findings suggest that both global cooling and global warming may reduce habitat sizes caused by range shift, leading to the local extinction of mammalian populations. Moreover, habitat fragmentation caused by human disturbance may have also accelerated the local extinction of the mammal species by hampering their movements, according to the authors. — M.S.
Genome analysis reveals population structure of Scotland and the Isles
Study examines genetic landscape of Scotland and surrounding isles. Image courtesy of iStock/Swen_Stroop.
Genome analysis has unearthed rich insights into the population histories of England, Wales, and Ireland, which are marked by invasions and migrations. However, the population structures of northern Britain, Scotland, and the surrounding isles remain understudied. Edmund Gilbert et al. (pp. 19064–19070) assembled and analyzed genome data from 2,544 British and Irish people to explore genetic diversity in previously undersampled regions. The authors identified 6 genetic clusters within Scotland—the northeast, the southwest, the Borders, the Hebrides, Orkney, and Shetland—with most Scots placing in the northeast or southwest clusters. Comparison of the British and Irish samples with genome data from 2,225 Scandinavians revealed high Norwegian ancestry in the Northern Isles clusters—as high as 23% in Shetland—and lower Norwegian ancestry in north Scotland, Argyll, the Isle of Man, and Ireland, with little observed elsewhere. Most of the Norwegian-like ancestry in Britain and Ireland appeared to originate from Hordaland and Sogn og Fjordane, counties in western Norway from which Norse Vikings are thought to have set forth. Additionally, the authors explored the possible British or Irish origins of ancient Gaels in Iceland, previously described through analysis of ancient DNA. The comparative analysis revealed that ancient Gael settlers who contributed to the founding of Iceland may have originated from a source population in the northwestern reaches of Britain or Ireland. Fine-scale population genetic analysis can aid the discovery of rare genetic variants that play major roles in human diseases, and the findings provide a basis for rare variant discovery in Britain and Ireland, according to the authors. — P.N.
Sex bias in mammalian specimen collections
Many mammalian species have a 1:1 sex ratio at birth, but previous studies have shown that male specimens are overrepresented in the fossil records of mammoths. To determine whether the specimen records of other mammals exhibit a similar bias, Graham Gower et al. (pp. 19019–19024) used ancient DNA to genetically determine the sex of 186 Pleistocene bison and 91 Pleistocene brown bear fossils. The authors sampled the fossils from Europe and North America and collected them from the field and museums. Approximately 75% and 64% of the bison and bear specimens were identified as male, respectively. The authors also found that across most ancient and modern mammalian orders, male specimens outnumbered female specimens in collections belonging to the American Museum of Natural History, the Natural History Museum in London, the Smithsonian Institution National Museum of Natural History, and the Royal Ontario Museum. The authors suggest that larger male ranges may increase their fossilization potential. Moreover, sex biases in fossil and museum collections may be ubiquitous and could bias scientific analyses, according to the authors. — M.S.