Early evidence of insect pollination of flowering plants
Artist’s reconstruction of A. burmitina feeding on eudicot flowers. Colors of beetles and flowers are artistic only.
Insects are thought to have pollinated flowering plants during the Cretaceous Period, when flowering plants rapidly diversified. However, direct evidence of insect pollination of Cretaceous flowering plants is lacking. Tong Bao et al. (pp. 24707–24711) report the discovery of a tumbling flower beetle preserved in mid-Cretaceous Burmese amber that bears evidence of insect pollination of flowering plants. Encased in the fragment of amber, which is approximately 99 million years old and was recovered from a mine in northern Myanmar, the beetle, Angimordella burmitina, exhibited a suite of evidence suggesting its role as a pollinator: a curved, compressed, and wedge-shaped body with a declined head that likely facilitated feeding inside flowers; well-developed hind legs to move between flowers; fine hairs on the thorax and abdomen, the height and spacing of which are apt for holding and transporting pollen; and modified mouthparts seemingly tailored for collecting and likely transporting pollen. The beetle’s thorax and abdomen were dusted with tricolpate pollen, a defining feature of the eudicot group of flowering plants. The pollen grains’ reticulate surfaces and signs of pollen clumping together suggest beetle-aided pollination. Previous evidence of insect pollination of flowering plants dates to the Middle Eocene, around 48–45 million years ago. Thus, the finding deepens the history of insect pollination of flowering plants by around 50 million years and suggests the existence of such mutualism at least as far back as 99 million years ago, according to the authors. — P.N.
Honeybees’ hydrofoiling locomotion
Honeybee (Apis mellifera). Image courtesy of Flickr/USGS Bee Inventory and Monitoring Lab.
When honeybees fall on the surface of water, their wetted wings lose aerodynamic ability. Nevertheless, the bees can move forward by beating their wings. Chris Roh and Morteza Gharib (pp. 24446–24451) report that such motion results from the wings acting as hydrofoils. Imaging of the waves and flow patterns generated by live honeybees on water indicated net backward transfer of momentum to the water, which is thought to impart equal forward momentum to the bee. The authors estimated that the magnitude of momentum imparted to the water, and hence to the bee, was sufficient to overcome hydrodynamic drag and propel the bee forward. Measurements of fluid flow under a mechanical honeybee wing model revealed a net horizontal momentum imparted to the water by the wing motion, and hence a net horizontal thrust, as well as periodic acceleration and deceleration of water that could provide additional forward motion via recoil. The results highlight the versatility of honeybees’ flapping wing systems, which can generate propulsion in fluids of widely differing densities. According to the authors, the hydrofoiling mechanism may increase honeybees’ chances of survival during water foraging, and the findings could inspire the design of aerial–aquatic hybrid vehicles that use the same mechanism. — B.D.
Unraveling the basis of beetle diversity
Beetles are among the most diverse groups of animals on Earth. Embedded images courtesy of Udo Schmidt (photographer).
Beetles, which belong to the order Coleoptera, account for a substantial fraction of animal species diversity on Earth, but the reasons for their evolutionary success remain unclear. Using large-scale genome data, Duane McKenna, Seunggwan Shin, et al. (pp. 24729–24737) reconstructed the beetle family tree, estimated timing and rates of beetle evolutionary diversification, and examined beetle genes thought to underpin specialized herbivory. The analyses resolved previously contested facets of the beetle family tree and indicated that beetles evolved in the Carboniferous Period, around 327 million years ago. Most present-day beetle groups likely originated before the end of the Cretaceous Period, 66 million years ago, around the time of the evolutionary ascendance of rapidly diversifying flowering plants. Further, the authors report, the diversification of plant-feeding beetles, which account for most beetle species, occurred after beetles acquired genes for plant cell wall-digesting enzymes. Such genes appear to have been acquired via horizontal transfer from fungi and bacteria and likely facilitated herbivory, including leaf and seed mining and stem and wood boring abilities, enabling beetles to adapt to and parallel the growing diversity of flowering plants. According to the authors, beetles owe their staggering diversity to an array of factors, including low rates of lineage extinction, codiversification with flowering plants, and horizontal gene transfer from microbes. — P.N.
Myeloid blast differentiation rate and leukemia
Hematopoietic stem cells in blood can not only reproduce themselves but also differentiate into blood cell lineages in a tightly regulated process. Acute myeloid leukemia (AML) is thought to result from multiple genetic events that block differentiation of primitive myeloid blast cells and increase the cells’ proliferation. Anupriya Agarwal et al. (pp. 24593–24599) examined the effects of perturbed differentiation on AML by using a mathematical model that accounted for various features of hematopoietic differentiation, including total number of each cell type, cell death and division rates, and the probability that each daughter cell differentiates into a particular cell type. Even a slight reduction in the differentiation rate was sufficient to produce an accumulation of myeloid blasts and to result in an AML phenotype. To experimentally validate the model, the authors collected blood samples from 12 patients with AML and analyzed cell populations with either interphase fluorescent in situ hybridization or by sequencing. The authors found that different leukemia-causing molecular abnormalities thought to block differentiation were present at similar levels in both mature and immature myeloid cells. The authors suggest that a reduction rather than a block in differentiation is responsible for the development of AML. According to the authors, understanding the mechanisms underlying skewed differentiation could help maximize the impact of therapies. — S.R.