Highlights in PNAS

New for January 16, 2019

Evolution

Terrestrial ancestors of winged insects

Polyneoptera is a lineage of winged insects called Pterygota, which comprises more than 40,000 species. The evolutionary history of Polyneoptera is ambiguous, and whether winged insects evolved in an aquatic or terrestrial environment remains unclear. Benjamin Wipfler et al. conducted phylogenomic analyses and reconstructed ancient polyneopteran traits, habitats, and lifestyles. Analysis of 106 existing insect species, including 3,014 protein-coding genes and 112 behavioral, ecological, and morphological characteristics, revealed that polyneopteran insects likely evolved from a ground-dwelling common ancestor that had long antennae and segmented abdominal appendages. The ancestor’s biting mouthparts, located below the head capsule, were similar to those of dragonflies. The authors report that the ancestor also had hardened forewings that would have made flight difficult, resulting in the evolution of triangular hind wings. The findings suggest that wings did not evolve in aquatic environments, as previously speculated. Although several ancestral Pterygota species lived on plants and trees, the common polyneopteran ancestor of modern-day Pterygota eventually returned to life on the ground. The findings also suggest that insects evolved wings for aerial descent, that changes in polyneopteran mouthpart orientation is a frequent evolutionary transition influenced by lifestyle, and that maternal care evolved independently within various insect species, according to the authors. — M.S.

"Evolutionary history of Polyneoptera and its implications for our understanding of early winged insects," by Benjamin Wipfler, et al.
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Physiology

How mites affect honey bee colonies

The parasitic mite Varroa destructor is a major driver of honey bee colony losses worldwide. The mites are thought to feed exclusively on a blood-like fluid called hemolymph. In contrast to this view, Samuel Ramsey et al. found that Varroa mites damage and exploit host bees primarily by consuming a liver-like tissue called fat body. The authors fed bees two fluorescent stains to mark the hemolymph and fat body and imaged both of these tissues as well as the gut contents of mites that fed on the bees. The fluorescence profile of the mites matched the fat body signal, but not the signal detected in the hemolymph. Moreover, mites that were exclusively fed hemolymph survived only 1.8 days on average, with 5% producing eggs, similar to starved mites. By contrast, mites that consumed only fat body survived 3.5 days on average, with 40% producing eggs. Taken together, the results suggest that the primary source of sustenance for Varroa is the fat body, which is essential for honey bees’ immune function, pesticide tolerance, and overwinter survival. According to the authors, the findings could lead to the development of ways to curb the destructive impact of Varroa on honey bee health. — J.W.

"Varroa destructor feeds primarily on honey bee fat body tissue and not hemolymph," by Samuel D. Ramsey, et al.
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Psychological and Cognitive Sciences

Institutionalization and cognitive development

Children who spend their early lives in institutions characterized by low caregiver consistency and little opportunity for social or cognitive stimulation are subject to psychosocial neglect. Childhood trauma and adversity are associated with negative outcomes in memory and executive function in young children. However, the trajectories of improvement among institutionalized children, particularly the benefits associated with a move to foster care, were previously unexplored. Mark Wade et al. analyzed data from the Bucharest Early Intervention Project, a randomized controlled trial in which the development of previously institutionalized children placed in foster care was tracked. The authors compared the development of 136 participants in the project with 72 never-institutionalized children. Growth in memory and executive function occurred in institutionalized, foster care, and never-institutionalized children between ages 8 and 16. However, some cognitive deficiencies persisted in institutionalized children, regardless of foster care placement; gaps in some cognitive deficiencies between institutionalized and never-institutionalized children widened; and difficulties with visual-spatial memory improved in children placed in foster care. According to the authors, institutionalization can produce persistent long-term cognitive effects, although opportunities for cognitive improvements exist before adolescence. — P.G.

"Long-term effects of institutional rearing, foster care, and brain activity on memory and executive functioning," by Mark Wade, Nathan A. Fox, Charles H. Zeanah, and Charles A. Nelson III
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New for January 9, 2019

Biophysics and Computational Biology

Visualizing flu virus uncoating in infected cells

The genome of influenza A virus (IAV) is comprised of eight segmented RNA strands enclosed in a coat. During infection, the virus is uncoated in the cytoplasm of host cells, viral RNA is imported into the host nucleus, and viral replication ensues. Viral uncoating represents an antiviral therapeutic target, but few researchers have observed the transient and dynamic event in detail. Chong Qin et al. fashioned IAV virions labeled with quantum dots and infected a canine kidney cell line with the labeled virions. Using single-particle tracking, the authors monitored viral uncoating in real time. Around 30% of IAV particles fused with late endosomes, a cellular sorting compartment, and shed their coats in the region surrounding the host nucleus within 30–90 minutes of infection. Treatment of host cells with amantadine, which blocks viral replication, or ammonium chloride, which blocks endosome maturation, sharply decreased uncoating efficiency. Viral ribonucleoprotein complexes (vRNP)—composed of proteins and viral RNA—from each virion separated into distinct units and entered the nucleus in a three-step process, indicating that vRNP segments are imported into the nucleus separately rather than as a bundle, as previously suggested. Treatment of host cells with importazole, which blocks nuclear import, greatly reduced vRNP import efficiency. According to the authors, the findings unveil a critical step in IAV infection and may aid the development of therapeutic strategies. — P.N.

"Real-time dissection of dynamic uncoating of individual influenza viruses," by Chong Qin, et al.
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Evolution

Putative signature of monogamy

Monogamy in vertebrates is thought to have evolved multiple times and marked by pair bonding, heightened territoriality, and offspring care by both parents. However, the neural and molecular basis of monogamy remain unclear. Rebecca Young et al. compared gene expression profiles in forebrain and midbrain tissues in monogamous and nonmonogamous reproductive-age males of 10 species from five evolutionary subgroups, or clades, of vertebrates—cichlid fishes, dendrobatid frogs, Passeroid songbirds, common voles, and deer mice. Each of the clades harbors both monogamous and nonmonogamous species. Across the clades, the authors identified common gene expression signatures potentially associated with monogamy, including 24 candidate genes. In monogamous males, genes implicated in neural development, synaptic activity, learning, memory, and cognitive function exhibited heightened expression, whereas genes implicated in gene expression were downregulated, suggesting enhanced neural plasticity in the face of tight gene regulation in monogamous males. Genes with heightened or reduced expression in monogamous males of one clade also showed correspondingly heightened or reduced expression in monogamous males of the other clade. Together, the findings suggest a common putative gene expression signature of monogamy in some vertebrate species, according to the authors. — P.N.

"Conserved transcriptomic profiles underpin monogamy across vertebrates," by Rebecca L. Young, et al.
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Physics

Self-propulsion of levitated droplets

Volatile liquid drops on a sufficiently hot solid can hover above the surface on a cushioning layer of their own vapor. This phenomenon is known as the Leidenfrost effect, and drops levitated in this manner are free from the constraints of friction to glide, bounce, and oscillate across the surface. Anaïs Gauthier et al. investigated an inverse Leidenfrost scenario, in which oil droplets at room temperature levitate above a cryogenic liquid on vapor generated by the bath. The authors demonstrate that ethanol and silicone oil droplets, initially at rest on a pool of liquid nitrogen, begin to self-propel after a few seconds, gliding in a straight line until disrupted by interactions with the edge of the container. In addition, the self-propulsion persists even after the droplets freeze and cool to the temperature of liquid nitrogen, lasting for 10 minutes or longer. According to the authors, this motion is driven by an asymmetry between the front and back of the drop that emerges in the thickness of the supporting film. — T.J.

"Self-propulsion of inverse Leidenfrost drops on a cryogenic bath," by Anaïs Gauthier, Christian Diddens, Rémi Proville, Detlef Lohse, and Devaraj van der Meer
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Some of the highlights have previously appeared on the PNAS media tipsheet. The articles in PNAS report original research by independent authors and do not necessarily represent the view of the National Academy of Sciences.

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