Cake or broccoli? Recency biases children's verbal responses.

One of the greatest challenges of developmental psychology is figuring out what children are thinking. This is particularly difficult in early childhood, for children who are prelinguistic or are just beginning to speak their first words. In this stage, children's responses are commonly measured by presenting young children with a limited choice between one of a small number of options (e.g., "Do you want X or Y?"). A tendency to choose one response in these tasks may be taken as an indication of a child's preference or understanding. Adults' responses are known to exhibit order biases when they are asked questions. The current set of experiments looks into the following question: do children demonstrate response biases? Together, we show that 1) toddlers demonstrate a robust verbal recency bias when asked "or" questions in a lab-based task and a naturalistic corpus of caretaker-child speech interactions, 2) the recency bias weakens with age, and 3) the recency bias strengthens as the syllable-length of the choices gets longer. Taken together, these results indicate that children show a different type of response bias than adults, recency instead of primacy. Further, the results may suggest that this bias stems from increased constraints on children's working memory.

Ribonucleotide reductases reveal novel viral diversity and predict biological and ecological features of unknown marine viruses.

Virioplankton play a crucial role in aquatic ecosystems as top-down regulators of bacterial populations and agents of horizontal gene transfer and nutrient cycling. However, the biology and ecology of virioplankton populations in the environment remain poorly understood. Ribonucleotide reductases (RNRs) are ancient enzymes that reduce ribonucleotides to deoxyribonucleotides and thus prime DNA synthesis. Composed of three classes according to O2 reactivity, RNRs can be predictive of the physiological conditions surrounding DNA synthesis. RNRs are universal among cellular life, common within viral genomes and virioplankton shotgun metagenomes (viromes), and estimated to occur within >90% of the dsDNA virioplankton sampled in this study. RNRs occur across diverse viral groups, including all three morphological families of tailed phages, making these genes attractive for studies of viral diversity. Differing patterns in virioplankton diversity were clear from RNRs sampled across a broad oceanic transect. The most abundant RNRs belonged to novel lineages of podoviruses infecting α-proteobacteria, a bacterial class critical to oceanic carbon cycling. RNR class was predictive of phage morphology among cyanophages and RNR distribution frequencies among cyanophages were largely consistent with the predictions of the "kill the winner-cost of resistance" model. RNRs were also identified for the first time to our knowledge within ssDNA viromes. These data indicate that RNR polymorphism provides a means of connecting the biological and ecological features of virioplankton populations.