Science

Urban rats are commensal pests that thrive in cities by exploiting the resources accompanying large human populations. Identifying long-term trends in rat numbers and how they are shaped by environmental changes is critical for understanding their ecology, and projecting future vulnerabilities and mitigation needs. Here, we use public complaint and inspection data from 16 cities around the world to estimate trends in rat populations. Eleven of 16 cities (69%) had significant increasing trends in rat numbers, including Washington D.C., New York, and Amsterdam. Just three cities experienced declines. Cities experiencing greater temperature increases over time saw larger increases in rats. Cities with more dense human populations and more urbanization also saw larger increases in rats. Warming temperatures and more people living in cities may be expanding the seasonal activity periods and food availability for urban rats. Cities will have to integrate the biological impacts of these variables into future management strategies.

Counter-speech is considered a promising tool to address hate speech online, notably, by promoting bystander reactions that could attenuate the prevalence or further dissemination of hate. However, it remains unclear which types of counter-speech are most effective in attaining these goals and which might backfire. Advancing the literature, we examined the effect of four types of counter-speech (i.e., educating the perpetrator, calling on others to intervene, diverting the conversation, and abusing the perpetrator) on a range of bystander behavioral intentions in an experimental study (N = 250, UK-based adults). Overall, counter-speech did not affect bystanders’ subsequent responses to hate speech. Having said this, as expected, diversionary counter-speech increased intentions to ignore hate speech, which suggests unintended consequences. The study illustrates that counter-speech may not be sufficiently impactful in regulating bystanders’ reactions to hate speech online.

The polar bear (Ursus maritimus) is the only Arctic land mammal that dives into water to hunt. Despite thermal insulation provided by blubber and fur layers and low Arctic temperatures, their fur is typically observed to be free of ice. This study investigates the anti-icing properties of polar bear fur. Here, we show that polar bear fur exhibits low ice adhesion strengths comparable to fluorocarbon-coated fibers, with the low ice adhesion a consequence of the fur sebum (hair grease). Lipid analyses reveal the presence of cholesterol, diacylglycerols, anteisomethyl-branched fatty acids, and the unexpected absence of squalene. Quantum chemical calculations predict low ice adsorption energies for identified lipids and high adsorption for squalene, suggesting that sebum composition is responsible for the observed anti-icing properties. Our work enhances understanding of polar bears and their interactions with their environment and builds on Inuit knowledge of natural anti-icing materials.