Â鶹ÒùÔº

This week, researchers reported that . Engineers created . And dark energy observations suggest that the universe could end in a "big crunch" at 33 billion years old.

Additionally, biologists reported on a bird vocalization that represents an interspecies warning about brood parasites. European bearded vulture nests are like museums of ancient human artifacts. And Japanese cellular biologists have uncovered previously unknown mechanisms by which stem cells differentiate into teeth and surrounding tissues:

Emergency alert

Parasitic birds lay their eggs in the nests of other species to offload the expense of raising their young. It's very economical! However, this puts an undue burden on the host birds, whose own offspring are often sacrificed as they raise their parasitic foster child, a burden that economists would call a "negative externality." A study published in Nature Ecology & Evolution now reports that birds across multiple species on four continents have a cooperative response to sightings of parasitic birds in their territories: a nearly identical warning vocalization.

According to the researchers, birds will come to investigate when they hear the call and eventually associate it with the presence of parasitic bird species. They believe that the prevalence of the call represents patterns of interspecies cooperation in global regions with complex networks of interactions between host birds and brood parasites.

Evolutionary ecologist William Feeney says, "For the first time, we've documented a vocalization that has both learned and innate components, potentially showing how learned signals may have evolved from innate calls in a way first suggested by Charles Darwin. It's like seeing how evolution can enable species to give learned meanings to sounds."

'It belongs in a museum!'

OK, not to belabor the point about the adaptive intelligence of birds, but another finding reported this week concerns the archaeological practices of bearded vultures. Native to European mountain ranges, bearded vultures nest in cliff caves, rock shelters and natural cornices. Nests constructed in safe spaces are reused by successive generations of birds, and as a result, researchers have now documented centuries worth of nesting material, which includes human-made or -altered objects, including a slingshot, shoes, a crossbow bolt and a decorated lance.

In the study, researchers in Spain examined 12 of the nests between 2008 and 2014, analyzing them layer by layer, "following established archaeological stratigraphic methods," according to the published study. "Thanks to the solidity of bearded vulture nest structures and their locations in the western Mediterranean, generally in protected places such as caves and rock shelters with relatively stable temperature and low humidity conditions, they have acted as natural museums, conserving historical material in good condition," the authors write.

Stem cell dentistry

Replacing lost teeth involves dental implants, dentures and often the xenotransplantation of donated bone into the jaw. However, researchers are seeking treatments to regenerate lost bone and teeth in patients via stem cell therapy. Noting the complexity of the processes of dental development, a team of Japanese and American researchers recently sought to learn more about the interplay of cell and tissue types, including the dental pulp, enamel and bone-forming cells of the jaw.

In their , they used genetically modified mice in the study to learn how stem cells ultimately differentiate to form teeth and bone, uncovering a previously unknown mesenchymal progenitor cell population and a new mechanism for root and alveolar bone formation. The progenitor cell lineages they discovered—one associated with root tooth development, the other with alveolar bone formation—provide a framework to understand tooth root formation and could eventually lead to the development of stem-cell-based regenerative therapies.