Each week delivers a mix of discoveries from the natural world. Here’s a snapshot of some recent research.
Now that’s how to make a home
Stingless bees of the genus Tetragonula, found in Australia and Southeast Asia, build their combs not as honeycombs but in 3D spirals.
In fact, say British and Spanish researchers, they create a variety of structures that can be classified as spirals, double spirals, targets (like a bullseye) and “more disordered terraces”.
More intriguingly, they suggest, the dynamics that influence the way the bees work are the same as those that influence how crystals grow on a molecular level, such that the structural development of the comb mirrors that of a crystal.
It’s thus an example of how the applicability of the same dynamics across different fields of science leads to similar patterns in very diverse systems, and of how complex structures can emerge from simple behavioural rules.
“Spiral and target patterns are found across nature from chemical oscillators to the heart, and from cellular slime moulds to the brain,” the researchers write in a paper in the Journal of the Royal Society Interface. “Common to these varied systems is that they are excitable media…”
The individual bee need only to take account of local information in order for the colony to be able to construct a complex structure, they add.
What are you doing up here?
A mouse living on the icy summit of a Chilean mountain is believed to be the highest-dwelling mammal ever documented.
Motivated by reported sightings, researchers from the US and Chile organised a scientific expedition to the Puna de Atacama and captured this yellow-rumped leaf-eared mouse (Phyllotis xanthopygus rupestris) on the very summit of Volcán Llullaillaco, 6739 metres above sea level.
This represents an altitudinal world record for mammals, they say, far surpassing all specimen-based records from the Himalayas and other mountain ranges.
“This discovery suggests that we may have generally underestimated the altitudinal range limits and physiological tolerances of small mammals simply because the world’s high summits remain relatively unexplored by biologists,” they write in a paper in the journal PNAS.
And it prompts many evolutionary and ecological questions. “Given the exceptionally broad altitudinal range of P. xanthopygus, have mice from the high Andes evolved genetically based adaptations to hypoxia that distinguish them from lowland conspecifics?”
The collective approach to finding food
Wild spider monkeys in a protected area near Punta Laguna, Mexico, live in a “fission-fusion” society and collectively work out good ways to divide up and conquer the forest, researchers say.
Somewhat surprisingly, those researchers include mathematicians and computer specialists and their findings are published in the journal Frontiers in Robotics and AI.
They used inductive game theory to determine what decision rules the monkeys use in deciding to stay on or leave a foraging team. In traditional game theory, researchers make assumptions about strategies in play. Inductive game theory asks what strategies the animals (or cells or neurons) are actually using.
The team found that a monkey’s decision to stay or leave a foraging team was influenced by the decisions of others. This suggests, they say, that monkeys take into account the opinions of their group mates about what a good team size is and use those opinions to inform their own decision-making.
The collective effects of these decisions produced a range of team sizes that worked well given the availability of fruiting trees in the monkeys’ forest.
But there is room for improvement. The team sizes the monkeys collectively computed were not a perfect match to the availability of fruiting trees.
The plight of polar bears
In much more sobering news, US and Canadian scientists have warned that we may lose most of the world’s polar bears by the end of this century as the sea ice around the Arctic melts.
Polar bears rely on sea ice to hunt, and when ice is absent, they are forced onto land where they are deprived of food. As Arctic sea ice declines in response to warming temperatures, polar bears must fast for longer periods.
However, the limit on how long polar bears can fast before the survival of adults and cubs begins to decline is unknown.
The researchers used dynamic energy budget models to determine the energy requirements of fasting polar bears and the thresholds that would limit survival.
They combined this with an Earth Systems Model that predicted the number of future ice-free days in order to estimate when thresholds would be surpassed for 13 subpopulations, representing 80% of all polar bears.
They found that cub survival would first be put at risk by longer fasts, whereas solitary adult females would be the last to be impacted. They also suggest that once these thresholds are reached, cub and adult survival would be persistently at risk afterwards.