WHICH ANIMALS BUILD CITIES IN THE SEA?

Like most members of its genus, the gloomy octopus ( Octopus tetricus) has long been considered a solitary animal. But a research team working in Australia’s Jervis Bay got a big surprise: They found a community of some 15 of the creatures living in a colony of dens surrounded by broken shells, bottles, and fishing lures. The scientists dubbed the site “Octlantis.” Contrary to their reputation for meeting only once a year to mate, the cephalopods were observed exhibiting “complex social interaction” as they foraged, fought, and mated. Given the difficulty of telling one octopus from another, the researchers are unsure whether the creatures are resident or transient. If they could tag an octopus, they might obtain an answer. But that’s not easy when it comes to an animal that has eight tentacles for removing any marker.

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Many trees exhibit a puzzling behavior: Depending on the species, they extend their branches only so far, as though trying not to touch any neighboring trees. The phenomenon is called “crown shyness,” and there are various theories to explain it. Some research indicates the behavior could help limit the spread of insect larvae from tree to tree. According to another theory, keeping their distance helps trees prevent damage that’s caused by branches colliding in a high wind. In any case, trees appear to have their preferences: While a beech tree stays at least 3 feet away from a neighboring ash, it practically cozies up to a linden.