A quick review of interesting research on living things from the last month.
The pallid bat (Antrozous pallidus) snatches up arthropods such as insects, centipedes, and scorpions, crawling on the ground and takes them up to a comfortable perch to eat. One of the creatures in its diet is the Arizona bark scorpion (Centruroides sculpturatus), the most venomous scorpion in North America. While agonisingly painful to a grown man, its venom can kill children. How does the scorpion-predator with a four-inch body size deal with the excruciating sting of its similar-sized prey?
There’s no doubt the bat gets stung by the scorpion as researchers from the University of California, Riverside, observed using high-speed video. But what makes the flying mammal oblivious to the pain and the venom, continuing to go about its nightly patrols. The researchers injected a calibrated dose of venom into four bats that suffered no ill-effects. By examining the bat’s gene transcriptome, the researchers identified amino acids that interfere with the venom’s ability to target sodium ion channels connected to pain receptors. Another mammal, the grasshopper mouse, uses different amino acids to do the same thing.
Many geckos drop their tails to make a quick getaway. With their predators distracted by the wriggling tails, the lizards escape with their lives. But the 14-centimetre-long fish-scale gecko (Geckolepis maculata) that lives in Madagascar’s limestone cliffs takes its strategy to an extreme – it rips its skin off.
More than a century ago, biologist W.J. Schmidt described little pieces of hard tissue embedded in the gecko’s skin. These bits are called osteoderms, made of the same substance as crocodiles’ armour-plated backs. While all crocodiles have these hard tissues, they are rare in geckos. But instead of using the osteoderms as armour, the fish-scale gecko lets its skin get torn off. Few believed Schmidt’s description of this contradictory strategy of evolving armour but not using it.
The gecko’s skin peeling easily didn’t help his case since most museum specimens look like skinned chicken.
Using CT (computerised tomography) scans to create 3D images, researchers from the US confirmed Schmidt’s description. They found the osteoderms are arranged in a mosaic within the scales, the largest among geckos.
Why does the gecko needs armour only to lose it at the first opportunity is still a mystery.
Scientists have puzzled over this question for a long time and offered a variety of answers. Studying Eurasian reed warblers (Acrocephalus scirpaceus) during their migration from Europe to sub-Saharan Africa, one study says they navigate by using magnetic variation to find their way.
The compass needle points to the magnetic north and not to the North Pole, where all lines of longitudes converge. If you stand on that spot in the North Pole, your compass will point to Ellesmere Island in northern Canada as north. The angle between magnetic and geographic north, called magnetic declination, is used by navigation instruments aboard aircraft and ocean-going vessels. Now researchers say the tiny 13-centimetre brown bird evolved this principle a long time before humans fabricated instruments to perform the same function. On its first migration, the warbler not only learns the route but also correlates it to the magnetic declination of each location, or its longitudinal position, along the way. The researchers say this is the first creature known to use this manner of navigation.
Another study says Scopoli’s shearwaters use their noses. These researchers outfitted one group of birds with magnets that interfered with their ability to sense the magnetic field and treated the nose of another group with zinc sulphate that causes a temporary loss of smell. While the seabirds went about their daily lives on Menorca Island, Spain, normally, one group suffered when it had to fly far out to sea to fish. Compared to the control and magnetically disturbed birds, anosmic ones seemed to become disoriented, their flight paths meandering without direction, when out of sight of land even though they could rely on the magnetic field. But once they could see the coastline, they realigned themselves and headed home. The birds with magnets strapped to their heads weren’t affected because most lost their artificial burdens at sea. The few that retained them probably relied on their sense of smell to navigate. This shows that the sense of smell was paramount for navigation say the researchers.
Perhaps different species of birds use specific methods to find their way around the world, or birds aren’t giving up all their secrets. We haven’t heard the last word on the subject yet.
A trapdoor spider (Moggridgea rainbow), found only on Australia’s Kangaroo Island, has a sedentary lifestyle, legging it no more than a couple of metres from where it hatched. But how this five rupee coin-sized arachnid found its way to the island bears no resemblance to its current habits. Researchers thought when the supercontinent of Gondwana broke up and the land mass that was to be Australia drifted apart from Africa about 95 million years ago, the spider may have separated from its South African relatives. After studying its genes and mapping the degree of separation from its kin, Australian researchers say the species may have evolved between two and 16 million years ago. Instead of setting adrift with the Australian land mass, it may have covered the 10,000-kilometre voyage on a raft of land and vegetation, secure from the elements in their silk-lined burrows.
Specialised infrared sensors located in pits on either side of their nose allows pit vipers to “see” its warm-blooded prey in the cool darkness. Even when they are blindfolded, the snakes can accurately strike at their prey. Researchers from China and the US experimented with the short-tailed pit viper (Gloydius brevicaudus) to determine how it used its dual visual systems.
When blindfolded, the snakes’ infrared sensors guided them to strike at their warm prey that stood out at room temperature. The researchers heated up one side of an enclosure to match the body temperature of mice (33º C). The blind snakes couldn’t detect the mice with their infrared sensors since the prey didn’t contrast against the background. But without blindfolds, they used their sight and pits successfully even when the mice didn’t thermally stand out from the enclosure wall.
The researchers ramped up the heat of the wall to 40º C. Although the rodents would stand out against the hot background, the snakes performed poorly. To be fair, the species’ natural riverine habitat in China and the Korean peninsula doesn’t get that hot.
The researchers concluded that pit vipers integrated their two visual systems to maximum advantage.
Animals do the most amazing things. Read about them in this series by Janaki Lenin.
Janaki Lenin is the author of My Husband and Other Animals. She lives in a forest with snake-man Rom Whitaker and tweets at @janakilenin.