Saturday, December 23, 2006
Two small, semiaquatic mammals can use their sense of smell even when underwater, according to a new study.
The finding stems from high-speed video that shows a star-nosed mole* rapidly blowing out bubbles of air and sucking them back in while foraging underwater.
The bizarre-looking rodent is already known as the world's fastest mammalian forager.
The mole has now displayed equal prowess as a lightning-fast underwater sniffer, blowing and inhaling air bubbles at a rate of five to ten times a second.
The bubbles make contact with a target, such as morsel of earthworm or fish, and apparently pick up the target's scent before being sucked back up the nose.
When you watch the video, "you're essentially seeing [the moles] sniffing underwater," said Kenneth Catania (lab), a biologist at Vanderbilt University in Nashville, Tennessee.
Based on the journal Nature paper:
"Olfaction: Underwater 'sniffing' by semi-aquatic mammals"
by Kenneth C. Catania
Terrestrial species that forage underwater face challenges because their body parts and senses are adapted for land - for example, it is widely held that mammals cannot use olfaction underwater because it is impossible for them to inspire air (sniff) to convey odorants to the olfactory epithelium. Here I describe a mechanism for underwater sniffing used by the semi-aquatic star-nosed mole (Condylura cristata) and water shrew (Sorex palustris). While underwater, both species exhale air bubbles onto objects or scent trails and then re-inspire the bubbles to carry the smell back through the nose. This newly described behaviour provides a mechanism for mammalian olfaction underwater.
*Current Info on star-nosed moles:
...Like many other moles, C. cristata is fossorial, digging a network of tunnels through moist soil. The tunnels are 3.3 to 7.6 cm wide, typically wider than tall, and can extend as much as 270 m along the edge of a suitably wet habitat. The mole digs shallow surface tunnels for foraging but, unlike the eastern mole, it does not dig deeper burrows for protection in the winter. The surface tunnels vary in depth from 3 to 60 cm, only occasionally coming close enough to the surface to cause a raised ridge. The loose soil dug from the tunnels is pushed out onto the surface, forming 'molehills' that can be 60 cm wide and 15 cm high. A spherical nest about 13 cm in diameter is constructed in the tunnel system above the water line, often under a log or similar protective object, and lined with dry leaves or grass. Unlike other North American moles, C. cristata is semiaquatic, so many of its tunnels open under the surface of a stream or lake. Its fossorial forelimbs also make good paddles and it swims underwater with alternate strokes of both front and hind feet, resulting in a characteristic zigzag motion. Condylura cristata is also more active on the surface than other moles, using runways (often made by other small mammals) through meadow or marsh vegetation. Condylura cristata is active throughout the winter, burrowing through snow and even swimming under the ice of frozen ponds. (Baker, 1983; Fisher, 1885; Hamilton, 1931; Hickman, 1983; Kurta, 1995; Lyon, 1936; Merriam, 1884; Rust, 1966; Tenny, 1871; Wiegert, 1961) supersensitive organs, identification of prey can be made in under half a second. [More]
**Current info on the water shrew:
Water shrews are solitary creatures, active throughout the day and night. Their activity patterns are characterized by two periods; one between sunset and 2300 h, the second occurs one hour prior to sunrise (Sorenson, 1962). For every 30 minutes of activity, the shrew spends the next hour resting (van Zyll de Jong, 1983).
When active, water shrews dive and swim in water to forage for food. Water shrews can control their own metabolic demands so that they can dive year-round, even in winter-cold bodies of water (Boernke, 1977). Each dive can last from 31.1 to 47.7 seconds (Beneski and Stinson, 1987). In water, the fur is lined with a layer of air that reduces their heat loss by 50% (Calder, 1969) as well as make them buoyant. Therefore, when water shrews swim or dive, they must paddle vigorously to keep from floating to the surface. The hind feet, and the stiff hairs on them, propel them through the water. Immediately after swimming, water shrews dry off their fur using the hind feet. Besides swimming, some water shrews have been seen walking on the surface of water (Jackson, 1928). It has been suggested that water shrews can walk on water because they can trap air bubbles in the stiff hairs of their feet (Jackson, 1928).[More]
Also reported in this week's Washington Post's Science Notebook