The Archer Fish’s ‘Water Pistol’

• Biologists have long known that at one point in their development, all vertebrate embryos tend to look alike. Beyond this point, however, the embryos of different species begin to develop features characteristic of that species. For example, all vertebrate embryos are segmented at a very early stage, but with further development the segments begin to specialize and end up as structures such as muscle groups. It may come as a shock to many that at one stage human embryos have tails and folds in the neck region that look like gills. In fish, these folds do indeed become gills, but in humans they form part of the jaw structure.

So what happens to our tails? Fortunately, with further development the tail shrinks and disappears, but in rare cases humans are born with tails—which are surgically removed. Recently scientists are coming to believe that all vertebrates share ancient genes, and that at one time during development these are turned on, and turned off as development proceeds. Then other genes are turned on that lead to the formation of a recognizable vertebrate, such as a fish or chimpanzee – or us.

There is a belief that ancient ancestral genes that are expressed as fertilized eggs develop into embryos that become adult vertebrates. Is it possible that during our embryonic development we recapitulate the kinds of ancestors from which we evolved? (news.discovery.com/animals/ancient-genes, Feb. 11, 2013; naturereviewsgenetics.com, Aug. 2006; newscientist.com, Aug. 2006; other sources)

Photo courtesy of National Academy of Sciences.

• The Archer Fish lives along the mangrove shorelines of east Africa and the Indo-Pacific islands all the way to northern Australia. Only 5-6 inches long, Toxotes jaculatrix lurks near the surface and watches for insects on low branches of vegetation. When a prey is sighted, the fish eases its snout above the surface and spits a jet of water at the insect with enough force to knock it off its perch and into the water. The fish quickly grabs the meal and moves into position for the next one. The jet of water can be launched a distance of about two yards with surprising accuracy, and the fish can shoot up to seven squirts in quick succession. The “water pistol” is fired when the fish places its tongue against a groove in the roof of its mouth to form a tube, then snaps its gills shut to force droplets into the air. To see one in action, go to wimp.com/waterpistol. (Current Biology, Feb. 21, 2006; PLOS/one, Oct. 24, 2012; other sources)

• Belgium enacted legislation that outlawed smoking in public and workplaces in 2006, banned smoking in restaurants in 2007, and in bars serving food in 2010. A research team investigated a possible relationship between the bans and preterm births; smoking during pregnancy is known to impair fetal growth and shorten gestation. The researchers found a 3.1 percent decline in preterm births in 2007 and a 2.7 percent drop in 2010. The study was done well, for the investigators accounted for factors that might have skewed the results, including the mother’s age, national origin, local air pollution, etc. They also make the point that smoking bans in Minnesota have led to a decrease in heart attacks, and similar bans in Scotland correlated with fewer cases of asthma. (Cox et al, 2013, BMJ (formerly called British Medical Journal), Feb. 13; Science News, March 23, 2013)