Clams light up the deepThe February 8, 2014

Disco clams produce flashy displays by bouncing light off reflective strips located on their lips. Susan Milius described marine biologist Lindsey Dougherty’s research on these aquatic spectacles, which might help clams lure in small prey, in “Disco clams put on a streak show” (SN: 2/8/14, p. 5).

“The display is striking and it’s astounding that it’s not bioluminescence,” online reader Brian Howells wrote. “Most puzzling is that these clams seem to prefer darker areas. What would the display look like under conditions of very low light? When divers bring high-output lights close to the clams the display looks like lightning. My feeling is that the display looks very different to the target animal.”

Dougherty, who took some time away from her clams to answer questions in the comments section of the story online, responds: “Much of the filming I did this summer was in natural lighting (without a dive light)…. The clams can be found very deep (up to 50 meters), so I’m very interested in examining physiological and structural differences between the shallow and deep organisms. It is very interesting how bright the display is even at dusk, when there is very low light. The display is likely visible to many sharp-eyed fish, crustaceans and cephalopods.”

A disco clam’s eyes are as showy as its lips. The clam’s eyes light up when photographed with a flash (top image) but go dim without it (bottom). Special reflective pigments in the eyes may be responsible for this display. Courtesy of L. Dougherty
Birds in sync

Susan Milius reported that northern bald ibises time their wing flaps to catch a little lift from the birds flying in front of them in “V-flying birds pick efficient flapping pattern” (SN: 2/8/14, p. 9).

Gary Nielsen wonders if the birds’ efficient coordination is a deliberate choice. “Ask any cyclist who has ridden in a pace line and they will tell you the spot close behind another rider uses less energy,” he wrote in an e-mail. “The wind can vary from directly in front of the line of cyclists or from the side, but that sweet spot is easily found by adjusting your position in relation to the leading rider and feeling for the spot that offers the easiest pedaling. A tired cyclist doesn’t need to be smart or well-coordinated, just aware of that spot in the line that uses the least energy … just like an ibis.”

Milius thinks that a tired cyclist makes a fine analogy. While the story doesn’t suggest that birds are actually calculating the advantages of flight patterns as they fly along, she says, “let’s not take evolutionary marvels for granted. It would be great to know more about how that perception of a sweet spot works and how a body maintains energy-saving rhythms.”

How pot changes the brain

The hormone pregnenolone can put a damper on the effects of cannabis on the rodent brain, as Laura Sanders mentioned in “Hormone hinders effect of pot” (SN: 2/8/14, p. 12).

Some online readers questioned whether the word “addiction” can apply to habitual marijuana use. “Cannabis was proven to be nonaddictive, quite a long time ago,” commented on the Science News website. “This article uses two terms interchangeably: ‘addiction’ and ‘dependence,’ ” added Jan Steinman. “I agree that pot is not physically addictive. But I have known many people who were dependent to the point that they couldn’t get through a day without several joints.”

The effects of marijuana may not be as severe as those of other mind-altering substances, says Sanders, but the drug does come with some biological baggage, particularly for young people. “While people still debate the difference between ‘addiction’ and ‘dependence,’ research suggests both can apply to some habitual marijuana users. Bodies and brains become accustomed to THC, the psychoactive substance in cannabis. Withdrawal symptoms can include anxiety, irritability and sleep problems. And some people have trouble limiting their marijuana intake and keep using it despite the desire to quit — hallmarks of addiction.”