Not Exactly Pocket Science is a set of shorter write-ups on new stories with links to more detailed takes by the world’s best journalists and bloggers. It is meant to complement the usual fare of detailed pieces that are typical for this blog.
Cold-proof tongue allows early chameleon to catch early insect
Chameleons are some of the most versatile of lizards. They live in baking deserts and freezing mountaintops and part of their success hinges on a weapon that works just as well in the warmth as in the cold – its tongue. Relying on stored elastic power for its ballistic strike, the chameleon’s tongue is largely cold-proof. At temperatures that would flummox most reptile muscles, the tongue carries on snatching insects with great efficiency.
Chameleon tongues can reach twice the length of their body in less than a tenth of a second, latching onto prey with a sticky, grasping tip. Rather than pushing it forward with muscle power, like a spear-thrower, the chameleon behaves more like an archer. It ratchets the tongue backwards by slowly contracting its muscles, as if it was drawing an arrow on a bow. It fires by relaxing its muscles, and the whole sticky snare shoots forward on its own momentum. Once the prey is caught, long muscles pull the tongue back into the mouth.
Christopher Anderson and Stephen Deban from the University of South Florida filmed veiled chameleons with a high-speed camera as they shot their tongues at dangling crickets. Their performance certainly improved as the temperature increased from 15 to 35C, but not by much. Even at low temperatures, the tongue shot out with impressive acceleration, speed and power that fell by just 10-20% across a ten degree gradient. When it retracted under muscular control, the effects of the chill were more obvious and a similar gradient led to a 40-60% fall in performance.
By freeing their killer strike from the constraints of temperature, chameleons have been able to exploit chilly windows of opportunity denied to other lizards. They can hunt during the early morning hours when insects are very active and they can expand across a wide range of habitats. They also have to waste less energy on the simple business of keeping warm. After all, why bother with central heating when you can catch food at body temperatures of 3.5C, as some chameleons can?
Image by Christopher V Anderson
Zebrafish babies shut off their eyes at night
Many animals find it harder to see in the darkness of night, but the larvae of zebrafish must find it particularly difficult. Every night, they essentially shut down their eyes, losing the ability to see. Fairda Emran found that the retinas of the baby fish responded normally to light during the day, but they were almost totally impassive after 90 minutes of darkness. The fish themselves totally failed to follow a moving target.
The babies’ body clocks drove this cycle of blindness. It kicked in every night and even if the fish were kept in darkness for several days, they always anticipated the arrival of daylight by restoring their sight. Only a flash of light at night managed to break this tidy cycle, restoring the zebrafishes’ vision at a time when they would normally be blind.
At five days of age, baby zebrafish have just used up all the yolk from their eggs and are starting to find their own food. For them, energy is a precious commodity and eyes are energy-guzzling appliances, even when they’re set to standby at night. It makes sense to just shut them off instead.