At the end of every month, Janaki Lenin will quickly review interesting recent research on living things.
The larval stage of the acorn worm is just a head
Various creatures like marine invertebrates go through a larval stage before metamorphosing into adults. Paul Gonzalez and team from Stanford University investigated the 40-centimetre-long acorn worm Schizocardium californicum from Morro Bay, California. Once they perfected the art of rearing and breeding these long worms in captivity, a task that took several months, the researchers sequenced the RNA from the different stages of the worm’s development. This would reveal which genes switched on or off and where.
In the larval stage, genes that control the development of the body were delayed. The larvae were no more than swimming heads that floated among plankton. When they were ready to transform into adults, the genes for the development of the trunk get activated and the worms reached full size. It’s likely that many other marine invertebrates go through their larval lives with only their heads.
Fragments of a bacterial gene turn male common pillbug into females
The common pillbug, a leggy invertebrate resembling a millipede, is a native of the Mediterranean. Sex chromosomes dictate the gender of the creatures. Females have ZW sex chromosomes while males are ZZ. Many females produce more female offspring than males.
Scientists from the Université de Poitiers, France, discovered that these mothers are genetically males with ZZ chromosomes. A chunk of the bacteria Wolbachia had inserted itself into the genes of these males, effectively turning them into fertile females. Although they had ZZ sex chromosomes, the Wolbachia fragments acted like the female W chromosome and appeared to supersede the actions of the double Z chromosomes. These feminized males in turn passed on their bacteria contaminated genes to the next generation.
Using mathematical models, the researchers predicted that ZW genetic females will eventually become extinct, leaving the entire population genetically male. Thereafter, the straight males will breed with males feminized by Wolbachia. The integration of the bacterial genetic information into the pillbug genome is thought to be of recent origin.
Water striders create no ripples
Water striders walk on water, on the look out for prey. Their legs tread lightly without breaking the surface tension. Each foot creates no more than a dimple on the water. To escape from their underwater predators, these light weight insects leap off the water. How do they achieve this? If they pushed their legs down too deep too fast, they would rupture the surface tension and become wet. They can’t jump as fast with wet bodies and predators can snatch them.
Using slow motion video recordings, researchers from Korea and Poland studied the biomechanics of the water striders’ escape. When the insects leap, they push against the water surface causing the dimples to deepen. But they seemed to know how much force to apply so they don’t break the surface tension. The researchers calculated the leg movements for a range of body sizes. The water striders’ body weights and leg structures were so carefully calibrated that they could move fast enough to escape without getting their legs wet.
The blind Vietnamese pygmy dormouse uses echolocation to climb trees
The pygmy dormouse from northern Vietnam spends part of its time digging through leaf mulch on the ground. But it can also climb tree branches with agility in the dark. Any observer watching it leap from branch to branch might be mistaken in thinking it can see. But its degenerated eyes can detect no more than light and dark. Instead of relying on its eyes, it has an unusual way of sensing its surroundings: echolocation. It uses rapid evenly-spaced, uniform pulses in the frequency of 50 to 100 kHz. These calls are so faint they cannot be detected by bat detectors. This may be because it doesn’t need such long range orientation as bats. The nocturnal rodent is the only other terrestrial mammal besides bats to use echolocation.
The researchers suggest that the discovery of this unique means of navigation could shed light on the evolution of echolocating bats. There are three prevailing theories: bats evolved flight first and then echolocation, echolocation first and then flight, and flight and echolocation simultaneously. Evidence for the second theory was dependent on finding a mammal that found its way around by echolocation but didn’t have the ability to fly. Now that researchers have uncovered how the Vietnamese pygmy dormouse navigate, evolutionary biologists can reconsider how bats evolved.
This study also has implications closer home. The Malabar spiny dormouse, a native of dense forests of the Western Ghats, wends its way around the ground and in trees at night. Since its eyes are much larger than the pygmy dormouse, the authors suggest that it may use a combination of sight and echolocation.