Orchid mantis’s secrets
It’s common for female insects to be larger than the males, by far. The bigger the female, the more eggs she can lay, is the usual explanation. Gavin Svenson, head of invertebrate biology at the Cleveland Museum of Natural History, USA, has found another reason for size differences in some elegant praying mantises of Southeast Asia. In the orchid mantises, the females, a rich creamy white with brown patches and flower-petal-mimicking lobes on their legs, are up to 4 inches long, much bigger than the males.
The females evolved their size and colouring to both mimic flowers and to be large enough to prey on the bees and other larger insects they attracted. The males stayed small and camouflaged, so they can stay hidden even while they move around to seek out females. Gavin and his colleagues, who reported their study in the journal Scientific Reports, said this kind of evolutionary split between the sexes, based on one sex being a better predator appears, to be unique.
Gavin said people are intrigued by mantises because they react differently from other insects. “They will turn and look at you,” he said. Museum visitors who encounter the occasional praying mantis display are often taken aback. “They’ll say, ‘Whoa, that thing made eye contact.’”
James Gorman
Explaining the other side of autumn leaves
As the autumn leaves change colour, you would have noticed that the top of the leaf is the most colourful, sometimes bright red, while the underside is comparatively drab. Why? Within the complex layered structure of a thin leaf, the largest share of the pigments involved in the colour change is found in a type of cell near the top surface called palisade cells, or the palisade parenchyma. Inside the palisade cells, in structures called chloroplasts, most of the leaf’s business of photosynthesis is carried on using the familiar green pigment called chlorophyll. The cells are near the top of the leaf, allowing the chlorophyll to absorb light energy to power the process. The cells of the underside, with far fewer chloroplasts, carry out other functions that do not rely on sunlight.
Responding to signals from the changing light, the aging leaf shuts down the water supply to its chlorophyll factories in the fall, often revealing yellow to orange pigments, called xanthophylls and carotenoids. The leaf also increases the production of the predominantly red pigments called anthocyanins, which are deposited in the palisade cells. Recent research has suggested that the anthocyanins have a protective role, keeping the leaf from suffering too much damage from sunlight and oxidation as its function tapers off. They, too, may show bright red as chlorophyll fades away. Eventually, all these bright pigments fade, leaving only the drab brown tannins.
C Claiborne Ray
Flamingo mating rules
Flamingoes are very good dancers. They twist and preen, they scratch their heads, they march in unison. They poke a wing in one direction and a leg in another. They bend forward, sticking their tails up; they vigorously flap their wings in a flashy red and black display. Flamingoes are serially monogamous. They mate for one year, get divorced, and find a new mate the next year. New mates are mutually agreed upon.
Now, researchers have discovered that birds with the largest repertoire of dance moves, and the ability to switch moves more quickly, are the ones who most often succeed in finding mates. Scientists carefully watched and photographed 50 male and 50 female birds during the mating season in the Camargue, in southern France, recording the type, timing and frequency of their gyrations.
During the average five-minute courtship sequence, the number of postures varied between two and eight, while the number of transitions between postures varied between two and 17. Combining the two numbers, the researchers created a ‘sexual display complexity’ score for each bird. Then they tracked the dancers to see who succeeded in producing chicks. As the mating season progressed, all the flamingoes improved their dancing with more varied moves and transitions, but both the youngest and the oldest birds received lower scores than the 20-year-olds.
In the end, successful breeders averaged 61 in sexual display complexity, while those that remained single came in at 41. But pairs tended to have similar scores — good dancers preferred similarly skilled partners. Why? “Good motor function is necessary in reproduction,” said the lead author, Charlotte Perrot. “Breeding in a very dense colony where space is limited requires birds to be adroit, and foraging to feed a chick also requires good motor performance.”