Behavior Brief

A round-up of recent discoveries in behavior research.

Jun 30, 2011
Cristina Luiggi

A ladybug with a parasitic wasp's cocoon between its legs.NUTMEG66 / FLICKR

Ladybug zombies
The parasitic wasp, Dinocampus coccinellae, infects the beloved garden beetle, the ladybug, in a gruesome scene that could fit right into one of the Alien movies. First, the wasp injects a single egg into the ladybug’s abdomen. Upon hatching, the larva eats away at the ladybug’s tissues for approximately three weeks, at which point it paralyzes the ladybug by severing the nerves to its legs and digs its way out into the world. Remarkably, the ladybug remains alive after this, remaining immobilized as the larva spins a cocoon between its legs.

According to a study published online on June 22 in the journal of the Royal Society, Biology Letters, it’s in the wasp’s best interest to keep the ladybug alive in this zombie-like state for as long as possible. The researchers found that while the ladybug is paralyzed, it still acts as a bodyguard for the wasp while it’s in its vulnerable cocoon stage. Wasp cocoons that were sheltered by a living ladybug had only a 35 percent chance of being eaten by predators, compared to 85 percent if the ladybug was dead. Presumably, the beetle’s bright coloration and its secretion of toxic, foul-smelling liquids—both of which wane after death—serve to ward off the cocoon-seeking predators.

Wandering ancient females
Next to nothing is known about the social lives of ancient human ancestors. However, earlier this month, a team of researchers from the University of Colorado at Boulder looked at tooth remains found in two South African caves to glean a few insights about the wandering tendencies of males and females of two hominid species that lived around two million years ago: Australopithecus africanus and Paranthropus robustus. Analyzing the ratios of two strontium isotopes that are incorporated into the tooth enamel early in life, the team was able to determine the geological setting where an individual had lived as a child, and found that females were more likely to have grown up in a region distant from the caves where they died. This suggests that, as is the case with modern chimpanzees, female hominids, but not males, tended to leave their social groups once they came of age. Had both sexes left for new social groups, as male and female gorillas do, there would have been an increased danger of violence instigated by the newcomer males, explained anatomist Owen LoveJoy. “New males are likely to turn aggressive once they join a new group, risking the lives of infants and juveniles,” he told Nature. “A society in which females left their homes is much more likely for early human ancestors.”

Why bats have hairy wings

Big brown bat in flight.
Big brown bat in flight.
ANGELL WILLIAMS / FLICKR

The purpose of the unusual microscopic hairs covering the wings of bats has long puzzled scientists. Because they are few and far between, they are probably not used for waterproofing or warmth. But the presence of sensory receptors tucked beneath the hairs suggests that bats use them for flight. Reporting in Proceedings of the National Academy of Sciences, neuroscientists at the University of Maryland, College Park, who were studying big brown bats and short-tailed fruit bats, found that the hairs act as very sensitive sensors of changes in the speed and direction of the air flowing through them, allowing the bats to adjust to the wind currents as they fly.

A Woolly affair
When the unforgiving arctic tundra was too much for the woolly mammoths, the warmer climates down south became more attractive—and so did the southern-dwelling Columbian mammoths. Researchers working at McMaster University’s Ancient DNA Centre in Canada sequenced the mitochondrial genomes of two Columbian mammoths unearthed in the Midwest, and found traces of interbreeding with the arctic variety—a species separated by one million years of evolution. Though hybridization of distinct but related species is frequently observed in nature when there is an overlap of living ranges, this is the first evidence that the ancient giants participated in the promiscuous behavior. The researchers suspect that, being much larger than their neighbors to the north, the Columbian mammoths likely outcompeted the woolly males for the attention of their females.