The ride of their lives

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The dispersal of froglets is not random

If the modern man wants tips on good childcare he need look no further than a couple of frogs in Papua New Guinea.

Scientists report the remarkable behaviour of two species in which males not only bear sole responsibility for looking after their offspring but also take the entire family for piggy-back rides through the forest.

"Male parental care is extremely rare in nature," David Bickford, a University of Miami researcher, told BBC News Online. "Very few species do it but for these frogs there are clear advantages."

Dr Bickford, who spent four years studying the animals high up in the mountains of Chimbu Province, reports his findings in the journal Nature.

Night ride

The frogs (Liophryne schlaginhaufeni and Sphenophryne cornuta) are unusual in that they develop from eggs directly into miniature adults - they have no aquatic tadpole phase.

I think [the female] is just too exhausted to take any part in looking after the clutch

Dr David Bickford

From the moment the eggs are laid by the female, the male will guard over them, protecting them from predators.

And then, when the froglets emerge, the male will carry the clutch on his back through the undergrowth, to drop them off many metres from where they were hatched.

Dr Bickford says as many as 34 froglets will ride piggy-back on their father. "They can ride for more than a week," the conservation and evolutionary biologist adds. "One male I recorded covered a distance of 55 metres."

The journey is made during the night; the family will hide under the leaf-litter during the day.

'Exhausted mother'

But this is not fun and games. Individual froglets jump off along the route to start a new life.

"What is truly amazing about this dispersal is that there is nothing random about it," says Dr Bickford. "It seems likely that they know when to jump off by instinct - distributing themselves evenly in both time and space."

This wide dispersal means the youngsters will face less competition for food, are less likely to be eaten by a predator and will not encounter the problems associated with inbreeding.

But where is the mother in all of this? Dr Bickford saw only males engage in the transport of froglets, but quite why this should be needs further investigation.

The researcher thinks it may have something to do with the levels of investment required of males and females at different stages of the reproduction process.

"I think she is just too exhausted to take any part in looking after the clutch. It takes a lot of energy to produce the eggs. These have very large yolk sacs to sustain the young in the early days. After giving birth, she just hops off."