Bijal P. Trivedi
National Geographic Today
August 7, 2002
Absentee dads are common in the animal kingdom—most
sow their seed and leave without further ado. But in remote
tropical rain forests of Papua New Guinea—where biodiversity
literally drips from the branches and new species abound—a
researcher has discovered some frog fathers that not only
guard the eggs but also provide transport, piggyback style,
for up to 24 froglets after they emerge from the shell.
The two species who practice piggyback paternal care—Liophryne
schlaginhaufeni and Sphenophryne cornuta—belong to a
family of frogs called microhylids.
"The microhylid frogs of New Guinea are the only known
large group of terrestrial vertebrates in which male care
predominates," wrote David Bickford, an evolutionary
biologist at the University of Miami in Coral Gables, Florida,
in a report published in the August 8th issue of the journal
Nature.
Microhylid frogs of Papua New Guinea, of which there are
at least 150 species, all undergo "direct development."
That is, they bypass the tadpole stage and develop from larvae
to miniature versions of the adult inside the egg. Direct
development is a key adaptation that allows the frog to reproduce
in regions without bodies of water nearby.
Parental Duties
After the mother lays the eggs in the leaf litter on the
forest floor, she is long gone. The father dutifully fertilizes
the eggs. Then, like a mother hen, he shelters the clutch,
warding off predators and hydrating the eggs for about a month
until they're ready to hatch. As the tiny froglets emerge
from their shells, usually a brood of up to 25, each climbs
onto the father's back. He waits patiently until every last
froglet is aboard.
Then the father departs with his brood on his back, like
an overloaded school bus, for an odyssey that lasts up to
nine days.
Traveling only after dark, he hops as far as 50 feet or so
per night. Along the way, one by one, the froglets leap off
to begin their own independent lives.
"This is really fascinating because, though males are
known to guard eggs, they have never been known to transport
the froglets," said Janalee P. Caldwell, specialist in
amphibian biology at the University of Oklahoma. "What
makes this particularly interesting is that the fathers are
transporting froglets that are fully developed and completely
independent at this point."
"One explanation for the father's behavior may be that
he wants to be sure that the progeny are his, and guards the
clutch to prevent other males from fertilizing the eggs,"
Bickford hypothesized. The advantage of this system is that
froglets are dispersed over a broad area, reducing the chance
of future inbreeding and competition for food, said Bickford.
"It is an interesting approach to ensure survival,"
said Darrel Frost, curator in the department of herpetology
at the American Museum of Natural History in New York.
Tales of these "frog transport events" have been
reported from Papua New Guinea, but neither the sex nor the
species were documented.
Frogwatch
Bickford discovered this unusual form of parental care via
daily surveys of the rain forest floor during a four-year
stay in the Chimbu Province of Papua New Guinea, where he
trained the local Pawaia people as research assistants. Here
he combed plots of damp leaf litter on his hands and knees
searching for frogs. When he discovered a vigilant frog father
hugging his clutch, he marked the area and returned at night
when the frogs are most active. But things became most interesting
when the eggs hatched and the father began to "transport."
A couple of hours before sunset, Bickford or a colleague
would return and mount a "24/7 vigil." Remaining
about ten feet (three meters) behind, the researcher would
follow the father by candlelight or with a dim red flashlight,
noting how far he traveled each night and when each froglet
leapt to independence.
"It was really tough, frustrating work," said Bickford.
"We lost a lot of frogs with our do-not-disturb attitude."
Male Parental Care Is Rare
The world of frogs harbors a wide spectrum of parental care.
There are some species of poisonous frogs in South America
where the males transport tadpoles, says Caldwell. "The
males crouch down in the leaf litter next to the hatching
eggs and the tadpoles wriggle up onto the father's back and
he transports them to water."
Mothers of the Jamaican cave frog species—Eleutherodactylus
cundalli—carry their froglets from the cave into the
rain forest. It is the only known example of female froglet
transport.
Male parental care is rare. There are isolated examples in
nature: the American burying beetle watches its larvae, and
male fish do the majority of egg guarding and cleaning. Male
seahorses take parental care to an extreme, assuming all responsibility
for the pregnancy and actually carrying the eggs around in
a chemically controlled pouch until they hatch.
Bickford anticipates that weighing the costs and benefits
of such varied parenting styles will reveal exactly how such
systems evolved.
Copyright National Geographic
Reprinted from http://news.nationalgeographic.com/news/2002/08/0807_020807_TVfrogs.html
