Calling the tune
New Scientist, 15 May 1999
THE call of a male Majorcan midwife toad keeps females ripening their eggs in anticipation of sex, a new study shows.
Lea, a postgraduate student at the Open University in Milton Keynes,
has studied three groups of female Majorcan midwife toads, Alytes
muletensis. All the toads had ripening eggs in their ovaries. To one
group, Lea played synthesised versions of the male calls. A second
group heard the call of a different species, while the third heard no
calls at all.
After a month, females from the first group had
many eggs that were ripe and ready for ovulation, while the females in
the other two groups had hardly any ripe eggs. Lea speculates that
stimulation of the female's auditory nerve fibres causes hormone
release in the part of the brain that controls reproductive behaviour.
finding makes sense given the sex roles of Majorcan midwife toads, says
Lea. The males are in short supply because after fertilising the eggs
they are celibate for a month while they raise the brood on their own.
"The males carry the eggs down the cliff faces to the pools where they
develop into tadpoles," says Lea.
Meanwhile, females squabble
over remaining males, who advertise their readiness to mate by calling.
Some females don't find a partner for the entire breeding season.
There's no point in wasting energy ripening eggs that have no hope of
being fertilised, Lea says.