Why eating males pays off
2008-10-22 09:50
Maggie Fox
Washington - Female spiders who eat
would-be suitors produce more babies, and those babies are
stronger and bigger, than spiders who stick to more mundane
fare, researchers reported on Tuesday.
And the merciless mother spiders waited until they had
mated with another - ensuring they would hatch spiderlings -
before consuming their new beaux, the researchers found.
They said their study is the first "natural" experiment to
prove correct the old folklore about spiders, and said it also
shows why such behaviour might be beneficial.
"Now we know that, at least in one species, sexual
cannibalism benefiting females occurs in nature," Dr Jordi
Moya-Larano of the Estacion Experimental de Zonas Aridas in
Spain, who led the study, said in a statement.
The Mediterranean tarantulas in the study did not eat their
mates, but instead ate males before courtship - and usually
after the females had already mated with another male, the
researchers found.
Unlucky victims
Some other studies have suggested that males may sacrifice
themselves for the sake of their offspring, but this study
showed that, at least in this species of spider, the males are
purely unlucky victims and only the babies benefit.
Some studies had also suggested that studying spiders in
the lab produced skewed results, perhaps because the creatures
were stressed or perhaps because they could not obtain all
their needed prey or nutrients.
So the researchers set up a field experiment in which they
watched the spiders, sometimes snatching the males from the
jaws of females before they were devoured.
"At natural rates of encounter with males, approximately a
third of L tarantula females cannibalised the male," they
wrote in their report, published in the Public Library of
Science journal PLoS ONE.
Sexual cannibalism
"The rate of sexual cannibalism increased with male
availability, and females were more likely to kill and consume
an approaching male if they had previously mated with another
male," they added.
"We show that females benefit from feeding on a male by
breeding earlier, producing 30% more offspring per egg
sac, and producing progeny of higher body condition.
Offspring
of sexually cannibalistic females dispersed earlier and were
larger later in the season than spiderlings of
non-cannibalistic females."
One theory had also held that females who ate males were
simply more aggressive and perhaps better hunters - but when
the males were saved just in time, those females did not
produce superior broods, suggesting that the male meals were an
important source of nutrition.
- Reuters