September 2019, ScientificAmerican.com 53ALONGKOT SUMRITJEARAPOL
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That is the hypothesis, at least. It is a reasonable no-
tion because in both cases, false signals are broad cast
not willy-nilly but only after thoughtful as sess ment of
the animals’ dynamic social world.
Given our own evolved tendencies toward intention-
al deception, it is no surprise that our closest living rela-
tives, monkeys and apes, are among the prime animal
con artists. Primatologist Frans de Waal of Emory Uni-
versity has recounted a time when Yeroen, a chimpanzee
at the Arnhem Zoo in the Netherlands, limped only in
the presence of his great rival Nikkie, a fake hobbling ap-
parently meant to gain sympathy. Systematic research
on chimpanzees and many kinds of monkeys shows that
these primates think up innovative ways to distract and
mislead social partners when there is a mating or food
prize at stake that they want for themselves.7% '%3 '73735"%
BUT THE INTRICACY, indeed the elegance, of animal de-
ception does not depend on conscious intent. The
magnificent spider of Australia hunts moths at night
using a ball of sticky silk termed a bolas. This grandi-
osely named arachnid is white in color with varied
markings across its body. Rather than spinning a web
to catch prey, this spider produces a single strand of
silk with a bolas at the end and flings the line at near-
by moths. Here is the magnificently Machiavellian
part: the bolas gives off a pheromone that mimics the
scent of a female moth. Lured by the irresistible odor,
male moths flutter close and become ensnared in the
sticky silk. The spiders may gobble the moths right
away or store them for a snack later on. Nothing about
the spiders’ deception suggests a thought-out strategy.
Instead evolution has promoted the behavior because
it benefits their reproductive success.
The same mechanism explains deception in fruit
flies. These insects are not shy about their cannibalistic
tendencies—young larvae readily consume older or in-
jured individuals. Yet they rarely slurp up fruit-fly eggs.
Ecologist Sunitha Narasimha of the University of Lau-
sanne in Switzerland and her team discovered why. It
turns out a pheromone exuded by the fruit-fly mother
seals the eggs, preventing telltale odors from leaking out,
which in turn masks their identity from the tiny canni-bals. It is a nifty way to disguise eggs in plain sight in a
species not known for straight-up parental protection.
Sex and reproduction offer a ripe context for the
sharing of false signals. Among birds, cuckoo females
are famous for depositing their eggs into the nests of
other females, then fleeing the scene. The nesting moth-
ers are fooled into expending labor to care for offspring
not their own. This behavior is widespread far beyond
cuckoos. Called conspecific brood parasitism, meaning
within-species cheating that deploys an egg as a free-
loader in a nest, it is practiced by 200 bird species.
In some animals, the deception starts before any
offspring are produced. Female brown trout some-
times quiver violently as though they are ready to lay
eggs even when they are not. In a 2001 study of this
startling behavior, Erik Petersson and Torbjörn Järvi,
both then at the National Board of Fisheries in Sweden,
called it “false orgasm.” In response, tricked males
spew their sperm yet fertilize nothing at all. Why do
the females spend this extra energy? They may just be
discouraging unwanted males. Intriguingly, though,
Petersson and Järvi found that the frequency of false
orgasm went up as females neared the time of genuine
spawning. So it could also be that females seek—and
achieve—release of sperm from multiple males be-
cause doing so boosts the vigor of their offspring.WILD LIARS:
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