Biology has met home-decorating TV. In spring, some male fish build nests of
algae where females visit and occasionally deposit eggs. In the wild, a nest's
murky mass looks to human eyes as if it would be perfect for camouflaging the
eggs. Yet, when scientists offered some males bits of shiny foil, the fish
went wild, taking home the bright strips and plac- ing them around the
entrance to the nests. Even though the strips hardly looked like camouflage,
the fish were making a canny decorating choice, researchers report in the
March Behavioral Ecology and Sociobiology. In tests, females preferred the
It's the first modern, controlled test showing that nest decor matters when
female fish pick their mates, says coauthor Sara Ostlund-Nilsson of the
University of Oslo in Norway.
Three-spined sticklebacks (Gasterosteous aculeatus) live in temperate waters
worldwide and build nests with varied architecture. On the Swedish coast,
Ostlund-Nilsson and Mikael Holmlund of Stockholm saw males tending nests of
greenish algae that often had around the entrance several strands of red algae
or of dead algae that had turned orange. The researchers had planned to study
camouflage but became interested in learning why males incorporate bright
accent colors if given the chance.
By cutting up the shiny foil from a Christmas candy, the researchers created
IS-millimeter-long strips. When male sticklebacks in aquariums were ready to
build nests, the researchers offered them foil in five colors as well as a
choice of sequins.
The sequins weren't of much interest to the fish, but the nest builders added
plenty of strips, especially red ones. The males themselves turn red in
breeding season, so Ostlund-Nilsson now wonders whether that color choice has
special significance. She imagines the fish's message as: "I'm red, but my
nest is even redder."
To set up a test of female response, the researchers replaced the decorators
with other males and then compared foil-decorated and unadorned nests held at
the time by males of similar size. When offered a choice, the females clearly
preferred the nest bedecked with shiny strips.
The finding makes an intriguing fit with an earlier study, says Felicity
Huntingford of the University of Glasgow. She and lain Barber of the
University of Wales in Aberystwyth found that most desirable males, those with
robust immune systems and high androgens, made the tidiest, most compact
nests. This result suggested that nest architecture could tip off females to
the appeal of the builder, but that study didn't test females' choice. "It's a
nice precursor to the new study," says Huntingford.
The findings on shiny strips remind Huntingford of bowerbirds. Males dis- play
collected ornaments, such as colorful feathers and plastic objects, around
twig structures. Females prefer males whose bowers have lots of decorator
touches (SN: 12/2/00, p. 362). The female thereby chooses a top-quality male
"who's good at getting and fighting for stuff," Huntingford says.
The Scandinavian test may have documented an underwater version of the
bowerbird strategy, in which females go for the glitter to find the best guy.
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