Fish That Decorate
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 placing 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 gaudy nests.
It's the first modern, controlled test showing that
nest decor matters when female fish pick their mates,
says coauthor Sara Östlund-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, Östlund-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 15-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 Östlund-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 Iain 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 display collected ornaments, such
as colorful feathers and plastic objects, around twig
structures. Females prefer males whose bowers have
lots of decorator touches. 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.
