lbaker
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Posted: 05 Oct 2007
Topic: Lizard Love Triangles Exposed
Saw this article in the recent Herpdigest newsletter and thought I'd post it up for everyone to read:
Lizard Love Triangles Exposed
By Charles Q. Choi, 10/3/07, LiveScience
A three-way sex struggle resembling the game rock-paper-scissors may
have existed for 175 million years or more in lizards, research now
suggests.
The reptilian triads may be far more common than previously
recognizedłand may even shape the way humans behave, the scientists said
"You either cooperate, or take by force, or take by deception," said
researcher Barry Sinervo, a behavioral geneticist at the University of
California, Santa Cruz. "It's one of those basic games that structures
life."
The scientists investigated European common lizards (Lacerta vivipara),
devoting five years to studying the lizards at five sites in the
Pyrenees mountain range on the border of France and Spain. They captured
more than 250 lizards per year and followed their successes and failures.
Sinervo and his colleagues found males adopt one of those three
strategies when pursuing females. A quick look at their gaudy-colored bellies
reveals which line of attack they will pursue.
Orange-bellied males are brutes that invade other lizards' territories
to mate with any female they can hold. But while they're gone,
yellow-bellied males sneak deceptively onto the vacant territory and mate with
undefended females. White-bellied males guard their mates closely and
ally with other white-bellied lizards to keep the yellows at bay. Thus
the analogy to rock-paper-scissorsłorange force defeats white
cooperation, cooperation defeats yellow deception and deception defeats force.
The researchers predicted this species would play the modified
rock-paper-scissors game due to a high population density, "which allows a
despotic type to flourish, which sets up conditions for cheaters, which in
turn sets up conditions for cooperators to invade," Sinervo told
LiveScience.
In practice, this game of sex leads to a steady cycling of which lizard
color type is prevalent every four to eight years. For instance,
orange aggressors may be dominant for a year or two, followed by yellow
deceivers, succeeded by white cooperators and then back to orange as the
cycle starts anew.
Scientists first conjectured that evolution would conjure up such
rock-paper-scissors games in 1968, but they were not actually discovered in
nature until 1996, when Sinervo uncovered an example in side-blotched
lizards (Uta stansburiana), which are among the most abundant lizards in
the arid western United States.
Surprisingly, the rock-paper-scissors game the researchers see in the
European common lizard is virtually exactly the same in the distantly
related side-blotched lizard, "even right down to the same colors,"
despite the fact that the two species are separated by 5,000 miles and 175
million years of evolution," Sinervo said.
Either this love triangle has evolved twice, "or it's a game that's
been played since the time of the dinosaurs, when the two species last
shared an ancestor," he explained. "These lizards separated from each
other even before the Atlantic ripped open." Sinervo and his colleagues
detailed their findings online Oct. 1 in the journal American Naturalist.
There are a few minor differences between how rock-paper-scissors is
played between the two species. In the American lizards, the throats, not
the bellies, are colored. Also, the counterpart of the white-bellied
form in Europe is a blue-throated form in North Americałalthough these
colors are similar when viewed in the ultraviolet spectrum, which
lizards can see.
The researchers speculated these rock-paper-scissors games might be
commonplace throughout the animal kingdom. Many examples could have eluded
detection since they may not rely on bright colors as they do in these
lizards. For instance, mammals could use rely on scents instead of
colors. "If we were Labrador retrievers, maybe we could smell the
rock-paper-scissors game all over the place," Sinervo said.
Such games would not be limited to competitions over sex between males.
For instance, humans play these games between aggressors, deceivers
and cooperators "along an economic axis, a reproductive axis, a familial
axis, a political axis," Sinervo said. Although systems with more than
three competing strategies could occur, he explained they would likely
tend to simplify themselves into a rock-paper-scissors arrangement
because triangular relationships are mathematically more stable.
Sinervo now seeks to determine which genes are responsible for this
mating game. If the same genes are responsible for rock-paper-scissors in
both lizard species, that would suggest the game is at least 175
million years old.
"Catching the sheer volume of lizards is a challenge, in multiple
populations, to track the genes across generations," Sinervo said.
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