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Gecko Pollinators Help "Save" Rare Flower

Scott Norris
for National Geographic News
April 23, 2007
 
On the island of Mauritius in the Indian Ocean, a brilliant green lizard and a palmlike shrub are helping to save a rare flowering plant from extinction.

The naturally occurring conservation partnership features the lizard—a species known as the blue-tailed day gecko—in an unusual role, researchers say: The lizard is the key pollinator of the threatened Trochetia flower.

The shrubby Pandanus plant does its part by providing the lizard a safe haven from predators as it performs pollinations, according to a new study.

Although insects also visited the Trochetia flowers, the research team found that the bugs did not carry much pollen from one blossom to another, proving the gecko is the main pollinator.

"An animal may visit flowers often, eating pollen or nectar, but not provide a good pollination service," said study leader Dennis Hansen of the University of Zurich in Switzerland.

"Our study is one of the few to provide evidence that lizards can indeed be efficient pollinators."

Lizard Stand-In

Previously, a nectar-sipping bird called the olive white-eye pollinated Trochetia, but the bird is nearly extinct.

Researchers say the flower's survival now largely depends on visits from the 5-inch-long (13-centimeter-long) gecko.

Like the birds, the geckos visit Trochetia plants to harvest nectar produced by the flowers. In the process they transfer pollen from one blossom to another.

But by venturing out on the exposed blossoms, geckos risk becoming lunch for the Mauritian kestrel, a type of falcon that preys on lizards. Safety for the gecko lies in dense, nearly impenetrable thickets of Pandanus plants growing around the flowers.

Hansen's team found that Trochetia flowers growing close to Pandanus patches received the lion's share of gecko visitations.

These flowers were able to bear fruit and reproduce, the researchers said, while those located farther from Pandanus plants often did not.

The team's findings, which appear in the April edition of the journal The American Naturalist, add to the growing number of examples of lizard pollination.

So far, almost all known cases occur on oceanic islands.

Jens Olesen, of the University of Aarhus in Denmark, is an expert on the little-studied phenomenon.

Olesen has assembled data showing that of more than 4,300 lizard species, only 71 are known to feed on flower nectar and, in the process, provide pollination services.

"Ninety-five percent of the flower-visiting lizard species are from islands," Olesen said.

Olesen and colleagues have suggested that a shortage of insects for the lizards to eat on remote islands may be what causes some species to become fruit- and nectar-eaters.

And Joan Roughgarden, an ecologist at Stanford University in California, thinks lizard pollination might evolve in island communities because pollinating birds and insects are in short supply.

"Lizards are available and other pollinators are not," Roughgarden said. "Bird faunas are usually [smaller] on islands, whereas lizards may be more abundant than on the mainland."

(Related news: "Buzz Kill: Wild Bees and Flowers Disappearing, Study Says" [July 21, 2006].)

Some island plants may even have special adaptations for attracting lizard pollinators.

Nectar of a Different Color

Trochetia flowers on Mauritius had puzzled scientists by producing nectar that is yellow or red in color. The nectar produced by almost all other flowers is clear.

In a separate paper last year, Hansen and colleagues said they had solved that mystery. Their experimental tests showed that colored nectar is an effective lure for enticing geckos to visit blossoms.

Hansen's team is now studying another rare Mauritian flower that appears to rely on geckos not only for pollination but also for seed dispersal.

"For both processes, the plants growing closer to Pandanus do better than ones further away," Hansen said.

Similar chains of positive interactions involving cover-providing plants and pollinating lizards may be widespread in island communities, he noted.

Maintaining such relationships may become increasingly important as native bird pollinators continue to decline and disappear.

"For island conservation management, the major take-home message is the need to promote habitat structural diversity, which provides [the foundation for] lizard-mediated interactions."

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