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Permian Pollen Eaters
8 May 1997 (All day)
Russia's Ural Mountains have yielded what may be the oldest evidence yet for pollen eating among insects. If confirmed, the findings, reported in the current issue of Lethaia, would turn back the clock on a crucial step in plant evolution--pollination by insects--by about 150 million years.
Plants got a new lease on life when they started trading nectar and pollen for assistance in cross-pollination from the insects. The vast majority of modern flowering plants (angiosperms) are pollinated in this way. The question of when this relationship was first established in preangiosperm plants has intrigued paleobotanists for many years. The record of pollen eating is sparse; the oldest widely accepted evidence comes from 110 million year old Lower Cretaceous rocks in Brazil and Russia.
Now Valentin Krassilov and Alexander Rasnitsyn of the Palaeontological Institute in Moscow report that they have discovered fossil pollen in the guts of 270 million year old insects preserved in the shale and sandstone rocks of Tchekarda, in the middle Urals near Perm, the geological home of the Permian Era. The Russians say they found partly digested pollen from various Permian seed plants (gymnosperms) in the guts of three different fossil insects, precursors of bark lice, plant hoppers, and stone flies.
If insects first discovered pollen as a food source in Permian times, that sets the engine of plant-insect coevolution moving far earlier than had been thought. According to the theory, pollen eating caused plants to compensate by increasing their pollen output. Cross-fertilization led to diversification of both plants and their insect predators, culminating in the evolution of the angiosperms.
Experts are withholding judgment on the Russians' claims. The particular pollen they found in the insects' guts, says paleobotanist Bill Chaloner of the University of London, was adapted for wind dispersal, and the bugs could have "inadvertently consumed the pollen while foraging for other plant tissue." The Russians, arguing that some of the insects' mouthparts are adapted to pollen eating, contend that they consumed it deliberately. Chaloner acknowledges that the Russians' evidence raises "some interesting questions on the timing of insect involvement in pollen biology." But he thinks they "make too much of a leap" when they, in essence, attempt to rewrite the long-term evolution of plant reproduction.