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CNR: Alamanacco della Scienza

Archivio

N. 9 - 23 mag 2012
ISSN 2037-4801

International info   a cura di Cecilia Migali

Tecnologia

Amber reveals the oldest pollination evidence

Amber from Cretaceous deposits (110-105 million-years ago) in Northern Spain has revealed the first ever record of insect pollination. Scientists have discovered in two pieces of amber six specimens of tiny insects covered with pollen grains, revealing the first record of pollen transport and social behavior in this group of animals. The results are published in the Proceedings of the National Academy of the Science (Pnas).

The most representative specimen was studied with synchrotron X-ray tomography at the European Synchrotron Radiation Facility (Esrf) to reveal in three dimensions and at very high resolution the pollen grain distribution over the insect's body. The pollen grains are very small and exhibit the adherent features needed so that insects can transport them. The scientists conclude that this pollen is from a kind of cycad or ginkgo tree, a kind of living fossil of which only a few species are known to science. Ginkgos trees are either male or female, and male trees produce small pollen cones whereas female trees bear ovules at the end of stalks which develop into seeds after pollination.

For which evolutionary reason did these tiny insects, 100 million years ago, collect and transport Gingko pollen? Their ringed hairs cannot have grown due to an evolutionary selection benefitting the trees. The benefit for the thrips can only be explained by the possibility to feed their larvae with pollen. This suggests that this species formed colonies with larvae living in the ovules of some kind of gingko for shelter and protection, and female insects transporting pollen from the male Gingko cones to the female ovules to feed the larvae and at the same time pollinate the trees.

Only amber can preserve behavioural features like pollination in such rich detail over millions of years. "This is the oldest direct evidence for pollination, and the only one from the age of the dinosaurs. The co-evolution of flowering plants and insects, thanks to pollination, is a great evolutionary success story. It began about 100 million years ago, when this piece of amber fossil was produced by resin dropping from a tree, which today is the oldest fossil record of pollinating insects. Thrips might indeed turn out to be one of the first pollinator groups in geological history, long before evolution turned some of them into flower pollinators", says Carmen Soriano, who led the investigation of the amber pieces with X-ray tomography at the Esrf.

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Fonte: Claus Habfast, European Synchrotron Radiation Facility (Esrf), tel. tel. + 33 666 662 384, email claus.habfast@esrf.fr