ABBERANT CLASSOPOLLIS POLLEN REVEAL EVIDENCE FOR ENVIRONMENTAL MUTAGENESIS IN CONIFERS DURING THE END-TRIASSIC MASS EXTINCTION

One of the most fundamental but least understood questions is the role of adaptive evolutionary responses to environmental stress. Polyploidy, or whole genome doubling, is regarded as an important evolutionary phenomenon. It is a key mechanism for plant speciation leading to new evolutionary lineages. It has been suggested that polyploid plant species may cope better with environmental stress than their diploid relatives, improving their survival chances during periods of dramatic biodiversity decline. So far, however, the fossil record of plants has remained largely unexplored as a source of confirming information on ancient whole genome doubling events.

We show for the first time new and compelling evidence for genetic mutations in the pollen record of conifers during the Triassic – Jurassic mass extinction. We demonstrate the presence of aberrant pollen clusters and an exceptional variability in pollen size of the conifer pollen Classopollis. Our data imply that this group of conifers produced unreduced pollen, which is regarded as one of the main mechanism of polyploid formation in modern land plants. Our data represents the oldest evidence for unreduced pollen yet documented from the fossil record of vascular plants. We suggest that that polyploidy may have reduced the extinction risk of these conifers during the Tr-J biotic crisis. Notably this conifer group appears to be hardly affected by environmental stress and becomes a very dominant vegetation element in the aftermath of the mass-extinction.