Co-opting animals to help with pollination is a major event in flower (angiosperm) biology – and is very much a do-or-die act. But have you ever considered that a similar role might be performed by animals in the case of non-flowering plants? I hadn’t, which is why the work of Todd Rosenstiel et al. was such a revelation to me.
Building upon the work of Nils Cronberg et al. – which showed that microarthropods are effective in facilitating the transfer of sperm between male and female bryophyte plants (and may be the only method of fertilisation where water is scarce or absent, which thereby prevent the independent movement of the motile sperm) – the present study investigated whether any chemical signals were involved in this felicitous facilitation of fertilisation. The team discovered not only that the moss Ceratodon purpureus emits volatile compounds, but also that those substances are similar in chemical diversity to those described in pollination mutualisms between flowering plants and insects. Furthermore, microarthropods – springtails in this case – were differentially attracted to female plants, where they could deposit any sperm they might just happen to have about their person. Finally, moss fertilisation rates were increased in the presence of the insects, even where water was present.
Not surprisingly, the group argue for the presence of a ‘scent-based “plant–pollinator-like” relationship that has evolved between two of Earth’s most ancient terrestrial lineages, mosses and microarthropods’. Nice one. And this very modern tale of an ancient sexual association is balanced by the work of Enrique Peñalver and colleagues on gymnosperm pollination in the Mesozoic. Examination of early Cretaceous amber from Spain revealed thrips covered by abundant Cycadopites pollen grains, which provides strong and direct evidence for specialised thrip pollination of these ancient gymnosperms approximately 105 million years ago – probably much as cycads are pollinated nowadays.