Beetle Pollination of Cycads in the Mesozoic

Abstract

Cycads, unlike modern wind-pollinated conifers and Ginkgo, are unusual in that they are an ancient group of gymnosperms pollinated by insects [1-3]. Although it is well documented that cycads were diverse and abundant during the mid-Mesozoic, little is known about their biogeography and pollination before the rise of angiosperms. Direct fossil evidence illuminating the evolutionary history of cycads is extremely rare [4, 5]. Here we report a specialized beetle-mediated pollination mode from the mid-Cretaceous of Myanmar, wherein a new boganiid beetle, Cretoparacucujus cycadophilus, with specialized pollen-feeding adaptations in its mouthparts and legs, was associated with many pollen grains of Cycadopites. Phylogenetic analyses indicate Cretoparacucujus as a sister group to the extant Australian Paracucujus, which pollinate the cycad Macrozamia riedlei. Our discovery, along with the current disjunct distribution of related beetle-herbivore (tribe Paracucujini) and cycad-host (tribe Encephalarteae) pairs in South Africa and Australia, indicate a probable ancient origin of beetle pollination of cycads at least in the Early Jurassic, long before angiosperm dominance and the radiation of flowering-plant pollinators later in the Cretaceous.

Generalist Pollen-Feeding Beetles during the Mid-Cretaceous

“…However, both records show pollen grains that are slightly smaller, 20 3 12.6 mm on average for the thrips and 12.15 3 7.17 mm on average for the scorpionfly, than the pollen described in this work. The Cycadopites pollen grains associated with the beetle Cretoparacucujus cycadophilus, from Cenomanian Myanmar amber (Cai et al, 2018), are similar in size to the pollen found adjacent to our kateretid specimen NIGP171364. The occurrence of a welldifferentiated margo encircling the sulcus in pollen associated with C. cycadophilus ( Figure 2) (Cai et al, 2018) Etymology: The generic name is derived from the prefix ''Prae-'' indicating a previous find, and the root ''-nymphaeapollenites,'' the most similar fossil pollen type, known only from the Cenozoic.…”

“…Extant water lilies occur worldwide in temperate to tropical climates in standing freshwater ecosystems (Schneider and Williamson, 1993;Borsch et al, 2008). Such an environment is consistent with recent (Labandeira, 2005); 3 (Lin et al, 2019); 4 (Peñ alver et al, 2012); 5 (Peñ alver et al, 2015); 6 (Peris et al, 2017); 7 (Cai et al, 2018); 8 (Huang et al, 2016); 9 (Bao et al, 2019);10 (Grimaldi et al, 2019). The different colors in the background illustrate the gymnosperm/angiosperm origin of the pollen grains found.…”

“…An Oedemeridae beetle was associated with Monosulcites pollen grains (Peris et al, 2017). In addition, in 99-million-year-old Myanmar amber, a beetle assigned to Boganiidae was associated with Cycadopites-type pollen grains (Cai et al, 2018), and a long-proboscid scorpionfly of y Pseudopolycentropodidae recently was described with associated Cycadopites-type pollen grains (Lin et al, 2019). Angiosperm pollen grains recovered from the gut and body surface of a permopsocid from the same amber deposit was interpreted as a strict case of pollinivory (Huang et al, 2016), although the authors did not indicate whether there was the presence of pollination.…”

A new species of Astreptolabis in mid-Cretaceous amber from northern Myanmar, with the discovery of the first male of Astreptolabidinae (Dermaptera)

“…Up to now, many than 1000 species of insects have been reported from Burmese amber (Grimaldi et al 2002;Ross 2019), including termites (Engel et al 2016;Zhao et al 2019), stick insects (Chen et al 2018(Chen et al , 2019, scorpionflies (Lin et al 2019), lots of wasps (Zhang et al 2018), beetles (Cai et al 2018), lacewings (Liu et al 2018), etc. ; however, earwigs are still quite rare compared to most of the other groups.…”

Did Beetles Pollinate Ancient Plants?

“…Although it is well documented that cycads were diverse and abundant during the mid-Mesozoic era when Gondwana began splitting, little is known about their distribution and pollination before the rise of angiosperms. The recent discovery of a beetle in a piece of amber from Myanmar (Figure 1), by Chenyang Cai and an international team of scientists [1], may fill in some of the gap in this knowledge.…”