Sunday 19 August 2018

Cretoparacucujus cycadophilus: A Cycad-associated Beetle from Cretaceous Burmese Amber.

Cycad’s are of particular interest to botanists and horticulturalists due to their unique evolutionary heritage; they are Gymnosperms (non-flowering Seed Plants), members of the group that includes Conifers and Ginkos, but among the closest non-flowering relatives of the Angiosperms (Flowering Plants). They large attractive plants, superficially resembling Palms, but producing large and often brightly coloured strobili, structures intermediate between cones and flowers; these are often pollinated by Beetles or Thrips.  Cycads are thought to have originated during the Permian, and became dominant Plants in many ecosystems during the Jurassic and Cretaceous, but suffered heavily during the End Cretaceous Extinction, and there are about 330 species surviving today, predominantly in the Southern Hemisphere, most of which diversity is thought to have arisen from a post-Cretaceous radiation.

In a paper published in the journal Current Biology on 16 August 2018, Chenyang Cai of the Key Laboratory of Economic Stratigraphy and Palaeogeography at the Nanjing Institute of Geology and Palaeontology, the Center for Excellence in Life and Paleoenvironment of the Chinese Academy of Sciences, and the School of Earth Sciences at the University of Bristol, Hermes Escalona of the Centre for Molecular Biodiversity Research at the Museum Alexander Koenig, and the Australian National Insect Collection, Liqin Li, also of the Center for Excellence in Life and Paleoenvironment of the Chinese Academy of Sciences, and of the State Key Laboratory of Palaeobiology and Stratigraphy at the Nanjing Institute of Geology and Palaeontology, Ziwei Yin of the Department of Biology at Shanghai Normal University, Diying Huang, again of the the Center for Excellence in Life and Paleoenvironment of the Chinese Academy of Sciences, and the State Key Laboratory of Palaeobiology and Stratigraphy at the Nanjing Institute of Geology and Palaeontology, and  Michael Engel of the Division of Entomology at the Natural History Museum of the University of Kansas, the Department of Ecology & Evolutionary Biology, also at the University of Kansas, describe a new species of Cycad associated Beetle from Cretaceous Burmese Amber.

Cretaceous ‘Burmese Amber’ has been extensively worked at several sites across northern Myanmar (though mostly in Kachin State) in the last 20 years. The amber is fairly clear, and often found in large chunks, providing an exceptional window into the Middle Cretaceous Insect fauna. This amber is thought to have started out as the resin of a Coniferous Tree, possibly a Cypress or an Araucaria, growing in a moist tropical forest. This amber has been dated to between 105 and 95 million years old, based upon pollen inclusions, and to about 98.8 million years by uranium/lead dating of ash inclusions in the amber.

The new Beetle is named Cretoparacucujus cycadophilus, where 'Cretoparacucujus' derives from 'Cretaceous' and 'Paracucujus', a modern genus of Beetles to which the nes species is thought to be related, and 'cycadophilus' means 'Cycad-lover'. It is considered to be a member of the Boganiidae, a small group of Beetles related to Ladybirds and Fungus Beetles, which are specialist pollen-feeders and pollinators, and within that group to the Paracucujinae, which are pollen-feedimg Beetles found today in southern Africa, Australia and New Caledonia.

Cretoparacucujus cycadophilus. (A) General habitus, dorsal view, under epifluorescence. (B) Head, dorsal view, under normal reflected light. Cai et al. (2018).

Cretoparacucujus cycadophilus has a large, wide head and a smooth, hairless surface. It has large hair-lines cavities on its mandibles, a feature associated with pollen-feeding. It appears to be closely related to the living genera Paracucujus from southwestern Australia, which is associated with the  Cycad Macrozamia riedlei, and Metacucujus, which is found in Southern Africa and associated with Cycads of the genus Encephalartos.

The Beetle was found associated with a number of pollen grains which appear to have been derived from a Cycad. Cai et al. note that such pollen-grains are hard to identify, as Cycad pollen is similar to the pollen of  Bennettitales, Czekanowskiales, Ginkgoales, Peltaspermales, Pentoxylales, and a few basal Angiosperm lineages, but feel that the excellent three-dimensional preservation of the pollen in amber allows for confident assignment. This is the first time Cycad remains have been described from Burmese amber, either as pollen or as fragments of plant material. The pollen grains are found in clumps, rather than individually, which is generally a feature of Insect (rather than wind) pollination, something which may explain the general absence of Cycad pollen from Burmese Amber.

Photomicrographs of Cycad pollen grains Associated with  Cretoparacucujus cycadophilus. (A) General view of Cretoparacucujus cycadophilus and aggregations of pollen grains by the beetle. (A’) Enlargement of an aggregation of three pollen grains. (A’’) Enlargement of a single grain. (B) Enlargement of three larger aggregations of pollen grains. (C) Enlargement of (B), showing 14 aggregated pollen grains. (D) Enlargement of (B), showing six aggregated pollen grains. Cai et al. (2018).

The Cycads Macrozamia  and Encephalartos are also closely related, forming the Tribe Encephalarteae. Genetic studies have suggested that these Cycads shared a most recent common ancestor in the Miocene, but this is in conflict with their distribution, on two fragments of the Gondwanan continent that split apart in the Jurassic. The discoverey of a Beetle that appears to have been associated with this group of Cycads in amber from the Cretaceous of Myanmar supports the idea that this group of Cycads is more ancient than assumed from molecular-clock evidence.

Geographic distribution of the known entomophilous Cycads of the Tribe Encephalarteae and their Boganiid pollinators. The phylogenetic relationships and divergence time of the widely separated lineages within Boganiinae are shown. The arrow indicates the divergence time estimated by separation of Gondwana in the Jurassic. Abbreviations: AU, Australia; MM, Myanmar; ZA, South Africa. Cai et al. (2018).

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