Palms (Arecaceae) and Meligethinae (Coleoptera, Nitidulidae): A Long Evolutionary Journey

Arecaceae (palms) constitute a highly diversified family of monocots, distributed especially in tropical and subtropical areas, including approximately 2600 species and 180 genera. Palms originated by the end of the Early Cretaceous, with most genus-level cladogenetic events occurring from the Eocene and Oligocene onward. Meligethinae (pollen beetles) are a large subfamily of Nitidulidae (Coleoptera), including just under 700 described species, and some 50 genera. Meligethinae are widespread in the Palearctic, Afrotropical, and Oriental Regions. All meligethine species are associated with flowers or inflorescences of several plant families, both dicots (the great majority) and monocots (around 7%); approximately 80% of known species are thought to be monophagous or strictly oligophagous at the larval stage. The origin of Meligethinae is debated, although combined paleontological, paleogeographical, and molecular evidence suggests placing it somewhere in the Paleotropics around the Eocene-Oligocene boundary, ca. 35-40 Mya. This article reviews the insect-host plant relationships of all known genera and species of Meligethinae associated with Arecaceae, currently including some 40 species and just under ten genera (including a possibly new African one). The role of adults as effective and important pollinators of their host palms (also in terms of provided ecosystem services) has been demonstrated in some common palm species. All Meligethinae living on palms show rather close phylogenetic relationships with one another and with the mainly Eastern Palearctic genus Meligethes Stephens, 1830 and related genera (associated with dicots of the families Rosaceae, Brassicaceae, or Cleomaceae). Molecular data suggests that the palm-associated Paleotropical genus Meligethinus Grouvelle, 1906 constitutes the sister-group of Meligethes and allied genera. Some hypotheses are presented on the evolution of Meligethinae associated with palms and their probably rather recent (early Miocene-Pleistocene) radiation on their host plants. Meligethinae likely radiated on palms long after the diversification of their hosts, and their recent evolution was driven by repeated radiation on pre-existing and diverse palm taxa, rather than ancient host associations and coevolution. Finally, this article also briefly summarized the relationships that other unrelated groups of Nitidulidae have established with palms around the world.