Coleopteran Pollinators of Annonaceae in the Brazilian Cerrado—A Review

Abstract

The evolutionary trajectories of insects and angiosperms appear to be intimately interconnected. Increases in the diversity of phytophagous beetles and angiosperms co-occur in the Mesozoic fossil record, and there is fossil evidence of pollinivory and pollination by insects, both in flowering plants and in gymnosperms. The oldest records of angiosperm pollination indicate flies as pollen vectors. A basal group of angiosperms, the order Magnoliales, has retained plesiomorphic characters such as dozens of pistils and stamens spiraling around the receptacle. In a family of this order, Annonaceae, over 90% of species are pollinated by beetles. In many Annonaceae species, flowers display wide spaces, referred to as floral chambers, where beetles can find shelter from weather conditions and predators, food in the form of pollen and tissues, and a mating site. Two basic types of floral chambers can be distinguished: small chambers visited by small beetles (Nitidulidae, Staphylinidae, Chrysomelidae, and Curculionidae) with diurnal and/or nocturnal activity and large and thermogenic floral chambers visited by beetles of the tribe Cyclocephalini (Scarabaeoidea, Melolonthidae). In the latter case, the heat that the flowers produce may serve as a resource for the beetles that visit them, resulting in smaller endothermy costs for the scarabs. This study reviewed the literature including PhD and MSc theses on cantharophilous Annonaceae in the Cerrado. In this biome, both types of associations are found, although cantharophilous Annonaceae represent a small portion of the plant species (<5%). Cantharophilous Annonaceae in the Cerrado share attributes according to the beetles that pollinate them: species pollinated by small beetles, for instance, may flower throughout the year, whereas Annonaceae pollinated by Cyclocephalini normally flower in the beginning of the rainy season (October/November), in synchrony with the phenological patterns of their pollinators. Cantharophilous Annonaceae flowers, regardless of their size, tend to have light colors and sweet and fruity odors. In addition to the lack of studies on the attraction of beetles by these floral characters, the taxonomic composition of the beetles that pollinate Annonaceae in the Cerrado is poorly known. This review attempts to discuss, in light of what has already been published, potential fields of investigation concerning pollinating beetles’ behavior and evolution.

Most diverse, most neglected: weevils (Coleoptera: Curculionoidea) are ubiquitous specialized brood-site pollinators of tropical flora

“…In the Annonaceae, a pantropical clade with more than 2400 species, cantharophily seems to be the most common pollination syndrome (Momose et al 1998;Gottsberger 1999;Saunders 2020). The Neotropical species in this plant family sum up to more than 950 species (Maas et al 2011), and it is in this region that cantharophilous flowers involving weevil pollination are the most widespread (Gottsberger 1999;Silberbauer-Gottsberger et al 2003;Saravy et al 2021). This set of interactions requires further investigations in this region since the weevil lineages involved remain unidentified and possibly include undescribed lineages (the pollinators of Annonaceae reported (Ochyromerini) are exclusively paleotropical; Alonso-Zarazaga & Lyal 1999).…”

Diversity of Insect Flower Visitors of Xylopia aromatica (Magnoliales, Annonaceae) in a Brazilian Savanna

“…On the other hand, coleopteran taxa are also important pollinators of plants from many families: nitidulids pollinate Arecaceae (palms) and Annonaceae [13][14][15][16][17]; weevils stand out as pollinators of Arecaceae, Annonaceae, and Cyclanthaceae [13,[18][19][20][21]; and many scarabs of the genus Cyclocephala have been reported as primary pollinators of plants of the families Annonaceae and Araceae [22][23][24].…”