Long-Proboscid Flies as Pollinators of Cretaceous Gymnosperms

Abstract

The great evolutionary success of angiosperms has traditionally been explained, in part, by the partnership of these plants with insect pollinators. The main approach to understanding the origins of this pervasive relationship has been study of the pollinators of living cycads, gnetaleans, and basal angiosperms. Among the most morphologically specialized living pollinators are diverse, long-proboscid flies. Early such flies include the brachyceran family Zhangsolvidae, previously known only as compression fossils from the Early Cretaceous of China and Brazil. It belongs to the infraorder Stratiomyomorpha, a group that includes the flower-visiting families Xylomyidae and Stratiomyidae. New zhangsolvid specimens in amber from Spain (ca. 105 mega-annum [Ma]) and Myanmar (100 Ma) reveal a detailed proboscis structure adapted to nectivory. Pollen clumped on a specimen from Spain is Exesipollenites, attributed to a Mesozoic gymnosperm, most likely the Bennettitales. Late Mesozoic scorpionflies with a long proboscis have been proposed as specialized pollinators of various extinct gymnosperms, but pollen has never been observed on or in their bodies. The new discovery is a very rare co-occurrence of pollen with its insect vector and provides substantiating evidence that other long-proboscid Mesozoic insects were gymnosperm pollinators. Evidence is thus now gathering that visitors and probable pollinators of early anthophytes, or seed plants, involved some insects with highly specialized morphological adaptations, which has consequences for interpreting the reproductive modes of Mesozoic gymnosperms and the significance of insect pollination in angiosperm success.

Pollinator Diversity: Distribution, Ecological Function, and Conservation

“…Fossil insects from China, Spain and Russia have revealed ancient groups of insects that appear, based on interpretations of their mouthparts and associated pollen grains, to have been pollinators; examples include mid-Mesozoic thrips (Thysanoptera), flies (Diptera), lacewings (Neuroptera), scorpionflies (Mecoptera) and beetles (Coleoptera) (Ren 1998;Ren et al 2009;Labandeira 2010;Labandeira et al, 2007Labandeira et al, , 2016Peñalver et al 2012Peñalver et al , 2015Peris et al in press). It is notable that lacewings and scorpionflies are no longer significant pollinators (in terms of diversity) compared to groups such as the bees (Hymenoptera) and butterflies and moths (Lepidoptera) that have replaced them over time (see section 2.1).…”

Early Cretaceous (Albian) spores and pollen from the Glen Rose Formation of Texas and their significance for correlation of the Potomac Group

“…Exesipollenites is strikingly more abundant in sample 79-25 than in other samples. It has been compared with both cupressaceous conifers and Bennettitales (van Konijnenburg-van Cittert 1971;Harris 1974;Peñalver et al 2015), but the most similar in situ pollen is that of the Jurassic bennettitalean flower Williamsoniella lignieri (Harris 1974), consistent with the presence of bennettitalean foliage in the Glen Rose and Potomac beds that are rich in Exesipollenites (Fontaine 1893;Upchurch & Doyle 1981).…”

Evolution of Lower Brachyceran Flies (Diptera) and Their Adaptive Radiation with Angiosperms

“…The Zhangsolvidae is an extinct family of brachyceran flies that erected by Nagatomi and Yang (1998) for the genus Zhangsolva cupressa found in the Early Cretaceous Laiyang Formation ( Figure 1D ; Zhang et al, 1993; Nagatomi and Yang, 1998; Arillo et al, 2015). Zhangsolvidae is a quite rare family that till now six species in four genera that found only in Cretaceous: five species and three genera in Early Cretaceous of China, Spain, Brazil and one species and genus in Late Cretaceous Burmese amber (Zhang et al, 1993; Nagatomi and Yang, 1998; Mazzarolo and Amorim, 2000; Wilkommen and Grimaldi, 2007; Arillo et al, 2015).…”

“…The middle Early Cretaceous to the early Late Cretaceous is a significant period for brachyceran flies, including the ecological success of some flower-visiting flies and extinction of several important groups, such as Eremochaetidae and Zhangsolvidae (Arillo et al, 2015; Zhang et al, 2016a). The extant family Tabanidae, Nemestrinidae, Bombyliidae are among the commonest pollinators of most extant basal angiosperms, and their early evolution are important for understanding the co-evolution between flies and angiosperms.…”