Pollinator sharing in dioecious figs (Ficus: Moraceae)

Abstract

As one of the most specialized pollination syndromes, the fig (Ficus)-fig wasp (Agaonidae) mutualism can shed light on how pollinator behaviour and specificity affect plant diversification through processes such as reproductive isolation and hybridization. Pollinator sharing among species has important implications for Ficus species delimitation and the evolutionary history of the mutualism. Although agaonid wasp pollinators are known to visit more than one host species in monoecious figs, pollinator sharing has yet to be documented in dioecious figs. The present study investigated the frequency of pollinator sharing among sympatric, closely-related dioecious figs in Ficus sections Sycocarpus and Sycidium. Molecular and morphological species identification established the associations between pollinating agaonid wasp species and host fig species. Cytochrome oxidase I was sequenced from 372 Ceratosolen pollinators of Ficus section Sycocarpus and 210 Kradibia pollinators of Ficus section Sycidium. The association between fig species and morphologically distinct clades of pollinator haplotypes was predominantly one-to-one. In Ceratosolen, six of 372 pollinators (1.5%) visited fig species other than the predominant host. No pollinator sharing was detected between the two Sycidium host species, although a rare hybrid shared Kradibia pollinators with both parental species. These findings point to low rates of pollinator sharing among closely-related dioecious fig species in sympatry, and perhaps lower rates than among monoecious figs. Such rare events could be evolutionarily important as mechanisms for gene flow among fig species. Differences in rates of pollinator sharing among fig lineages might explain the conflicting phylogenetic patterns inferred among monoecious figs, dioecious figs, and their respective pollinators.

Pollinator sharing and gene flow among closely related sympatric dioecious fig taxa

“…Previous studies have reported a significant amount of pollinator sharing in monoecious figs [13,17,19,29], while pollinator sharing in dioecious figs was predicted to be rather low [19,28] [19], only this study experimentally compared the ratio of taxa within same section and that from different sections. The pollinator sharing ratio may be overestimated with wasps collected from receptive syconia if wasps have lower survival on 'non-typical' hosts, compared with the ratio calculated based on wasps emerging from syconia in the male flower phase [14].…”

Faster speciation of fig‐wasps than their host figs leads to decoupled speciation dynamics: Snapshots across the speciation continuum

“…Once emerged, we collected ten female and ten male pollinating wasps for storage in 100% ethanol. A second collection of five males and five females was done using tubes filled with colour changing silica gel topped with cotton wool as per (Moe et al, ). For each tree, we used a single female fig‐wasp from the silica gel collections for DNA extraction.…”

Floral volatiles, pollinator sharing and diversification in the fig–wasp mutualism: insights from Ficus natalensis , and its two wasp pollinators (South Africa)

“…In some cases, coexistence of distantly related pollinators has been documented [14]. Genetic data on other species suggest that, while more than one wasp species may occur across the fig-distribution range, a single pollinator species is usually present locally [11,15,16]. In some cases, the two wasp species pollinating the same Ficus species are associated with different environments [8].…”

“…There are numerous observations of agaonid wasps associated with a Ficus species that sometimes also visit (and pollinate) another Ficus species [16]. The importance of such events in terms of the potential for genetic introgression among Ficus species should not be understated [7].…”