More examples of breakdown the 1:1 partner specificity between figs and fig wasps

Yaolin Liao,Yongxia Jia,Hui Yu,Stephen G Compton,Yufen Cheng

doi:10.1186/s40529-021-00323-8

Abstract

BackgroundThe obligate mutualism between fig trees (Ficus, Moraceae) and pollinating fig wasps (Agaonidae) is a model system for studying co-evolution due to its perceived extreme specificity, but recent studies have reported a number of examples of trees pollinated by more than one fig wasp or sharing pollinators with other trees. This will make the potential of pollen flow between species and hybridization more likely though only few fig hybrids in nature have been found. We reared pollinator fig wasps from figs of 13 Chinese fig tree species and established their identity using genetic methods in order to investigate the extent to which they were supporting more than one species of pollinator (co-pollinator).ResultsOur results showed (1) pollinator sharing was frequent among closely-related dioecious species (where pollinator offspring and seeds develop on different trees); (2) that where two pollinator species were developing in figs of one host species there was usually one fig wasp with prominent rate than the other. An exception was F. triloba, where its two pollinators were equally abundant; (3) the extent of co-pollinator within one fig species is related to the dispersal ability of them which is stronger in dioecious figs, especially in small species.ConclusionsOur results gave more examples to the breakdown of extreme specificity, which suggest that host expansion events where pollinators reproduce in figs other than those of their usual hosts are not uncommon among fig wasps associated with dioecious hosts. Because closely related trees typically have closely related pollinators that have a very similar appearance, the extent of pollinator-sharing has probably been underestimated. Any pollinators that enter female figs carrying heterospecific pollen could potentially generate hybrid seed, and the extent of hybridization and its significance may also have been underestimated.

Highlights

The obligate mutualism between fig trees (Ficus, Moraceae) and pollinating fig wasps (Agaonidae) is a model system for studying co-evolution due to its perceived extreme specificity, but recent studies have reported a number of examples of trees pollinated by more than one fig wasp or sharing pollinators with other trees
We address the following questions (1) is there any difference on the extent of pollinator sharing between monoecious and dioecious Ficus? and (2) where two pollinators are present, does one species with predominate rate (> 85 %)? (3) is there any difference on co-pollinator across geographical distribution between monoecious and dioecious Ficus?
The breakdown of 1:1 specificity among sympatric monoecious and dioecious fig species Phylogenetic analyses of the Cytochrome oxidase I (COI) sequences detected 13 pollinator species that had reproduced within the figs of the 13 Ficus species, but there was not a 1:1 concordance between them

Summary

Introduction

The obligate mutualism between fig trees (Ficus, Moraceae) and pollinating fig wasps (Agaonidae) is a model system for studying co-evolution due to its perceived extreme specificity, but recent studies have reported a number of examples of trees pollinated by more than one fig wasp or sharing pollinators with other trees. This will make the potential of pollen flow between species and hybridization more likely though only few fig hybrids in nature have been found. Sampling intensity is again rarely sufficient to confirm this pattern of a single species of pollinator routinely servicing each Ficus species at any given location

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