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

Abstract

Background 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. 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). Results Our 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. Conclusions Our 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.

Comparison of chloroplast genomes and phylogenomics in the Ficus sarmentosa complex (Moraceae)

“…Due to insufficient genetic differentiation, the genus Ficus is taxonomically complex and contains many sympatric species, including the F. pedunculosa group, F. punctata group, F. chartacea group, and F. subulata group, among others [1,3,4]. Meanwhile, widely not-strict one-to-one obligate mutualism between fig trees and fig wasps has resulted in frequent hybridization and introgression among Ficus species [5][6][7][8], which has so far hindered research on the taxonomy and evolutionary history [9]. Our current understanding of the Ficus phylogenetic framework is the result of research on a few nuclear loci, such as ITS, ETS, G3pdh, GBSSI, and waxy [3,4,[10][11][12][13][14].…”

Theoretical Models of Obligate Mutualism to Link Micro- with Macro-Coevolutionary Dynamics

“…However, empirical observations, even in these relatively simple systems, often show degrees of discordance through patterns of host-switching and host-range expansion (i.e., having positive fitness with new host species while also maintaining its association with the ancestral host) resulting in 1-1 violations (Cruaud et al, 2012; Satler et al, 2019). In fig-fig wasp studies, the existence of hybrid complexes and a “messy” cophylogenetic relationship suggests that the 1-1 “rule’ is infrequently obeyed (Machado et al, 2005; Marussich and Machado, 2007; Yu et al, 2021). Explaining cophylogenetic discordance in these diverse lineages has, consequently, been a macro-coevolutionary research priority for many evolutionary biologists.…”

Pollinator sharing and hybridization in a pair of dioecious figs sheds light on the pathways to speciation

“…Under a cospeciation scenario, fig species complexes may represent the last step toward complete fig speciation, especially when two or more morphologically distinct fig species are associated with sister wasp species. In these cases, pollinator sharing due to incomplete wasp specialization or heterospecific visitation may occur ( Moe & Weiblen, 2012 ; Souto‐Vilarós et al, 2019 ; Wang et al, 2016 ), especially among closely related figs (e.g., Cornille et al, 2012 ; Kerdelhué et al, 1999 ; Wang et al, 2016 ; Yu et al, 2021 , 2022 ). It was expected to be more frequent among monoecious figs than among dioecious figs based on fig wasp barcoding data ( Yang et al, 2015 ).…”