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"Th ese chemical compounds released by fi gs comprise mainly mono-and sesquiterpenes ( Grison et al., 1999 ; Grison-Pigé et al., 2002 ; Dudareva and Pichersky, 2006 ; Hossaert-McKey et al., 2010 ). Experimental studies have revealed that these volatiles are emitted through the ostiole in Ficus burtt-davyi , section Galoglychia ( van Noort et al., 1989 ), and are, more precisely, produced inside the fi g cavity in F. carica , section Ficus ( Hossaert-McKey et al., 1994 ). Knowledge of the volatiles responsible for the attraction of pollinators by fi gs and their role in maintaining pollinator specifi city and gene fl ow rapidly expanded, but there was not a parallel increase in understanding of the location and structure of the glands responsible for producing the volatiles. "
[Show abstract][Hide abstract] ABSTRACT: Premise of the study:
Fig trees (Moraceae) have remarkable enclosed inflorescences called figs or syconia. The flowers are pollinated by host-specific fig wasps that enter the fig to lay their eggs. This nursery pollination system is one of the most studied of tropical mutualism interactions, but the source of the volatiles that attract fig wasps to their specific host figs has not been confirmed. The fragrance is the basis of host selection and, therefore, of reproductive isolation among sympatric Ficus species. This study locates and characterizes the glands likely to be responsible for pollinator attraction and also protection from herbivory in the figs of nine Ficus species representing all the major lineages within the genus.
Figs with receptive pistillate flowers were examined using light and scanning electron microscopy. Tests for histolocalization of substances were employed to detect glandular activity throughout the figs.
A great diversity of glands is found throughout the fig, and for the first time, the sites producing fragrances are identified. Scent glands are present on the ostiolar bracts and the outer layers of the fig receptacle. Laticifers and phenolic-producing idioblasts, epidermis, and trichomes associated with fig protection occur on the ostiolar bracts, the fig receptacle, and floral tissues.
The volatiles produced by glands on the ostiolar bracts are candidate sources for the long-distance attraction of pollinator fig wasps. Scent glands on the outer layers of the receptacle may also play a role in chemical perception of the figs or may be related to their protection. The high cost to the plants if the figs are eaten and the temperature conditions required for nursery pollination are likely the factors that led to the selection of phenolic glands and laticifers during the group's evolution.
American Journal of Botany 09/2015; 102(10). DOI:10.3732/ajb.1500279 · 2.60 Impact Factor
"The females then have to gain entry through the ostiole, which acts as a physical barrier. The ostiolar bracts become looser at the receptive phase to make penetration easier (Verkerke, 1986), but a proportion of pollinator females fail to pass successfully through the ostiole (Liu et al., 2013) in spite of their morphological adaptations to aid entry (Ramirez, 1974; van Noort et al., 1989; Verkerke, 1989). "
[Show abstract][Hide abstract] ABSTRACT: 1. Fig trees (Ficus spp.) and their host-specific pollinator fig wasps (Agaonidae) are partners in an obligate mutualism. Receptive phase figs release specific volatiles to attract their pollinators, and this is generally effective in preventing pollinator species from entering figs of the wrong hosts.2. If entry is attempted into atypical host figs, then ostiole size and shape and style length may also prevent reproduction. In spite of these barriers, there is increasing evidence that fig wasps enter atypical hosts, and that this can result in hybrid seed and fig wasp offspring.3. This study examines the basis of pollinator specificity in two dioecious fig species from different geographical areas. Kradibia tentacularis pollinates Ficus montana in Asia. Ficus asperifolia from East Africa is closely related but is pollinated by a different species of Kradibia.4. In glasshouses, K. tentacularis was attracted to its normal host, F1s and backcrosses, but only rarely entered figs of F. asperifolia. Foundresses were able to lay eggs in hybrids, backcrosses, and F. asperifolia, although flower occupancy was lowest in F. asperifolia figs and intermediate in hybrids.5. The fig wasp failed to reproduce in female F. montana, male F. asperifolia, and male F1s, and most but not all backcrosses to F. montana. This was a result of the failure to initiate gall production.6. Host specificity in this fig wasp is strongly influenced by host volatiles, but the ability to gall may be the ultimate determinant of whether it can reproduce.
"Olfactory attraction is considered a reasonable way by which fig trees attract huge number of these tiny specific pollinators from far away. Although chemical attraction was suggested more than 50 years ago (Condit, 1947), studies on it are still preliminary (Barker, 1985; Baijnath et al., 1986; Bronstein, 1987, 1992; van Noort et al., 1989; Ware et al., 1993; Ware and Compton, 1994; Gibernau et al., 1997; Grison et al., 1999). An investigation using fig-bearing trees and arrays of sticky traps baited with figs suggested that the wasps are attracted to the trees by volatiles emanating from the figs and that wasps are specifically attracted to figs of their host species only at the time when figs are ready to be pollinated (Ware and Compton, 1994). "