Diversity of fig glands is associated with nursery mutualism in fig trees

Abstract

PREMISE OF THE STUDY:Fig trees (Moraceae) have remarkable enclosed infl orescences called fi gs or syconia. The fl owers are pollinated by host-specifi c fi g wasps that enter the fi g 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 fi g wasps to their specifi c host fi gs has not been confi rmed. 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 fi gs of nine Ficus species representing all the major lineages within the genus. METHODS:Figs with receptive pistillate fl owers were examined using light and scanning electron microscopy. Tests for histolocalization of substances were employed to detect glandular activity throughout the fi gs. KEY RESULTS:A great diversity of glands is found throughout the fi g, and for the fi rst time, the sites producing fragrances are identifi ed. Scent glands are present on the ostiolar bracts and the outer layers of the fi g receptacle. Laticifers and phenolic-producing idioblasts, epidermis, and trichomes associated with fi g protection occur on the ostiolar bracts, the fi g receptacle, and fl oral tissues. CONCLUSIONS:The volatiles produced by glands on the ostiolar bracts are candidate sources for the long-distance attraction of pollinator fi g wasps. Scent glands on the outer layers of the receptacle may also play a role in chemical perception of the fi gs or may be related to their protection. The high cost to the plants if the fi gs 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.

Trichomes that secrete substances of a mixed nature in the vegetative and reproductive organs of some species of Moraceae

“…In Moraceae, phenolic-secreting trichomes have been reported only for Ficus species, for which the authors inferred these same functions for the trichomes (Souza et al 2015). In contrast, the polysaccharides observed in the exudate of secretory trichomes of Artocarpus heterophyllus, Dorstenia cayapia, Maclura tinctoria and Sorocea bonplandii may act in the protection against organ desiccation and in organ lubrication, as suggested for the secretory trichomes of Leonotis leonurus (Lamiaceae, Ascenção & Pais 1998) and Ficus enormis (Moraceae, Machado et al 2013).…”

“…The parameters of distribution, morphology and exudate composition of secretory trichomes are important for the understanding of the function of these structures. Only the present study and two studies conducted on Ficus (Machado et al 2013;Souza et al 2015) have been performed within this context.…”

“…(Ficeae), Maclura tinctoria (Maclureae), Morus sp., Sorocea bonplandii and Streblus asper (Moreae) (Shah & Kachroo 1975;Gangadhara & Inamdar 1977;Tobe & Takaso 1996;Wu & Kuo-Huang 1997;Jacomassi & Machado 2003;Jacomassi et al 2007;Munir et al 2011;Duarte et al 2012). In the organs involved in reproduction, secretory trichomes have been detected in the bracts and peduncle of the inflorescence of Brosimum gaudichaudii (Jacomassi et al 2010), along the syconium of Ficus species (Machado et al 2013;Souza et al 2015) and in the sepals and hypantium (flower and fruit) of Sorocea bonplandii (Souza & Rosa 2005).…”

“…In addition, studies about the secretory content of trichomes in Moraceae were performed only for Brosimum gaudichaudii (Jacomassi et al 2007;2010) and Ficus (Machado et al 2013;Souza et al 2015), in which the authors observed the presence of lipids, polysaccharides and/ or phenolic compounds in the trichome exudate. In Ficus species these trichomes seem to act in the organ lubrication or in the protection against herbivores and UV radiation (Machado et al 2013;Souza et al 2015). No functions were raised for the secretory trichomes found in B. gaudichaudii.…”

Sistemática e biogeografia de besouros curculionídeos (Curculionoidea; Coleoptera) associados a figueiras (<i>Ficus</i>; Moracae)

“…On the pre-floral stage or A phase, the fig is immature and the uniloculate female flowers are still in development. Next, the female stage (B phase) is marked by the anthesis of pistilate, when volatile substances will start to be released to attract the pollinating wasps (Grison-Pigé et al, 2002;Souza et al, 2015). On this phase, wasps carrying pollen actively storing pollen in their thoracic "pockets', Galil & Eisikowitch, 1969;Ramírez, 1969), exit the fig by a hole made by the male wasps and fly in search for receptive figs.…”