Exploring defensive functional traits of fig walls through comparative anatomy on Ficus (Moraceae)
Date Issued
2015
Date
2015
Author(s)
Fan, Kang-Yu
Abstract
Nonpollinating fig wasps (NPFWs) compete pollinating fig wasps over the resource provided by figs or feed on pollinating fig wasp larvae. Therefore, they negatively affect the fig-fig wasp mutualism by reducing the fitness of pollinating fig wasps and fig trees. Most of the NPFWs probe on the fig surface and oviposit through the fig wall from the outside of the figs. Thus, the fig wall serves as the first defense structure against the external oviposition by NPFWs. Previous studies mainly explored the effects of NPFWs on pollinating fig wasps. However, few studies investigated the defensive mechanism in figs. Therefore, the first part of this study aims to examine fig wall structure among species in Taiwan and then explores the efficacy of defensive functional traits. To compare the tissue structure of the fig wall on 22 Ficus species (24 taxa) from six subgenera in Taiwan, paraffin and free-hand sections were made and histochemically stained. The results showed that 17 fig walls of the 24 sampled taxa underwent further differentiation, including aerenchyma formation and sclerification. Based on the fig wall structure, four types of fig wall were described as follows: type I (no further differentiation), type II (aerenchyma formation), type III (sclerification), and type IV (tannin deposition). The fig walls of dioecious species either shared similar anatomical traits (type I or II) between female and male figs, or presented different types (e.g. type I in female fig walls and type III in male fig walls). For the second part, fig walls of three monoecious species, Ficus caulocarpa, F. subpisocarpa, and F. microcarpa, with five developmental phases were compared. The results showed that sclerification happened before the visitation by parasitoids and inquilines. In F. microcarpa, tanninferous cells formed at early developmental stage (late A phase) and degraded before ripening (D phase). In conclusion, the mechanical (thick fig wall, aerenchyma formation, and sclerification) defenses deter NPFWs from ovipositing, whereas the chemical defenses (tannin deposition) may target insect non-hymenopteran herbivores. Monoecious figs with sclerified thin fig wall were associated with more NPFW species (e.g. F. caulocarpa, F. microcarpa, and F. subpisocarpa). Dioecious figs with thick type II fig wall were associated with less NPFW species (e.g. F. pumila var. pumila). This study can provide a new aspect to answer how key traits have coevolved among figs, pollinators and NPFWs.
Subjects
Ficus
nonpollinating fig wasp
fig wall
defensive functional trait
comparative anatomy
Type
thesis
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