Structure and function of the fig

Summary An overview is given of the functional anatomy of the fig. The fig is the site of pollination and oviposition, it produces wasps, seeds and pollen, and it is the unit of dispersal. Therefore the fig acts as both a flower and a fruit. When a flower is both fertilized and receives a wasp egg, it eventually produces a wasp. Fertilization in flowers that do not recieve a wasp egg initiates seed production. Wide variation exists in the structural features of figs among different subgenera and sections. Monoecious species and gynodioecious species have different strategies for maintaining the symbiosis with the pollinating fig wasps. Monoecious species produce wasps and seeds in a single fig type and show imperfect heterostyly. Gynodioecious species have specialized figs for wasp and for seed production and are characterized by perfect heterostyly.     

昆虫对榕树的适应进化

传粉榕小蜂和榕树形成了传粉昆虫与植物间互利共生的典范.除了传粉榕小蜂外,榕果内还存在多类非传粉榕小蜂以及蝇类、蛾类、甲虫类等昆虫,这些昆虫在形态和生活史等方面形成了对榕树的适应;一些种类对榕树具有种层次上的寄主专一性,存在对寄主植物的适应辐射.而那些生活在榕树其它部位的昆虫对榕树的寄主专一性则相对较低.     

Constraints on convergence: hydrophobic hind legs allow some male pollinator fig wasps early access to submerged females

Pollinator fig wasps (Hymenoptera: Agaonidae) display numerous adaptations linked to their obligate association with fig trees (Ficus). Ceratosolen fig wasps pollinate figs that often fill temporarily with liquid, and one clade has males with unusually long hind legs. We investigated their morphology and behaviour. Scanning electron microscopy (SEM) revealed that the cuticle of their hind legs is highly modified and covered with numerous hydrophobic setae and microtrichia that can prevent blockage of the wasps’ large propodeal spiracles by liquids. In deep liquid, the males floated on the surface, but when only a thin layer of liquid was present, the legs allowed males to access females without the risk of drowning. Access to females was facilitated by an air bubble that forms between the hind legs and maintains a column of air between the spiracles and the centre of the figs. Sexual selection should favour males that can gain earlier access to mates, and the modified legs represent an adaptation to achieve this. Convergent adaptations are known in some unrelated non-pollinating fig wasps that develop in similar liquid-filled figs, but these species have enlarged hydrophobic peritremata at the ends of their metasoma to protect the spiracles located there. Unlike non-pollinating fig wasps, pollinator males need to insert their metasoma deep into females’ galls during mating. This difference in mating behaviour has constrained the extent of convergence.     

First record of a non-pollinating fig wasp (Hymenoptera: Sycophaginae) from Dominican amber,with estimation of the size of its host figs

Fig trees and their pollinating fig wasps arose about 75 million years ago in the Cretaceous period. Several other groups of chalcid wasps also utilize figs for larval development, including sycophagines, the putative sister group to pollinating fig wasps. Whereas stone and amber fossil pollinators are known, no fossils representing non-pollinating fig wasp groups have been confirmed previously. Here, we describe the first Sycophaginae from the c.15–20 Ma Dominican amber, Idarnes thanatos sp. nov. Farache, Rasplus, Pereira and Compton, and discuss its relationships within the Idarnes carme species group. Additionally, we use linear regression to compare body size, ovipositor sheaths length, and host fig size data from extant Idarnes species to estimate the size of its host figs. Idarnes thanatos was most likely associated with small to medium sized figs (diameter ≤1.0 cm), that were likely to have been dispersed by birds and primates. The discovery of this close relative of extant non-pollinating fig wasps suggests that early Miocene and modern fig wasp communities may share similar ecological and functional features.     

Notice

Illustrated keys are given for the identification of larval stages of five species of north-east Atlantic Palaemoninae: Palaemon adspersus, P. elegans, P. longirostris, P. serratus and Palaemonetes varians. Larval diagnoses for the subfamily and for early stages are also included. Recent developments in the functional morphology of larval palaemonids especially eyes, swimming and ontogenetic processes are reviewed.     

A new species of Josephiella (Hymenoptera: Agaonidae) forming leaf galls on Ficus microcarpa L. (Moraceae)

A second species of Josephiella Narendran, J. microcarpae, is described and figured, based on specimens reared in Hawaii, California and the Canary Islands. This wasp develops in galls on the leaves of Ficus microcarpa L., a widely cultivated ornamental banyan tree that is native to South-East Asia and adjacent islands. It has not been found on any other hosts. Both sexes are described, and males, which are apparently all fully winged, are relatively rare. We postulate that this wasp is a recent introduction into Hawaii, California and the Canary Islands, from an unknown location in South-East Asia, where Ficus microcarpa is native.     

A mutualism at the edge of its range

Summary Comparing populations that differ in access to mutualists can suggest how traits associated with these interactions have evolved. I discuss geographical and seasonal variation in the success of a primarily tropical mutualism (the fig/pollinator interaction), and evaluate some possible adaptations allowing it to persist at the edge of its range. Pollinators probably have difficulty in seasonal sites because 1) fig trees flower rarely in winter and 2) trees that do flower are less detectable and more difficult to reach. Fig biologists believe that seasonality must have selected for adaptations allowing pollinators to survive winter. However, geographical comparisons do not support two current ideas, the synchrony-breakdown hypothesis and the specificity-breakdown hypothesis. I pose two alternatives: plasticity of fruit and wasp developmental time, and adaptations of free-living fig wasps. I also distinguish between the impact of seasonality on monoecious versus dioecious figs; the latter group appear better adapted to reproduce in cool climates. A combination of comparative, observational, and experimental approaches has great potential for advancing our understanding of mutualisms.