A temperate pollinator with high thermal tolerance is still susceptible to heat events predicted under future climate change

1. Mutualisms may be particularly vulnerable to climate change as interacting species are likely to respond differently, which could destabilise interactions. 2. Temperate zone insects typically experience mean temperatures below their thermal optima, making them less vulnerable than tropical insects to small increases in mean temperature. However, they are likely to experience a higher frequency of extreme heat events, putting mutualism persistence in jeopardy. 3. This study investigated the potential impacts of climate change on Pleistodontes imperialis, a temperate Australian fig wasp that pollinates Port Jackson figs (Ficus rubiginosa). Wasp emergence and longevity were measured at temperatures ranging from those commonly experienced in nature (25 °C) to high values (> 40 °C) that are currently infrequent, but which are becoming more common with climate change. 4. Wasp emergence was unaffected by temperatures up to 39 °C, but it declined drastically above 39 °C. Adult longevity was unaffected by temperatures up to 30 °C, but decreased at 35 °C and above. Low humidity reduced wasp longevity across all temperatures. 5. Fitness reductions were observed at temperatures ～5 °C above the summer daily mean maximum, suggesting that P. imperialis has a high thermal tolerance, but is vulnerable to extreme heat. Figs located in the shade may provide protected microhabitats under hot conditions. 6. Tropical pollinators may be threatened by small increases in mean temperature. In contrast, it is shown here that temperate pollinators may face a different primary threat from climate change – the increasing frequency of extreme heat events – despite their higher thermal tolerances.     

Synchronized fruiting between trees of Ficus thonningii in seasonally dry habitats

Abstract. The strategy of flowering available to monoecious fig-trees ( Ficus spp., Moraceae) is restricted by the obligate mutualistic relationship they have with their pollinating wasps (Hymenoptera, Agaonidae). Flowering should be synchronous within a tree, asynchronous between trees, random in the yearly cycle, and irregular from year to year. Exceptions have been predicted to occur in a population that inhabits both seasonally dry and adjacent riparian habitats. Ficus thonningii B1 meets these criteria in Harare, Zimbabwe. The vegetative and reproductive phenologies of twenty-five mature trees growing close together but in three habitats (watered, non-watered and intermediate) were studied over 32 months. Trees were generally deciduous between April and August in all habitats. In contrast fruiting phenology was habitat dependant. Watered trees conformed to the general model, but half the trees in the seasonally dry habitat flowered synchronously in the cool dry season. This strategy may result in these trees having relatively superior female reproductive function.     

The role of animals in the colonization of the Krakatau Islands by fig trees (Ficus species)

Abstract. Since the biologically extirpating eruption of Krakatau (Sunda Strait) in 1883, Rakata (Krakatau's remnant) and two closely adjacent islands, Sertung and Panjang, have been colonized by over 200 species of vascular plants. They now carry species-poor mixed tropical forest, including some twenty-three species of Ficus . Data on the sequence of colonization over the last century by twenty-four Ficus species, twenty-three species of volant frugivores, and by agaonid fig-wasps, presumably from the large islands of Java and Sumatra, each some 44 km distant, are summarized. The potential of the volant frugivores as dispersers of fig seeds is assessed, the pollination problems involved in the colonization of islands by figs are reviewed and patterns of colonization by fig species and by their bird and bat dispersers are identified and discussed.
In 1930 a new island, Anak Krakatau, emerged from Krakatau's submerged caldera. This active volcano suffered a self-sterilizing eruption in 1952/1953 and has been colonized, under considerable constraint from its own volcanic activity, probably largely from the (selected) species pool present on Rakata, Sertung and Panjang, 2–4 km away. Its vegetation is at an earlier successional stage (grassland and Casuarina woodland) than that of the three older islands, and in 1992 the Casuarina woodland was in an early stage of transition to mixed forest. The colonization of Anak Krakatau by Ficus species, agaonid wasps and volant frugivores over a critical decade (1982–92) is reviewed, including preliminary assessments of the effects of pollinator limitation on four pioneer fig species and indications of a possible effect of the presence of avian raptors, particularly the peregrine falcon, on fig colonization and forest diversification.     

Sacred hills of Imerina and the voyage of Ficus lutea Vahl (Amontana) in Madagascar

Humans have favored the presence of Ficus species within anthropogenic landscapes and near human settlements throughout the planet due to a number of beliefs and for practical purposes. An intimate or mutualistic relationship between Ficus spp and human societies has been suggested but explanations about the motivations of these proximities between humans and Ficus remain very fragmentary. The case study presented in this paper, which was conducted in the sacred hills located in the surroundings of an urban area, Antananarivo, capital city of Madagascar, inhabited by the Merina, aims at finding some answers to the following two questions. To what extent are Ficus species integrated into the ecologies of human groups, understood here as interactions between humans (social, political and economic dimensions)? 2) Do humans introduce Ficus species into new habitats, potentially offering new ecological opportunities? This study builds on initial work conducted in Madagascar in the region of Fianarantsoa in Betsileo rural communities. Results shown in this paper suggest that: 1) the kings of Imerina, the region located in the north-eastern part of the High Plateau of Madagascar, have planted Ficus species abundantly, especially Ficus lutea Vahl and Ficus. polita Vahl, to claim ownership upon new territories of the Imerina and symbolically establish their political hegemony. Marriages with women from non-Merina cultural groups, such as the Sakalava inhabiting the Western Coast, and the use of Ficus species as symbols of power has contributed, with other activities, to the unification process of Madagascar; 2) The ecological distribution of F. lutea has been substantially manipulated by people from Imerina by planting this species quite abundantly in the sacred hills surrounding Antananarivo, an area where this species is at its ecological limit of distribution and also in faraway places such as the Western coast where the tree is not naturally distributed.     

Chemical composition of volatiles from the syconia of Ficus microcarpa and host recognition behavior of pollinating fig wasps

Aims Chemical communication plays a key role in host plant recognition of pollinators. There are two recognized types of chemical communication between syconia and their pollinating fig wasps: one is “generalization”, of which the wasps respond to the relative ratio of multiple compounds, and the other is “specialization”, of which the key signal is a single uncommon, possibly unique, compound. The aims of this study were to identify the chemical composition of volatiles from the syconia of Ficus microcarpa at different developmental phases, and to determine if the signaling between F. microcarpa and its pollinating fig wasp, Eupristina verticillata, is of generalized type, or of specialized type.Methods The volatiles from syconia of F. microcarpa were extracted using solid-phase micro extraction (SPME) at different developmental phases (pre-female, female (before and after pollination), interfloral, male and postfloral phases) and the chemical compounds were identified by gas chromatography mass spectrometry (GC-MS). We then tested the behavioral responses of E. verticillata to fresh syconia at different developmental phases using two-choice olfactometers.Important findings There were 21 volatile compounds identified from the syconia at different developmental phases, which were mainly fatty acid derivatives, terpenoids and aromatic compounds. The components of the volatiles apparently differed among the developmental stages. The contents of terpenoids declined, but the contents of fatty acid derivatives increased, from before the pollination to after the pollination. Especially, the characteristic compounds of 2-heptanone and 3-octanone before the pollination disappeared, D-limonene decreased after the pollination, but copanene, cyclohexane and 2-hexenal increased. The results of the two-choice olfactometer experiment showed that the pollinating fig wasps had higher selection ratio to chemicals found in the female phase syconia than those in other phases; whereas the volatile compounds from the male phase syconia had the function pushing the pollinating fig wasps to leave the natal syconia so that there existed the “push-pull” responses by fig wasps to volatiles released by their host syconia. We conclude that there are multiple chemical compounds playing the roles in host recognition of pollinating fig wasp E. verticillata. The mutualistic relationship between F. microcarpa and E. verticillata is maintained by the chemical communication of “generalization” strategy.     

The dominant exploiters of the fig/pollinator mutualism vary across continents,but their costs fall consistently on the male reproductive function of figs

1. Fig trees (Moraceae: Ficus) are keystone species, whose ecosystem function relies on an obligate mutualism with wasps (Chalcidoidea: Agaonidae) that enter fig syconia to pollinate. Each female flower produces one seed (fig female reproductive function), unless it also receives a wasp egg, in which case it supports a wasp. Fig male reproductive function requires both male flowers and pollinator offspring, which are the only vectors of fig pollen. 2. The mutualism is exploited by other wasps that lay eggs but provide no pollination service. Most of these non‐pollinating fig wasps (NPFWs) do not enter syconia, but lay eggs through the wall with long ovipositors. Some are gall‐makers, while others are parasitoids or lethal inquilines of other wasps. 3. Ficus is pan‐tropical and contains >750 fig species. However, NPFW communities vary across fig lineages and continents and their effects on the mutualism may also vary. This provides a series of natural experiments to investigate how the costs to a keystone mutualism vary geographically. 4. We made the first detailed study of the costs of NPFWs in a fig (Ficus obliqua G. Forst) from the endemic Australasian section Malvanthera. In contrast to the communities associated with section Americana in the New World, wasps from the subfamily Sycoryctinae (Chalcidoidea: Pteromalidae) dominated this community. 5. These sycoryctine wasps have a negative impact on pollinator offspring numbers, but not on seed production. Consequently, while the NPFW fauna varies greatly at high taxonomic levels across continents, we show that the consistent main effect of locally dominant exploiters of the mutualism is to reduce fig male reproductive function.     

The Use of Asian Ficus Species for Restoring Tropical Forest Ecosystems

Fig (Ficus spp.) trees have been promoted as framework species for tropical forest restoration throughout Asia, because they are considered to be keystone species. This article presents optimal propagation and planting techniques for six Asian dioecious Ficus species, which will enable their inclusion in forest restoration plantings across the Asia‐Pacific region: Ficus auriculata, F. fulva, F. hispida, F. oligodon, F. semicordata, and F. variegata. Nursery experiments compared the growth performance of propagating planting stock from seed and from leafy cuttings, whereas field experiments assessed the cost‐effectiveness and the relative performance of (1) direct seeding, (2) planting stock from seed, and (3) planting stock from cuttings. The most efficient method of producing Ficus spp. was from seed. Propagation from cuttings was much less successful. Seedlings produced from seed had the highest rates of growth and survival both in the nursery and in field trials. In field trials, use of planting stock from seed was also more cost‐effective than direct seeding and vegetative propagation. Establishment costs calculated on the basis of “per plant established” were $1.14 for seed, $6.95 for cutting, and $25.88 for direct seeding.