In neotropical forests, adults of many large scarab beetle species spend most of their time inside the floral chambers of heat-producing flowers, where they feed and mate throughout the night and rest during the following day, before briefly flying to another flower. Here we measure floral temperatures in Philodendron solimoesense (Araceae) in French Guiana and the respiration rates of Cyclocephala colasi beetles at floral and ambient temperatures, and show that the the beetles' extra energy requirements for activity are 2.0-4.8 times greater outside the flower than inside it. This finding indicates that heat produced by the flower constitutes an important energy reward to pollinators, allowing them to feed and mate at a fraction of the energy cost that would be required outside the flower.

We studied interspecific and ontogenetic relationships between the size of a leaf and the primary diameter of the internode bearing it. Although these two variables are known to be strongly correlated across species, the form of this relationship has not been studied. In a re‐analysis of published data on interspecific comparisons of 69 temperate tree species, we showed the existence of a strong relationship between twig cross‐sectional area (before secondary growth) and surface area of leaves borne by it, within each of three morphological groups, deciduous angiosperms, evergreen angiosperms, and gymnosperms. Within each of these groups, this relationship is isometric: across species, primary cross‐sectional area of the stem increases proportionally with leaf surface area. When we consider the relationship between the cross‐sectional area of a twig and the surface area of one leaf borne by it, the y‐intercepts for this relation are different for the three groups. However, when total leaf surface area per first‐year shoot is considered, no differences remained between gymnosperms and evergreen angiosperms, but deciduous angiosperms continued to be distinct. This difference between deciduous and evergreen groups could be due to differences in leaf volume (evergreen species have thicker leaves than deciduous) or in traits related to a trade‐off between life span of leaves and their physiological behaviour. We present results of the first quantitative study of the relationship between leaf size and primary diameter of the stem during ontogeny. Both these parameters increase during development of the plant from seedling to adult. For the four tree species examined, the relationship between primary cross‐sectional area of the stem and leaf surface area is also isometric. These results bear on a functional interpretation of the relationship between leaf and stem dimensions, suggesting that vascular supply is directly proportional to the requirements of leaves supported by the stem.

The pollination of Philodendron solimoesense (subgenus Meconostigma) was studied in four populations of French Guiana. Flowering is asynchronous within each population during July, and the flowering cycle is a 2-d process. Numerous insects visit Philodendron inflorescences, but the main pollinator seems to be Cyclocephala colasi (Scarabaeidae, Dynastinae). The pollination process displays aspects typical of beetle pollination: the production of heat and of a strong odor, the presence of a food reward (stigmatic secretion and sterile male flowers), and the presence of a copulation chamber. Flower heat production is important (ca. 11 degrees C above the ambient air) and may help to volatilize the fragrance. Attraction and choice-test experiments showed that C. colasi is not likely to depend on chemical information (such as pheromone) to localize conspecifics but may rely instead on stimuli produced by the inflorescences in order to meet mating partners.

The discontinuous gas-exchange cycles (DGCs) observed in many quiescent insects have been a cause of debate for decades, but no consensus on their evolutionary origin or adaptive significance has been achieved. Nevertheless, three main adaptive hypotheses have emerged: (i) the hygric hypothesis suggests that DGCs reduce respiratory water loss; (ii) the chthonic hypothesis suggests that DGCs facilitate gas exchange during environmental hypoxia, hypercapnia, or both; and (iii) the oxidative-damage hypothesis suggests that DGCs minimize oxidative tissue damage. However, most work conducted to date has been based on single-species investigations or nonphylogenetic comparative analyses of few species, despite calls for a strong-inference, phylogenetic approach. Here, we adopt such an approach by using 76 measurements of 40 wild-caught species to examine macrophysiological variation in DGC duration in insects. Potential patterns of trait variation are first identified on the basis of the explicit a priori predictions of each hypothesis, and the best phylogenetic generalized least-squares fit of the candidate models to the data is selected on the basis of Akaike's information criterion. We find a significant positive relationship between DGC duration and habitat temperature and an important interaction between habitat temperature and precipitation. This result supports the hygric hypothesis. We conclude that the DGCs of insects reduce respiratory water loss while ensuring adequate gas exchange.hypoxia ͉ phylogenetic generalized least squares ͉ precipitation ͉ strong inference ͉ temperature

International audienceIn the mutualism between figs (Ficus spp., Moraceae) and their species-specific fig wasp pollinators (Hymenoptera: Agaonidae), location of a receptive host tree by the adult insect is a critical step. The adult female wasp lives only a few days, and must usually fly to a different tree than her natal tree to locate receptive figs. Trees in receptive phase often occur at very low densities. Reproductive success of both fig and wasp depends on transmission of a very strong signal by the plant. Some evidence exists for the role of olfaction in location of receptive hosts by fig wasps, but very little work has been done on the chemical ecology of host location and host specificity. Here the first experimental evidence is presented for long-distance olfactory attraction of wasps by volatile substances produced by receptive figs, and for short-distance or contact chemostimulation by host volatiles that elicit entry of the wasp into the fig. In studies using Ficus carica L., pentane extracts of receptive-phase figs attract the pollinator Blastophaga psenes L. from distances of at least 5 m in the field. Short-distance chemostimulation was demonstrated in laboratory bioassays. Pentane extracts of receptive figs, when painted onto the ostiole of non-receptive figs, elicit entry of pollinator wasps. Figs emit volatile compounds attractive to pollinating wasps only during the period of receptivity; pentane extracts of non-receptive figs are not attractive. A simple reliable procedure is described to compare the attractivity of different types of extracts (total, internal, and external extracts) and of different fractions, in the first step towards identifying attractant substances

International audienceFig trees (Ficus) have closed inflorescences. Closure is an efficient protection of flowers against non-specialist predators and harsh external environmental conditions. Each Ficus species is pollinated by a single insect species, an agaonid wasp, capable of forcing its way through a bract-covered pore, the ostiole, to gain access to the flowers. Figs also provide oviposition sites for the wasps. The fig/pollinator interaction is a classic example of mutualism. It has been widely assumed that, once pollinators have entered a fig, oviposited and pollinated, they die trapped within the fig. In this paper, we present observations under natural conditions and results of field experiments on three very different fig species (Ficus aurea Nutt., F. carica L. and F. microcarpa L.) showing that some pollinators do exit or try to exit from the fig after pollination and oviposition. Moreover, experimental results demonstrate that in at least one species (F. carica), the pollinator is able to oviposit successively in two different figs. The frequency of re-emergences from figs after pollination varies among species and this may be related to variations in pollination dynamics depending on environmental constraints such as the abundance of trees and tree phenology. Several factors that may favour pollinators that leave figs after pollination and oviposition are discussed. They include competition between pollinators for oviposition sites, and minimising of the risk of vertical transmission of parasites and pathogens

Summary 1.In central Corsica, Helicodiceros muscivorus (Schott ex. K. Koch) produces a protogynous inflorescence that resembles the anal area of a dead mammal and produces a foetid scent during the few hours after sunrise. Flies enter the floral chamber, pollinate the female florets and become trapped until the next morning, when pollen is shed from the male florets and the flies are released. 2. The exposed appendix exhibits a strong, unimodal episode of thermogenesis associated with scent production, reaching a maximum of 30 ° C at 15 ° C ambient temperature. The male florets in the floral chamber are highly thermogenic throughout the second night and generally maintain stable floret temperatures of about 24 ° C at ambient temperatures down to 13 ° C. 3. Maximum respiration rates of the appendix (0·45 µ mol CO 2 s − 1 g − 1 ) and the male florets (0·82 µ mol s − 1 g − 1 ) may be the highest recorded for plant tissue. 4. Thermogenesis of the appendix does not depend on ambient temperature, but that of the male florets increases with decreasing ambient temperature in most cases. However, the pattern of heat production by the males appears related more to time than to ambient temperature, hence the term 'pseudo-thermoregulation'. 5 . The behaviour and thoracic temperatures of flies emerging from captivity suggests that male floral warming does not enhance their activity.

The pollination ecology of Arum italicum was studied in south‐western France. This plant attracts olfactory dung‐breeding flies through deceit. These insects are principally represented by Diptera, all belonging to saprophyte families. The volatilization of the odouriferous compounds, responsible for their attraction, is achieved through the production of heat by the appendix. The insects are trapped for 24 h in order to participate in both sexual phases of the protogynous inflorescence. The male flowers produce three heat events during flowering. These peaks of heat seem to be involved in the spathe movements, since they occur during the opening of the inflorescence and the liberation of the insects. The last male heat event may be linked with the liberation of pollen and its dispersion by stimulating trapped flies. According to their frequency and pollen‐load, two Psychoda species appear to be the most efficient pollinators (P. crassipenis and P. pusilla). Nevertheless, each of the other attracted species could play a significant role under different spatio‐temporal conditions. Experiments on self‐pollination have shown that obligate cross‐pollination is necessary for A. italicum to set seeds. Moreover, hand‐ and natural‐pollinated plants showed similarly high abortion frequencies suggesting that seed set may be more constrained by resources rather than by pollination limitation. © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 141, 205–214.