Microclimates within microcosms are often stated to shelter occupants from adverse conditions, yet our limited knowledge narrows our ability to estimate the vulnerability to warming of species exploiting them. We characterized the microclimate temperature of the floral chamber of a thermogenic plant that produces heat in the context of pollination syndrome. Pollinators (Psychoda moth flies) of Arum italicum are trapped within the floral chamber for 24 h, thereby potentially exposing insects to dangerous temperatures. We report a strong temperature gradient across the floral chamber. We propose two hypotheses for the role of this temperature gradient in the pollination syndrome depending on environmental context. Under moderate conditions, the system relies on the exact position of the thermogenic organ to discourage insects from escaping the chamber, while temperature at the bottom of the chamber corresponds to the moth fly's preferred temperature, motivating the insect to remain there long enough to get covered by pollen. Under extreme conditions, the floral chamber may provide a thermal reward to avoid the Psychoda fly from reaching its thermal limits. Our comprehensive mechanistic analysis of the microclimate in a thermogenic flower highlights the importance of coevolutionary trajectories between temperature regulation by plants and their pollinators' thermal biology. This article is part of the theme issue 'Life in natural microcosms'.

Floral volatile organic compounds (VOCs), synthesized and released by osmophores, constitute a distinctive characteristic of many Araceae species. The floral biology of the genus Spathicarpa, precisely the origin of floral VOCs, remains largely unexplored. Preliminary findings from studies on Spathicarpa hastifolia suggest that synandria, the clusters of male reproductive structures, may contribute to VOCs production. Synandria samples from different flowering stages were collected, fixed for light and electron microscopy, and analyzed for VOCs using dynamic headspace extraction and gas chromatography-mass spectrometry. The apical portion of each synandrium exhibits an epidermis covered with tightly arranged papillae and an underlying layer of starch-rich parenchyma. Starch reserves remain stable until the late staminate phase, when starch grain number and size decrease. Terpene-based secretions were detected in the epidermal cells and the underlying layers of both connective and theca regions of the synandria. These secretory cells exhibit densely packed cytoplasm, enriched in organelles, throughout the pre-anthesis and staminate phases, with abundant starch reserves, lipid droplets in the cytosol, and a sinuous plasma membrane. The dominant organelles include the endoplasmic reticulum, mitochondria, and plastids. The floral scent emissions were primarily composed of a single VOC, 3‑hydroxy-2-butanone (acetoin), which is likely produced by bacteria associated with the floral tissues rather than true osmophores. These findings support the hypothesis that Spathicarpa synandria represent glandular structures that have lost their primary function, potentially vestigial osmophores or nectaries. Further investigation is needed to elucidate the precise role of Spathicarpa synandria in VOC production, including identifying VOC-producing enzymes and characterizing bacterial communities associated with synandria.

ABSTRACT Most angiosperms are pollinated by animals, with insects being the most abundant and diverse pollinators. However, our knowledge about the diversity of Diptera as floral visitors and pollinators, and about their attraction to flowers, is still limited. Fly‐deceptive plant species, such as Arum maculatum, are ideal model systems to explore these interactions, as their floral scents often mimic (parts of) the ecological niches associated with the dipteran life cycle (e.g., mating, breeding). In this study, we investigated the species and sex identity of lesser dung flies (Sphaeroceridae), the second most abundant dipteran floral visitor family of A. maculatum after Psychodidae, across 10 populations of this plant species north and south of the Alps. Using previously published data on floral scent and fruit set, we also tested in a single southern A. maculatum population, where psychodids were limited and sphaerocerids abundant visitors, whether the abundance of the two predominant fly species, Spelobia clunipes and S. cambrica (and their sexes), correlates with inter‐individual differences in floral scent compounds and fruit set. Of the 20 sphaerocerid species identified across all populations, nine are newly reported as floral visitors of A. maculatum, and two represent new country‐specific records. The sex ratio of the flies was balanced within each region, and in the focal southern population the abundance of S. clunipes and S. cambrica correlated with the absolute amount of certain floral scent compounds, with some differences between the sexes of these species. The abundance of both sexes of only S. clunipes correlated with fruit set, suggesting that this species is a potential pollinator of A. maculatum. Overall, our data show that A. maculatum is visited by a high diversity of sphaerocerids both north and south of the Alps. This diversity is higher than for psychodid flies, the most abundant visitors of this plant species. Our data suggest that A. maculatum exhibits a mixed deceptive strategy.

Wild bees (Hymenoptera: Anthophila) and hoverflies (Diptera: Syrphidae), the two major groups of insect pollinators, are undergoing alarming declines worldwide, including Europe. The lack of accessible and verified spatial and temporal occurrence records currently challenges efforts to understand and mitigate this decline. Here, we compiled datasets from diverse sources, including taxonomists, national experts, public repositories, museum collections, published literature, verified open-access platforms, and aggregated datasets from previous European projects. The collected data were standardised, cleaned and validated by taxonomists and national experts. This collective effort resulted in two databases comprising more than 4.34 million and 1.04 million records for wild bees and hoverflies, respectively. The databases cover 97% of the European bee fauna (2,083 species out of 2,138 recorded in Europe) and 97% of the European hoverfly fauna (886 species out of 913 recorded in Europe). These standardised databases constitute essential resources for future assessments of status and trends, habitat associations, and other research and conservation initiatives to protect and understand wild pollinators on the European continent.

All known species of the Caladieae tribe are beetle-pollinated, with floral volatiles linked to thermogenesis playing a key role in attracting pollinators. In Caladium bicolor, the inflorescences emit a strong scent that attracts nocturnal cyclocephaline beetles, though the exact site of scent emission remains debated. This study identified the osmophore and examined tissues and subcellular structures involved in scent production. Preliminary observations indicated the staminate portion of the spadix as the scent source. Microscopic analyses revealed that the secretory region is composed of papillary epidermis and underlying secretory parenchyma. Stomata exhibited signs of exudate release. Starch reserves in the parenchyma decreased during peak thermogenesis and constitute the energy source for this process. The distal portion of the synandria exhibited cells with cytoplasm rich in mitochondria, plastids, and other organelles. In addition to being fundamental in the process of thermogenesis, mitochondria, in association with plastids, plays a key role in the biosynthesis of some components of the floral bouquet, primarily terpenes. The cell structure, combined with active exudate production and pronounced thermogenesis in the fertile staminate portion, strongly supports its role as the primary site of floral fragrance emission.

In natural ecosystems, species are interacting with many others constituting complex networks. Analysis of these networks enables us to describe and visualize ecological communities, which can vary greatly depending on the habitat and the season. Here, we have studied insect floral visitors explicitly considering the four main orders Hymenoptera, Coleoptera, Diptera, and Lepidoptera over nine months in 2022 across three sites in South-West Corsica. We recorded 2,848 insect–flower interactions involving 241 insect morpho-species and 54 plant species. Seven plant species accounted 61

Background:In any ecosystems, seasonality is a key factor conditioning the temporal variation on an annual scale in combination with differences in the organism phenology. This seasonality is marked in the Mediterranean Region with four contrasting seasons: a hot, dry summer, a mild winter and sometimes a very rainy spring and autumn. With a large surface area and its large range of habitats from seaside to alpine biotopes, Corsica Island represents a biodiversity hotspot with a high rate of endemism. Amongst diverse groups, insects, notably the main orders of pollinators composed of Coleoptera, Hymenoptera, Diptera and Lepidoptera, represent a large proportion of the insular richness. New information:Our sampling effort focused on the insects from these four orders visiting flowers in a characteristic thermo-Mediterranean vegetation. Our database is an insight into the Corsican anthophilous insects biodiversity from three sites separated by a few kilometres in the region of Ajaccio (SW Corsica) during nine consecutive months in 2023, completing our database for the year 2022 published in this journal. In total, 3714 specimens were sampled in 2023 and 311 species or morpho-species identified from 154 genera and 50 families. Coleoptera were by far the most abundant order representing about 54% of the sampled specimens. The most diverse order was the Hymenoptera representing 44% of the species. Our continuous survey has shown that these orders vary between seasons both in terms of abundance and diversity, resulting in changing communities.

Botanical gardens play a crucial role in botanical research by maintaining living collections of plants that serve educational and scientific purposes. This article examines the significance of living collections, using the Araceae family as a case study. Botanical gardens worldwide house diverse collections that contribute to studies in systematics, taxonomy, anatomy, morphology, floral biology, pollination ecology, phytochemistry, and medicine. The Araceae family, with its extensive diversity and distribution, provides an excellent model for comparative studies. Historical and contemporary research has utilized these collections to advance knowledge in specific areas. For instance, molecular systematics has benefited from these collections, as have studies on calcium oxalate crystal production, floral anatomy and development, pollen-ovule ratios, pollen viability, seed size and growth type, thermogenesis, and pollination syndromes. The article highlights the indispensable role of living collections in facilitating research that would be challenging to conduct solely in the field. It underscores the need for continued investment in botanical gardens to preserve their scientific and educational value, and outlines future research opportunities that living collections can offer.

Background and Aims Integrative approaches are mandatory to comprehend the evolution of deceptive pollination strategies, by combining the co-variations in different floral traits and the behaviour of the insects. We applied an ecophysiological approach to compare floral traits (scent and thermogenesis) in two deceptive sympatric Arum that are pollinated mainly by Psychoda moth flies. We hypothesized that floral traits diverged between the two arums to minimize their interference in attraction of pollinators.Methods We measured several floral traits, including the timing of anthesis, thermogenesis patterns and floral volatile organic compounds, in Arum italicum and Arum maculatum. Additionally, we conducted laboratory experiments to determine the diel activity rhythm of the moth fly Psychoda sigma. We compared the activity window of the fly with the timing of anthesis, and we compared the two arums in the ability of their volatiles to increase pollinator activity.Key Results The main thermogenesis peak involved in pollinator attraction was cooler and occurred slightly earlier during the day in A. maculatum compared with A. italicum. The fly P. sigma appeared to be nocturnal, hence inflorescences emitting their floral scent before sunset are less likely to be visited by pollinators owing to the relatively short attractive (few hours) female phase. Regarding scents, we confirmed a strong differentiation between the two Arum species. Behavioural assays with P. sigma revealed a slightly stronger stimulation to the odour of A. maculatum compared with A. italicum.Conclusions Our integrative approach highlights that the two Arum species exhibit slightly shifted daily timing of anthesis, indicating a fine-tuned variation in their attractive volatiles and thermogenesis sequences in relationship to pollinator behaviour. A trade-off might exist between odour specificity and the ability to maximize volatile emission. These findings illustrate how evolutionarily close and sympatric species have shifted their attraction systems, potentially reducing competition within sympatric populations.

Helichrysum italicum (Roth) G. Don (Asteraceae) is a valuable medicinal and aromatic plant native to a variety of habitats across the Mediterranean region. However, genetic studies of this morphologically diverse species have been limited by the scarcity of species-specific DNA markers. To address this limitation, we generated the first de novo transcriptome assembly comprising 24,806 transcripts from young shoots containing leaves and flowers, developed EST-SSR markers, and evaluated their utility in population genetic analysis. Seventy-eight primer pairs were designed, of which 23 showed successful amplification, polymorphism, and transferability to Helichrysum litoreum Guss. and Helichrysum arenarium (L.) Moench. A subset of 12 EST-SSRs was used to genotype 270 individuals from 12 natural populations of H. italicum in Corsica (France), along with one outgroup population from Croatia. The polymorphic information content ranged from 0.250 to 0.796, and Shannon’s information index ranged from 0.588 to 1.843, indicating the markers’ suitability for population genetic studies. Analysis of molecular variance revealed that 15% of the total genetic variation was attributable to differences among populations. Discriminant analysis of principal components and Bayesian clustering in STRUCTURE identified distinct population clusters corresponding to geographic locations. Notably, the southernmost coastal populations were clearly differentiated from the others.

The Neotropical tribe Spathicarpeae (Araceae) exhibits unique floral traits, among which staminodes seem to be crucial for reproductive biology in most of its genera. Given the existing gap in the literature on pollination ecology, along with the uncertainties regarding nectar secretion, we studied Spathicarpa hastifolia to describe staminode ultrastructure, investigate secretory processes, and characterize the composition of exudates sought by floral visitors. Flower buds and flowers in different anthesis phases were collected, fixed, and processed for light and electron microscopy. Flowers of S. hastifolia lack a perianth and comprise a gynoecium surrounded by staminodes. Staminodes exude a hyaline fluid during the pistillate and staminate phases of anthesis, attracting floral visitors like cockroaches, ants, and sap beetles. The staminodes are slightly globose, vascularized, and covered by a uniseriate epidermis with widespread stomata that are mostly open pores. The ground tissue is a starch-rich parenchyma whose starch content varies throughout the day due to synthesis and hydrolysis cycles. Chemical analyses showed that staminode exudates constitute sucrose-rich nectar. On the other hand, the fused stamens or synandria exude tiny drops of liquid from their tops, sometimes containing sugars, but in too low concentration to be qualified as nectar. The structure of the secretory cells of staminodes, both from the epidermis and parenchyma, was shown to be compatible with nectar synthesis. Mitochondria, plastids, rough endoplasmic reticulum, and vacuoles prevail in these cells. Altogether, our results show that the staminodes of S. hastifolia are floral nectaries whose secretory activity extends throughout the entire period of anthesis and mediates interactions with potential pollinators.

Background Flower traits and pollinator activity patterns can vary over the course of a single day. Therefore, the pollination processes occurring over short time scales are crucial to sustain the complex dynamics of plant-pollinator interactions. Here, we characterized the diel patterns of flower opening ( e.g. anthesis), scent emission, and insect visits in highly dimorphic male (rewarding) and female (deceptive) inflorescences of the ivory palm ( Phytelephas aequatorialis) , a thermogenic dioecious species endemic to western Ecuador. We conducted field experiments using artificial scented-baits (designated as artificial flowers) consisting of a heating plate (simulating thermogenesis) and p-methylanisole (the primary odor compound in inflorescences of both sexes) in two different amounts to mimic female and male inflorescences. Results We found that female inflorescences open synchronously at dawn and dusk, while male inflorescences can open at any time throughout the day. Both sexes emitted floral odors consistently throughout the day. Even though male inflorescences emitted greater quantities of p-methylanisole, artificial flowers with different amounts of p-methylanisole attracted a similar diversity and abundance of insects throughout the day. Furthermore, male and female artificial flower attracted an equal abundance of visitors within five minutes of the emission of p-methylanisole. Conclusions The findings suggest that, despite sexual dimorphism in opening time, intersexual mimicry in P. aequatorialis is sustained by a consistent odor release, which optimizes the probability of both sexes being visited by the same insect community during the day.

Pollination is a key tenet of ecosystem sustainability and food security, but it is threatened by climate change. While many studies investigated the response of plant-pollination traits to temperature, few attempted multifactorial and integrative approaches with multiple floral traits. We determined which plant-pollination traits were disrupted by environmental changes and the consequence for plant fitness. We focused on the thermogenic plant, Arum italicum, which relies on floral scent and heat production to attract its pollinators with a deceptive strategy. In a field mesocosm, we measured the response of floral phenology, thermogenesis traits, scent and plant fitness to experimental changes in shade level, water supply and soil temperature. In the laboratory, we exposed plants to extreme heat to determine the thermoregulation ability at high temperatures. Plant fitness decreased dramatically in response to soil warming and the level of shade. While both factors caused a lower number of inflorescences, soil warming was mostly responsible for the crash in number of fruits. The plant traits related to thermogenesis and scent were relatively resilient to the environmental changes in the mesocosm and were unlikely to produce the observed decrease in plant fitness. First, environmental changes only weakly modified the scent composition. Second, the appendix regulated its maximal temperature almost perfectly, while stamen regulated imperfectly. In the laboratory experiment, the appendix maintained a thermal gradient supposedly to improve scent emission while stamen became cooler than ambient air, possibly preventing the pollinators from overheating within the floral chamber. By contrast, the phenology of flowering was drastically modified. Flowers appeared earlier in the season in response to soil warming (by 39 days) or absence of shade (by 19 days). At the daily scale, flowering hour did not change across the season resulting in plants flowering before sunset late in the season and before the pollinator activity window (mostly nocturnal). The strong shift observed in the flowering period may induce a temporal mismatch with this pollinator both early and late in the season when the insects may not be active so early in the spring and during daytime, respectively, thereby altering plant fitness.Read the free Plain Language Summary for this article on the Journal blog. Read the free Plain Language Summary for this article on the Journal blog.image

Floral scents vary spatially within flowers and inflorescences, with effects on pollinator behaviour. Here, we restudied the spatial scent pattern of Arum maculatum, an Araceae, with a higher spatial resolution than previously. The inflorescence of this species consists of a spadix, whose distal part is a sterile osmophore called the appendix, whereas its basal part bears sterile and fertile male and female flowers. This spadix is surrounded by a spathe, which forms a floral chamber around the flowers. So far, it was known that the appendix is responsible for the emission of most of the volatiles, but some volatiles were specifically found within the floral chamber, with the organ(s) responsible for their emission being unclear. By repeatedly collecting (dynamic headspace) and analysing (gas chromatography/mass spectrometry) the scent of whole inflorescences and of inflorescences with the spathe and the various zones of the spadix sequentially removed, we determined and quantified all scent compounds of the major units of the inflorescence of A. maculatum. We confirm that the inflorescence scent is mainly composed of scents released by the appendix, and we for the first time provide evidence that the male flower zone of the spadix also contributes to the inflorescence scent. Future studies are needed to test whether, and if, how, this spatial scent pattern in A. maculatum affects the movement of pollinators within the inflorescence and their pollination effectiveness.

Background The Mediterranean Region represents a biodiversity hotspot with a high rate of endemism. In its western part, Corsica Island is notable in terms of biodiversity due to its large surface and its large range of habitats from seaside to alpine biotopes. Amongst diverse groups, insects, notably the main orders of pollinators composed of Coleoptera, Hymenoptera, Diptera and Lepidoptera, represent a good part of the insular richness. New information Our sampling effort focused on the insects from these four orders visiting flowers in a characteristic thermo-Mediterranean vegetation. Our database is an insight into the Corsican floral visitor biodiversity from three sites separated by a few kilometres in the region of Ajaccio during 13 months over two successive years. In total, 4012 specimens were sampled and 252 species or morpho-species identified from 133 genera and 47 families. Beetles were by far the most abundant order representing about 54% of the sampled specimens. The most diverse order was the Hymenoptera representing 39% of the species. Our continuous survey showed that these orders are temporally dynamic both between years and between seasons in terms of abundance and diversity.

Helichrysum italicum (Roth) G. Don is a Mediterranean medicinal plant with great potential in the cosmetics, culinary and pharmaceutical fields due to its unique bioactive compounds. Its recent introduction into agroecosystems has enhanced the exploitation of genetic diversity in natural populations, although limited molecular markers have made this challenging. In the present study, primers were designed for all 43 SSRs (72.1% mononucleotide, 21% dinucleotide and 6.9% trinucleotide repeats) identified in the chloroplast genome. Populations from Cape Kamenjak (Croatia) and Corsica (France) were analyzed with ten carefully selected cpSSR markers. From the initial set of 16 cpSSRs amplified in all samples, 6 cpSSR markers were removed due to low-length polymorphisms, size homoplasy and nucleotide polymorphisms that could not be detected with allele length. Of the 38 haplotypes detected, 32 were unique to their geographic origin. The highest number of private haplotypes was observed in the Cape Kamenjak population (seven out of nine detected). Based on clustering analyses, the Kamenjak population was the most similar to the Capo Pertusato (south Corsica) population, although only one sub-haplotype was shared. Other Corsican populations were more similar to each other. A cross-species transferability test with Helichrysum litoreum Guss. and Helichrysum arenarium (L.) Moench was successfully conducted and private alleles were identified.

AbstractWildfire pressure involves today to implement silvicultural practices that provide a good compromise between reducing fire risk and maintaining ecological functioning. Thinning reduces tree density and low branches, but results in the deposition of a considerable biomass of woody debris on the ground (up to 4800 g m2 in this study). They can be eliminated by prescribed burning, but this raises questions about the fire intensity that can be generated and the impact on soil fauna. We undertook the monitoring of a thinning and prescribed burning operation, separated and combined, in November 2020, in a Pinus laricio stand prone to fire risk, located in Bavella, Corsica. Fuel load was determined, and temperature measurements in the soil were performed using K‐type thermocouples. Soil arthropod populations were monitored using pitfall traps, in particular Collembola, Acari, Aranae, and Coleoptera. The combination of thinning and burning resulted in a fire intensity of 75.8 versus 8.4 kW m−1 for burning alone. Maximum temperature rise measured at −2 cm below the surface was less than 5°C for both treatments. The combination of thinning and burning did not result in higher fire intensity at ground level than burning alone, and the soil showed high insulation capacity. Most of the woody debris that burned was small‐diameter, and large‐diameter debris remained unconsumed. This burning, performed during a period of low biological activity, had no effect on soil arthropods, and the presence of large debris may have provided refuge areas. Collembola group was the faster to recover, and were followed by cohorts of predators in summer, especially Acari. Our results suggest that a combination of burning and thinning in autumn may be beneficial for fire prevention. However, the decomposition of woody debris in relation to fire risk, and the occurrence of pests after these treatments need to be monitored.

Symplocarpus foetidus (L.) Salisb. (eastern skunk cabbage) occurs across a broad geographic range of northeastern North America, blooming in winter between December and March. The inflorescences are well-known for their thermogenic and thermoregulatory metabolic capabilities. The perceptual qualities of their fetid floral aroma have been described widely in the literature, but to date the floral volatile composition remained largely unknown. Here we present a detailed study of the floral scent produced by S. foetidus collected from intact female- and male-stage inflorescences and from dissected floral parts. Our results show a large range of biosynthetically diverse volatiles including nitrogen- and sulfur-containing compounds, monoterpenes, benzenoids, and aliphatic esters and alcohols. We document high inter-individual variation with some organ-specific volatile trends but no clear strong variation based on sexual stage. Multivariate data analysis revealed two distinct chemotypes from our study populations that are not defined by sexual stage or population origin. The chemotype differences may explain the bimodal perceptual descriptions in earlier work which vary between highly unpleasant/fetid and pleasant/apple-like. We discuss the results in ecological contexts including potential for floral mimicry, taking into account existing pollination studies for the species. We also discuss the results in evolutionary contexts, comparing our scent data to published scent data from the close sister species Symplocarpus renifolius. Future work should more closely examine the chemotype occurrence and frequency within these and other populations, and the impact these chemotypes may have on pollinator attraction and reproductive success.