An unusual tricosatriene is crucial for male fungus gnat attraction and exploitation by sexually deceptive Pterostylis orchids

Mosquito pollination of plants: an overview of their role and an assessment of the possible contribution of disease vectors

Mosquitoes visit flowers to obtain sugar or other nutrients and therefore possibly serve as major or minor pollinators of some plant species. They also often derive plant nutrients from other sources, such as extrafloral nectaries and honeydew. In a few cases, the plant-mosquito relationship is close, and mosquito pollination has been confirmed. Most plant species visited by mosquitoes, however, appear to depend on multiple means of pollination, particularly other flower-feeding insects. In addition, most mosquito species visit the flowers of many kinds of plants, possibly dispersing pollen in both biologically meaningful and irrelevant ways. This apparent lack of selectivity by both plants and mosquitoes liberates each of them from dependence on an unreliable pollen vehicle or nutrient source. A hypothetical pollinating role for the two top vectors of devastating human-disease pathogens, Anopheles gambiae or Aedes aegypti, relies on indirect evidence. So far, this evidence suggests that their participation in pollen transfer of native, introduced, or beneficial plants is negligible. The few plant species likely to be pollinated by these vectors are mostly invasive, harmful weeds associated with humans. That conclusion draws support from four characteristics of these vectors: (1) the numerous alternative potential pollinators of the flowers they visit; (2) their common use of diverse non-floral sources of nutrients; (3) the females' infrequent sugar feeding and heavy reliance on human blood for energy; and (4) their relatively low population densities. From these traits it follows that focused suppression or elimination of these two vectors, by whatever means, is highly unlikely to have adverse effects on pollination in endemic biotic communities or on ornamental plants or food crops.

Practical preparation of unsaturated very-long-chain fatty acids (VLCFAs) and very-long-chain alkene pollinator attractants

To prepare very-long-chain fatty acids and alkenes (VLCFAs and VLC alkenes) that are known pollinator attractants for sexually deceptive orchids, and biosynthetic precursors thereof, we applied a methodology allowing us to prepare monounsaturated VLCFAs with chain lengths up to 28 carbons and VLC alkenes up to 31 carbons. We implemented a coupling reaction between commercially available terminal alkynes and bromoalkanoic acids to prepare VLCFAs, allowing the products to be formed in two steps. For VLC alkenes, with many alkyltriphenylphosphonium bromides commercially available, we applied a Wittig reaction approach to prepare (Z)-configured monoenes in a single step. Using practical methods not requiring special reagents or equipment, we obtained 11 VLCFAs in > 90% isomeric purity, and 17 VLC alkenes in > 97% isomeric purity. Such general and accessible synthetic methods are essential for chemical ecology and biochemistry research to aid researchers in unambiguously identifying isolated semiochemicals and their precursors.

Chemistry, biosynthesis and biology of floral volatiles: roles in pollination and other functions

Covering: 2010 to 2023Floral volatiles are a chemically diverse group of plant metabolites that serve multiple functions. Their composition is shaped by environmental, ecological and evolutionary factors. This review will summarize recent advances in floral scent research from chemical, molecular and ecological perspectives. It will focus on the major chemical classes of floral volatiles, on notable new structures, and on recent discoveries regarding the biosynthesis and the regulation of volatile emission. Special attention will be devoted to the various functions of floral volatiles, not only as attractants for different types of pollinators, but also as defenses of flowers against enemies. We will also summarize recent findings on how floral volatiles are affected by abiotic stressors, such as increased temperatures and drought, and by other organisms, such as herbivores and flower-dwelling microbes. Finally, this review will indicate current research gaps, such as the very limited knowledge of the isomeric pattern of chiral compounds and its importance in interspecific interactions.

Pollination by sexual deception

The flower is arguably the centrepiece of angiosperm evolution. Its primary function is to secure pollination - the transfer of pollen from the anther (male) to the stigma (female). As plants are sessile organisms, the extraordinary diversity of flowers in large part reflects countless alternative evolutionary solutions to achieve this critical step in the flowering plant life cycle. The majority of flowering plants, some 87% by one estimate, depend on animals for pollination, with most of these paying for the service of pollination via food rewards of nectar or pollen. As in human economic systems, however, some cheating and deception occurs, with the pollination strategy of sexual deception being one such example.

Many different flowers make a bouquet: Lessons from specialized metabolite diversity in plant-pollinator interactions

Flowering plants have evolved extraordinarily diverse metabolites that underpin the floral visual and olfactory signals enabling plant-pollinator interactions. In some cases, these metabolites also provide unusual rewards that specific pollinators depend on. While some metabolites are shared by most flowering plants, many have evolved in restricted lineages in response to the specific selection pressures encountered within different niches. The latter are designated as specialized metabolites. Recent investigations continue to uncover a growing repertoire of unusual specialized metabolites. Increased accessibility to cutting-edge multi-omics technologies (e.g. genome, transcriptome, proteome, metabolome) is now opening new doors to simultaneously uncover the molecular basis of their synthesis and their evolution across diverse plant lineages. Drawing upon the recent literature, this perspective discusses these aspects and, where known, their ecological and evolutionary relevance. A primer on omics-guided approaches to discover the genetic and biochemical basis of functional specialized metabolites is also provided.

A new species of Mycomya Rondani, 1856 (Diptera: Mycetophilidae) common to southeast Australia, Tasmania, and New Zealand

Mycomya quadrimaculata sp. nov. is described from specimens collected in southeast Australia, Tasmania, and New Zealand. A key and type photographs of known Australian and New Zealand Mycomya species are provided. The relative abundance, observed distribution, and morphological affinities of the new species suggests that it is adventive and a recent introduction to New Zealand. Wing characters indicate that the new species is most closely aligned with a subgroup of the Australian Mycomya fauna.

Molecular mechanisms of adaptive evolution in wild animals and plants

Wild animals and plants have developed a variety of adaptive traits driven by adaptive evolution, an important strategy for species survival and persistence. Uncovering the molecular mechanisms of adaptive evolution is the key to understanding species diversification, phenotypic convergence, and inter-species interaction. As the genome sequences of more and more non-model organisms are becoming available, the focus of studies on molecular mechanisms of adaptive evolution has shifted from the candidate gene method to genetic mapping based on genome-wide scanning. In this study, we reviewed the latest research advances in wild animals and plants, focusing on adaptive traits, convergent evolution, and coevolution. Firstly, we focused on the adaptive evolution of morphological, behavioral, and physiological traits. Secondly, we reviewed the phenotypic convergences of life history traits and responding to environmental pressures, and the underlying molecular convergence mechanisms. Thirdly, we summarized the advances of coevolution, including the four main types: mutualism, parasitism, predation and competition. Overall, these latest advances greatly increase our understanding of the underlying molecular mechanisms for diverse adaptive traits and species interaction, demonstrating that the development of evolutionary biology has been greatly accelerated by multi-omics technologies. Finally, we highlighted the emerging trends and future prospects around the above three aspects of adaptive evolution.

The volatile chemistry of orchid pollination

Covering: up to September 2022Orchids are renowned not only for their diversity of floral forms, but also for their many and often highly specialised pollination strategies. Volatile semiochemicals play a crucial role in the attraction of a wide variety of insect pollinators of orchids. The compounds produced by orchid flowers are as diverse as the pollinators they attract, and here we summarise some of the chemical diversity found across orchid taxa and pollination strategies. We focus on compounds that have been experimentally demonstrated to underpin pollinator attraction. We also highlight the structural elucidation and synthesis of a select subset of important orchid pollinator attractants, and discuss the ecological significance of the discoveries, the gaps in our current knowledge of orchid pollination chemistry, and some opportunities for future research in this field.

Pathogenic fungus uses volatiles to entice male flies into fatal matings with infected female cadavers

To ensure dispersal, many parasites and pathogens behaviourally manipulate infected hosts. Other pathogens and certain insect-pollinated flowers use sexual mimicry and release deceptive mating signals. However, it is unusual for pathogens to rely on both behavioural host manipulation and sexual mimicry. Here, we show that the host-specific and behaviourally manipulating pathogenic fungus, Entomophthora muscae, generates a chemical blend of volatile sesquiterpenes and alters the profile of natural host cuticular hydrocarbons in infected female housefly (Musca domestica) cadavers. Healthy male houseflies respond to the fungal compounds and are enticed into mating with female cadavers. This is advantageous for the fungus as close proximity between host individuals leads to an increased probability of infection. The fungus exploits the willingness of male flies to mate and benefits from altering the behaviour of uninfected male host flies. The altered cuticular hydrocarbons and emitted volatiles thus underlie the evolution of an extended phenotypic trait.

Seed dispersal: Hungry hornets are unexpected and effective vectors

A new study finds that, in the forests of tropical China, hungry hornets are lured to the fruits of Aquilaria sinensis by highly volatile compounds structurally similar to volatiles from herbivore-damaged leaves. The hornets disperse the short-lived seeds rapidly to optimal new habitats.

Are some species ‘robust’ to exploitation? Explaining persistence in deceptive relationships

Animals and plants trick others in an extraordinary diversity of ways to gain fitness benefits. Mimicry and deception can, for example, lure prey, reduce the costs of parental care or aid in pollination–in ways that impose fitness costs on the exploited party. The evolutionary maintenance of such asymmetric relationships often relies on these costs being mitigated through counter-adaptations, low encounter rates, or indirect fitness benefits. However, these mechanisms do not always explain the evolutionary persistence of some classic deceptive interactions.

Sexually deceptive pollination (in which plants trick male pollinators into mating with their flowers) has evolved multiple times independently, mainly in the southern hemisphere and especially in Australasia and Central and South America. This trickery imposes considerable costs on the males: they miss out on mating opportunities, and in some cases, waste their limited sperm on the flower. These relationships appear stable, yet in some cases there is little evidence suggesting that their persistence relies on counter-adaptations, low encounter rates, or indirect fitness benefits. So, how might these relationships persist?

Here, we introduce and explore an additional hypothesis from systems biology: that some species are robust to exploitation. Robustness arises from a species’ innate traits and means they are robust against costs of exploitation. This allows species to persist where a population without those traits would not, making them ideal candidates for exploitation. We propose that this mechanism may help inform new research approaches and provide insight into how exploited species might persist.

Anthocyanin and Flavonol Glycoside Metabolic Pathways Underpin Floral Color Mimicry and Contrast in a Sexually Deceptive Orchid

Sexually deceptive plants secure pollination by luring specific male insects as pollinators using a combination of olfactory, visual, and morphological mimicry. Flower color is a key component to this attraction, but its chemical and genetic basis remains poorly understood. Chiloglottis trapeziformis is a sexually deceptive orchid which has predominantly dull green-red flowers except for the central black callus projecting from the labellum lamina. The callus mimics the female of the pollinator and the stark color contrast between the black callus and dull green or red lamina is thought to enhance the visibility of the mimic. The goal of this study was to investigate the chemical composition and genetic regulation of temporal and spatial color patterns leading to visual mimicry, by integrating targeted metabolite profiling and transcriptomic analysis. Even at the very young bud stage, high levels of anthocyanins were detected in the dark callus, with peak accumulation by the mature bud stage. In contrast, anthocyanin levels in the lamina peaked as the buds opened and became reddish-green. Coordinated upregulation of multiple genes, including dihydroflavonol reductase and leucoanthocyanidin dioxygenase, and the downregulation of flavonol synthase genes (FLS) in the callus at the very young bud stage underpins the initial high anthocyanin levels. Conversely, within the lamina, upregulated FLS genes promote flavonol glycoside over anthocyanin production, with the downstream upregulation of flavonoid O-methyltransferase genes further contributing to the accumulation of methylated flavonol glycosides, whose levels peaked in the mature bud stage. Finally, the peak anthocyanin content of the reddish-green lamina of the open flower is underpinned by small increases in gene expression levels and/or differential upregulation in the lamina in select anthocyanin genes while FLS patterns showed little change. Differential expression of candidate genes involved in specific transport, vacuolar acidification, and photosynthetic pathways may also assist in maintaining the distinct callus and contrasting lamina color from the earliest bud stage through to the mature flower. Our findings highlight that flower color in this sexually deceptive orchid is achieved by complex tissue-specific coordinated regulation of genes and biochemical pathways across multiple developmental stages.

Viruses Infecting Greenhood Orchids (Pterostylidinae) in Eastern Australia

The Australasian biogeographic realm is a major centre of diversity for orchids, with every subfamily of the Orchidaceae represented and high levels of endemism at the species rank. It is hypothesised that there is a commensurate diversity of viruses infecting this group of plants. In this study, we have utilised high-throughput sequencing to survey for viruses infecting greenhood orchids (Pterostylidinae) in New South Wales and the Australian Capital Territory. The main aim of this study was to characterise Pterostylis blotch virus (PtBV), a previously reported but uncharacterised virus that had been tentatively classified in the genus Orthotospovirus. This classification was confirmed by genome sequencing, and phylogenetic analyses suggested that PtBV is representative of a new species that is possibly indigenous to Australia as it does not belong to either the American or Eurasian clades of orthotospoviruses. Apart from PtBV, putative new viruses in the genera Alphaendornavirus, Amalgavirus, Polerovirus and Totivirus were discovered, and complete genome sequences were obtained for each virus. It is concluded that the polerovirus is likely an example of an introduced virus infecting a native plant species in its natural habitat, as this virus is probably vectored by an aphid, and Australia has a depauperate native aphid fauna that does not include any species that are host-adapted to orchids.

Fly Pollination of Kettle Trap Flowers of Riocreuxiatorulosa (Ceropegieae-Anisotominae): A Generalized System of Floral Deception

Elaborated kettle trap flowers to temporarily detain pollinators evolved independently in several angiosperm lineages. Intensive research on species of Aristolochia and Ceropegia recently illuminated how these specialized trap flowers attract particular pollinators through chemical deception. Morphologically similar trap flowers evolved in Riocreuxia; however, no data about floral rewards, pollinators, and chemical ecology were available for this plant group. Here we provide data on pollination ecology and floral chemistry of R. torulosa. Specifically, we determined flower visitors and pollinators, assessed pollen transfer efficiency, and analysed floral scent chemistry. R. torulosa flowers are myiophilous and predominantly pollinated by Nematocera. Pollinating Diptera included, in order of decreasing abundance, male and female Sciaridae, Ceratopogonidae, Scatopsidae, Chloropidae, and Phoridae. Approximately 16% of pollen removed from flowers was successfully exported to conspecific stigmas. The flowers emitted mainly ubiquitous terpenoids, most abundantly linalool, furanoid (Z)-linalool oxide, and (E)-β-ocimene—compounds typical of rewarding flowers and fruits. R. torulosa can be considered to use generalized food (and possibly also brood-site) deception to lure small nematocerous Diptera into their flowers. These results suggest that R. torulosa has a less specific pollination system than previously reported for other kettle trap flowers but is nevertheless specialized at the level of Diptera suborder Nematocera.

Pollination: Orchids attract unusual pollinators by means of novel chemical compounds

Sexually deceptive pollination is widespread in orchids, yet studies of its chemical basis have been mostly limited to species pollinated by bees and wasps. Two new studies in orchids demonstrate the novel chemistry of deceptive pollination by unusual pollinators.