The chemical and visual bases of the pollination of the Neotropical sexually deceptive orchid Telipogon peruvianus

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.

The effect of global warming on the Australian endemic orchid Cryptostylis leptochila and its pollinator

Ecological stability together with the suitability of abiotic conditions are crucial for long-term survival of any organism and the maintenance of biodiversity and self-sustainable ecosystems relies on species interactions. By influencing resource availability plants affect the composition of plant communities and ultimately ecosystem functioning. Plant-animal interactions are very complex and include a variety of exploitative and mutualistic relationships. One of the most important mutualistic interactions is that between plants and their pollinators. Coevolution generates clustered links between plants and their pollen vectors, but the pollination and reproductive success of plants is reduced by increase in the specialization of plant-animal interactions. One of the most specialized types of pollination is sexual deception, which occurs almost exclusively in Orchidaceae. In this form of mimicry, male insects are attracted to orchid flowers by chemical compounds that resemble insect female sex pheromones and pollinate the flowers during attempted copulations. These interactions are often species-specific with each species of orchid attracting only males of one or very few closely related species of insects. For sexually deceptive orchids the presence of a particular pollen vector is crucial for reproductive success and any reduction in pollinator availability constitutes a threat to the orchid. Because global warming is rapidly becoming the greatest threat to all organisms by re-shaping the geographical ranges of plants, animals and fungi, this paper focuses on predicting the effect of global warming on Cryptostylis leptochila, a terrestrial endemic in eastern Australia that is pollinated exclusively via pseudo copulation with Lissopimpla excelsa. As a species with a single pollinator this orchid is a perfect model for studies on the effect of global warming on plants and their pollen vectors. According to our predictions, global warming will cause a significant loss of suitable niches for C. leptochila. The potential range of this orchid will be 36%-75% smaller than currently and as a result the Eastern Highlands will become unsuitable for C. leptochila. On the other hand, some new niches will become available for this species in Tasmania. Simultaneously, climate change will result in a substantial expansion of niches suitable for the pollinator (44-82%). Currently ca. 71% of the geographical range of the orchid is also suitable for L. excelsa, therefore, almost 30% of the areas occupied by C. leptochila already lack the pollen vector. The predicted availability of the pollen vector increased under three of the climate change scenarios analysed. The predicted habitat loss is a serious threat to this orchid even with the potential colonization of Tasmania by this plant. In the reduced range of C. leptochila the pollen vector will also be present assuring fruit set in populations of this orchid. The genetic pool of the populations in New South Wales and Queensland will probably be lost.

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.

Specialization for Tachinid Fly Pollination in the Phenologically Divergent Varieties of the Orchid Neotinea ustulata

Despite increased focus on elucidating the various reproductive strategies employed by orchids, we still have only a rather limited understanding of deceptive pollination systems that are not bee- or wasp-mediated. In Europe, the orchid Neotinea ustulata has been known to consist of two phenologically divergent varieties, neither of which provide rewards to its pollinators. However, detailed studies of their reproductive biology have been lacking. Our study aimed to characterize and understand the floral traits (i.e., morphology, color, and scent chemistry) and reproductive biology of N. ustulata. We found that the two varieties differ in all their floral traits; furthermore, while Neotinea ustulata var. ustulata appears to be pollinated by both bees (e.g., Anthophora, Bombus) and flies (e.g., Dilophus, Tachina), var. aestivalis is pollinated almost entirely by flies (i.e., Nowickia, Tachina). Tachinids were also found to be much more effective than bees in removing pollinaria, and we show experimentally that they use the characteristic dark inflorescence top as a cue for approaching inflorescences. Our results thus suggest that while both N. ustulata varieties rely on tachinids for pollination, they differ in their degree of specialization. Further studies are, however, needed to fully understand the reproductive strategy of N. ustulata varieties.

Sexual deception of a beetle pollinator through floral mimicry

Sexual mimicry is a complex multimodal strategy used by some plants to lure insects to flowers for pollination.^1-4 It is notable for being highly species-specific and is typically mediated by volatiles belonging to a restricted set of chemical compound classes.^3,4 Well-documented cases involve exploitation of bees and wasps (Hymenoptera)^5,6 and flies (Diptera).^7-9 Although beetles (Coleoptera) are the largest insect order and are well known as pollinators of both early and modern plants,^10,11 it has been unclear whether they are sexually deceived by plants during flower visits.^12,13 Here we report the discovery of an unambiguous case of sexual deception of a beetle: male longhorn beetles (Chorothyse hessei, Cerambycidae) pollinate the elaborate insectiform flowers of a rare southern African orchid (Disa forficaria), while exhibiting copulatory behavior including biting the antennae-like petals, curving the abdomen into the hairy lip cleft, and ejaculating sperm. The beetles are strongly attracted by (16S,9Z)-16-ethyl hexadec-9-enolide, a novel macrolide that we isolated from the floral scent. Structure-activity studies^14,15 confirmed that chirality and other aspects of the structural geometry of the macrolide are critical for the attraction of the male beetles. These results demonstrate a new biological function for plant macrolides and confirm that beetles can be exploited through sexual deception to serve as pollinators.