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Stevenson, P. C.

Publications and source records attributed to Stevenson, P. C..

6 recordsLinked to original sources
bioRxiv2025

Two hundred years of changes in orchid pollination revealed using herbarium specimens

Orchids are one of the most diverse plant families and are renowned for their highly specialised interactions with pollinators. Despite growing evidence of orchid population decline, pollinator decline and rising concerns for orchid reproductive success, long-term changes remain poorly understood. To address this gap, we analysed changes in pollinarium removal, as a proxy for pollination success, in herbarium specimens of three species-rich orchid genera (Disa, Oncidium and Ophrys) hosted at the Royal Botanic Gardens, Kew, which has a rich and diverse orchid collection spanning the past two centuries. The selected genera occur in different major regions (subtropical and tropical Africa, predominantly temperate Europe, and tropical America, respectively). Our analysis reveals that pollinarium removal declined significantly in Disa and Oncidium, particularly among species with deceptive strategies or specialised pollination mechanisms. In contrast, Ophrys showed a significant increase, driven by Apidae-pollinated species, whereas pollinarium removal for Andrenidae-pollinated species declined over time. These contrasting findings reflect the role of orchid identity, pollinator availability and pollination strategy in shaping reproductive success under anthropogenic change. Overall, this study demonstrates the power of herbarium specimens to reveal long-term ecological changes, providing unique insights into the response of specific plant-pollinator interactions to increasing anthropogenic pressure.

plant biology↗
bioRxiv2025

Specialization and adaptation in pollen sterol use by wild bees

O_LISterols are essential metabolites in eukaryots, acting as stabilizing components of membranes and steroid hormone precursors. Unlike other animals, insects cannot biosynthesise sterols de novo so must acquire them from diet. Honeybees selectively uptake a subset of pollen sterols for use in their own tissues, rather than converting b-sitosterol or stigmasterol to cholesterol, as occurs in most insect herbivores because they do not have the chemical architecture to modify sterols like other insects. We do not know if this strategy is also employed by other bee species. C_LIO_LIHere, we measured the sterol profiles of 56 species representing all families of UK bees to identify whether the same pollen sterols are used by solitary and eusocial bee species. C_LIO_LIThe {Delta}5 sterols 24-methylenecholesterol, isofucosterol and {beta}-sitosterol which are common components of pollen sterolomes were also the main sterols found in all bee species. Campesterol and cholesterol were recorded almost universally in bees but in proportionately small amounts, despite their low abundance in pollen. C_LIO_LIOur data suggest an ecological rather than phylogenetic driver of bee sterols because related species differed as a function of pollen diet. Generalist species contained more 24-methlyenecholesterol than their specialist congeners suggesting a trade-off between competition for food and desirable sterols. Asteraceae specialists have adapted to use pollen sterols that are not used by generalists, potentially gaining an advantage over these species. Despite the uptake of less common sterols by specialists, they still relied on similar sterols to other bee species. The dietary requirements of specialists could be fulfilled by pollen from non-host species, suggesting that while essential, sterols are not the primary driving force of pollen foraging choices. C_LI

biochemistry↗
bioRxiv2024

Essential sterols from engineered yeast prevent honeybee colony population decline

Honeybees, the worlds most important crop pollinators, are increasingly facing pollen starvation arising from agricultural intensification and climate change. Frequent flowering dearth periods and high-density rearing conditions weaken colonies, often leading to their demise. Beekeepers provide colonies with pollen substitutes, but these feeds cannot sustain brood production because they lack essential sterols found in pollen. Here, we describe a technological breakthrough in honeybee nutrition with wide-reaching impacts on global food security. We first measured the quantity and proportion of sterols found in honeybee tissues. Using this information, we genetically engineered a strain of the oleaginous yeast, Yarrowia lipolytica, to produce a mixture of essential sterols for bees and incorporated it into an otherwise nutritionally complete diet. Colonies fed exclusively with this diet reared brood for significantly longer than those fed diets without suitable sterols. Incorporating sterol supplements into pollen substitutes using this method will enable beekeepers to rear healthier, longer-lived colonies to meet the growing demands for global crop pollination. It could also reduce competition between bee species for access to natural floral resources, stemming the decline of wild bee populations.

synthetic biology↗
bioRxiv2021

Agri-environment nectar chemistry suppresses parasite social epidemiology in an important pollinator

Emergent infectious diseases are a principal driver of biodiversity loss globally. The population and range declines of a suite of North American bumblebees, a group of important pollinators, have been linked to emergent infection with the microsporidian Nosema bombi. Previous work has shown that phytochemicals in pollen and nectar can negatively impact parasites in individual bumblebees, but how this relates to social epidemiology and by extension whether plants can be effectively used as disease management strategies remains unexplored. Here we show that caffeine, identified in the nectar of Sainfoin, a constituent of agri-environment schemes, significantly reduced N. bombi infection intensity in individual bumblebees and, for the first time, that such effects impact social epidemiology, with colonies reared from wild caught queens having lower prevalence and intensity of infection. Furthermore, infection prevalence was lower in foraging bumblebees from these colonies, suggesting a likely reduction in population-level transmission. Our results demonstrate that phytochemicals can impact pollinator disease epidemiology and that planting strategies, which increase floral abundance to support biodiversity could be co-opted as disease management strategies.

ecology↗
bioRxiv2020

Pollen sterols are associated with phylogenetics and environment but not with pollinators

O_LIPhytosterols are primary plant metabolites that have fundamental structural and regulatory functions. They are also essential nutrients for phytophagous insects, including pollinators, that cannot synthesize sterols. Despite the well-described composition and diversity in vegetative plant tissues, few studies have examined phytosterol diversity in pollen. C_LIO_LIWe quantified 25 pollen phytosterols in 122 plant species (105 genera, 51 families) to determine their composition and diversity across plant taxa. We searched literature and databases for plant phylogeny, environmental conditions, and pollinator guilds of the species to examine the relationships with pollen sterols. C_LIO_LI24-methylenecholesterol, sitosterol and isofucosterol were the most common and abundant pollen sterols. We found phylogenetic clustering of twelve individual sterols, total sterol content and sterol diversity, and of sterol groupings that reflect their underlying biosynthesis pathway (24 carbon alkylation, ring B desaturation). Plants originating in tropical-like climates (higher mean annual temperature, lower temperature seasonality, higher precipitation in wettest quarter) were more likely to record higher pollen sterol content. However, pollen sterol composition and content showed no clear relationship with pollinator guilds. C_LIO_LIOur study is the first to show that pollen sterol diversity is phylogenetically clustered and that pollen sterol content may adapt to environmental conditions. C_LI

biochemistry↗