Novel plant‐microbe interactions: rapid evolution of a legume‐rhizobium mutualism in restored prairies

Susan M. Magnoli, Jennifer A. Lau, 2020

1. When plants colonize new habitats, the novel interactions they form with new mutualists or enemies can immediately affect plant performance. These novel interactions also may provoke rapid evolutionary responses and can be ideal scenarios for investigating how species interactions influence plant evolution.
2. To explore how mutualists influence the evolution of colonizing plant populations, we capitalized on an experiment in which two former agricultural fields were seeded with identical prairie seed mixes in 2010. Six years later, we compared how populations of the legume Chamaecrista fasciculata from these sites and their original (shared) source population responded to nitrogen‐fixing rhizobia from the restoration sites in a greenhouse reciprocal cross‐inoculation experiment.
3. We found that the two populations differed both from their original source population and from each other in the benefits they derive from rhizobia, and that one population has evolved reduced allocation to rhizobia (i.e., forms fewer rhizobium‐housing nodules).
4. Synthesis. Our results suggest that these plant populations have evolved different ways of interacting with rhizobia, potentially in response to differences in rhizobium quality between sites. Our study illustrates how microbial mutualists may shape plant evolution in new environments and highlights how variation in microbial mutualists potentially may select for different evolutionary strategies in plant hosts. 

https://besjournals.onlinelibrary.wiley.com/doi/abs/10.1111/1365-2745.13366#.Xj_TdLoXtQ0.twitter

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In memoriam

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Dancing bees evaluate agricultural forage resources as inferior to central urban land 

Samuelson et al., 2019

Recent evidence suggests that flower-rich areas within cities could play an important role in pollinator conservation, but direct comparison of agricultural and urban areas has proved challenging to perform over large scales. Here we use the waggle dances of honeybees (Apis mellifera L.) to evaluate floral resource availability over the entire season at deeply urban or agricultural sites. Through analysis of 3378 dances that were performed over two years by 20 colonies in SE England, we show that foraging trip distance is consistently lower at urban sites across the entire season, implying a higher availability of forage in heavily urbanized areas. Urban bees also collected nectar with a higher mean sugar content. From the self-reported perspective of a generalist pollinator, the modern agricultural landscapes that we studied provided insufficient and transient resources relative to heavily urbanised areas, which may represent important refuges within an impoverished landscape.

Example waggle dance plots from one urban site (BUR) and one agricultural site (YAL). Each circle shows the dances recorded on a single filming period (up to 3 hours) during spring (fortnight 3), summer (fortnight 6) and autumn (fortnight 11). Waggle dances are displayed as probability heatmaps generated from 1000 simulations of each dance allowing incorporation of variability in distance and angle communication 29. Dance plots are overlaid on GIS land-use maps (radius 2500m) produced for land-use preference analysis. For waggle dance plots for all 183 site-fortnight combinations.

https://www.biorxiv.org/content/10.1101/2019.12.19.882076v1

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Amazonas 

@Astro_Alex

@Astro_Alex

  @astro_timpeake

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Elevated rates of positive selection drive the evolution of pestiferousness in the Colorado potato beetle (Leptinotarsa decemlineata, Say) 

Cohen et al., 2019

Insect pests are characterized by expansion, preference and performance on agricultural crops, high fecundity and rapid adaptation to control methods, which we collectively refer to as pestiferousness. Which organismal traits and evolutionary processes facilitate certain taxa becoming pests remains an outstanding question for evolutionary biologists. In order to understand these features, we set out to test the relative importance of genomic properties that underlie the rapid evolution of pestiferousness in the emerging pest model: the Colorado potato beetle (CPB), Leptinotarsa decemlineata Say. Within the Leptinotarsa genus, only CPB has risen to pest status on cultivated Solanum. Using whole genomes from ten closely related Leptinotarsa species, we reconstructed a high-quality species tree of this genus. Within this phylogenetic framework, we tested the relative importance of four drivers of rapid adaptation: standing genetic variation, gene family expansion and contraction, transposable element variation, and protein evolution. Throughout approximately 20 million years of divergence, Leptinotarsa show little evidence of gene family turnover or transposable element variation contributing to pest evolution. However, there is a clear pattern of pest lineages experiencing greater rates of positive selection on protein coding genes, as well as retaining higher levels of standing genetic variation. We also identify a suite of positively selected genes unique to the Colorado potato beetle that are directly associated with pestiferousness. These genes are involved in xenobiotic detoxification, chemosensation, and hormones linked with pest behavior and physiology.

Proportion of genes under positive selection (results from adaptive branch-site random 880 effect model) to total genes explained by branch length with significant phylogenetic dependence, 881 Blomberg’s K (1.4593) > 1; PIC.variance p-value = 0.008991009. 

https://www.biorxiv.org/content/10.1101/870543v1

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Still life of artichoke, asparagus, green cabbage, onions, beans, carrots, and other vegetables, all upon a wooden bench
Adriaen van Ultrecht. 1641

Exploiting chemical ecology to manage hyperparasitoids in biological control of arthropod pests

Cusumano et al., 2019

Insect hyperparasitoids are fourth trophic level organisms that commonly occur in terrestrial food webs, yet they are relatively understudied. These top‐carnivores can disrupt biological pest control by suppressing the populations of their parasitoid hosts, leading to pest outbreaks, especially in confined environments such as greenhouses where augmentative biological control is used. There is no effective eco‐friendly strategy that can be used to control hyperparasitoids. Recent advances in the chemical ecology of hyperparasitoid foraging behavior have opened opportunities for manipulating these top‐carnivores in such a way that biological pest control becomes more efficient. We propose various infochemical‐based strategies to manage hyperparasitoids. We suggest that a push‐pull strategy could be a promising approach to ‘push’ hyperparasitoids away from their parasitoid hosts and ‘pull’ them into traps. Additionally, we discuss how infochemicals can be used to develop innovative tools improving biological pest control (i) to restrict accessibility of resources (e.g. sugars and alternative hosts) to primary parasitoid only or (ii) to monitor hyperparasitoid presence in the crop for early detection. We also identify important missing information in order to control hyperparasitoids and outline what research is needed to reach this goal. Testing the efficacy of synthetic infochemicals in confined environments is a crucial step towards the implementation of chemical ecology‐based approaches targeting hyperparasitoids. © 2019 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Infochemical‐based searching behavior of hyperparasitoids. (A) In the natural environment, hyperparasitoids find their parasitoid hosts by exploiting plant‐derived chemical cues (HIPVs) and cues associated with the parasitized herbivores. (B) In the agricultural environment, the same infochemicals could be used in management strategies to divert hyperparasitoids away from parasitized herbivores and lure them towards point‐source attraction devices such as sticky traps. HIPVs, herbivore‐induced plant volatiles; mVOCs, microbial volatile organic compounds.

https://doi.org/10.1002/ps.5679 
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The Plague Stone in Penrith 

Sitting incongruously beside the main road is this little noticed and unloved stone. But the story it tells is as fascinating as it is sad. In 1597 the Plague struck in Penrith. Normal life in the town was suspended as the disease tore through the population. Farmers living around Penrith were too terrified of the plague to risk bringing their goods to market. So there were serious food shortages to compound the townsfolks’ problems. So plague stones were set up around the outskirts of the town. These stones had a hollow filled with vinegar. Townsfolk left coins in the vinegar and retreated a safe distance. Farmers then brought food and left it by the stone and took the money. The plague finally released its grip after 15 months having killed almost half of the population of the town. Such stones were quite common around England but few now remain.

 

https://bit.ly/34MDLoq

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Nothing Gold Can Stay 
By Robert Frost 

Nature’s first green is gold, 
Her hardest hue to hold. 
Her early leaf’s a flower; 
But only so an hour. 
Then leaf subsides to leaf. 
So Eden sank to grief, 
So dawn goes down to day. 
Nothing gold can stay.
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Individual Specialization and Multihost Epidemics: Disease Spread in Plant-Pollinator Networks
Stephen P. Ellner, Wee Hao Ng, nd Christopher R. Myers. 2020

Many parasites infect multiple species and persist through a combination of within- and between-species transmission. Multispecies transmission networks are typically constructed at the species level, linking two species if any individuals of those species interact. However, generalist species often consist of specialized individuals that prefer different subsets of available resources, so individual- and species-level contact networks can differ systematically. To explore the epidemiological impacts of host specialization, we build and study a model for pollinator pathogens on plant-pollinator networks, in which individual pollinators have dynamic preferences for different flower species. We find that modeling and analysis that ignore individual host specialization can predict die-off of a disease that is actually strongly persistent and can badly over- or underpredict steady-state disease prevalence. Effects of individual preferences remain substantial whenever mean preference duration exceeds half of the mean time from infection to recovery or death. Similar results hold in a model where hosts foraging in different habitats have different frequencies of contact with an environmental reservoir for the pathogen. Thus, even if all hosts have the same long-run average behavior, dynamic individual differences can profoundly affect disease persistence and prevalence.

https://www.journals.uchicago.edu/doi/abs/10.1086/708272?journalCode=an

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Linking species‐level network metrics to flower traits and plant fitness 

Lázaro et al., 2019

Theoretical models indicate that the structure of plant‐pollinator networks has important implications for the reproduction and survival of species. However, despite the growing information on the mechanisms underlying such structure, it is still difficult to predict the functional consequences of species’ structural positions in such networks. From the plant perspective, species position and roles in pollination networks might be related to traits describing flower attractiveness, availability, and dependence on pollinators. In turn, both network metrics and plant traits might influence plant species fitness.

During two field seasons, we collected data from the 23 most abundant plant species in a rich coastal community, to evaluate the association between population and floral traits (floral abundance at population level and flowers per individual, flower shape and size, flowering length, nectar volume, pollinator dependence), species‐level network metrics (linkage level, specialisation –d’–, weighted closeness centrality, network roles related to modularity), and plant fitness (seeds/flower, seed weight).

Flowering length, flower size, flower abundance and pollinator dependence were positively related to greater generalisation, as measured by various indices. More abundant species and those with larger flowers showed higher linkage levels (i.e. higher number of pollinator species), whereas longer flowering periods were negatively related to d’ and positively related to closeness centrality and important roles in the network. Likewise, plants species more dependent on pollinators occupied more central positions in the network. Furthermore, centrality in the networks was significantly associated with plant fitness. Specifically, central species in the network produced more and heavier seeds than the others. However, other plant traits, such as flower size and pollinator dependence had additional direct effects on seed production. 

Synthesis. Our study highlights how population and floral traits define the positions and roles of species structuring the pollination communities. Moreover, the relationships between network metrics and plant reproduction indicate, for the first time, the functional implications of these structural positions at the inter‐specific level of community assembly. 

 

https://doi.org/10.1111/1365-2745.13334 

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 “Social ecology is based on the conviction that nearly all of our present ecological problems originate in deep-seated social problems. It follows, from this view, that these ecological problems cannot be understood, let alone solved, without a careful understanding of our existing society and the irrationalities that dominate it. To make this point more concrete: economic, ethnic, cultural, and gender conflicts, among many others, lie at the core of the most serious ecological dislocations we face today—apart, to be sure, from those that are produced by natural catastrophes.”  

Murray Bookchin, Social Ecology and Communalism
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Spatial Population Genetics: It's About Time

Gideon S. Bradburd and Peter L. Ralph, 2019

Many important questions about the history and dynamics of organisms have a geographical component: How many are there, and where do they live? How do they move and interbreed across the landscape? How were they moving a thousand years ago, and where were the ancestors of a particular individual alive today? Answers to these questions can have profound consequences for our understanding of history, ecology, and the evolutionary process. In this review, we discuss how geographic aspects of the distribution, movement, and reproduction of organisms are reflected in their pedigree across space and time. Because the structure of the pedigree is what determines patterns of relatedness in modern genetic variation, our aim is to thus provide intuition for how these processes leave an imprint in genetic data. We also highlight some current methods and gaps in the statistical toolbox of spatial population genetics.

https://www.annualreviews.org/doi/abs/10.1146/annurev-ecolsys-110316-022659
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