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1. The shape of aroma: Measuring and modeling citrus oil gland distribution

   https://doi.org/10.1002/ppp3.10333  

   Amézquita, Erik J. ; Quigley, Michelle Y. ; Ophelders, Tim ; Seymour, Danelle ; Munch, Elizabeth ; Chitwood, Daniel H. ( September 2022 , PLANTS, PEOPLE, PLANET)

   Citrus are intrinsically connected to human health and culture, preventing human diseases like scurvy and inspiring sacred rituals. Citrus fruits come in a stunning number of different sizes and shapes, ranging from small clementines to oversized pummelos, and fruits display a vast diversity of flavors and aromas. These qualities are key in both traditional and modern medicine and in the production of cleaning and perfume products. By quantifying and modeling overall fruit shape and oil gland distribution, we can gain further insight into citrus development and the impacts of domestication and improvement on multiple characteristics of the fruit.

   Citrus come in diverse sizes and shapes, and play a key role in world culture and economy. Citrus oil glands in particular contain essential oils which include plant secondary metabolites associated with flavor and aroma. Capturing and analyzing nuanced information behind the citrus fruit shape and its oil gland distribution provide a morphology‐driven path to further our insight into phenotype–genotype interactions.

   We investigated the shape of citrus fruit of 51 accessions based on 3D X‐ray computed tomography (CT) scan reconstructions. Accessions include members of the three ancestral citrus species as well as related genera, and several interspecific hybrids. We digitally separate and compare the size of fruit endocarp, mesocarp, exocarp, and oil gland tissue. Based on the centers of the oil glands, overall fruit shape is approximated with an ellipsoid. Possible oil gland distributions on this ellipsoid surface are explored using directional statistics.

   There is a strong allometry along fruit tissues; that is, we observe a strong linear relationship between the logarithmic volume of any pair of major tissues. This suggests that the relative growth of fruit tissues with respect to each other follows a power law. We also observe that on average, glands distance themselves from their nearest neighbor following a square root relationship, which suggests normal diffusion dynamics at play.

   The observed allometry and square root models point to the existence of biophysical developmental constraints that govern novel relationships between fruit dimensions from both evolutionary and breeding perspectives. Understanding these biophysical interactions prompts an exciting research path on fruit development and breeding.

    

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2. Phased diploid genome assemblies and pan-genomes provide insights into the genetic history of apple domestication

   https://doi.org/10.1038/s41588-020-00723-9  

   Sun, Xuepeng ; Jiao, Chen ; Schwaninger, Heidi ; Chao, C. Thomas ; Ma, Yumin ; Duan, Naibin ; Khan, Awais ; Ban, Seunghyun ; Xu, Kenong ; Cheng, Lailiang ; et al ( November 2020 , Nature Genetics)

   Domestication of the apple was mainly driven by interspecific hybridization. In the present study, we report the haplotype-resolved genomes of the cultivated apple (Malus domesticacv. Gala) and its two major wild progenitors,M. sieversiiandM. sylvestris. Substantial variations are identified between the two haplotypes of each genome. Inference of genome ancestry identifies ~23% of the Gala genome as of hybrid origin. Deep sequencing of 91 accessions identifies selective sweeps in cultivated apples that originated from either of the two progenitors and are associated with important domestication traits. Construction and analyses of apple pan-genomes uncover thousands of new genes, with hundreds of them being selected from one of the progenitors and largely fixed in cultivated apples, revealing that introgression of new genes/alleles is a hallmark of apple domestication through hybridization. Finally, transcriptome profiles of Gala fruits at 13 developmental stages unravel ~19% of genes displaying allele-specific expression, including many associated with fruit quality.

    

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3. Neighborhood diversity simultaneously increased and decreased susceptibility to contrasting herbivores in an early stage forest diversity experiment

   https://doi.org/10.1111/1365-2745.13097  

   Grossman, Jake J. ; Cavender‐Bares, Jeannine ; Reich, Peter B. ; Montgomery, Rebecca A. ; Hobbie, Sarah E. ; Shefferson, ed., Richard ( December 2018 , Journal of Ecology)

   Forest structure and diversity can regulate tree vulnerability to damage by insects and pathogens. Past work suggests that trees with diverse neighbours should experience less leaf herbivory and less damage from specialist herbivores and diseases, and that the effect of neighbourhood diversity should be strongest at small spatial scales.

   In an early stage temperate tree diversity experiment, we monitored damage from leaf removing herbivores, specialist (gallers and leaf miners) herbivores, and two specialist fungal diseases (maple leaf anthracnose and cedar apple gall rust) over 3 years. The experimental design included treatments that varied independently in phylogenetic and functional diversity and we made our analyses across four spatial scales (1–16 m²).

   Neighborhood diversity simultaneously increased leaf removal for some species, decreased it for others, and had no effect on yet others. Height apparency—the difference between a focal plant’s height and its neighbours’—was the best single predictor of leaf removal across species and spatial scales, but the strength and direction of its effect were also species‐specific.

   Specialist pathogens and fungal foliar diseases showed signs of associational resistance and susceptibility. Oaks (Quercusspp.) were more resistant to leaf miners and maples were more resistant to anthracnose when surrounded by diverse neighbours (associational resistance). In contrast, birches (Betula papyrifera) were more susceptible to leaf miners and eastern red cedars (Juniperus virginiana) were more susceptible to cedar apple gall rust (Gymnosporangium juniperi‐virginianae) infection in diverse environments (associational susceptibility).

   Herbivore and pathogen damage was better predicted by community structure and diversity at small spatial scales (1 and 4 m²) than large scales (9 and 16 m²), suggesting a characteristic spatial scale for these biodiversity‐ecosystem functioning effects.

   Synthesis.Humans control forest diversity through selective harvesting and planting in natural stands and plantations. Our experimental demonstration of the role of local community structure and diversity in suppressing some forms of pest and pathogen damage to trees suggests that forest management can be most effective when diversity is considered at small spatial scales and the underlying biology of particular pests, pathogens, and hosts is taken into account. Pictured here: the “galls” formed by cedar apple gall rust (Gymnosporangium juniperae‐virginiae) on eastern red cedar (Juniperus virginiana) in early spring release wind‐dispersed teleospores. Junipers showed associational susceptibility: greater susceptibility to gall rust with more diverse neighbours.

    

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4. A reversal in sensory processing accompanies ongoing ecological divergence and speciation in Rhagoletis pomonella

   https://doi.org/10.1098/rspb.2021.0192  

   Tait, Cheyenne ; Kharva, Hinal ; Schubert, Marco ; Kritsch, Daniel ; Sombke, Andy ; Rybak, Jürgen ; Feder, Jeffrey L. ; Olsson, Shannon B. ( March 2021 , Proceedings of the Royal Society B: Biological Sciences)

   null (Ed.)

   Changes in behaviour often drive rapid adaptive evolution and speciation. However, the mechanistic basis for behavioural shifts is largely unknown. The tephritid fruit fly Rhagoletis pomonella is an example of ecological specialization and speciation in action via a recent host plant shift from hawthorn to apple. These flies primarily use specific odours to locate fruit, and because they mate only on or near host fruit, changes in odour preference for apples versus hawthorns translate directly to prezygotic reproductive isolation, initiating speciation. Using a variety of techniques, we found a reversal between apple and hawthorn flies in the sensory processing of key odours associated with host fruit preference at the first olfactory synapse, linking changes in the antennal lobe of the brain with ongoing ecological divergence. Indeed, changes to specific neural pathways of any sensory modality may be a broad mechanism for changes in animal behaviour, catalysing the genesis of new biodiversity. 

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5. Light and temperature mediate algal stimulation of heterotrophic activity on decomposing leaf litter

   https://doi.org/10.1111/fwb.13465  

   Pope, Cody A. ; Halvorson, Halvor M. ; Findlay, Robert H. ; Francoeur, Steven N. ; Kuehn, Kevin A. ( January 2020 , Freshwater Biology)

   Recent evidence suggests that periphytic algae stimulate plant litter heterotrophs (fungi and bacteria) in the presence of light, but few studies have tested whether this stimulation varies across gradients of light, which may covary with temperature.

   We exposed field‐conditionedTypha domingensislitter to fully‐crossed, short‐term gradients of temperature (15, 20, 25, and 30°C) and light (0, 25, 53, 123, and 388 µmol quanta m⁻² s⁻¹) and measured responses of litter‐associated algal, fungal, and bacterial production rates and β‐glucosidase, β‐xylosidase, and phenol oxidase enzyme activities in the laboratory.

   Increased light stimulated algal production rates, from immeasurable production under darkness to >200 µg algal C g⁻¹detrital C hr⁻¹at the highest light level, with the greatest light sensitivity and maximal photosynthetic rates at 25°C. In turn, increased light stimulated fungal production rates, especially at the two highest temperatures and most strongly at 25°C where light stimulated fungal production by a mean of 65 µg C g⁻¹detrital C hr⁻¹, indicating 2.1‐fold stimulation by light. Bacterial production rates also responded to light, indicated by stimulation of a mean of 16 µg C g⁻¹detrital C hr⁻¹(1.6‐fold) at 15°C, but stimulation was weaker at higher temperatures. Enzyme activities increased strongly with elevated temperature but were not affected by light.

   Our experimental evidence suggests algae differentially stimulate litter‐associated bacteria and fungi in a light‐dependent manner that further depends on temperature. These findings advance understanding of the onset of algal stimulation of heterotrophy, including algal‐induced priming effects during litter decomposition, in response to common covarying environmental gradients subject to global change.

    

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