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1. The Sphagnum cuspidatum complex: phylogeny, species delimitation, and morphology

   https://doi.org/10.1093/biolinnean/blad111  

   Robinson, Sean C; Nieto-Lugilde, Marta; Duffy, Aaron M; Martinez_Muñoz, Katherine; Aguero, Blanka; Merced, Amelia; Hassel, Kristian; Flatberg, Kjell Ivar; Shaw, A Jonathan (September 2023, Biological Journal of the Linnean Society)

   Abstract The use of species as a concept is an important metric for assessing biological diversity and ecosystem function. However, delimiting species based on morphological characters can be difficult, especially in aquatic plants that exhibit high levels of variation and overlap. The Sphagnum cuspidatum complex, which includes plants that dominate peatland hollows, provides an example of challenges in species delimitation. Microscopic characters that have been used to define taxa and the possibility that these characters may simply be phenoplastic responses to variation in water availability make species delimitation in this group especially difficult. In particular, the use of leaf shape and serration, which have been used to separate species in the complex, have resulted in divergent taxonomic treatments. Using a combination of high-resolution population genomic data (RADseq) and a robust morphological assessment of plants representing the focal species, we provide evidence to evaluate putative species in this complex. Our data support the recognition of S. cuspidatum, S. fitzgeraldii, S. mississippiense, and S. trinitense as genetically distinct species that can be separated morphologically. These results indicate that S. viride does not differ genetically from S. cuspidatum. Our results are broadly relevant to other aquatic groups where leaf shape and marginal teeth are used to distinguish species. 

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2. Habitat‐adapted microbial communities mediate Sphagnum peatmoss resilience to warming

   https://doi.org/10.1111/nph.18072  

   Carrell, Alyssa A.; Lawrence, Travis J.; Cabugao, Kristine Grace M.; Carper, Dana L.; Pelletier, Dale A.; Lee, Jun Hyung; Jawdy, Sara S.; Grimwood, Jane; Schmutz, Jeremy; Hanson, Paul J.; et al (March 2022, New Phytologist)

   Summary Sphagnumpeatmosses are fundamental members of peatland ecosystems, where they contribute to the uptake and long‐term storage of atmospheric carbon. Warming threatensSphagnummosses and is known to alter the composition of their associated microbiome. Here, we use a microbiome transfer approach to test if microbiome thermal origin influences host plant thermotolerance.We leveraged an experimental whole‐ecosystem warming study to collect field‐grownSphagnum, mechanically separate the associated microbiome and then transfer onto germ‐free laboratorySphagnumfor temperature experiments. Host and microbiome dynamics were assessed with growth analysis, Chlafluorescence imaging, metagenomics, metatranscriptomics and 16S rDNA profiling.Microbiomes originating from warming field conditions imparted enhanced thermotolerance and growth recovery at elevated temperatures. Metagenome and metatranscriptome analyses revealed that warming altered microbial community structure in a manner that induced the plant heat shock response, especially the HSP70 family and jasmonic acid production. The heat shock response was induced even without warming treatment in the laboratory, suggesting that the warm‐microbiome isolated from the field provided the host plant with thermal preconditioning.Our results demonstrate that microbes, which respond rapidly to temperature alterations, can play key roles in host plant growth response to rapidly changing environments. 

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3. Phylogenomic structure and speciation in an emerging model: the Sphagnum magellanicum complex (Bryophyta)

   https://doi.org/10.1111/nph.18429  

   Shaw, A. Jonathan; Piatkowski, Bryan; Duffy, Aaron M.; Aguero, Blanka; Imwattana, Karn; Nieto‐Lugilde, Marta; Healey, Adam; Weston, David J.; Patel, Megan N.; Schmutz, Jeremy; et al (October 2022, New Phytologist)
4. Ecological differentiation and sympatry of cryptic species in the Sphagnum magellanicum complex (Bryophyta)

   https://doi.org/10.1002/ajb2.16401  

   Nieto‐Lugilde, Marta; Nieto‐Lugilde, Diego; Piatkowski, Bryan; Duffy, Aaron M; Robinson, Sean C; Aguero, Blanka; Schuette, Scott; Wilkens, Richard; Yavitt, Joseph; Shaw, A Jonathan (September 2024, American Journal of Botany)

   Abstract PremiseSphagnum magellanicum(Sphagnaceae, Bryophyta) has been considered to be a single semi‐cosmopolitan species, but recent molecular analyses have shown that it comprises a complex of at least seven reciprocally monophyletic groups, that are difficult or impossible to distinguish morphologically. MethodsNewly developed barcode markers and RADseq analyses were used to identify species among 808 samples from 119 sites. Molecular approaches were used to assess the geographic ranges of four North American species, the frequency at which they occur sympatrically, and ecological differentiation among them. Microhabitats were classified with regard to hydrology and shade. Hierarchical modelling of species communities was used to assess climate variation among the species. Climate niches were projected back to 22,000 years BP to assess the likelihood that the North American species had sympatric ranges during the late Pleistocene. ResultsThe species exhibited parallel morphological variation, making them extremely difficult to distinguish phenotypically. Two to three species frequently co‐occurred within peatlands. They had broadly overlapping microhabitat and climate niches. Barcode‐ versus RADseq‐based identifications were in conflict for 6% of the samples and always involvedS. diabolicumvs.S. magniae. ConclusionsThese species co‐occur within peatlands at scales that could permit interbreeding, yet they remain largely distinct genetically and phylogenetically. The four cryptic species exhibited distinct geographic and ecological patterns. Conflicting identifications from barcode vs. RADseq analyses forS. diabolicumversusS. magniaecould reflect incomplete speciation or hybridization. They comprise a valuable study system for additional work on climate adaptation. 

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5. Functional trait evolution in Sphagnum peat mosses and its relationship to niche construction

   https://doi.org/10.1111/nph.15825  

   Piatkowski, Bryan T.; Shaw, A. Jonathan (April 2019, New Phytologist)

   Summary Species in the genusSphagnumcreate, maintain, and dominate boreal peatlands through ‘extended phenotypes’ that allow these organisms to engineer peatland ecosystems and thereby impact global biogeochemical cycles. One such phenotype is the production of peat, or incompletely decomposed biomass, that accumulates when rates of growth exceed decomposition. Interspecific variation in peat production is thought to be responsible for the establishment and maintenance of ecological gradients such as the microtopographic hummock‐hollow gradient, along which sympatric species sort within communities.This study investigated the mode and tempo of functional trait evolution across 15 species ofSphagnumusing data from the most extensive studies ofSphagnumfunctional traits to date and phylogenetic comparative methods.We found evidence for phylogenetic conservatism of the niche descriptor height‐above‐water‐table and of traits related to growth, decay and litter quality. However, we failed to detect the influence of phylogeny on interspecific variation in other traits such as shoot density and suggest that environmental context can obscure phylogenetic signal. Trait correlations indicate possible adaptive syndromes that may relate to niche and its construction.This study is the first to formally test the extent to which functional trait variation amongSphagnumspecies is a result of shared evolutionary history. 

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