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1. Phylogenetic structure in the Sphagnum recurvum complex (Bryophyta) in relation to taxonomy and geography

   https://doi.org/10.1002/ajb2.1525  

   Duffy, Aaron_M; Aguero, Blanka; Stenøien, Hans_K; Flatberg, Kjell_Ivar; Ignatov, Michael_S; Hassel, Kristian; Shaw, A_Jonathan (September 2020, American Journal of Botany)

   PremiseTheSphagnum recurvumcomplex comprises a group of closely related peat mosses that are dominant components of many northern wetland ecosystems. Taxonomic hypotheses for the group range from interpreting the whole complex as one polymorphic species to distinguishing 6–10 species. The complex occurs throughout the Northern Hemisphere, and some of the putative species have intercontinental ranges. Our goals were to delimit the complex and assess its phylogenetic structure in relation to morphologically defined species and intercontinental geography. MethodsRADseq analyses were applied to a sample of 384 collections from Europe, North America, and Asia. The data were subjected to maximum likelihood phylogenetic analyses and analyses of genetic structure using the software STRUCTURE and multivariate ordination approaches. ResultsTheS. recurvumcomplex includesS. angustifolium,S. fallax,S. flexuosum,S. pacificum, andS. recurvumas clades with little evidence of admixture. We also resolved an unnamed clade that is referred to here asS. “pseudopacificum.” We confirm thatS. balticumandS. obtusumare nested within the complex. Species with bluntly acute to obtuse stem leaf apices are sister to those with acute to apiculate leaves. Most of the species exhibit some differentiation between intraspecific population systems disjunct on different continents. ConclusionsWe recognize seven species in the amendedS. recurvumcomplex, includingS. balticumandS. obtusum, in addition to the informal cladeS. “pseudopacificum.” Although we detected some geographically correlated phylogenetic structure within widespread morphospecies, our RADseq data support the interpretation that these species have intercontinental geographic ranges. 

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2. Clonality, local population structure and gametophyte sex ratios in cryptic species of the Sphagnum magellanicum complex

   https://doi.org/10.1093/aob/mcad077  

   Shaw, A. Jonathan; Duffy, Aaron M.; Nieto-Lugilde, Marta; Aguero, Blanka; Schuette, Scott; Robinson, Sean; Loveland, James; Hicks, Karen A.; Weston, David; Piatkowski, Bryan; et al (July 2023, Annals of Botany)

   Abstract Background and AimsSphagnum (peatmoss) comprises a moss (Bryophyta) clade with ~300–500 species. The genus has unparalleled ecological importance because Sphagnum-dominated peatlands store almost a third of the terrestrial carbon pool and peatmosses engineer the formation and microtopography of peatlands. Genomic resources for Sphagnum are being actively expanded, but many aspects of their biology are still poorly known. Among these are the degree to which Sphagnum species reproduce asexually, and the relative frequencies of male and female gametophytes in these haploid-dominant plants. We assess clonality and gametophyte sex ratios and test hypotheses about the local-scale distribution of clones and sexes in four North American species of the S. magellanicum complex. These four species are difficult to distinguish morphologically and are very closely related. We also assess microbial communities associated with Sphagnum host plant clones and sexes at two sites. MethodsFour hundred and five samples of the four species, representing 57 populations, were subjected to restriction site-associated DNA sequencing (RADseq). Analyses of population structure and clonality based on the molecular data utilized both phylogenetic and phenetic approaches. Multi-locus genotypes (genets) were identified using the RADseq data. Sexes of sampled ramets were determined using a molecular approach that utilized coverage of loci on the sex chromosomes after the method was validated using a sample of plants that expressed sex phenotypically. Sex ratios were estimated for each species, and populations within species. Difference in fitness between genets was estimated as the numbers of ramets each genet comprised. Degrees of clonality [numbers of genets/numbers of ramets (samples)] within species, among sites, and between gametophyte sexes were estimated. Sex ratios were estimated for each species, and populations within species. Sphagnum-associated microbial communities were assessed at two sites in relation to Sphagnum clonality and sex. Key ResultsAll four species appear to engage in a mixture of sexual and asexual (clonal) reproduction. A single ramet represents most genets but two to eight ramets were dsumbers ansd text etected for some genets. Only one genet is represented by ramets in multiple populations; all other genets are restricted to a single population. Within populations ramets of individual genets are spatially clustered, suggesting limited dispersal even within peatlands. Sex ratios are male-biased in S. diabolicum but female-biased in the other three species, although significantly so only in S. divinum. Neither species nor males/females differ in levels of clonal propagation. At St Regis Lake (NY) and Franklin Bog (VT), microbial community composition is strongly differentiated between the sites, but differences between species, genets and sexes were not detected. Within S. divinum, however, female gametophytes harboured two to three times the number of microbial taxa as males. ConclusionsThese four Sphagnum species all exhibit similar reproductive patterns that result from a mixture of sexual and asexual reproduction. The spatial patterns of clonally replicated ramets of genets suggest that these species fall between the so-called phalanx patterns, where genets abut one another but do not extensively mix because of limited ramet fragmentation, and the guerrilla patterns, where extensive genet fragmentation and dispersal result in greater mixing of different genets. Although sex ratios in bryophytes are most often female-biased, both male and female biases occur in this complex of closely related species. The association of far greater microbial diversity for female gametophytes in S. divinum, which has a female-biased sex ratio, suggests additional research to determine if levels of microbial diversity are consistently correlated with differing patterns of sex ratio biases. 

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3. Contemporary range position predicts the range‐wide pattern of genetic diversity in balsam poplar ( Populus balsamifera L.)

   https://doi.org/10.1111/jbi.13811  

   Gougherty, Andrew V.; Chhatre, Vikram E.; Keller, Stephen R.; Fitzpatrick, Matthew C.; Comes, ed., Hans‐Peter (February 2020, Journal of Biogeography)

   Abstract AimPatterns of genetic diversity within species’ ranges can reveal important insights into effects of past climate on species’ biogeography and current population dynamics. While numerous biogeographic hypotheses have been proposed to explain patterns of genetic diversity within species’ ranges, formal comparisons and rigorous statistical tests of these hypotheses remain rare. Here, we compared seven hypotheses for their abilities to describe the geographic pattern of two metrics of genetic diversity in balsam poplar (Populus balsamifera), a northern North American tree species. LocationNorth America. TaxonBalsam poplar (Populus balsamiferaL.). MethodsWe compared seven hypotheses, representing effects of past climate and current range position, for their ability to describe the geographic pattern of expected heterozygosity and per cent polymorphic loci across 85 populations of balsam poplar. We tested each hypothesis using spatial and non‐spatial least‐squares regression to assess the importance of spatial autocorrelation on model performance. ResultsWe found that both expected heterozygosity and per cent polymorphic loci could best be explained by the current range position and genetic structure of populations within the contemporary range. Genetic diversity showed a clear gradient of being highest near the geographic and climatic range centre and lowest near range edges. Hypotheses accounting for the effects of past climate (e.g. past climatic suitability, distance from the southern edge), in contrast, had comparatively little support. Model ranks were similar among spatial and non‐spatial models, but residuals of all non‐spatial models were significantly autocorrelated, violating the assumption of independence in least‐squares regression. Main conclusionsOur work adds strong support for the “Central‐Periphery Hypothesis” as providing a predictive framework for understanding the forces structuring genetic diversity across species’ ranges, and illustrates the value of applying a robust comparative model selection framework and accounting for spatial autocorrelation when comparing biogeographic models of genetic diversity. 

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4. Adaptation to lower latitudes and lower elevations precedes the evolution of hummingbird pollination in western North American Penstemon

   https://doi.org/10.1002/ajb2.1857  

   Hamilton, Ashley M.; Wessinger, Carolyn A. (June 2022, American Journal of Botany)

   Abstract PremiseA switch in pollinator can occur when a plant lineage enters a new habitat where the ancestral pollinator is less common, and a novel pollinator is more common. Because pollinator communities vary according to environmental tolerances and availability of resources, there may be consistent associations between pollination mode and specific regions and habitats. Such associations can be studied in lineages that have experienced multiple pollinator transitions, representing evolutionary replicates. MethodsOur study focused on a large clade ofPenstemonwildflower species in western North America, which has repeatedly evolved hummingbird‐adapted flowers from ancestral bee‐adapted flowers. For each species, we estimated geographic ranges from occurrence data and inferred environmental niches from climate, topographical, and soil data. Using a phylogenetic comparative approach, we investigated whether hummingbird‐adapted species occupy distinct geographic regions or habitats relative to bee‐adapted species. ResultsHummingbird‐adapted species occur at lower latitudes and lower elevations than bee‐adapted species, resulting in a difference in their environmental niche. Bee‐adapted species sister to hummingbird‐adapted species are also found in relatively low elevations and latitudes, similar to their hummingbird‐adapted sister species, suggesting ecogeographic shifts precede pollinator divergence. Sister species pairs—regardless of whether they differ in pollinator—show relatively little geographic range overlap. ConclusionsAdaptation to a novel pollinator may often occur in geographic and ecological isolation from ancestral populations. The ability of a given lineage to adapt to novel pollinators may critically depend on its ability to colonize regions and habitats associated with novel pollinator communities. 

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5. Convergent niche shifts of endangered parrots (genus Amazona ) during successful establishment in urban southern California

   https://doi.org/10.1111/ddi.13817  

   Ramirez, Brenda R.; Freeland, Rowdy J.; Muhlheim, Allison; Zellmer, Amanda J.; DeRaad, Devon A.; Kirsch, Eliza J.; Mutchler, Marquette J.; Secor, Maeve B.; Reckling, Kelsey R.; Schedl, Margaret E.; et al (February 2024, Diversity and Distributions)

   Abstract AimIntroduced species offer insight on whether and how organisms can shift their ecological niches during translocation. The genusAmazonaoffers a clear test case, where sister species Red‐crowned (A. viridigenalis) and Lilac‐crowned Parrots (A. finschi) have established breeding populations in southern California following introduction via the pet trade from Mexico where they do not coexist. After establishment in the 1980s, introduced population sizes have increased, with mixed species flocks found throughout urban Los Angeles. Here, we investigate the differences between the environmental conditions of the native and introduced ranges of these now co‐occurring species. LocationSouthern California and Mexico. MethodsUsing environmental data on climate and habitat from their native and introduced ranges, we tested whether Red‐crowned and Lilac‐crowned Parrots have divergent realized niches between their native ranges, and whether each species has significantly shifted its realized niche to inhabit urban southern California. We also analysed data from Texas and Florida introductions of Red‐crowned Parrots for comparative analysis. ResultsThere are significant differences in the native‐range niches of both parrot species, but a convergence into a novel, shared environmental niche into urban southern California, characterized by colder temperatures, less tree cover and lower rainfall. Texas and Florida Red‐crowned Parrots also show evidence for niche shifts with varying levels of niche conservatism through the establishment of somewhat different realized niches. Main ConclusionsDespite significant niche shifts, introduced parrots are thriving, suggesting a broad fundamental niche and an ability to exploit urban resources. Unique niche shifts in different U.S. introductions indicate thatAmazonaparrots can adapt to diverse environmental conditions, with cities offering a resource niche and the timing of introduction playing a crucial role. Cities can potentially serve as refugia for threatened parrot species, but the risk of hybridization between species emphasizes the need for ongoing monitoring and genetic investigations. 

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