Search for: All records

We used nuclear genomic data and statistical models to evaluate the ecological and evolutionary processes shaping spatial variation in species richness inCalochortus(Liliaceae, 74 spp.).Calochortusoccupies diverse habitats in the western United States and Mexico and has a center of diversity in the California Floristic Province, marked by multiple orogenies, winter rainfall, and highly divergent climates and substrates (including serpentine). We used sequences of 294 low-copy nuclear loci to produce a time-calibrated phylogeny, estimate historical biogeography, and test hypotheses regarding drivers of present-day spatial patterns in species number. Speciation and species coexistence require reproductive isolation and ecological divergence, so we examined the roles of chromosome number, environmental heterogeneity, and migration in shaping local species richness. Six major clades—inhabiting different geographic/climatic areas, and often marked by different base chromosome numbers (n = 6 to 10)—began diverging from each other ~10.3 Mya. As predicted, local species number increased significantly with local heterogeneity in chromosome number, elevation, soil characteristics, and serpentine presence. Species richness is greatest in the Transverse/Peninsular Ranges where clades with different chromosome numbers overlap, topographic complexity provides diverse conditions over short distances, and several physiographic provinces meet allowing immigration by several clades. Recently diverged sister-species pairs generally have peri-patric distributions, and maximum geographic overlap between species increases over the first million years since divergence, suggesting that chromosomal evolution, genetic divergence leading to gametic isolation or hybrid inviability/sterility, and/or ecological divergence over small spatial scales may permit species co-occurrence. 

Abstract Previous meta‐analyses suggested that carnivorous plants—despite access to N, P, and K from prey—have significantly lower leaf concentrations of these nutrients than noncarnivores. Those studies, however, largely compared carnivores in nutrient‐poor habitats with noncarnivores in more nutrient‐rich sites, so that the differences reported might reflect habitat differences as much as differences in nutrient‐capture strategy. Here we examine three carnivorous and 12 noncarnivorous plants in the same nutrient‐poor bog to compare their foliar nutrient concentrations, assess their patterns of nutrient limitation using leaf NPK stoichiometry, and estimate percentage N derived from prey by carnivores using a mixing model for stable N isotopes. We hypothesized that (1) carnivore leaf nutrient concentrations approach or exceed those of noncarnivores in the same nutrient‐poor habitat; (2) species in different functional groups show different patterns of stoichiometry and apparent nutrient limitation; and (3) noncarnivores might show evidence of using other means of nutrient acquisition or conservation to reduce nutrient limitation. At Fallison Bog in northern Wisconsin, carnivorous plants (Drosera rotundifolia,Sarracenia purpurea,Utricularia macrorhiza) showed significantly lower leaf percentage C and N:P ratio, higher δ¹⁵N, and no difference from noncarnivores in leaf N, P, K, and δ¹³C. Sedges had significantly lower leaf percentage P, percentage C, and N:K ratio, and higher K:P ratio than nonsedges restricted to theSphagnummat, and may tap peat N via aerenchyma‐facilitated peat oxidation (oxipeditrophy). Evergreen ericaceous shrubs exhibited significantly higher levels of percentage C and lower values of δ¹⁵N than mat nonericads.Calla palustris—growing in the nutrient‐rich moat at the bog's upland edge—had very high values of leaf N, K, δ¹⁵N, and N:P ratio, suggesting that it may obtain nutrients from minerotrophic flows from the adjacent uplands and/or rapidly decaying peat. Stoichiometric analyses indicated that most species are N limited. A mixing model applied to δ¹⁵N values for carnivores, noncarnivores, and insects produced an estimate of 50% of leaf N derived from prey forUtricularia, 42% forSarracenia, and 41% forDrosera. 

Abstract Winter annuals comprise a large fraction of warm-desert plant species, but the drivers of their diversity are little understood. One factor that has generally been overlooked is the lack of obvious means of long-distance seed dispersal in many desert-annual lineages, which could lead to genetic differentiation at small spatial scales and, ultimately, to speciation and narrow endemism. If our gene-flow hypothesis is correct, individual winter-annual species should have populations with genetic spatial structures implying short distances of gene flow. To test this idea, we sampled six populations of Eschscholzia parishii (Papaveraceae) in three pairs of watersheds within a 28-km radius in southern California. We quantified genetic diversity and structure and inferred the distance of gene flow in these populations using single nucleotide polymorphisms derived from genotyping-by-sequencing. Estimated distances of gene flow were quite small (σ = 10.4–14.9 m), with strong genetic structure observed within and between populations. Kinship declined steeply with ln distance (r2 = 0.85). Petal size and shape differed significantly between the northernmost and southernmost populations. These findings support the hypothesis that the high diversity of warm-desert winter annuals might result, in part, from genetic differentiation within species at small spatial scales driven by poor seed dispersal. 

Abstract Mycoheterotrophy is an alternative nutritional strategy whereby plants obtain sugars and other nutrients from soil fungi. Mycoheterotrophy and associated loss of photosynthesis have evolved repeatedly in plants, particularly in monocots. Although reductive evolution of plastomes in mycoheterotrophs is well documented, the dynamics of nuclear genome evolution remains largely unknown. Transcriptome datasets were generated from four mycoheterotrophs in three families (Orchidaceae, Burmanniaceae, Triuridaceae) and related green plants and used for phylogenomic analyses to resolve relationships among the mycoheterotrophs, their relatives, and representatives across the monocots. Phylogenetic trees based on 602 genes were mostly congruent with plastome phylogenies, except for an Asparagales + Liliales clade inferred in the nuclear trees. Reduction and loss of chlorophyll synthesis and photosynthetic gene expression and relaxation of purifying selection on retained genes were progressive, with greater loss in older nonphotosynthetic lineages. One hundred seventy-four of 1375 plant benchmark universally conserved orthologous genes were undetected in any mycoheterotroph transcriptome or the genome of the mycoheterotrophic orchid Gastrodia but were expressed in green relatives, providing evidence for massively convergent gene loss in nonphotosynthetic lineages. We designate this set of deleted or undetected genes Missing in Mycoheterotrophs (MIM). MIM genes encode not only mainly photosynthetic or plastid membrane proteins but also a diverse set of plastid processes, genes of unknown function, mitochondrial, and cellular processes. Transcription of a photosystem II gene (psb29) in all lineages implies a nonphotosynthetic function for this and other genes retained in mycoheterotrophs. Nonphotosynthetic plants enable novel insights into gene function as well as gene expression shifts, gene loss, and convergence in nuclear genomes.