Clayton J Visger

California State University, Sacramento | CSUS · Department of Biological Sciences

Nearly four decades ago, Roose & Gottlieb (Roose & Gottlieb 1976 Evolution 30, 818-830. (doi:10.2307/2407821)) showed that the recently derived allotetraploids Tragopogon mirus and T. miscellus combined the allozyme profiles of their diploid parents (T. dubius and T. porrifolius, and T. dubius and T. pratensis, respectively). This classic paper add...

Polyploidy has long been considered a major force in plant evolution. G. Ledyard Stebbins, Jr., an architect of the Modern Synthesis, elegantly addressed a broad range of topics, from genes to chromosomes to deep phylogeny, but some of his most lasting insights came in the study of polyploidy. Here, we review the immense impact of his work on polyp...

• Whereas population genetic studies have examined allopolyploids, comparable studies of naturally occurring autopolyploids remain rare. To address fundamental questions regarding autopolyploidy, we undertook a detailed population genetic study of one of the classic examples of autopolyploidy, Galax urceolata (Diapensiaceae), which comprises diploi...

Premise of the Study Studies of gene expression and polyploidy are typically restricted to characterizing differences in transcript concentration. Using diploid and autotetraploid Tolmiea, we present an integrated approach for cross‐ploidy comparisons that account for differences in transcriptome size and cell density and make multiple comparisons...

Premise of study: Polyploidy is common in eukaryotes and is of major evolutionary importance over both short and long time-scales. Compared to allopolyploids, autopolyploids remain understudied; they are often morphologically cryptic and frequently remain taxonomically unrecognized, although there is increasing recognition of the high frequency of...

Conservation actions for rare species are often based on estimates of population size and number, which are challenging to capture in natural systems. Instead, many definitions of populations rely on arbitrarily defined distances between occurrences, which is not necessarily biologically meaningful despite having utility from a conservation managem...

Taxa with geographically disjunct distributions and that are endemic or narrowly endemic face the real and immediate threat of local extinction because of inbreeding depression, genetic drift, and environmental stochasticity. These threats are amplified by the predicted changes in climate anticipated within the next 50 years, pointing to the increa...

Bisphenol A (BPA) is an environmentally prevalent endocrine disrupting chemical that can impact human health and may be an environmental risk factor for neurodevelopmental disorders. BPA has been associated with behavioral impairment in children and a variety of neurodevelopmental phenotypes in model organisms. We used Drosophila melanogaster to ex...

The calcareous glades and barrens of the southeastern United States, often referred to as ‘cedar glades,’ comprise a diverse and unique flora. Many of the plant species in these communities are threatened or endangered. The highest concentration of limestone cedar glades lies in the Central Basin of Middle Tennessee, where these habitats are highly...

Elucidating the dynamic distribution of organismal lineages has been central to biology since the nineteenth century, yet the difficulty of combining biogeographic methods with shifts in habitat suitability remains a limitation. This integration, however, is critical to understanding geographic distributions, present and past, as well as the time-e...

Studies of gene expression and polyploidy are typically restricted to characterizing differences in transcript concentration. Integrating multiple methods of transcript analysis, we document a difference in transcriptome size, and make multiple comparisons of transcript abundance in diploid and autotetraploid Tolmiea . We use RNA spike-in standards...

Factors explaining global distribution patterns have been central to biology since the 19th century, yet failure to combine dispersal-based biogeography with shifts in habitat suitability remains a present-day setback in understanding geographic distributions present and past, and time-extended trajectories of lineages. The lack of methods in a sui...

Diploid organisms have two complete sets of chromosomes. Polyploidy, often referred to now as whole genome duplication or doubling (WGD), is defined as the presence of three or more complete chromosome sets in an organism. This definition has a long history, tracing to the early 1900s, when researchers first observed the formation of a higher chrom...

Investigators have long searched for a polyploidy paradigm-rules or principles that might be common following polyploidization (whole-genome duplication, WGD). Here we attempt to integrate what is known across the more thoroughly investigated polyploid systems on topics ranging from genetics to ecology. We found that while certain rules may govern...

Premise of the study: The Campanulaceae are a diverse clade of flowering plants encompassing more than 2300 species in myriad habitats from tropical rainforests to arctic tundra. A robust, multigene phylogeny, including all major lineages, is presented to provide a broad, evolutionary perspective of this cosmopolitan clade. Methods: We used a ph...

At the intersection of geological activity, climatic fluctuations, and human pressure, the Mediterranean Basin – a hotspot of biodiversity – provides an ideal setting for studying endemism, evolution, and biogeography. Here, we focus on the Roucela complex (Campanula subgenus Roucela), a group of 13 bellflower species found primarily in the eastern...

Figure S6. Results from diversification analyses.

Figure S1. Sample accessions.

Figure S2. Plastid, Nuclear, and Combined Trees.

Figure S4. Summary statistics for BioGeoBEARS models from three separate analyses.

Figure S3. Beast Chronogram for Campanuloideae.

Figure S5. Chronogram inferred using a multispecies coalescent approach (*BEAST).

Isolated oceanic islands are characterized by patterns of biological diversity different from that on nearby continental mainlands. Isolation can provide the opportunity for evolutionary divergence, but also set the stage for hybridization between related taxa arriving from different sources. Ferns disperse by haploid spores, which are produced in...

Ferns are one of the few remaining major clades of land plants for which a complete genome sequence is lacking. Knowledge of genome space in ferns will enable broad-scale comparative analyses of land plant genes and genomes, provide insights into genome evolution across green plants, and shed light on genetic and genomic features that characterize...

Tragopogon includes two classic examples of recently formed allopolyploid species in North America: T. mirus and T. miscellus . Older Tragopogon allotetraploids from Eurasia offer ideal taxa for comparing the longer term outcomes of allopolyploidy. To help resolve the ancestry of one of these older polyploids, phylogenetic analyses of multiple popu...