Diversity2014, 6(4), 751-770; doi:10.3390/d6040751 (registering DOI) - published 26 November 2014 Show/Hide Abstract
Abstract: Understanding the individual and interactive roles of consumer species is more than academic when the host plant is a subject of intense conservation interest. In a mesocosm experiment, we compared effects of common invertebrate grazers in San Francisco Bay seagrass (Zostera marina, eelgrass) beds, finding that some species (a native opisthobranch, Phyllaplysia taylori; a native isopod, Idotea resecata; and an introduced gastropod, Ilyanassa obsoleta) enhanced eelgrass growth through removal of epiphytic algae, as is often predicted for small invertebrate grazers on seagrasses, while one (an introduced caprellid amphipod, Caprella cf. drepanochir) had neutral effects. In contrast, the putatively-introduced gammaridean amphipod, Ampithoe valida, had strong negative effects on eelgrass (in addition to epiphytes) through consumption, as we had previously observed in the field during restoration programs. We tested whether other common grazer species could influence the effects of the eelgrass-grazing Ampithoe, and found that Idotea induced production of phenolic compounds and limited eelgrass damage by Ampithoe, without affecting Ampithoe abundance. These results have implications for restoration strategies, and contribute to a growing awareness of the importance of trait-mediated indirect grazer interactions through grazer-induced changes in plant traits, providing the first example in a seagrass system.
Diversity2014, 6(4), 705-750; doi:10.3390/d6040705 - published 12 November 2014 Show/Hide Abstract
Abstract: Cattle are our most important livestock species because of their production and role in human culture. Many breeds that differ in appearance, performance and environmental adaptation are kept on all inhabited continents, but the historic origin of the diverse phenotypes is not always clear. We give an account of the history of cattle by integrating archaeological record and pictorial or written sources, scarce until 300 years ago, with the recent contributions of DNA analysis. We describe the domestication of their wild ancestor, migrations to eventually all inhabited continents, the developments during prehistory, the antiquity and the Middle Ages, the relatively recent breed formation, the industrial cattle husbandry in the Old and New World and the current efforts to preserve the cattle genetic resources. Surveying the available information, we propose three main and overlapping phases during the development of the present genetic diversity: (i) domestication and subsequent wild introgression; (ii) natural adaptation to a diverse agricultural habitat; and (iii) breed development.
Diversity2014, 6(4), 681-704; doi:10.3390/d6040681 - published 6 November 2014 Show/Hide Abstract
Abstract: Biological invasions of aquatic systems disrupt ecological communities, and cause major changes in diversity and ecosystem function. The Laurentian Great Lakes of North America have been dramatically altered by such invasions, especially zebra (Dreissena polymorpha) and quagga (D. rostriformis bugensis) mussels. Responses to mussel invasions have included increased water clarity, and decreased chlorophyll and phytoplankton abundance. Although not all systems have responded similarly, in general, mussels have changed nutrient dynamics and physical habitat conditions. Therefore examination of different impacts can help us further understand mechanisms that underlie ecosystem responses to biological invasions. To aid our understanding of ecosystem impacts, we sampled established locations along a well-studied trophic gradient in Green Bay, Lake Michigan, after the 1993 zebra mussel invasion. A strong trophic gradient remained during the period sampled after the mussel invasion (2000–2012). However, mean summer chlorophyll increased and other measures of phytoplankton biomass (microscope and electronic cell counting) did not change significantly. Multivariate analyses of phytoplankton community structure demonstrate a significant community shift after the invasion. Cyanobacteria increased in dominance, with Microcystis becoming the major summer taxon in lower Green Bay. Diatom diversity and abundance also increased and Chlorophyta became rare. Phytoplankton responses along the trophic gradient of Green Bay to zebra mussel invasion highlight the importance of mussel effects on nutrient dynamics and phytoplankton diversity and function.
Diversity2014, 6(4), 665-680; doi:10.3390/d6040665 - published 20 October 2014 Show/Hide Abstract
Abstract: Genotyping-by-sequencing (GBS) has recently emerged as a promising genomic approach for exploring plant genetic diversity on a genome-wide scale. However, many uncertainties and challenges remain in the application of GBS, particularly in non-model species. Here, we present a GBS protocol we developed and use for plant genetic diversity analysis. It uses two restriction enzymes to reduce genome complexity, applies Illumina multiplexing indexes for barcoding and has a custom bioinformatics pipeline for genotyping. This genetic diversity-focused GBS (gd-GBS) protocol can serve as an easy-to-follow lab guide to assist a researcher through every step of a GBS application with five main components: sample preparation, library assembly, sequencing, SNP calling and diversity analysis. Specifically, in this presentation, we provide a brief overview of the GBS approach, describe the gd-GBS procedures, illustrate it with an application to analyze genetic diversity in 20 flax (Linum usitatissimum L.) accessions and discuss related issues in GBS application. Following these lab bench procedures and using the custom bioinformatics pipeline, one could generate genome-wide SNP genotype data for a conventional genetic diversity analysis of a non-model plant species.
Diversity2014, 6(4), 652-664; doi:10.3390/d6040652 - published 15 October 2014 Show/Hide Abstract
Abstract: Chinese privet (Ligustrum sinense) was the most prevalent invasive shrub in the forestlands of Eastern Texas in 2006. We analyzed extensive field data collected by the Forest Inventory and Analysis Program of the U.S. Forest Service to quantify the range expansion of Chinese privet from 2006 to 2011. Our results indicated the presence of Chinese privet on sampled plots increased during this period. Chinese privet spread extensively in the north. Results of logistic regression, which classified 73% of the field plots correctly with regard to species presence and absence, indicated probability of invasion was correlated positively with elevation, adjacency (within 300 m) to water bodies, and site productivity, and was correlated negatively with stand age, site preparation (including clearing, slash burning, chopping, disking, bedding, and other practices clearly intended to prepare a site for regeneration), artificial regeneration (which refers to planting or direct seeding that results in at least 50% of the stand being comprised of stocked trees), and distance to the nearest road. Habitats most at risk to further invasion (likelihood of invasion > 40%) under current conditions occurred primarily in Northeast Texas. Practicing site preparation and artificial regeneration reduced the estimated probabilities of further invasion.
Diversity2014, 6(4), 633-651; doi:10.3390/d6040633 - published 29 September 2014 Show/Hide Abstract
Abstract: The Salix alba L. (white willow)—Salix fragilis L. (crack willow) complex includes closely related polyploid species, mainly tetraploid (2n= 4x= 76), which are dioecious and hence obligate allogamous. Because little is known about the genome constitution and chromosome behavior of these pure willow trees, genetic analysis of their naturally occurring interspecific polyploid hybrids is still very difficult. A two-way pseudo-testcross strategy was exploited using single-dose AFLP markers in order to assess the main inheritance patterns of tetraploid biotypes (disomy vs. tetrasomy) in segregating populations stemmed from S. alba × S. fragilis crosses and reciprocals. In addition, a genomic in situ hybridization (GISH) technology was implemented in willow to shed some light on the genome structure of S. alba and S. fragilis species, and their hybrids (allopolyploidy vs. autopolyploidy). The frequency of S. alba-specific molecular markers was almost double compared to that of S. fragilis-specific ones, suggesting the phylogenetic hypothesis of S. fragilis as derivative species from S. alba-like progenitors. Cytogenetic observations at pro-metaphase revealed about half of the chromosome complements being less contracted than the remaining ones, supporting an allopolyploid origin of both S. alba and S. fragilis. Both genetic segregation and genomic hybridization data are consistent with an allotetraploid nature of the Salix species. In particular, the vast majority of the AFLP markers were inherited according to disomic patterns in S. alba × S. fragilis populations and reciprocals. Moreover, in all S. alba against S. fragilis hybridizations and reciprocals, GISH signals were observed only on the contracted chromosomes whereas the non-contracted chromosomes were never hybridized. In conclusion, half of the chromosomes of the pure species S. alba and S. fragilis are closely related and they could share a common diploid ancestor, while the rest of chromosomes are morphologically differentiated in either S. alba or S. fragilis and they should derive from distinct diploid ancestors.