Limited information is available on the presence of microplastics in freshwater systems, and even less is known about the toxicological implications of the exposure of aquatic organisms to plastic particles. The present study was conducted to evaluate the effects of microplastic ingestion on the freshwater amphipod, Hyalella azteca. Hyalella azteca was exposed to fluorescent polyethylene microplastic particles and polypropylene microplastic fibers in individual 250-mL chambers to determine 10-d mortality. In acute bioassays, polypropylene microplastic fibers were significantly more toxic than polyethylene microplastic particles; 10-d lethal concentration 50% values for polyethylene microplastic particles and polypropylene microplastic fibers were 4.64 × 10(4) microplastics/mL and 71.43 microplastics/mL, respectively. A 42-d chronic bioassay using polyethylene microplastic particles was conducted to quantify effects on reproduction, growth, and egestion. Chronic exposure to polyethylene microplastic particles significantly decreased growth and reproduction at the low and intermediate exposure concentrations. During acute exposures to polyethylene microplastic particles, the egestion times did not significantly differ from the egestion of normal food materials in the control; egestion times for polypropylene microplastic fibers were significantly slower than the egestion of food materials in the control. Amphipods exposed to polypropylene microplastic fibers also had significantly less growth. The greater toxicity of microplastic fibers than microplastic particles corresponded with longer residence times for the fibers in the gut. The difference in residence time might have affected the ability to process food, resulting in an energetic effect reflected in sublethal endpoints.

With high productivity and stress tolerance, numerous grass genera of the Andropogoneae have emerged as candidates for bioenergy production. To optimize these candidates, research examining the genetic architecture of yield, carbon partitioning, and composition is required to advance breeding objectives. Significant progress has been made developing genetic and genomic resources for Andropogoneae, and advances in comparative and computational genomics have enabled research examining the genetic basis of photosynthesis, carbon partitioning, composition, and sink strength. To provide a pivotal resource aimed at developing a comparative understanding of key bioenergy traits in the Andropogoneae, we have established and characterized an association panel of 390 racially, geographically, and phenotypically diverse Sorghum bicolor accessions with 232,303 genetic markers. Sorghum bicolor was selected because of its genomic simplicity, phenotypic diversity, significant genomic tools, and its agricultural productivity and resilience. We have demonstrated the value of sorghum as a functional model for candidate gene discovery for bioenergy Andropogoneae by performing genome-wide association analysis for two contrasting phenotypes representing key components of structural and non-structural carbohydrates. We identified potential genes, including a cellulase enzyme and a vacuolar transporter, associated with increased non-structural carbohydrates that could lead to bioenergy sorghum improvement. Although our analysis identified genes with potentially clear functions, other candidates did not have assigned functions, suggesting novel molecular mechanisms for carbon partitioning traits. These results, combined with our characterization of phenotypic and genetic diversity and the public accessibility of each accession and genomic data, demonstrate the value of this resource and provide a foundation for future improvement of sorghum and related grasses for bioenergy production.

Environmental pressures may vary over the geographic range of a species, exposing subpopulations to divergent functional demands. How does exposure to competing demands shape the morphology of species and influence the divergence of populations? We explored these questions by performing selection experiments on juveniles of the Hawaiian goby Sicyopterus stimpsoni, an amphidromous fish that exhibits morphological differences across portions of its geographic range where different environmental pressures predominate. Juvenile S. stimpsoni face two primary and potentially opposing selective pressures on body shape as they return from the ocean to freshwater streams on islands: (1) avoiding predators in the lower reaches of a stream; and (2) climbing waterfalls to reach the habitats occupied by adults. These pressures differ in importance across the Hawaiian Islands. On the youngest island, Hawai'i, waterfalls are close to shore, thereby minimizing exposure to predators and placing a premium on climbing performance. In contrast, on the oldest major island, Kaua'i, waterfalls have eroded further inland, lengthening the exposure of juveniles to predators before migrating juveniles begin climbing. Both juvenile and adult fish show differences in body shape between these islands that would be predicted to improve evasion of predators by fish from Kaua'i (e.g., taller bodies that improve thrust) and climbing performance for fish from Hawai'i (e.g., narrower bodies that reduce drag), matching the prevailing environmental demand on each island. To evaluate how competing selection pressures and functional tradeoffs contribute to the divergence in body shape observed in S. stimpsoni, we compared selection imposed on juvenile body shape by (1) predation by the native fish Eleotris sandwicensis versus (2) climbing an artificial waterfall (∼100 body lengths). Some variables showed opposing patterns of selection that matched predictions: for example, survivors of predation had lower fineness ratios than did control fish (i.e., greater body depth for a given length), whereas successful climbers had higher fineness ratios (reducing drag) than did fish that failed. However, most morphological variables showed significant selection in only one treatment rather than opposing selection across both. Thus, functional tradeoffs between evasion of predators and minimizing drag during climbing might influence divergence in body shape across subpopulations, but even when selection is an important contributing mechanism, directly opposite patterns of selection across environmental demands are not required to generate morphological divergence.

No abstract

The increased need for intestinal absorption of unsaturated fatty acids in cattle is driven mainly by nutritional guidelines that promote reduced intake of saturated fatty acids by humans, and by reports of enhanced animal performance (such as reproductive performance) when additional essential fatty acids are supplied. A duodenal flow dataset was compiled from 25 published studies that provided up to 93 observations on fatty acid intakes and ruminal outflows across a multitude of unprotected and protected fat sources. Control diets with no added fat and diets containing unprotected fat sources had similar and predictable ruminal losses of unsaturated fatty acids (86% for linolenic and oleic acids, and 82% for linoleic acids). Rumen protection technologies that have emerged over the years involve either encapsulation of unsaturated fatty acids inside a microbial-resistant shell (such as formaldehyde-treated or lipid encapsulated), or alteration of fatty acid structure (such as calcium salts or fatty amides) to resist action of microbial enzymes. Calcium salts of fatty acids, because they are available commercially, comprised the majority of observations in the duodenal flow dataset. Meta-analysis of the duodenal dataset that included random study effects revealed only a few instances where protected fat sources gave ruminal losses of polyunsaturated fatty acids that were appreciably lower than what was seen for unprotected fats. Future challenges include enhancing protection characteristics of existing rumen-protected fat sources, and development and commercialization of novel protection strategies.

The seed oil concentrations of large‐seeded, low‐oil and small‐seeded, high‐oil sunflower (Helianthus annuus L.; x = 17) cultivars differ by 180 to 280 g kg−1 We identified quantitative trait loci (QTL) for seed oil and other seed traits in a low‐ × high‐oil (RHA280 × RHA801) recombinant inbred line (RIL) mapping population segregating for apical branching (B), phytomelanin pigment (P), and hypodermal pigment (Hyp) loci. B, Hyp, and P mapped to linkage groups 10, 16, and 17, respectively. The seed oil concentrations of RHA280 and RHA801 were 254 and 481 g kg−1, respectively. Composite interval mapping (CIM) identified 40 QTL for seed oil concentration, 100‐seed weight, seed length, width and depth, kernel and pericarp weight, and kernel‐to‐pericarp weight ratio in 14 DNA marker intervals on 10 of 17 linkage groups. Twenty‐four of the QTL were tightly linked to B, P, and Hyp and may have been partly or wholly caused by the pleiotropic effects of B, P, and Hyp Multilocus QTL analyses were performed using B, P, Hyp, and four DNA marker loci as independent variables in mixed linear models. Seventy percent of the additive effects (39/56) and 42% of the additive × additive and additive × additive × additive effects (189/448) were significant (p < 0.05). The linked, pleiotropically acting, and epistatically interacting QTL identified for seed traits in RHA280 × RHA801 were presumably targeted by selection in the transition from large‐seeded, low‐oil to small‐seeded, high‐oil cultivars in sunflower.

No abstract

Abstract. Plants possessing generalized dispersal syndromes are likely to be more invasive than those relying on specialist dispersal agents. To address this issue on a local and regional scale, avian seed dispersal of the invasive alien Chinese tallow tree (Sapium sebiferum (L.) Roxb.) was assessed in forests and spoil areas of South Carolina and along forest edges in Louisiana during the 1997–99 fruiting seasons. Tallow trees in these floristically distinct habitats had a few common and many casual visitors, and considerable species overlap among habitats was found. However, bird species differed in the importance of dispersing and dropping seeds among habitats. Important dispersal agents common to forests and spoil areas of South Carolina included Northern Flicker, American Robin and Red‐winged Blackbird, whereas Red‐bellied Woodpecker and European Starling were important in the former and latter habitat, respectively. In Louisiana, Red‐bellied Woodpecker, American Robin, Northern Cardinal and Eastern Bluebird dispersed many seeds. Nearly all species foraging on seeds were winter residents. Estimated numbers of seeds dispersed and dropped were higher in spoil areas of South Carolina than in Louisiana because of higher numbers of individuals per visit, higher seed consumption and seed dropping rates, and longer foraging durations. Within South Carolina, more seeds were dispersed and dropped in spoil areas than in forests because of higher numbers of birds per visit. These findings show that among habitats, tallow tree attracts diverse but variable coteries of dispersal agents that are qualitatively similar in seed usage patterns. We suggest that its generalized dispersal syndrome contributes to effective seed dispersal by many bird species throughout its range. Effects of differential avian use among locales may include changes in local bird communities, and differing tallow tree demographics and invasion patterns.