Comparison between continuous grazing and rotational grazing on roller chopped rangeland in central-west of La Pampa province

El control de la vegetación leñosa y la planificación posterior del pastoreo contribuirían a aumentar la oferta forrajera y la producción ganadera en pastizales del centro-oeste de la Provincia de La Pampa. El objetivo del presente trabajo fue comparar la dinámica de la vegetación y la respuesta animal en un pastizal rolado sometido a pastoreo continuo o pastoreo rotativo. La mitad de un área rolada de 200 ha se pastoreo en forma continua con terneros de recría, mientras que la restante mitad se pastoreo en forma rotativa mediante la subdivisión en cuatro parcelas de igual tamaño. Durante cuatro años consecutivos se realizaron mediciones sobre la vegetación (herbácea y leñosa) y sobre los animales. En el periodo de mediciones las lluvias fueron similares o superaron (hasta en un 33%) el promedio anual histórico. Los tratamientos de pastoreo (continuo y rotativo) no afectaron en forma diferencial la densidad de las gramíneas perennes palatables ni la cobertura de la vegetación leñosa, mientras que la disponibilidad de MS total promedio de las gramíneas perennes palatables fue mayor bajo pastoreo rotativo. La ganancia diaria de peso promedio de los animales en recría fue mayor bajo pastoreo continuo en tres de los cuatro años de medición. En el contexto del presente estudio no se expresó el potencial esperado del pastoreo rotativo, lo cual se interpreta en relación a las lluvias y a una potencial desmejora de la calidad del forraje consumido por los animales.Woody vegetation control and further grazing planning would contribute to increase forage availability and livestock production in rangelands of central-west La Pampa Province. The objective of present study was to compare vegetation dynamics and animal response in a roller chopped rangeland under continuous or rotational grazing. Half of a roller chopped area of 200 ha was continuously grazed with stocker cattle, whereas the other half was rotationally grazed through its subdivision in four parcels of equal size. Vegetation (herbaceous, woody) and animal responses were measured along a period of four consecutive years. During the study period rainfall was similar or above (up to 33%) the long-term annual average. Grazing treatments (continuous, rotational) did not differentially affect either density of palatable perennial grasses or woody vegetation cover, whereas total average DM availability of palatable perennial grasses was higher under rotational grazing. Average daily gain of stockers was higher under continuous grazing on three out of the four years of measurements. The expected potential of rotation grazing was not expressed under the context of present study, which is interpreted in relation to rainfall conditions and a potential deterioration in forage quality ingested by animals.Fil: Adema, E. O.. Instituto Nacional de Tecnología Agropecuaria. Centro Regional La Pampa-San Luis. Estación Experimental Agropecuaria Anguil; ArgentinaFil: Butti, L. R.. Instituto Nacional de Tecnología Agropecuaria. Centro Regional La Pampa-San Luis. Estación Experimental Agropecuaria Anguil; ArgentinaFil: Babinec, Francisco José. Instituto Nacional de Tecnología Agropecuaria. Centro Regional La Pampa-San Luis. Estación Experimental Agropecuaria Anguil; Argentina. Universidad Nacional de La Pampa. Facultad de Agronomía; ArgentinaFil: Distel, Roberto Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiarida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiarida; Argentin

Composition and Function of a Novel Consortial Endosymbiosis in the Shipworm Lyrodus pedicellatus

Enormous quantities of wood and other woody plant materials(including leaves, bark, shoots, stems and nuts) are produced annually inthe environment. In fact, cellulose, the major component of woodymaterials, is thought to be the most abundant biological material on earth.This remarkably strong and enduring molecule is a polymer of glucose(sugar) linked by a type of chemical bond that makes it indigestible tomost living organisms. Therefore, this rich source of food energy isavailable to only a few animals (e.g., termites and ruminants) that candigest cellulose with the aid of microbes living in their guts.Surprisingly, some marine animals can also digest wood. The mostimportant group is the wood-boring clams, commonly known as shipworms. Unlike termites and ruminants, these animals lack microorganisms in their gut.Instead they harbor enormous numbers of symbiotic bacteria inside the cellsof their gills. These bacteria fall into at least four closely relatedfamilies based on DNA analyses. The PIs have proposed that these bacteriaproduce cellulolytic enzymes that are transported from the gills to thegut. The purpose of this investigation is to explore the diversity anddistribution of symbiont types in the shipworm gills, to determine if eachsymbiont type contributes different cellulolytic enzymes, and to discoverhow the host uses these bacterial products to exploit cellulose as a foodsource. These investigations should result in the discovery of newcellulolytic enzymes that may have industrial applications in such areas aspaper and textile processing and fuel (ethanol) production via biomassconversion of agricultural wastes. These efforts will also help the PIs tounderstand the physiology of symbiotic bacterial infections that arebeneficial rather than harmful to their hosts

Collaborative Research: Functional and Genomic Analysis of Polysymbiosis in the Wood-boring Bivalve Lyrodus pedicellatus

Each day massive quantities of wood and woody plant materials enter the oceans, providing resources upon which a large variety of marine organisms depend. However, the biological communities supported by marine wood are only poorly understood. Globally, the most important consumers of marine wood are wood-boring bivalves of the family Teredinidae (shipworms, primarily found above 150 m) and Pholadidae (subfamily Xylophagainae, primarily found in the deep sea, 150-8000 m). These clams depend on intracellular endosymbiotic bacteria (endocytobionts) to help them consume a substrate (lignocellulose) that cannot be utilized by most other animals. Two functions have been proposed for symbionts of wood-boring bivalves; 1) production of enzymes to facilitate lignocellulose digestion (xylotrophy) and 2) nitrogen fixation (diazotrophy) to supplement the host.s nitrogen-deficient diet. The purpose of the proposed research is to explore the physiological ecology of symbiotic xylotrophy in shipworms using molecular, biochemical and microbiological techniques. Three questions are foremost in this investigation; 1) What genetic variation occurs in symbiont populations within and between host species? 2) What is the quantitative contribution of symbionts to lignocellulose digestion and nitrogen fixation? and 3) What physical and biochemical mechanisms are involved in transfer of nutrients and enzymes between host and symbiont compartments

An Investigation of the Evolution of Autotrophic Endosymbioses in Bivalves By Comparative Molecular Phylogenetic Analysis of Host and Symbiont rRNA Sequences

Symbiotic associations between animals and bacteria are extremely diverse and commonplace in nature. In fact, it is difficult to find examples of animal species whose existence is not profoundly influenced by symbiotic associations with bacteria. For example, mitochondria (the structures within human cells that generate the energy for metabolic processes) are thought to have arisen from ancient bacteria that long ago formed a symbiotic association with the ancestor of all living animals. The support provided for this project will allow investigation of a type of symbiosis commonly found in clams and worms from deep-sea hydrothermal vents (marine hot springs) that can be used as a model system for studying the questions of how bacterial symbioses become established and what role they may play in the creation of new animal and bacterial species. This will be accomplished by comparing the primary DNA sequence (genetic code) of genes which are found in both symbionts and hosts. Computer analysis will be used to generate family trees demonstrating the relationships among symbionts and hosts. Comparison of the branching patterns of host and symbiont trees should reveal the point(s) in the lineages these hosts and symbionts first became associated and what impact their association has had on the diversification of the partner species. This understanding will lay the historical and conceptual foundation upon which future studies of the physiology and ecology of animal bacterial associations will be built. Symbiotic associations ranging from enteric bacteria in the human gut to nitrogen fixing bacteria associated with plant roots or luminous light organs in deep-sea fish provide a broad range of benefits to their hosts. Consequently, symbioses between bacteria and animals are critically important to our ecosystems, agriculture and health. This study will provide an experimental model system to address major questions about how bacterial/host symbioses came to exist and what role they have played in the history of life on earth

Collaborative Research: Toward Environmental Genomics: Can We Estimate Bacterial Diversity in the Ocean?

Environmental genomics, wherein the total genomic diversity of a natural community may be sampled and analyzed in an ecological context, remains an elusive goal. This is due, at least in part, to (I) a lack of reliable estimates of total community diversity and (II) a lack of information regarding the exact phylogenetic, genomic and ecological units measured by commonly used diversity estimators. Although ribosomal RNA approaches have provided the first steps towards diversity estimation, and are widely used as a proxy for unique bacterial types in natural populations, the genomic unit a ribotype measures remains largely unexplored. It is generally believed that ribotype is a poor indicator of ecotype because its slow molecular clock does not track many other genomic changes that are significant with respect to physiological functions and ecological roles. Further, there are reasons to believe microbes in typical natural environments encounter forces much different from those that shape genome evolution among the cultivated opportunists and pathogens that predominate in genomic studies. This project is using an approach that will allow the systematic sampling of environmental genomes by capturing large gene fragments anchored to ribosomal genes (the current standard biomarker for diversity estimation) as well as methods by which this approach can be extended to reassembling larger genome regions of uncultivated bacteria. The goals of this investigation are: 1) to estimate total ribotype diversity in a coastal marine environment taking into account new developments in understanding of PCR artifacts and new statistical approaches toward estimating sampling coverage, 2) to explore the relationship of ribotype diversity to genome diversity by sampling sequences contiguous to rRNA genes in abundant ribotypes, 3) to explore the mechanisms that may contribute to shaping genomes in natural communities, and 4) to continue development of methods to automate and extend the reach of genomic research in natural communities. This research will provide (I) boundaries for bacterial diversity estimates in the environment and (II) insights into how processes that are important in shaping the structure and dynamics of microbial communities may also be influential in shaping the evolution of microbial genomes

Evolution of Endosymbiosis in (xylotrophic) Wood-Eating Bivalves

A grant has been awarded to Dr. Daniel L. Distel of the University of Maine to investigate the evolution of wood-boring clams. Though not well known to the general public, wood-boring clams are destructive species that may be considered the marine equivalent of termites. They include many diverse species that cause more than a billion dollars in damage to wooden structures, boats, and fishing gear annually in marine environments worldwide. The most destructive of these are the shipworms ; worm-like clams that burrow into and eat wood. These voracious wood eaters can destroy a twelve-inch diameter pier piling in less than one year\u27s time. Though they look like worms, molecular evidence suggests that they are closely related to the common steamer clam , a staple of New England cuisine. The purpose of this investigation is to use molecular data from several genes to reveal the evolutionary relationships of wood boring clams to other more common bivalves and to use these data to better understand how their destructive habits have evolved, including the role of associated bacteria.Although wood can be treated with broad-spectrum chemical biocides to control wood-borer damage, use of the most effective treatments has recently been restricted or banned in many states and nations due to environmental concerns. New environmentally sound control methods are critically needed, particularly in low-income coastal communities where wood is the only affordable marine construction material. Such control measures must be targeted specifically to wood-boring species to minimize ecological impact. Evolutionary studies will tell us how these nuisance species developed the ability to destroy wood and what makes them different from other more desirable and economically important marine species. This knowledge will be essential for developing control methods that are safe and highly specific to these destructive organisms

The Impact of Chronic Stress on Childhood Obesity and the Protective Effects of Parental Warmth

Mexican American children have the highest rates of obesity in the U.S. Mexican American children may experience chronic stress, which has been linked to child obesity. Hair cortisol accumulation has been implicated as a mechanism for this association. Highly sensitive parenting may buffer the harmful effects of chronic stress and hair cortisol on obesity. Thus, the aims of this project were to 1) identify the direct and indirect effects of chronic stress and hair cortisol on children\u27s zBMI and 2) examine the protective effects of parental warmth. This study examined hair cortisol levels, zBMI and chronic stress of children ages 6-10 from low-income Mexican-origin families. Parental warmth was assessed through video-taped family interactions and parent self-report. Chronic stress and hair cortisol levels were not associated, however, hair cortisol was positively related to child zBMI. Parental warmth moderated the relation between chronic stress and zBMI. Clinical and research implications are discussed

A hypothetico-deductive approach to assessing the social function of chemical signalling in a non-territorial solitary carnivore

The function of chemical signalling in non-territorial solitary carnivores is still relatively unclear. Studies on territorial solitary and social carnivores have highlighted odour capability and utility, however the social function of chemical signalling in wild carnivore populations operating dominance hierarchy social systems has received little attention. We monitored scent marking and investigatory behaviour of wild brown bears Ursus arctos, to test multiple hypotheses relating to the social function of chemical signalling. Camera traps were stationed facing bear ‘marking trees’ to document behaviour by different age sex classes in different seasons. We found evidence to support the hypothesis that adult males utilise chemical signalling to communicate dominance to other males throughout the non-denning period. Adult females did not appear to utilise marking trees to advertise oestrous state during the breeding season. The function of marking by subadult bears is somewhat unclear, but may be related to the behaviour of adult males. Subadults investigated trees more often than they scent marked during the breeding season, which could be a result of an increased risk from adult males. Females with young showed an increase in marking and investigation of trees outside of the breeding season. We propose the hypothesis that females engage their dependent young with marking trees from a young age, at a relatively ‘safe’ time of year. Memory, experience, and learning at a young age, may all contribute towards odour capabilities in adult bears

Ecological succession of a Jurassic shallow-water ichthyosaur fall.

After the discovery of whale fall communities in modern oceans, it has been hypothesized that during the Mesozoic the carcasses of marine reptiles created similar habitats supporting long-lived and specialized animal communities. Here, we report a fully documented ichthyosaur fall community, from a Late Jurassic shelf setting, and reconstruct the ecological succession of its micro- and macrofauna. The early 'mobile-scavenger' and 'enrichment-opportunist' stages were not succeeded by a 'sulphophilic stage' characterized by chemosynthetic molluscs, but instead the bones were colonized by microbial mats that attracted echinoids and other mat-grazing invertebrates. Abundant cemented suspension feeders indicate a well-developed 'reef stage' with prolonged exposure and colonization of the bones prior to final burial, unlike in modern whale falls where organisms such as the ubiquitous bone-eating worm Osedax rapidly destroy the skeleton. Shallow-water ichthyosaur falls thus fulfilled similar ecological roles to shallow whale falls, and did not support specialized chemosynthetic communities