Reverberating effects of resource exchanges in stream-riparian food webs.

Fluxes of materials or organisms across ecological boundaries, often termed "resource subsidies," directly affect recipient food webs. Few studies have addressed how such direct responses in one ecosystem may, in turn, influence the fluxes of materials or organisms to other habitats or the potential for feedback relationships to occur among ecosystems. As part of a large-scale, multi-year experiment, we evaluated the hypothesis that the input of a marine-derived subsidy results in a complex array of resource exchanges (i.e., inputs, outputs, feedbacks) between stream and riparian ecosystems as responses disperse across ecological boundaries. Moreover, we evaluated how the physical properties of resource subsidies mediated complex responses by contrasting carcasses with a pelletized salmon treatment. We found that salmon carcasses altered stream-riparian food webs by directly subsidizing multiple aquatic and terrestrial organisms (e.g., benthic insect larvae, fishes, and terrestrial flies). Such responses further influenced food webs along indirect pathways, some of which spanned land and water (e.g., subsidized fishes reduced aquatic insect emergence, with consequences for spiders and bats). Subsidy-mediated feedbacks manifested when carcasses were removed to riparian habitats where they were colonized by carrion flies, some of which fell into the stream and acted as another prey subsidy for fishes. As the effects of salmon subsidies propagated through the stream-riparian food web, the sign of consumer responses was not always positive and appeared to be determined by the outcome of trophic interactions, such that localized trophic interactions within one ecosystem mediated the export of organisms to others.

Extrinsic vs. intrinsic food shortage and the strength of feeding links: effects of density and food availability on feeding rate of Hyphydrus ovatus.

We use field and laboratory experiments to determine whether Hyphydrus ovatus, a predatory aquatic beetle, is food limited, and whether any food shortage results from depletion of prey by these predators (intrinsic food shortage) or is independent of predation by these beetles (extrinsic food shortage). In the laboratory, differences in feeding rate influence body fat content, thus making fat content a useful index of recent feeding history. H. ovatus collected during the breeding season have fat contents significantly greater than those of H. ovatus starved for 25 days, but not significantly different from those of H. ovatus fed ad libitum for 25 days, indicating that natural feeding rates are near the maximum possible. H. ovatus confined at a density 60 times greater than natural show reduced fat content and feeding rate relative to natural, indicating that at very high densities H. ovatus is capable of depleting its prey. Addition of supplemental natural prey (primarily Cladocera) to experimental enclosures resulted in an order of magnitude increase in prey availability, and a significant increase in fat content and feeding rate of confined H. ovatus. Adults of this species do not appear to be food limited during the breeding season, and extraordinarily high densities of adults seem to be necessary to produce intrinsic food shortage. These results suggest that feeding links between H. ovatus an its principal prey do not have major effects on population dynamics under typical field conditions, and call into question the assumption that closely coupled predator-prey interactions are the sole explanation for observed food-web patterns.

Paraparesia espástica por HTLV-I: 20 años después. A propósito de un caso / Spastic paraparesis by HTLV-I: 20 years later. About a case / Paraparesia espástica pelo HTLV-I: 20 anos depois. Sobre um caso

Resumen: Se describe un caso de paraparesia espástica asociada al retrovirus HTLV-I, en una paciente de 34 años, cuyo diagnóstico se realizó 17 años después del inicio de su enfermedad. El mismo se obtuvo mediante la determinación de anticuerpos en sangre y líquido cefalorraquídeo. En la literatura nacional existen solo dos casos publicados previamente. El objetivo de la presentación del caso es recordar las principales características epidemiológicas, clínicas y paraclínicas de dicha patología, así como restablecer la importancia de considerar al HTLV-Ia la hora de búsqueda etiológica de una mielopatía crónica, y mantener los controles en sangre de donantes y hemoderivados para eliminar una de las principales vías de contagio.

Abstract: A case of spastic paraparesis associated with HTLV-I retrovirus was described in a 34-year-old patient whose diagnosis was made 17 years after the onset of his disease. It was obtained by determining antibodies in blood and cerebrospinal fluid. In the national literature there are only two previously published cases. The objective of the presentation of the case is to recall the main epidemiological, clinical and paraclinical characteristics of said pathology, as well as to re-establish the importance of considering the HTLV-Ia the etiological search time of a chronic myelopathy, and to maintain the blood controls of donors and blood products to eliminate one of the main routes of infection.

Resumo: Um caso de paraparesia espástica associado a retrovírus HTLV-I foi descrito em um paciente de 34 anos cujo diagnóstico foi feito 17 anos após o início da doença. Foi obtido pela determinação de anticorpos no sangue e no líquido cefalorraquidiano. Na literatura nacional existem apenas dois casos publicados anteriormente. O objetivo da apresentação do caso é relembrar as principais características epidemiológicas, clínicas e paraclínicas da referida patologia, bem como restabelecer a importância de considerar o HTLV-Ia o tempo de busca etiológica de uma mielopatia crônica e manter o controle sanguíneo dos doadores. e hemoderivados para eliminar uma das principais vias de infecção.