Ocorrência de poliúria-polidpsia em eqüinos estabulados - descrição de dois casos de polidipsia psicogênica Incidence of two cases of polyuria-polydipsia in confined horses

Dois eqüinos da raça Brasileira de Hipismo, machos, quatro anos de idade, apresentando sinais de poliúria-polidipsia, foram submetidos a completa avaliação clínica e a exames de sangue e urina. Não foram observadas alterações clínicas, hematológicas ou bioquímicas, a não ser um decréscimo na gravidade específica da urina de ambos os animais (1,009 e 1,008). Realizou-se um teste de privação de água de 24 horas e durante esse período a gravidade especifica da urina subiu gradualmente até atingir a normalidade (1,028 e 1,026, respectivamente). O comportamento anormal ocorreu por confinamento excessivo. Os resultados clínicos e de laboratório e o teste de privação de água indicam o diagnóstico de polidipsia psicogênica.<br>Two four-year-old male Brasileiro de Hipismo breed horses presenting signs of polyuria-polydipsia, were submitted to a complete clinical evaluation as well as having blood and urine samples collected for laboratory analysis. No clinical, hematological or biochemical abnormalities were observed, but a significant decrease in urine specific gravity was detected in both horses. One of the horses presented 1,009 and the other 1,008. A 24-hour water deprivation test was carried out and, during this period, the urine specific gravity gradually increased reaching the normal values of 1,028 and 1,026. The abnormal behavior occured as a consequence of an excessive confinement. The clinical and laboratory results associated to the 24-hour water deprivation test indicated a diagnosis of psychogenic polydipsia

Large size in an island-dwelling bird: intraspecific competition and the Dominance Hypothesis

Differences between island- and mainland-dwelling forms provide several classic ecological puzzles. Why, for instance, are island-dwelling passerine birds consistently larger than their mainland counterparts? We examine the 'Dominance hypothesis', based on intraspecific competition, which states that large size in island passerines evolves through selection for success in agonistic encounters. We use the Heron Island population of Capricorn silvereyes (Zosterops lateralis chlorocephalus), a large-bodied island-dwelling race of white-eye (Zosteropidae), to test three assumptions of this hypothesis; that (i) large size is positively associated with high fitness, (ii) large size is associated with dominance, and (iii) the relationship between size and dominance is particularly pronounced under extreme intraspecific competition. Our results supported the first two of these assumptions, but provided mixed evidence on the third. On balance, we suggest that the Dominance Hypothesis is a plausible mechanism for the evolution of large size of island passerines, but urge further empirical tests on the role of intraspecific competition on oceanic islands versus that on mainlands