Serum Gastrin levels in Pigs

Serum gastrin levels were measured in 11 young pigs during starvation and one and two hours after feeding. The mean basal value was 57 -+- 16 pg/ml and was not affected by anaesthesia. Gastrin levels' at one and two hours after feeding were significantly higher than the basal levels. However, the rise was much less than that noted in humans, suggesting a species difference

Evolution of cooperation: Cooperation defeats defection in the cornfield model

"Cooperation" defines any behavior that enhances the fitness of a group (e.g. a community or species), but which, by its nature, can be exploited by selfish individuals, meaning, firstly, that selfish individuals derive an advantage from exploitation which is greater than the average advantage that accrues to unselfish individuals. Secondly, exploitation has no intrinsic fitness value except in the presence of the "cooperative behavior". The mathematics is described by the simple Prisoner's Dilemma Game (PDG). It has previously been shown that koinophilia (the avoidance of sexual mates displaying unusual or atypical phenotypic features, such as mutations) stabilizes any inherited strategy in the simple or iterated PDG, meaning that it cannot be displaced by rare forms of alternative behavior which arise through mutation or occasional migration. In the present model equal numbers of cooperators and defectors (in the simple PDG) were randomly spread in a two-dimensional "cornfield" with uniformly distributed resources. Every individual was koinophilic, and interacted (sexually and in the PDG tournaments) only with individuals from within its immediate neighborhood. This model therefore tested whether cooperation can outcompete defection or selfishness in a straight, initially equally matched, evolutionary battle. The results show that in the absence of koinophilia cooperation was rapidly driven to extinction. With koinophilia there was a very rapid loss of cooperators in the first few generations, but thereafter cooperation slowly spread, ultimately eliminating defection completely. This result was critically dependent on sampling effects of neighborhoods. Small samples (resulting from low population densities or small neighborhood sizes) increase the probability that a chance neighborhood comes to consist predominantly of cooperators. A sexual preference for the most common phenotype in the neighborhood then makes that phenotype more common still. Once this occurs cooperation's spread becomes almost inevitable. © 2003 Elsevier Ltd. All rights reserved.Articl

Profitability of short term reversal strategies on the Johannesburg Stock Exchange

Short term reversal strategies involve the frequent buying (or selling) of loser (or winner) stocks in order to profit in the short run if prices revert. Several studies report profitability of these strategies while others reject profitability due to trading costs. This study reports profitability of a short term reversal rule when trading in large capitalization Johannesburg Stock Exchange listed stocks, while allowing for trading costs and taking trade execution skills into account. Evaluation of the performance of the rule is done in terms of newly introduced reward and risk measures based on daily cash flows and market exposures respectivel

Effects of autumn nitrogen nutrition and a winter restbreaking spray on the growth, development and chemical composition of young 'Golden Delicious' apple trees grown in sand culture

Omission of N during autumn on pot-grown 'Golden Delicious/Merton 793' apple trees resulted in accelerated leaf-drop and lower total N, soluble N, protein N, P and Ca, and higher starch, total sugars and K in the dormant terminal shoots in comparison with a full autumn N treatment. Omission of both autumn N and the artificial rest-breaking spray resulted in delayed bud-break and flowering but the effect of these two treatments was inter-dependent. Neither the autumn application of N alone nor the rest-breaking spray alone resulted in completely satisfactory bud-breaking and flowering. Omission of autumn N and/or the rest-breaking spray reduced flower number per tree. Omission of both factors resulted in very poor fruit-set while, where only one of these two factors was omitted, the fruit-set was not reduced. Fruit-set was strongly related to the time of flowering. Autumn N nutrition also showed a residual effect on growth and the leaf nutritional status the following season. © 1979.Articl

Low repeatability of preferred body temperature in four species of Cordylid lizards: Temporal variation and implications for adaptive significance

Preferred body temperatures (Tsel) of ectotherms are important for ecological and evolutionary studies. In lizards, the measurement of Tsel is controversial for several reasons, generally related to hypotheses addressing how Tsel may evolve in the wild. Although seldom explicitly tested, evolutionary hypotheses of adaptation to local climate require that Tsel meets the conditions of natural selection, which include repeatability, heritability and a link to fitness. Here, we investigated repeatability (τ, intra-class correlation coefficient) of Tsel at several time-scales using four Cordylid species from heterogeneous thermal habitats. Although there was significant inter-individual variation within days (P 0.05). Repeatability was low in all species investigated (from 0 to 0.482) when compared against other estimates of repeatability of Tsel in the literature. Irrespective of how Tsel was calculated, it showed inconsistent and variable temporal effects across species. Furthermore, repeatability of Tsel did not change with acclimation to laboratory conditions. These data have implications for understanding the evolution of thermoregulation in these and other ectotherms.Centre of Excellence for Invasion Biolog

Composição mineral e severidade de "bitter pit" em maçãs 'Catarina' Mineral composition and bitter pit severity in 'Catarina' apples

Maçãs 'Catarina', colhidas na maturação comercial em pomar no município de São Joaquim-SC, foram separadas em quatro lotes de 14 frutos, de acordo com a severidade de incidência de "bitter pit": nula (nenhuma lesão/fruto), baixa (1-2 lesões/fruto), moderada (3-5 lesões/fruto) e alta (6-18 lesões/fruto). Foram determinadas as concentrações de Ca, Mg, K e N na casca e na polpa de cada fruto. Foram verificadas relação linear (P < 0,05) negativa entre os valores médios de Ca na casca, e positiva entre as relações Mg/Ca, (K+Mg)/Ca e (K+Mg+N)/Ca também na casca, com o número médio de manchas/fruto nas diferentes categorias de severidade de "bitter pit". Para a polpa, o aumento na severidade de "bitter pit" foi acompanhado de redução apenas nas concentrações de Ca e Mg. A análise multivariada (análise canônica discriminante) mostrou que a relação Mg/Ca na casca foi o atributo mineral que melhor discriminou frutos com diferentes níveis de severidade ao "bitter pit", e que, portanto, elevados valores desta relação são indicativos de frutos com alta suscetibilidade a esse distúrbio na cultivar Catarina.<br>'Catarina' apples were harvested at the commercial maturity in an orchard in São Joaquim-SC and segregated in four lots of 14 fruits with different levels of bitter pit severity: null (none pit/fruit), low (1-2 pits/fruit), moderate (3-5 pits/fruit), and high (6-18 pits/fruit). Nutritional analysis (Ca, Mg, K, and N) in the skin and flesh tissues were performed on individual fruits of each severity level. The average number of pits/fruit (calculated for each lot of bitter pit severity) showed a negative linear relationship (P < 0.05) with the skin Ca content, and a negative linear relationship (P < 0.05) with the ratios of Mg/Ca, (K+Mg)/Ca, and (K+Mg+N)/Ca in the skin. For the flesh, the increasing of bitter pit severity was accompanied by significant reduction of Ca and Mg contents. The multivariate analysis (canonical discriminant analysis) showed that the Mg/Ca ratio in the skin provided the best discrimination between the lots of fruit with different levels of bitter pit severity. Therefore, for 'Catarina' apples, increasing values of the Mg/Ca ratio in the skin are indicative of fruits with increasing bitter pit susceptibility