Reproductive strategies of Atlantic salmon: ecology and evolution

Atlantic salmon (Salmo solar, Salmonidae) show a diversity of life history, behavioural and morphological adaptations for reproduction which have evolved as an outcome of competition to maximize reproductive success. Reproductive traits of females have been shaped principally by natural selection for offspring production and survival, those of males by sexual selection for access to matings. Female Atlantic salmon invest approximately six times more energy in offspring production (i.e. gonads) than males and face an important trade-off between number and size of eggs to produce that will maximize the number of surviving offspring. Timing of breeding and the construction of nests appear adapted to increase offspring survival. The most important determinant of female breeding success is body size because it affords high fecundity, access to breeding territories and decreased probability of nest destruction. Asynchronous female spawning and the male ability to spawn rapidly and repeatedly results in male-biased operational sex ratios that generate intense male competition for mates. This has likely been responsible for the evolution of elaborate male secondary sexual characters associated with fighting and status signalling. Furthermore, it has given rise, through frequency-dependent selection, to two alternative male breeding phenotypes: (1) large, anadromous males; and (2) small, mature male parr. Anadromous males invest heavily in behavioural activity on the spawning grounds, searching and fighting for mates and courting them, with body size being an important determinant of their breeding success. This behavioural activity carries a heavy cost, as anadromous males have significantly reduced survival relative to females. In contrast, mature male parr invest proportionally more in testes for sperm competition and attempt to sneak access to matings. While this behaviour also carries costs in terms of subsequent growth and survival, male parr are more likely to breed again, either prior to or following a migration to sea, than anadromous males. While knowledge about the breeding of Atlantic salmon is detailed, we are only beginning to understand the ultimate causes and/or functional significances of their reproductive strategies. Predictive models of the life history variation are developing, focusing on the need for empirical study and testing of life history and reproductive patterns.     

Nationalism and Belonging in India,Pakistan and South Central Asia: Some Comparative Observations

The criteria invoked in the definition of national identity are commonly derived from contexts other than those of the nation-state itself—most notably those of territoriality, language/culture, kinship/descent and religion. It therefore follows that in seeking to understand the kind of identity or belongingness invoked in a particular instance of national ideology it is necessary to explore not only the kind of nation-state envisaged, but also those non-national forms of belonging or community from which the national ideology may itself be historically derived. In this paper I seek to develop this argument by comparing some of the principal forms of nationalism found in India, Pakistan and Central Asia. I pay particular attention to the importance of the concept qawm, which in Pakistan, Afghanistan and elsewhere in Central Asia, is used to refer to a wide variety of groups to which people owe allegiance. Such usages alert us to the important fact that the nation, as ‘imagined community’, may have its origins as a political movement among sentiments and allegiances which draw on pre-modern social arrangements and are in tension with ‘nationalist’ exclusivism. Even when the nation (as nation-state) has been secured, so-called ‘nationalist’ revivalism, while taking the nation for granted, may in fact appeal to sentiments of a different kind.     

Detection of extracellular proteinase of Pseudomonas fragi by enzyme-linked immunosorbent assay

A double-antibody-sandwich, enzyme-linked immunosorbent assay was developed to detect an extracellular proteinase produced by Pseudomonas fragi. The method was capable of detecting 4 g/ml of the proteinase in spiked samples of buffer and broth and 4.2 g/ml in a broth culture of the organism. The assay detected the presence of proteinase at bacterial densities of approximately 10⁴ cfu/ml, which develop after incubation for 15 h at 25°C in a broth medium. All assays could be completed within 7 h. This assay is of value in plotting proteolytic expression in relation to the growth cycle of Ps. fragi in broth culture and may be of value, with development, in other more complex milieux.     

Small population instability and island settlement patterns

A model of extinction probability, based on the general theory of island biogeography [MacArthur and Wilson, 1967], is proposed for humans on oceanic islands; extinction probability is determined by island carrying capacity, frequency and amplitude of fluctuations in resources determining carrying capacity, and the net costs of contact and exchange between population units. The model predicts that extinction probability will determine island settlement patterns within an island group resulting in nonsettlement of islands with low carrying capacities and settlement of all islands with high carrying capacities. Data examined from the Marshall Islands tend to support the model. The model is extended to initial atoll colonization patterns. Possible requirements for initial settlement are suggested.Deceased.     

Autoradiographic localization of ornithine decarboxylase in mouse kidney by use of radiolabeled α-difluoromethylornithine

Summary Ornithine decarboxylase, a key enzyme in polyamine biosynthesis and cell growth, has been localized in mouse kidney by autoradiography after administration of radiolabeled -difluoromethylornithine. This drug is an enzyme-activated irreversible inhibitor of ornithine decarboxylase and forms a covalent bond with the enzyme. It was found that ornithine decarboxylase is present in all cell types studied but that the highest content occurs in the proximal convoluted tubules followed by the distal convoluted tubules and the collecting tubules. The majority of the enzyme is located in the cytoplasm but about 10–15% is present in the nuclei (often associated with nucleolus-like components) of the cells of the proximal and distal convoluted tubules. The labeled ornithine decarboxylase was lost rapidly from both nucleus and cytoplasm of all the cell types examined, and labeling by radioactive -difluoromethylornithine was greatly reduced if the mice were pretreated for 5 h with cycloheximide to block protein synthesis. These results indicate that ornithine decarboxylase turns over rapidly in all of the cells.     

Effects of a nonperssor analogue of vasopressin on plasma renin activity and salt and water excretion in water-loaded,anesthetized dogs

The object of this study was to determine the importance of vasoconstrictor activity in the suppression of renin secretion by vasopressin. Arginine vasopressin (AVP) (0.05 and 0.1 ng/kg/min) and a nonpressor analogue of vasopressin, 1-deamino-[4-threonine, 8-D-arginine]-vasopressin (dTDAVP) (0.01 and 0.05 ng/kg/min), were infused intravenously in anesthetized hypophysectomized dogs. Neither dTDAVP nor AVP influenced arterial pressure or heart rate but both suppressed plasma renin activity. Infusion of dTDAVP at 0.01 and 0.05 ng/kg/min suppressed plasma renin activity to 86±4% (p<0.05) and 63±6% (p<0.01) of the control values respectively. Infusion of AVP at 0.05 and 0.1 ng/kg/min suppressed plasma renin activity to 60±8% (p<0.01) and 59±12% (p<0.05) of the central values respectively. dTDAVP and AVP both produced significant increases in sodium excretion. These data demonstrate that vasoconstrictor activity is not required for the effects of vasopressin on renin secretion and sodium excretion.