Endocrine Control of Calcium Metabolism in Teleosts

It is evident that fishes regulate their serum calcium efficientlybut that endocrine systems involved may be different from thosein tetrapods. A functional parathyroid gland has not yet beendemonstrated in fishes. The majority of evidence indicates thatcalcitonin has little or no effect on fish calcium regulation.Instead, the corpuscles of Stannius and the pituitary glandare necessary for maintaining fish serum calcium levels. Inthe killifish, Fundulus heteroclitus, the removal of the corpusclesproduces hypercalcemia in sea water but not in artificial seawater deficient in calcium. Transplants of the corpuscles orthe administration of corpuscle homogenate corrects the increasein calcium. On the other hand, hypophysectomy elicits hypocalcemiaunder calcium deficient conditions but not in calcium rich seawater. Replacement therapy with pituitary homogenate or hypophysialtransplant prevents the fall in calcium. It is postulated thatthe hypocalcemic corpuscles of Stannius and the hypercalcemicpituitary gland enable the euryhaline killifish to regulateits serum calcium levels in high calcium sea water and low calciumfresh water, respectively.     

Temporal partitioning of a floral resource by territorial hummingbirds

Most studies of territoriality in hummingbirds have focused on intraspecific competition for resources and the consequences for the spatial distribution of individuals within a habitat. As a result, we know little of the effects of interspecific competition for resources and less still of temporal resource partitioning. Here I describe the interactions of four species of tropical hummingbird which defended the same territory at different stages in the flowering period and at different times of the day. The pattern of territory defence was greatly influenced by the dominance hierarchy between species and the costs and benefits of territory ownership. I used a simple economic model to calculate the predicted territory size based on four potential strategies. Hummingbirds appeared to be defending territories of the smallest economical size, agreeing with two hypotheses: (1) that hummingbirds minimize the cost of territory ownership and (2) that hummingbirds maximize the time spent sitting. The model predicted accurately the observed pattern of territory acquisition; hummingbirds initiated defence as soon as the territory contained sufficient resources and were either displaced by a larger species or replaced by a smaller one as the value of the territory changed.     

The Influence of Sucrose and Abscisic Acid on the Determination of Grain Number in Wheat

Using detached ears of wheat cultured in nutrient solution theeffect of sucrose and ABA supply on grain number was examined.In ears detached prior to ear emergence, to correspond withthe time of pollen mother cell meiosis, higher levels of sucroseuptake were associated with higher grain number per ear. ABAindirectly caused a reduction in grain number by decreasinguptake of sucrose through decreasing stomatal conductance andtranspiration. There was possibly also a direct effect of ABAon grain number. At higher levels of ABA the negative effecton grain number was decreased by increasing the sucrose concentration.In ears detached one to three days after anthesis grain numberwas also influenced by the amount of sucrose taken up. althoughgrain number was not as sensitive to the sucrose supply at thistime as it was at meiosis. The influence of ABA following anthesiswas limited to an indirect effect on grain number through reductionsin sucrose uptake. Key words: Wheat, Sucrose, ABA, Grain number     

Rapid indexing of the sunblotch disease of avocados using a complementary DNA probe to avocado sunblotch viroid

A routine procedure has been established for the sensitive and specific detection of avocado sunblotch viroid in partially purified nucleic acid extracts of avocado leaves by hybridisation analysis with ³²P-complementary DNA prepared against the purified viroid. Avocado sunblotch viroid was shown to be present in 12 avocado trees that had indexed positive in a biological test for sunblotch disease but was absent from 10 trees that indexed negative. The complete correlation between sunblotch disease and the presence of viroid indicates that the complementary DNA hybridisation assay procedure can be used for the indexing of sunblotch disease. The overall procedure of leaf extraction and hybridisation analysis can be completed in 5 days and is to be compared with up to 2 yr required for indexing by biological methods. The level of avocado sunblotch viroid in partially purified nucleic acid extracts of a number of different sources of sunblotch infected avocado leaves was found to vary 10 000-fold from 0.2% to 2 × 10^-5% by weight. The lower limit of detectability of the viroid by the hybridisation assay is considered to be about 10^-5% by weight; this is at least 10³ times more sensitive than the detection of the viroid by polyacrylamide gel electrophoresis of the leaf nucleic acid extracts followed by staining.     

Mark–release–recapture experiments with Anopheles gambiae s.l. in Banambani Village, Mali, to determine population size and structure

Mark–release–recapture experiments with Anopheles gambiae s.l. were performed during the wet seasons of 1993 and 1994 in Banambani, Mali. All recaptured mosquitoes were identified to species by PCR analysis and, when possible, by chromosomal analysis to chromosomal form. Two species of the An. gambiae complex were present: An. gambiae s.s. and An. arabiensis ; their ratio differed greatly from one year to the next. Three chromosomal forms of An. gambiae s.s. were found – Bamako, Savanna and Mopti. The drier 1993 was characterized by a high frequency of An. arabiensis and of the Mopti chromosomal forms of An. gambiae s.s. These trends were consistent with large-scale geographical patterns of abundance along a precipitation gradient. We observed no difference in dispersal between the two species, nor among the chromosomal forms of An. gambiae s.s. Therefore, in this situation at least, it is reasonable to group such data on the An. gambiae complex as a whole for analysis. Population size of An. gambiae s.l. females in the village was estimated to be 9000–11 000 in 1993 and 28 000 in 1994. The corresponding numbers were somewhat higher when independently-derived values of daily survival were used. These were consistent with estimates of effective population size obtained from patterns of gene frequency change.     

Alcohol and the Identity Struggle: Some Effects of Economic Change on Interpersonal Relations

This paper proposes to examine the apparent increase in interpersonal conflict that often accompanies economic change. Focusing initially on the drinking behavior of the Naskapi Indians of Schefferville, Quebec, it is held that when economic change results in the introduction of new ways of access of persons to goods or activities that serve to maintain identities, there will be an increase in frequency of identity struggles, and a corresponding increase in those ritualized or formalized social interactions which serve as identity-resolving forums.     

Animal Life Without Oxygen: Basic Biochemical Mechanisms

A variety of animals are now known to be facultative anaerobes,capable of utilizing molecular oxygen when it is present andcapable of sustained anaerobiosis when it is absent. Duringanoxia these organisms rely upon the simultaneous catabolismof carbohydrate and amino acids. In probing the mechanisms utilized,this essay accounts for (1) the maintenance of redox balanceduring anoxia, (2) the sources of energy in the form of ATP,and (3) the formation of a multiplicity of anaerobic end products.