Molecular evolution of the period gene in Drosophila athabasca

We measured nucleotide variability within and between the three semispecies of the Drosophila athabasca complex, at the period (per) gene by using a polymerase chain reaction-based four-cutter restriction- enzyme analysis. The levels of polymorphism varied considerably between the three semispecies. Our results for per, combined with previous data for X-linked allozymes, suggest that the X chromosome in the western- northern semispecies is less variable than expected under an equilibrium-neutral model. Both the pattern of divergence between the semispecies and a cladistic clustering of per haplotypes support the previously hypothesized grouping of eastern A and eastern B as the two most recently diverged semispecies. A 21-bp in-frame segment in the region of per which shares sequence similarity with the neuronal development gene single minded is deleted in all eastern A and eastern B flies examined but is present in all of the western-northern flies and all other published per sequences. Despite these hints that there may be significant differences at the per gene between the semispecies, especially the western-northern group versus the two eastern groups, there is no compelling evidence that per is involved in the mating song differences between the semispecies.      

The Symptoms and Cause of Guava Wilt in South Africa

Wilt of guava (Psidium guajava), a serious disease occurring in most guava producing areas of the Northern and Mpumalanga provinces of South Africa, was shown to be induced by a fungus tentatively identified as Penicillium vermoesenii. This fungus is the cause of a blight of ornamental palms in the United States and Belgium and its occurrence on guava is enigmatic. Pathogenicity tests were conducted in the glasshouse and under field conditions. Symptoms on trees include wilting, chlorosis and defoliation.     

Influences of weather on reproductive function in male Song sparrows, Melospiza melodia

The avian reproductive cycle is integrated and timed by a variety of environmental factors that include day length, availability of food, nest sites, presence of a mate, etc. However, reproduction can be delayed or disrupted by inclement weather and, until recently, the endocrine responses of avian species to storms were entirely unknown. This communication describes changes in endocrine state in free-living male Song sparrows, Melospiza melodia, during gonadal recrudescence after a severe winter, and in response to storms in early spring and summer. Both the severe winter weather and an early spring snow storm delayed testicular development, and depressed circulating levels of testosterone. The sparrows did not appear to be stressed, however, since body mass and fat deposits were higher than in birds sampled during the previous spring after a less severe winter.
A second storm occurred in late May and early June when Song sparrows were feeding young. Curiously, plasma levels of testosterone were not affected, but the sparrows did appear to be stressed since there was a significant decline in body mass, and a marked increase in circulating levels of corticosterone. These data suggest that the effects of inclement weather on reproductive function can vary in relation to the stage in the reproductive cycle when the storm strikes, and that the endocrine mechanisms underlying acclimatization to severe meteorological conditions are also different.     

Assessing and predicting the success of Najas flexilis (Willd.) Rostk. & Schmidt, a rare European aquatic macrophyte, in relation to lake environmental conditions

Najas flexilis (Willd.) Rostk. & Schmidt is a submerged annual macrophyte, rare in Europe, which is protected under the EC Habitats Directive. N. flexilis appears to be decreasing in the British Isles, its main stronghold in Europe. We outline the environmental conditions required for N. flexilis growth, comparing between present and recently extinct sites for the plant. Plant traits (leaf area/shoot length; and reproductive number/shoot length) can be used to assess N. flexilis population success, and models are produced that can predict this. Both the comparison between present and extinct sites, and the models, suggest that eutrophication and acidification of lakes are the main threats to N. flexilis. Acidification appears to reduce the ability of N. flexilis to produce seeds (potentially fatal for an annual). On the other hand, eutrophication leads to conditions where N. flexilis, an obligate carbon dioxide utiliser, cannot photosynthesise due to the predominance of bicarbonate rather than dissolved carbon dioxide in lake water.     

Seasonal changes in song nuclei and song behavior in Gambel's white-crowned sparrows

In males of several songbird species, the morphology of forebrain nuclei that control song changes seasonally. The only seasonally breeding songbird in which seasonal changes in the structure of song control nuclei have been reported not to occur is the nonmigratory Nuttall's subspecies of white-crowned sparrow. In the present study, we manipulated photoperiod and plasma testosterone concentrations in captive male white-crowned sparrows of the migratory Gambel's subspeices. Males exposed to photoperiods and plasma testosterone concentrations typical of those experienced by wild breeding males had larger song control nuclei than males held on a winter photoperiod. We also found seasonal change in stereotypy of spectral and temporal parameters of song in wild Gambel's white-crowned sparrows. We hypothesize that seasonal changes in song control nuclei may correlate with seasonal changes in song stereotypy. © 1995 John Wiley & Sons, Inc.     

Combined influence of magnesium concentration and polymerase chain reaction specificity enhancers

Abstract The importance of an optimal magnesium concentration (6.5 mM), as well as the inclusion of a specific polymerase chain reaction enhancer, to obtain the correct fragment after amplification was examined during this study. In contrast to tetramethylammonium chloride, dimethyl sulphoxide did not enhance the specificity of amplification at different magnesium concentrations, but rather altered the specificity, resulting in the amplification of a larger fragment.     

Prolactin secretion in a brood parasite, the brown-headed cowbird, Molothrus ater

Blood samples were collected from a free-living population of male and female brown-headed cowbirds, Molothrus ater , during the breeding season and plasma levels of prolactin were measured by radioimmunoassay. Prolactin concentrations in both sexes increased significantly in mid to late May; peak levels were reached by June and were maintained throughout June and into July. Prolactin levels in juveniles were significantly lower than in adults but were still elevated. Prolactin has been implicated in parental care in several avian species; however, cowbirds are brood parasites with complete absence of parental behaviour, suggesting that prolactin must function in another capacity in cowbirds, or that cowbirds have developed target tissue insensitivity to this hormone.     

Specificities of cation permeabilities induced by some crown ethers in mitochondria.

A series of macrocyclic crown ethers have been assayed as ionophores using respiring rat liver mitochondria, and the same compounds have been subjected to physicochemical investigation. Association constants and stoichiometries for the complexes with potassium, rubidium, and cesium were measured in methanol. Rates of transport of potassium bromide through aqueous/organic/aqueous systems and the partition coefficient from water into the organic phase were also measured and found to be in the same rank order as the association constants. Effective uptake by the mitochondria was clearly correlated with the complexing by the cation by one or more molecules of ionophore. Thus, for all three cations the most effective compound was the largest, i.e., di-t-butyldibenzo-30-crown-10, capable of wrapping around the cation. Other compounds giving measurable uptake were those which form sandwich complexes, one cation to two crown molecules; those containing five oxygen atoms induced greater uptake of potassium than of the other two alkali metals, while compounds containing six or seven oxygen atoms had greater effects on cesium or rubidium than on potassium. Within a structurally similar series of compounds the rank orders for uptake differed from those for the association constants; in particular, compounds having one benzene ring on an 18-membered crown compound were ineffective on all cations studied; effective compounds contained two benzene rings. In contrast to X-537A and A23187, none of the compounds caused release of magnesium from the mitochondria.