Biological destruction of coral reefs

The major agents of biological destruction of coral reefs can be divided into grazers, etchers and borers. Each of these groups is reviewed on a world wide basis, together with the mechanisms by which they destroy the coral substrate. Rates of bioerosion attributed to major agents of grazers, etchers and borers are given, together with limitations of some of the measurements. Recent work is highlighting the variability in rates of bioerosion both over time and space. Factors which may be responsible for this variability are discussed. Bioerosion is a major factor influencing reef morphology and the ways in which this is achieved is discussed in some detail. Although the review concentrates mainly on present day reefs, some attempt is made to consider the impact of bioerosion on older reefs.     

The segmental pectoralis major muscle flap: a function-preserving procedure

A function-sparing pectoralis major muscle flap is presented. The flap is a medially based segmental transfer of a single intercostal portion of the pectoralis major muscle supplied by a single perforating branch of the internal thoracic artery. The segmental terminal nerve distribution of the medial and lateral pectoral nerves permits preservation of the remainder of the muscle in situ. Six cases of this procedure are presented with five successful outcomes. The single exception was in the loss of the distal tip when used to cover an irradiated carotid sheath to the base of the skull.     

The differential effect of 2-deoxyguanosine on concanavalin A-induced suppressor and cytotoxic activity

The effect of 2-deoxyguanosine (dGuo) on the generation in vitro of nonspecific suppressor cells in murine spleen cell cultures by concanavalin A (Con A) is examined. The experiments indicate that dGuo abrogates the generation of nonspecific suppressor activity by lectin stimulation of murine spleen cells. When comparisons were made between the effect of this nucleoside on the generation of suppressor and cytotoxic cells by Con A stimulation of murine spleen cells, it was found that dGuo only affected the generation of suppressor cells. The development of lectin-stimulated cytotoxicity was not affected by dGuo. In addition it was found that dGuo does not affect the NK activity of murine spleens.     

The evolution of alternative mating strategies in variable environments

Summary We assessed the influence of phenotypic plasticity in age at maturity on the maintenance of alternative mating strategies in male Atlantic salmon,Salmo salar. We calculated the fitness,r, associated with the parr and the anadromous strategies, using age-specific survival data from the field and strategy-specific fertilization data from the laboratory. The fitness of each strategy depended largely on mate competition (numbers of parr per female, i.e. parr frequency) and on age at maturity. Fitness declined with increasing numbers of parr per female with equilibrium frequencies (at which the fitnesses of each strategy are equal) being within the range observed in the wild. Equilibrium parr frequencies declined with decreasing growth rate and increasing age at maturity. Within populations, the existence of multiple age-specific sets of fitness functions suggests that the fitnesses of alternative strategies are best represented as multidimensional surfaces. The points of intersection of these surfaces, whose boundaries encompass natural variation in age at maturity and mate competition, define an evolutionarily stable continuum (ESC) of strategy frequencies along which the fitnesses associated with each strategy are equal. We propose a simple model that incorporates polygenic thresholds of a largely environmentally-controlled trait (age at maturity) to provide a mechanism by which an ESC can be maintained within a population. An indirect test provides support for the prediction that growth-rate thresholds for parr maturation exist and are maintained by stabilizing selection. Evolutionarily stable continua, maintained by negative frequency-dependent selection on threshold traits, provide a theoretical basis for understanding how alternative life histories can evolve in variable environments.     

Tension headaches

In order to assess the effectiveness of verbal relaxation instructions and EMG relaxation training on the relief of tension headaches, 18 medically documented tension-headache sufferers were randomly assigned to one of three conditions:(1) Jacobson-Wolpe autogenic-relaxation training,(2) EMG relaxation training, or(3) EMG relaxation training combined with Jacobson-Wolpe autogenic instructions. The two EMG-assisted groups showed significantly better results, compared to the verbal group, in terms of reduction of headache activity and the rate at which reduction took place. Thus, EMG-assisted relaxation procedures seem the treatment method of choice for relief of tension headaches.     

The dynamics of three shrub species in a fire-prone temperate savanna: the interplay between the seed bank, seed rain and fire regime

A model was developed to assess how the seed rain and fire regime affect seed bank dynamics and seedling establishment of three native shrub species (Acanthostyles buniifolius, Baccharis pingraea and Baccharis dracunculifolia) with different regeneration strategies, in temperate South American savanna. Seed bank and seed rain were quantified for each species under different fire regimes, and their relative roles in regeneration were evaluated. All species had short-term persistent seed banks and high annual variability in seed production. A high proportion of seeds deposited in the seed rain produced seedlings after fire; few entered the soil seed bank. Fire killed a high proportion of the seeds in the soil seed bank. Seedlings derived from the seed rain had a higher probability of surviving for 2 years than seedlings emerging from the soil seed bank. In the absence of fire, establishment depended on germination both from the seed rain and the soil seed bank, whereas with annual fire, establishment was primarily dependent on germination of seeds arriving in the annual seed rain, regardless of species’ regeneration strategies. These results help to explain changes in the vegetation of South American temperate savannas as a result of changes in fire regime and grazing management during the last 50 years. By revealing the crucial roles of the soil seed bank and seed rain in regeneration, this study provides vital information for the development of appropriate management practices to control populations of shrub species with different regeneration strategies in South American temperate savannas.