ALBERT

Description: Species that reach the end of a life-history stage (transform) at relatively fixed sizes may often grow nonasymptotically before transforming. Many species of squid and at least some larval frogs, fish, and insects appear to follow this pattern. When data on body size at a range of ages are available for such taxa, they are often described well by exponential curves or by power curves that are concave upward. When such data are transformed to mean sizes for ages or age classes, they are likely to fit asymptotic growth models such as the logistic and Gompertz curves. These curves are good descriptions of the behavior of the population mean but poor descriptions of the pattern followed by any individual in the population. Analyzing and presenting data on size at age using mean sizes can thus lead to incorrect interpretations of growth patterns and should be avoided.

Description: Using metabolic (in vivo) labeling methods and immunoblotting (Western) analysis, we determined the threshold induction temperature for enhanced synthesis of heat-shock proteins (HSP70 and HSP90) and the constitutive levels of these two classes of HSPs, respectively, in brain, gill, and liver of four species of marine teleost fishes acclimatized to a common temperature (10°C). For a given tissue of a species and among tissues of a species, little variation was found in HSP induction temperatures. However, among tissues of a species, the constitutive levels of HSPs differed substantially. Among species, wide variation was found in induction temperature (up to 8°C when averaged for all tissues) and HSP concentration (greater than 10-fobld differences for a single tissue). These results, obtained by analysis of animals from natural populations, contradict many of the assumptions, based largely on in vitro studies of isolated cells and tissues, about the dependence of the HSP threshold induction temperature and HSP concentrations on the previous acclimatization temperature. The wide variation in the HSP threshold induction temperatures among the different species and the wide variation in constitutive HSP levels among and within species may reflect, in addition to recent thermal exposure, the thermal history of the species during its evolution and the occurrence in the individual's habitat of other stressors that, like temperature, are capable of activating the heat-shock (stress) response.

Description: The accuracy of the tritiated water (HTO) and sodium-22 () turnover methods as estimators of dietary water and sodium intake was evaluated in emperor penguins fed separate diets of squid and fish. Emperor penguins assimilated 76.2% and 81.8% of available energy in the squid and fish diets, respectively. Both isotopes had equilibrated with body water and exchangeable sodium pools by 2 h after intramuscular injection. The tritium method yielded reliable results after blood isotope levels had declined by 35%. On average the tritium method underestimated water intake by 2.9%, with a range of-10.3% to + 11.1%. The method underestimated Na intake on average by 15.9% with the errors among individuals ranging from -37.2% to -1.8%. Discrepancies with turnover were sign ficantly greater with the squid diet than the fish diet. The results confirm the reliability of the tritium method as an estimator of food consumption by free-living emperor penguins (provided seawater and freshwater ingestion is known) and support the adoption of the method to derive an approximation of seawater intake by tritiated emperor penguin chicks and by tritiated adults on foraging trips of short duration.

Description: The volume of air trapped in the feathers and the body density of 36 species of water bird were determined by water displacement experiments. Body density was higher and the volume of air trapped in plumage was lower in species that were most reliant on diving for foraging. Accordingly, we predict that habitually diving species have substantially reduced energy expenditure while underwater and correspondingly higher aerobic dive limits than infrequent divers. This agrees with field observations. Following Boyle's law, aerobic dive limits are predicted to increase with increasing dive depth due to a reduction in upthrust following volumetric reduction of feather-trapped air caused by hydrostatic pressure. It appears energetically more costly for diving birds to forage near the surface than at greater depths. Reduced plumage air to minimize underwater swimming costs, however, probably increases heat loss. The use of fat for insulation is not compatible with minimized flight costs. Frequent divers have higher flight costs than infrequent divers. We predict that the amount of air in the feathers and the amount of subcutaneous fat in aquatic birds are regulated in such a way as to minimize energy expenditure as a function of the temperature of the environment as well as diving and flying rhythms.

Description: Since the mid-19th century biologists have considered the east tropical Pacific to be a barrier for the dispersal of coastal marine invertebrate species. More recently it has been maintained that this is so because planktonic larvae are unable to cross such a large expanse of ocean. Therefore, it seems extraordinary that no observations have been made to determine whether larvae of invertebrates are actually transported by the major currents of that region. Plankton samples in the present study show that invertebrate larvae do occur within the east tropical Pacific including, but not restricted to, those of gastropods, polychaetes, sipunculans, decapod crustacea, echinoderms, and coelenterates-though as a rule, their occurrence there is significantly less than within the central tropical Pacific. Data from larval distributions suggest that the east tropical Pacific may act as a substantial impediment to many invertebrate forms, but that it is not a complete barrier to dispersal. Accordingly, the region is best considered a filter. It allows only species with a potential for an exceptionally long larval life to pass i.e., those with teleplanic larvae, while it blocks other forms that are restricted to a shorter time in the plankton owing to an inability to delay metamorphosis or lack of an alternate mode of dispersal. The capacity for dispersal by planktonic larvae differs among the various taxa.

Description: The 18,500 yr. b.p. Cape Riva (CR) eruption of Santorini vented several km3 or more of magma, generating four eruption units: a basal Plinian fall deposit (CR-A) and three pyroclastic flow deposits (CR-B to CR-D upwards). CR-B and CR-D are welded ignimbrites; CR-C consists predominantly of up to 25 m thick coarse, lithic-rich co-ignimbrite lag breccias resulting from a climactic phase of the eruption. The initial Plinian phase occurred from a localized vent in N Santorini, and subsequent column collapse resulted in emplacement of CR-B. Towards the end of CR-B, new conduits were activated and pyroclastic flows discharged from multiple vents to generate the lag breccias (CR-C). CR-D probably records a return to a localized vent as the eruption waned. The eruption sampled a zoned magma chamber containing rhyodacite overlying andesite, and leaks of these magmas were manifested as the Skaros-Therasia lavas preceding the CR eruption. Plinian and initial ignimbrite stages occurred while the magma chamber was overpressured; subsequent underpressuring, due to magma discharge, caused fracturing of the chamber roof, caldera collapse, and eruption of pyroclastic flows from multiple vents. Activation and widening of new conduits during collapse resulted in the rapid escalation of discharge rate favoring the formation of lag breccias by: (i) promoting erosion of lithic debris at the surface vent; and (ii) raising surface exit pressures, thereby resulting in a dramatic increase in the grain size of the ejecta.