Reproductive development and energy stores were characterized for sockeye salmon (Oncorhynchus nerka) maturing in the wild (Pick Creek, Bristol Bay, Alaska). Between freshwater entry and the start of spawning, ovaries increased in mass by 87.1% and secondary sexual characters increased in linear dimension by 13.0-47.4%. Between the start of spawning and death, secondary sexual characters decreased in relative size by 3.3-12.7%. Mass-specific somatic energy declined from freshwater entry (6.7% fat, 20.6% protein, 6.6 kJ·g-1) to the start of spawning (1.6% fat, 18.0% protein, 4.5 kJ·g-1) and finally to death (0.1% fat, 14.4% protein, 2.9 kJ·g-1). Stored fat appeared to be used primarily for upriver migration and egg production, whereas stored protein appeared to be used primarily for the development of secondary sexual characters and metabolism during spawning. Most development of secondary sexual characters occurred late in maturation, perhaps to forestall deterioration of muscle tissue. Relative to populations with long freshwater migrations, Bristol Bay sockeye salmon stored less fat before entering fresh water and used less fat before death. The total energy cost of reproduction (freshwater entry until death, including gonad investment) was 74.1% for females and 66.1% for males, higher than levels typically reported for iteroparous salmonids.

Measurements of the hygroscopic properties of sub‐micrometer atmospheric aerosol particles were performed with hygroscopic tandem differential mobility analysers (H‐TDMA) at 5 sites in the subtropical north‐eastern Atlantic during the second Aerosol Characterization Experiment (ACE‐2) from 16 June to 25 July 1997. Four of the sites were in the marine boundary layer and one was, at least occasionally, in the lower free troposphere. The hygroscopic diameter growth factors of individual aerosol particles in the dry particle diameter range 10–440 nm were generally measured for changes in relative humidity (RH) from <10% to 90%. In the marine boundary layer, growth factors at 90% RH were dependent on location, air mass type and particle size. The data was dominated by a unimodal growth distribution of more‐hygroscopic particles, although a bimodal growth distribution including less‐hygroscopic particles was observed at times, most often in the more polluted air masses. In clean marine air masses the more‐hygroscopic growth factors ranged from about 1.6 to 1.8 with a consistent increase in growth factor with increasing particle size. There was also a tendency toward higher growth factors as sodium to sulphate molar ratio increased with increasing sea‐salt contribution at higher wind speeds. During outbreaks of European pollution in the ACE‐2 region, the growth factors of the largest particles were reduced, but only slightly. Growth factors at all sizes in both clean and polluted air masses were markedly lower at the Sagres, Portugal site due to more proximate continental influences. The frequency of occurrence of less‐hygroscopic particles with a growth factor of ca. 1.15 was greatest during polluted conditions at Sagres. The free tropospheric 50 nm particles were predominately less‐hygroscopic, with an intermediate growth factor of 1.4, but more‐hygroscopic particles with growth factors of about 1.6 were also frequent. While these particles probably originate from within the marine boundary layer, the less‐hygroscopic particles are probably more characteristic of lower free tropospheric air masses. For those occasions when measurements were made at 90% and an intermediate 60% or 70% RH, the growth factor G(RH) of the more‐hygroscopic particles could be modelled empirically by a power law expression. For the ubiquitous more‐hygroscopic particles, the expressions G(RH)=(1−RH/100)−0.210 for 50 nm Aitken mode particles and G(RH)=(1−RH/100)−0.233 for 166 nm accumulation mode particles are recommended for clean marine air masses in the north‐eastern Atlantic within the range 0

No abstract

Abstract. The hygroscopic properties of submicrometer aerosol particles were studied with a Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA) in the remote marine tropospheric boundary layer (MBL) over the Pacific and Southern Oceans in connection with the southern hemisphere marine First Aerosol Characterization Experiment (ACE 1) in October-December 1995. The H-TDMA was placed on board the ship R/V NOAA Discoverer and measured the hygroscopic diameter growth of individual aerosol particles when taken from a dry state to a relative humidity (RH) of 89-90%. Measurements were performed for the particles with dry diameters of 35, 50, 75, and 150 (or 165) nm. The natural aerosol present in the remote MBL largely consists of two types, a sea-salt component and a non-sea-salt (nss) sulfate component. Since their hygroscopic behavior is significantly different, the H-TDMA could clearly distinguish between these two types and thus make in situ measurements of the mixing state of the MBL aerosol. During the ACE 1 intensive campaign in the Southern Ocean south of Australia, the hygroscopic diameter growth factors at RH = 90% for the nss-sulfate aerosol particles were 1.62, 1.66, and 1.78 at dry particle diameters of 35, 50, and 150 nm, respectively, and for time periods with remote marine air masses. These values exceed those normally found in continental polluted environments. The growth factors for the externally mixed sea-salt particles were even higher (2.12 and 2.14 for 50 and 150 nm). The corresponding values for the Pacific Ocean (at RH = 89%) for the nss-sulfate particles were 1.56, 1.59, 1.61, and 1.63 for 35, 50, 75, and 165 nm. Particle deliquescence and RH hysteresis between RH --68-90% was only observed in air masses north of the South Pacific Gyre, and then only for the Aitken mode particles (particle diameters -20-80 nm). The occurrence of externally mixed sea-salt particles could be linked to conditions with high wind speeds in connection with frontal passages or low pressure systems. Nevertheless, the number of externally mixed 150 nm sea-salt particles was found to be poorly correlated with local wind speed, probably due to a rather long life-time of these submicrometer particles. Particles with hygroscopic growth factors significantly less than those of the nsssulfate particles (denoted less hygroscopic particles) were only present during periods with anthropogenic influence.

The antagonistic pleiotropy theory of senescence postulates genes or traits that have opposite effects on early-life and late-life performances. Because selection is generally weaker late in life, genes or traits that improve early-life performance but impair late-life performance should come to predominate. Variation in the strength of age-specific selection should then generate adaptive variation in senescence. We demonstrate this mechanism by comparing early and late breeders within a population of semelparous capital-breeding sockeye salmon (Oncorhynchus nerka). We show that early breeders (but not late breeders) are under strong selection for a long reproductive lifespan (RLS), which facilitates defence of their nests against disturbance by later females. Accordingly, early females invest less energy in egg production while reserving more for nest defence. Variation along this reproductive trade-off causes delayed or slower senescence in early females (average RLS of 26 days) than in late females (reproductive lifespan of 12 days). We use microsatellites to confirm that gene flow is sufficiently limited between early and late breeders to allow adaptive divergence in response to selection. Because reproductive trade-offs should be almost universal and selection acting on them should typically vary in time and space, the mechanism described herein may explain much of the natural variation in senescence.