Helium-3 in different carriers from pelagic clays of DSDP Hole 91-596B and Core LR-44-GPC-3

To better understand the composition, characteristics of helium diffusion, and size distribution of interplanetary dust particles (IDPs) responsible for the long-term retention of extraterrestrial 3He, we carried out leaching, stepped heating, and sieving experiments on pelagic clays that varied in age from 0.5 Ma to ~90 Myr. The leaching experiments suggest that the host phase(s) of 3He in geologically old sediments are neither organic matter nor refractory phases, such as diamond, graphite, Al2O3, and SiC, but are consistent with extraterrestrial silicates, Fe-Ni sulfides, and possibly magnetite. Stepped heating experiments demonstrate that the 3He release profiles from the magnetic and non-magnetic components of the pelagic clays are remarkably similar. Because helium diffusion is likely to be controlled by mineral chemistry and structure, the stepped heating results suggest a single carrier that may be magnetite, or more probably a phase associated with magnetite. Furthermore, the stepped outgassing experiments indicate that about 20% of the 3He will be lost through diffusion at seafloor temperatures after 50 Myrs, while sedimentary rocks exposed on the Earth's surface for the same amount of time would lose up to 60%. The absolute magnitude of the 3He loss is, however, likely to depend upon the 3He concentration profile within the IDPs, which is not well known. Contrary to previous suggestions that micrometeorites in the size range of 50-100 µm in diameter are responsible for the extraterrestrial 3He in geologically old sediments [Stuart, F.M., Harrop, P.J., Knott, S., Turner, G., 1999. Laser extraction of helium isotopes from Antarctic micrometeorites: source of He and implications for the flux of extraterrestrial 3He flux to earth. Geochimica et Cosmochimica Acta, 63, 2653-2665, doi:10.1016/S0016-7037(99)00161-1], our sieving experiment demonstrates that at most 20% of the 3He is carried by particles greater than 50 µm in diameter. The size-distribution of the 3He-bearing particles implies that extraterrestrial 3He in sediments record the IDP flux rather than the micrometeorite flux.

Stomach content and parasite characteristics of M. scorpius from Frobisher Bay, Baffin Island

Shorthorn sculpin (Myoxocephalus scorpius) from Frobisher Bay, Baffin Island, is a slow growing long-lived species. A wide range of diet items were present in the stomachs of the shorthorn sculpins sampled but 2-3 diet items (amphipod species) comprised 99.5 % of total food consumed. These amphipods were present in the stomachs in similar proportions among all age classes of shorthorn sculpin. Several new host records for parasites were reported and mean numbers of parasite species increased with shorthorn sculpin age. The increased diversity of parasite species and higher d15N values in older/larger individuals suggest that their diets were more diverse and the prey items consumed had higher d15N values. By contrast, the value of d13C in dominant diet items masked the d13C values of minor diet items. We conclude that parasites and stable isotope values provide complementary data on feeding patterns of the shorthorn sculpin. The ubiquitous marine acanthocephalan, Echinorhynchus gadi, was found at high prevalences (87-100 %) and mean intensities (28-35), and were localized in the midgut. In contrast to other studies on acanthocephalans, E. gadi did not influence fish condition as measured by condition factor, liver somatic and gonado-somatic indices.

The effect of repeated exposure to parasite genotypes of the eyefluke Diplostomum pseudospathaceum on infection rate and immunization in three-spined sticklebacks

Adaptive immunity in vertebrates can confer increased resistance against invading pathogens upon re-infection. But how specific parasite genotypes affect the transition from innate to adaptive immunity is poorly understood. Here, we investigated the effects of homologous and heterologous exposures of genetically distinct parasite lineages of the eye fluke Diplostomum pseudospathaceum on gene expression patterns of adaptive immunity in sticklebacks (Gasterosteus aculeatus). We showed that observable differences were largely attributable to final exposures and that there is no transcription pattern characteristic for a general response to repeated infections with D. pseudospathaceum. Final exposure did not unify expression patterns of heterologous pre-exposed fish. Interestingly, heterologous final exposures showed similarities between different treatment groups subjected to homologous pre-exposure. The observed pattern was supported by parasite infection rates and suggests that host immunization was optimized towards an adaptive immune response that favored effectiveness against parasite diversity over specificity.