ALBERT

Description: We present a new method to obtain samples for the measurement of helium isotopes and neon in water, to replace the classical sampling procedure using clamped-off Cu tubing containers that we have been using so far. The new method saves the gas extraction step prior to admission to the mass spectrometer, which the classical method requires. Water is drawn into evacuated glass ampoules with subsequent flame sealing. Approximately 50% headspace is left, from which admission into the mass spectrometer occurs without further treatment. Extensive testing has shown that, with due care and with small corrections applied, the samples represent the gas concentrations in the water within ±0.07% (95% confidence level; ±0.05% with special handling). Fast evacuation is achieved by pumping on a small charge of water placed in the ampoule. The new method was successfully tested at sea in comparison with Cu-tubing sampling. We found that the ampoule samples were superior in data precision and that a lower percentage of samples were lost prior to measurement. Further measurements revealed agreement between the two methods in helium, 3He and neon within ±0.1%. The new method facilitates the dealing with large sample sets and minimizes the delay between sampling and measurement. The method is applicable also for gases other than helium and neon. Highlights ► We describe a novel method to obtain water samples for the measurement of helium isotopes and neon. ► No sample treatment is required between sampling and measurement. ► The method is highly accurate, mechanically simple and well suited for oceanographic work. ► A comparison with Cu-tubing samples has shown full agreement.

Description: After the last glaciations, Icelandic freshwater systems were colonised by only a small number of fish species from adjacent ancestral marine populations. Among these, the three-spined stickleback ( Gasterosteus aculeatus) could fill free niches and diversify. As in similar systems in the northern hemisphere, these fish show signs of recent genetic and morphological parallel divergence, which might be a first step towards further differentiation and might in the long run lead to establishment of reproductive isolation and therefore speciation. This is first examined at a large geographic scale, where colonisation can be shown to have occurred in one main wave and genetic isolation by distance is demonstrated. On a finer scale, recent divergence led to the formation of sympatric ecomorphs that differ in their habitat use and several morphological characteristics, and are genetically differentiated. My study supports the view that contrasting parasite communities between habitats or niches within a habitat could be a driver of this divergence. Their selection on the immune genes of the major histocompatibility complex (MHC), combined with female mate choice for sympatric morphs carrying resistance MHC alleles, could drive the evolution of the system towards diversification. Using natural replicates of sympatric three-spined stickleback ecomorphs, I found evidence for such a pattern, where suspected sympatric morphs carrying different parasite communities show low MHC allele overlap as well as signs of genetic differentiation. On the other hand, the suspected morphs that did not show contrasting parasite communities display overlapping MHC allele pools and no sign of neutral genetic differentiation. Furthermore, signatures of antagonistic evolutionary arms races between parasites and their hosts' adaptive immune defence are identified in a truly sympatric system. In a final pilot study of adaptive immune gene expression patterns, the importance of this proximal factor of parasite resistance for adaptive processes is highlighted. Here again, we show that contrasting immune defence between sympatric morphs further supports the role of parasite mediated selection for ecological host speciation.