Control of Diapause by Acidic pH and Ammonium Accumulation in the Hemolymph of Antarctic Copepods

Life-cycles of polar herbivorous copepods are characterised by seasonal/ontogenetic vertical migrations and diapause to survive periods of food shortage during the long winter season. However, the triggers of vertical migration and diapause are still far from being understood. In this study, we test the hypothesis that acidic pH and the accumulation of ammonium (NH4+) in the hemolymph contribute to the control of diapause in certain Antarctic copepod species. In a recent study, it was already hypothesized that the replacement of heavy ions by ammonium is necessary for diapausing copepods to achieve neutral buoyancy at overwintering depth. The current article extends the hypothesis of ammonium-aided buoyancy by highlighting recent findings of low pH values in the hemolymph of diapausing copepods with elevated ammonium concentrations. Since ammonia (NH3) is toxic to most organisms, a low hemolymph pH is required to maintain ammonium in the less toxic ionized form (NH4+). Recognizing that low pH values are a relevant factor reducing metabolic rate in other marine invertebrates, the low pH values found in overwintering copepods might not only be a precondition for ammonium accumulation, but in addition, it may insure metabolic depression throughout diapause

Recruitment and body size in relation to temperature in juvenile Patagonian toothfish (Dissostichus eleginoides) at South Georgia

Recruitment variability in juvenile Patagonian toothfish (Dissostichus eleginoides), a commercially important, deepwater nototheniid fish, was examined at the sub-Antarctic island of South Georgia, South Atlantic. Data from 13 demersal trawl surveys conducted over a 20-year period were analysed. Abundance of the 1(+) juvenile fish cohort (13-15 month old dependent on survey date) was found to vary inter-annually and was found to be inversely correlated with the sea surface temperature (SST) conditions experienced by adults prior to spawning. Environmental temperatures experienced by toothfish eggs and larvae were not significantly correlated with juvenile density. The mean length of 1(+) fish attained after 13-15 months was higher in years of high juvenile abundance and was significantly inversely correlated with SST in the summer prior to adult spawning. Trends in toothfish recruitment variability mirrored those previously observed in a range of krill-dependent land-based predators at South Georgia for whom non-seasonal, large-scale climatic events such as El Nino Southern Oscillation (ENSO) are considered the most likely underlying drivers of variability in breeding success. The drivers of recruitment variability in toothfish are not fully understood but a range of possible mechanisms are considered. A better understanding of recruitment variability holds great interest for fisheries managers and could be used refine forecasts of years of good or poor recruitment for the toothfish fishery at South Georgia

Genome-wide association analyses identify variants in developmental genes associated with hypospadias

Item does not contain fulltextHypospadias is a common congenital condition in boys in which the urethra opens on the underside of the penis. We performed a genome-wide association study on 1,006 surgery-confirmed hypospadias cases and 5,486 controls from Denmark. After replication genotyping of an additional 1,972 cases and 1,812 controls from Denmark, the Netherlands and Sweden, 18 genomic regions showed independent association with P < 5 x 10(-8). Together, these loci explain 9% of the liability to developing this condition. Several of the identified regions harbor genes with key roles in embryonic development (including HOXA4, IRX5, IRX6 and EYA1). Subsequent pathway analysis with GRAIL and DEPICT provided additional insight into possible genetic mechanisms causing hypospadias