Long-term decline in krill stock and increase in salps within the Southern Ocean

Antarctic krill (Euphausia superba) and salps (mainly Salpa thompsoni) are major grazers in the Southern Ocean, and krill support commercial fisheries. Their density distributions have been described in the period 1926-51, while recent localized studies suggest short-term changes. To examine spatial and temporal changes over larger scales, we have combined all available scientific net sampling data from 1926 to 2003. This database shows that the productive southwest Atlantic sector contains >50% of Southern Ocean krill stocks, but here their density has declined since the 1970s. Spatially, within their habitat, summer krill density correlates positively with chlorophyll concentrations. Temporally, within the southwest Atlantic, summer krill densities correlate positively with sea-ice extent the previous winter. Summer food and the extent of winter sea ice are thus key factors in the high krill densities observed in the southwest Atlantic Ocean. Krill need the summer phytoplankton blooms of this sector, where winters of extensive sea ice mean plentiful winter food from ice algae, promoting larval recruitment and replenishing the stock. Salps, by contrast, occupy the extensive lower-productivity regions of the Southern Ocean and tolerate warmer water than krill. As krill densities decreased last century, salps appear to have increased in the southern part of their range. These changes have had profound effects within the Southern Ocean food web.     

Visual and auditory evoked potentials: Specificity of reticular formation modulating influences

Zusammenfassung Adrenalinzufuhr wie auch hochfrequente elektrische Reizung am pontinischen Gehirnstamm führen zu Potentialverstärkung, wenn diese nicht visuell, sondern auditiv geweckt wurde. Entsprechende Versuche mit Acetylcholin führten zu keinem Erfolg, was für die Spezifität der retikularen Einflüsse spricht.

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Supported by NSF grant No. GB 4706-X to J. S. and NASA predoctoral fellowship to T.D.L.     

Epistasis and the release of genetic variation during long-term selection

It is an enigma how long-term selection in model organisms and agricultural species can lead to marked phenotypic changes without exhausting genetic variation for the selected trait. Here, we show that the genetic architecture of an apparently major locus for growth in chicken dissects into a genetic network of four interacting loci. The interactions in this radial network mediate a considerably larger selection response than predicted by a single-locus model.     

Vitamin C and the immune response

Summary The inclusion of vitamin C in the drinking water of BALB/c mice was without effect on the humoral antibody response to sheep red blood cells and bacterial lipopolysaccharide. However, there was a significantly increased cell-mediated immune response as determined by increased T-lymphocyte responses to concanavalin A. This might suggest a mechanism, along with interferon enhancement, for the possible protection by vitamin C against some viral infections.We thank Miss Wendy Treat for excellent technical assistance.     

Animal behaviour: continuous activity in cetaceans after birth

All mammals previously studied take maximal rest or sleep after birth, with the amount gradually decreasing as they grow to adulthood, and adult fruitflies and rats die if they are forcibly deprived of sleep. It has therefore been assumed that sleep is necessary for development and serves a vital function in adults. But we show here that, unlike terrestrial mammals, killer-whale and bottlenose-dolphin neonates and their mothers show little or no typical sleep behaviour for the first postpartum month, avoiding obstacles and remaining mobile for 24 hours a day. We find that neonates and their mothers gradually increase the amount of time they spend resting to normal adult levels over a period of several months, but never exceed these levels. Our findings indicate either that sleep behaviour may not have the developmental and life-sustaining functions attributed to it, or that alternative mechanisms may have evolved in cetaceans.     

Clues to the functions of mammalian sleep

The functions of mammalian sleep remain unclear. Most theories suggest a role for non-rapid eye movement (NREM) sleep in energy conservation and in nervous system recuperation. Theories of REM sleep have suggested a role for this state in periodic brain activation during sleep, in localized recuperative processes and in emotional regulation. Across mammals, the amount and nature of sleep are correlated with age, body size and ecological variables, such as whether the animals live in a terrestrial or an aquatic environment, their diet and the safety of their sleeping site. Sleep may be an efficient time for the completion of a number of functions, but variations in sleep expression indicate that these functions may differ across species.