32 research outputs found
Role of melatonin in the control of depth distribution of Daphnia magna
Previous studies confirmed the presence of melatonin in Daphnia magna and demonstrated diurnal fluctuations in its concentration. It is also known that in several invertebrate species, melatonin affects locomotor activity. We tested the hypothesis that this hormone is involved in the regulation of Daphnia diel vertical migration (DVM) behaviour that is well recognized as the adaptive response to predation threat. Using 'plankton organs', we studied the effect of three concentrations of exogenous melatonin (10-5, 10-7, 10-9 M) on DVM of both female and male D. magna in the presence or absence of chemical cue (kairomone) of planktivorous fish. Depth distribution was measured six times a day, using infrared-sensitive closed circuit television cameras. Our results showed a significant effect of melatonin on the mean depth of experimental populations, both males and females, but only when melatonin was combined with fish kairomone. Females stayed, on average, closer to the surface than males, both responding to the presence of kairomone by descending to deeper strata. In the presence of exogenous melatonin and with the threat of predation, Daphnia stayed closer to the surface and their distribution was more variable than that of individuals, which were exposed to the kairomone alone. Approaching the surface in the presence of predation threat seems to be maladaptive. We postulate the role of melatonin as a stress signal inhibitor in molecular pathways of response to predation threat in Cladocera
The overwintering of Antarctic krill, Euphausia superba, from an ecophysiological perspective
A major aim of this review is to determine
which physiological functions are adopted by adults and
larvae to survive the winter season with low food supply
and their relative importance. A second aim is to clarify the
extent to which seasonal variation in larval and adult krill
physiology is mediated by environmental factors with a
strong seasonality, such as food supply or day light. Experimental
studies on adult krill have demonstrated that speciWc
physiological adaptations during autumn and winter,
such as reduced metabolic rates and feeding activity, are
not caused simply by the scarcity of food, as was previously
assumed. These adaptations appear to be inXuenced
by the local light regime. The physiological functions that
larval krill adopt during winter (reduced metabolism,
delayed development, lipid utilisation, and variable growth
rates) are, in contrast to the adults, under direct control by
the available food supply. During winter, the adults often
seem to have little association with sea ice (at least until
early spring). The larvae, however, feed within sea ice but
mainly on the grazers of the ice algal community rather
than on the algae themselves. In this respect, a miss-match
in timing of the occurrence of the last phytoplankton
blooms in autumn and the start of the sea ice formation, as
has been increasingly observed in the west Antarctic Peninsula
(WAP) region, will impact larval krill development
during winter in terms of food supply and consequently the
krill stock in this region
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Ultrafast Au(III)-Mediated Arylation of Cysteine
Through mechanistic work and rational design, we have developed the fastest organometallic abiotic Cys bioconjugation. As a result, the developed organometallic Au(III) bioconjugation reagents enable selective labeling of Cys moieties down to picomolar concentrations and allow for the rapid construction of complex heterostructures from peptides, proteins, and oligonucleotides. This work showcases how organometallic chemistry can be interfaced with biomolecules and lead to a range of reactivities that are largely unmatched by classical organic chemistry tools