133,228 research outputs found
The capacity to maintain ion and water homeostasis underlies interspecific variation in Drosophila cold tolerance
Many insects, including Drosophila, succumb to the physiological effects of chilling at temperatures well above those causing freezing. Low temperature causes a loss of extracellular ion and water homeostasis in such insects, and chill injuries accumulate. Using an integrative and comparative approach, we examined the role of ion and water balance in insect chilling susceptibility/ tolerance. The Malpighian tubules (MT), of chill susceptible Drosophila species lost [Na+] and [K+] selectivity at low temperatures, which contributed to a loss of Na+ and water balance and a deleterious increase in extracellular [K+]. By contrast, the tubules of chill tolerant Drosophila species maintained their MT ion selectivity, maintained stable extracellular ion concentrations, and thereby avoided injury. The most tolerant species were able to modulate ion balance while in a cold-induced coma and this ongoing physiological acclimation process allowed some individuals of the tolerant species to recover from chill coma during low temperature exposure. Accordingly, differences in the ability to maintain homeostatic control of water and ion balance at low temperature may explain large parts of the wide intra- and interspecific variation in insect chilling tolerance
Fine scales of decay of operator semigroups
Motivated by potential applications to partial differential equations, we
develop a theory of fine scales of decay rates for operator semigroups. The
theory contains, unifies, and extends several notable results in the literature
on decay of operator semigroups and yields a number of new ones. Its core is a
new operator-theoretical method of deriving rates of decay combining
ingredients from functional calculus, and complex, real and harmonic analysis.
It also leads to several results of independent interest.Comment: Version 2 includes numerous minor corrections, and is the authors'
final version. The pape will be published in the Journal of the European
Mathematical Society in April 201
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Delayed chilling appears to counteract flowering advances of apricot in southern UK
Temperatures are rising across the globe, and the UK is no
exception. Spring phenology of perennial fruit crops is to a large extent
determined by temperature during effective chilling (endo-dormancy) and
heat accumulation (eco-dormancy) periods. We used the apricot flowering
records of the UK National Fruit Collections (NFC) to determine the
influence of temperature trends over recent decades (1960 to 2014) on
apricot (Prunus armeniaca L.) flowering time. Using Partial Least Squares
(PLS) regression, we determined the respective periods for calculating
chill and heat accumulation. Results suggested intervals between
September 27th and February 26th and between December 31st and April 12th
as the effective chilling and warming periods, respectively. Flowering
time was correlated with temperature during both periods, with warming
during chilling corresponding to flowering delays by 4.82 d°C-1, while
warming during heat accumulation was associated with bloom advances by
9.85 d°C-1. Heat accumulation started after accumulating 62.7 ± 5.6 Chill
Portions, and flowering occurred after a further 3744 ± 1538 Growing
Degree Hours (above a base temperature of 4°C, with optimal growth at
26°C). When examining the time series, the increase in temperature during
the chilling period did not appear to decrease overall chill accumulation
during the chilling period but to delay the onset of chill accumulation
and the completion of the the average chill accumulation necessary to
start heat accumulation. The resulting delay in heat responsiveness
appeared to weaken the phenology-advancing effect of spring warming.
These processes may explain why apricot flowering time remained
relatively unchanged despite significant temperature increases. A
consequence of this may be a reduction of frost risk for early flowering
crops such as apricot in the UK
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