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521.
Many eurythermal organisms alter composition of their membranes to counter perturbing effects of environmental temperature
variation on membrane fluidity, a process known as homeoviscous adaptation. Marine intertidal gastropods experience uniquely
large thermal excursions that challenge the functional integrity of their membranes on tidal and seasonal timescales. This
study measured and compared membrane fluidity in marine intertidal snail species under three scenarios: (1) laboratory thermal
acclimation, (2) thermal acclimatization during a hot midday low tide, and (3) thermal acclimatization across the vertical
intertidal zone gradient in temperature. For each scenario, we used fluorescence polarization of the membrane probe DPH to
measure membrane fluidity in individual samples of gill and mantle tissue. A four-week thermal acclimation of Tegula funebralis to 5, 15, and 25°C did not induce differences in membrane fluidity. Littorina keenae sampled from two thermal microhabitats at the beginning and end of a hot midday low tide exhibited no significant differences
in membrane fluidity, either as a function of time of day or as a function of thermal microhabitat, despite changes in body
temperature up to 24°C within 8 h. Membrane fluidities of a diverse group of snails collected from high, middle, and low vertical
regions of the intertidal zone varied among species but did not correlate with thermal microhabitat. Our data suggest intertidal
gastropod snails do not exhibit homeoviscous adaptation of gill and mantle membranes. We discuss possible alternatives for
how these organisms counter thermal excursions characteristic of the marine intertidal zone. 相似文献
522.
Julie K. Desjardins Kelly A. Stiver John L. Fitzpatrick Nicole Milligan Glen J. Van Der Kraak Sigal Balshine 《Behavioral ecology and sociobiology》2008,62(5):785-794
Among taxonomically widespread cooperatively breeding vertebrates, those with non-breeding helpers-at-the-nest provide an
excellent opportunity to understand the proximate mechanisms underlying care and allocare. In this study, we examined androgen
levels in relation to care behavior in a cooperatively breeding cichlid fish, Neolamprologus pulcher, from Lake Tanganyika. We concentrated on androgens, as these hormones have been linked to the defense behavior, and the
defense of young is a common form of parental care in fishes. N. pulcher dominant female breeders performed the most care and also displayed the highest levels of plasma testosterone (T) compared
with other individuals within the social group. We also found that dominant male breeders provided a similar amount of care
as did the subordinate helpers, but breeding males had the highest levels of 11-ketotestosterone (11KT), an important androgen
in fish. Breeders had higher levels of both androgens (T and 11KT) compared to helpers. There was a weak but significant positive correlation between T levels and the frequency of
care regardless of sex and status. Our results suggest that androgens may promote defense of young and are in contrast to
the commonly reported trade-off between androgen and parental care. 相似文献
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Outdoor versus indoor contributions to indoor particulate matter (PM) determined by mass balance methods 总被引:2,自引:0,他引:2
Kopperud RJ Ferro AR Hildemann LM 《Journal of the Air & Waste Management Association (1995)》2004,54(9):1188-1196
This study compares an indoor-outdoor air-exchange mass balance model (IO model) with a chemical mass balance (CMB) model. The models were used to determine the contribution of outdoor sources and indoor resuspension activities to indoor particulate matter (PM) concentrations. Simultaneous indoor and outdoor measurements of PM concentration, chemical composition, and air-exchange rate were made for five consecutive days at a single-family residence using particle counters, nephelometers, and filter samples of integrated PM with an aerodynamic diameter of less than or equal to 2.5 microm (PM2.5) and PM with an aerodynamic diameter of less than or equal to 5 microm (PM5). Chemical compositions were determined by inductively coupled plasma mass-spectrometry. During three high-activity days, prescribed activities, such as cleaning and walking, were conducted over a period of 4-6 hr. For the remaining two days, indoor activities were minimal. Indoor sources accounted for 60-89% of the PM2.5 and more than 90% of the PM5 for the high-activity days. For the minimal-activity days, indoor sources accounted for 27-47% of PM2.5 and 44-60% of the PM5. Good agreement was found between the two mass balance methods. Indoor PM2.5 originating outdoors averaged 53% of outdoor concentrations. 相似文献
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