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921.
922.
The aim of the current work was to evaluate the effect of preschoolers' television (TV) watching time on the prevalence of obesity even after controlling for their total energy intake and their physical activity status. A representative sample of 2,374 Greek children aged 1–5 years was examined (“Growth, Exercise and Nutrition Epidemiological Study in preSchoolers”, GENESIS study). Children's TV watching time on a usual weekday and at a usual weekend was recorded. The overall mean of children's TV viewing time was 1.32 h/day. The majority of participants (74.0%) spent <2 h/day watching TV whereas only 3.1% spent >4 h/day in front of a TV set. Overall, 65.2% of participants were normal weight, 17.2% were overweight, and the rest 17.6% were obese. The prevalence of obesity was significantly higher among those with TV viewing time ≥2 h/day (21.7%) compared to those watching TV <2 h/day (16.1%, P = 0.003). TV viewing time remained significantly associated with the likelihood of being obese even after controlling for potential confounders (i.e., socio demographic and other characteristics and physical activity status) only among children aged 3–5 years. However, further adjusting for children's total energy intake revealed that the association between the TV viewing time and the probability of being obese was no longer statistically significant. On the other hand, physical activity status continued to be an independent factor of being obese. The current findings support the hypothesis that the effect of TV viewing time on childhood obesity is independent of physical activity status and may be attributed to the increased total energy intake during TV watching.  相似文献   
923.
  1. Movement behaviours of adult aquatic insects can produce distinct spatial distribution patterns. Studies of adult abundance with distance away from water bodies are common and may invoke flight capability to explain species differences. In contrast, distribution patterns along river channels are poorly described, but are no less important for understanding population dynamics. Longitudinal patterns in adult abundance along short river lengths may differ between sexes and at different life stage transitions between aquatic and terrestrial environments, i.e. at emergence and oviposition. Flight capability is unlikely to influence longitudinal patterns created at emergence, but may influence local abundances of mature females seeking to lay eggs. We tested hypotheses about how local abundances of mature females might differ according to oviposition habits and flight capability.
  2. We surveyed abundances of mature female caddisflies at adjacent riffle–pool pairs along short river lengths with homogeneous riparian cover. Our survey included nine species in three families (Hydrobiosidae, Leptoceridae, Hydropsychidae), which encompassed multiple different oviposition habits and a range of wing sizes and shapes. Several of the species oviposit preferentially in riffles. Accordingly, we tested for differences in female abundance between channel units (adjacent riffle–pool pairs). We also tested whether females attained higher abundances in some places along channels than others (i.e. over larger spatial scales and regardless of channel unit) which imply movements along the channel and aggregation in some locations. Wing morphology was used as a proxy measure of flight capability and included measures of wing span, area, aspect ratio and the second moment of wing area.
  3. Three distinctly different distribution patterns of mature female caddisflies were identified. The abundance of three species varied over larger scales only (multiple channel units). Six species that oviposit preferentially in riffles had higher female abundances at riffles than pools, but for only one did abundances also vary over larger scales. There was no association between these different patterns and measures of wing morphology, after removing metrics that were correlated and that differed systematically between taxonomic families. However, we could not reject the hypothesis that some aspect of flight behaviour may have contributed to observed patterns.
  4. The diverse but distinct distributions of mature female caddisflies we observed along short channel lengths are novel and suggest that species differ in their propensity for movement along streams, which could have consequences for local densities of eggs and juveniles in the aquatic environment. The degree to which population sizes are coupled across the terrestrial-to-aquatic transition is rarely investigated in aquatic insects and may provide fresh insight into sources of spatial variation within populations. Similarly, a more nuanced approach to research on the flight of aquatic insects, including age- and sex-specific phenomena, may provide greater insight into the diverse ecological functions and consequences of movement.
  相似文献   
924.
Frequent convergent evolution in phylogenetically unrelated taxa points to the importance of ecological factors during evolution, whereas convergent evolution in closely related taxa indicates the importance of favourable pre-existing characters (pre-adaptations). We investigated the transitions to arboreal life in oribatid mites (Oribatida, Acari), a group of mostly soil-living arthropods. We evaluated which general force—ecological factors, historical constraints or chance—was dominant in the evolution of arboreal life in oribatid mites. A phylogenetic study of 51 oribatid mite species and four outgroup taxa, using the ribosomal 18S rDNA region, indicates that arboreal life evolved at least 15 times independently. Arboreal oribatid mite species are not randomly distributed in the phylogenetic tree, but are concentrated among strongly sclerotized, sexual and evolutionary younger taxa. They convergently evolved a capitate sensillus, an anemoreceptor that either precludes overstimulation in the exposed bark habitat or functions as a gravity receptor. Sexual reproduction and strong sclerotization were important pre-adaptations for colonizing the bark of trees that facilitated the exploitation of living resources (e.g. lichens) and served as predator defence, respectively. Overall, our results indicate that ecological factors are most important for the observed pattern of convergent evolution of arboreal life in oribatid mites, supporting an adaptationist view of evolution.  相似文献   
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928.
Like most solitary carnivores, the home ranges of male American mink overlap with those of several females, but each female typically shares its range with only a single male. Nevertheless, female mink produce multiply sired litters. Unusually among mammals, the physiological characteristics of female American mink make them highly suited to multiple paternity, suggesting that polyandry in the species may result from female behaviour rather than from coercion by males. In a free-choice experiment on captive-bred animals, all female mink mated multiply, with seven of the eight mating with all three available partners. Since females sometimes resisted copulations, multiple mating in this species may result from their behaviour rather than male coercion. Females visited males nonrandomly, but visiting patterns did not predict mating patterns, suggesting disparate social and mating preferences. There was no evidence for precopulatory female choice, since the allocation of copulations among available males did not deviate significantly from the expected distribution. Females mated multiply only around the predicted times of ovulation, contrary to the expectation that they should be more selective at times of peak fertility. Larger males copulated for longer in total: copulation duration is probably under male control, suggesting that larger males could influence mating duration, perhaps increasing their share of paternity by greater sperm transfer. Our observations suggest that in wild populations, mating patterns could be influenced by female preference for multiple partners.  相似文献   
929.
IsdG and IsdI are paralogous heme degrading enzymes from the bacterium Staphylococcus aureus. Heme bound by these enzymes is extensively ruffled such that the meso-carbons at the sites of oxidation are distorted toward bound oxygen. In contrast, the canonical heme oxygenase family degrades heme that is bound with minimal distortion. Trp-66 is a conserved heme pocket residue in IsdI implicated in heme ruffling. IsdI variants with Trp-66 replaced with residues having less bulky aromatic and alkyl side chains were characterized with respect to catalytic activity, heme ruffling, and electrochemical properties. The heme degradation activity of the W66Y and W66F variants was approximately half that of the wild-type enzyme, whereas the W66L and W66A variants were inactive. A crystal structure and NMR spectroscopic analysis of the W66Y variant reveals that heme binds to this enzyme with less heme ruffling than observed for wild-type IsdI. The reduction potential of this variant (−96 ± 7 mV versus standard hydrogen electrode) is similar to that of wild-type IsdI (−89 ± 7 mV), so we attribute the diminished activity of this variant to the diminished heme ruffling observed for heme bound to this enzyme and conclude that Trp-66 is required for optimal catalytic activity.  相似文献   
930.
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