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1.
Michael E. Baker 《Biochemical and biophysical research communications》2010,399(2):215-220
11β-Hydroxysteroid dehydrogenase-type 2 (11β-HSD2) regulates the local concentration of cortisol that can activate the glucocorticoid receptor and mineralocorticoid receptor, as well as the concentration of 11-keto-testosterone, the active androgen in fish. Similarly, 17β-HSD2 regulates the levels of testosterone and estradiol that activate the androgen receptor and estrogen receptor, respectively. Interestingly, although human 11β-HSD2 and 17β-HSD2 act at different positions on different steroids, these enzymes are paralogs. Despite the physiological importance of 11β-HSD2 and 17β-HSD2, details of their origins and divergence from a common ancestor are not known. An opportunity to understand their evolution is presented by the recent sequencing of genomes from sea urchin, a basal deuterostome, and amphioxus, a basal chordate, and the availability of substantial sequence for acorn worm and elephant shark, which together provide a more complete dataset for analysis of the origins of 11β-HSD2 and 17β-HSD2. BLAST searches find an ancestral sequence of 17β-HSD2 in sea urchin, acorn worm and amphioxus, while an ancestral sequence of 11β-HSD2 first appears in sharks. Sequence analyses indicate that 17β-HSD2 in sea urchin may have a non-enzymatic activity. Evolutionary analyses indicate that if acorn worm 17β-HSD2 is catalytically active, then it metabolizes novel substrate(s). 相似文献
2.
Predators and parasitoids may contribute to controlling the population sizes of phytophagous insects, and this has been shown
to benefit plants. Phytophagous insects may also be killed by other herbivores (intraguild predation), usually larger-sized
vertebrates that ingest insects accidentally while feeding on common food sources. We studied the intraguild predation on
acorn weevils by ungulates and assessed the consequences for weevil populations. Infested acorns are prematurely abscised
and the weevil larvae finish their development inside the acorns after being dropped. Our results show that weevil larvae
were killed by ungulates eating the infested acorns on the ground. Ungulates did not discriminate between infested and sound
acorns, and the probability of a larva being incidentally eaten was inversely related to acorn availability. Thus, predation
risk was enhanced by the premature drop of infested acorns when acorn availability on the ground was low. Predation rates
on infested acorns were much higher where ungulates were present, and acorn infestation rates were significantly lower. However,
ungulates did not provide the oaks any net benefit, since the reduction of infestation rates was not enough to compensate
for the large amounts of sound acorns eaten by ungulates. Seed predation is usually studied as a progressive loss of seeds
by pre- and post-dispersal predators, but the interactions between them are usually not considered. We show that intraguild
predation on insects by large ungulates had an effect on the structure of the foraging guild, as the proportion of acorns
predated by insects decreased; however, replicating the same experimental design in different ecological scenarios would increase
the strength of these results. In conclusion, the present study shows the importance of considering the multi-trophic interactions
between seed predators in order to have a complete picture of granivory. 相似文献
3.
The relationship between seed size and fitness in plants may depend on offspring density, especially in cases where seed size affects the outcome of competition. We investigated the relationship between seed mass, germination, intraspecific competition and seedling height in a glasshouse experiment on three European white oak species (Quercus robur, Q. petraea, Q. pubescens). Within offspring families, seed mass showed a moderate, but statistically significant effect on seedling height, i.e. seedlings from heavier seeds were slightly taller. In contrast, competition caused pronounced inequality in seedling height in pairs of competing seedlings, but in only 55.2% of all pairs the dominant competitor arose from the heavier seed. It is thus possible that a positive effect of seed mass on seedling growth can be mediated through the density of conspecific seedlings and that heterogeneity in offspring density will contribute to the maintenance of seed mass variation in oak populations. 相似文献
4.
Zhong Yao Kenshi Sakai Xujun Ye Tetsuya Akita Yuko Iwabuchi Yoshinobu Hoshino 《Ecological Informatics》2008,3(3):237-244
Alternate bearing of acorn is a well-marked yield variability phenomenon in forest production. In Japan, this phenomenon is also related to wildlife management (e.g. of animals such as wild pigs, that rely on acorn as their major feed source). Effective management of animals dependent on acorn will require accurate estimation of acorn yield at an early stage. In this paper, we proposed a way to estimate acorn yield from the canopy reflectance values of individual trees. Using an Airborne Imaging Spectrometer for Application (AISA) Eagle System, hyperspectral images in 72 visible and near-infrared wavelengths (407–898 nm) were acquired over an acorn forest in Japan 10 times over three consecutive years (2003–2005) during the early acorn growing season. The canopy spectral reflectance values for individual trees at each wavelength were extracted from the images, and important wavelengths were determined as estimating factors by the B-matrix technique based on partial least squares (PLS) analysis. Yield-estimating models were then developed by multiple linear regression (MLR). Three models obtained from images acquired on June 27 in 2003, July 13 in 2004 and June 21 in 2005 estimated acorn yield well in comparison with ground truth, indicating that the procedure has considerable potential. The study also demonstrated the B-matrix technique based on PLS analysis to be reliable and efficient in identifying important wavelengths for determining suitable estimating factors that best contribute to the estimation model. 相似文献
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The resource allocation for vegetative growth and female reproduction in three tree species of subgenus Cyclobalanopsis (Quercus, Fagaceae), i.e., Q. salicina, Q. sessilifolia, and Q. acuta, were examined on a per-individual basis in two consecutive reproductive seasons, in order to test whether these trees fit
the predictions of the masting hypotheses about resource matching versus resource switching. Since the three Quercus species have a biennial fruiting habit, it takes 3 years for the observation of two reproductive events. Female flower and
acorn production per tree were investigated by using a seed-trap method and a numerical analysis of seed dispersal. The net
production of each individual was estimated as the sum of the annual increase in the dry mass of vegetative organs and reproductive
investment per tree. In the data analyses, the three species were pooled, since all 12 sample trees of the subgenus apparently
showed masting in the same year, with no exceptions. Female flower and acorn production per individual tree changed considerably
between years. The net production per tree increased with tree size, but did not differ between years. Therefore, the reproductive
allocation (proportion of a plant’s annual assimilated resources which are used for reproduction) differed dramatically between
years. On the other hand, within a year, the reproductive allocation increased with increasing net production per tree. These
results suggest that the switching of resource allocation between years within an individual are occurring in subgenus Cyclobalanopsis species, and the intensity of the switching increases with increasing tree size. 相似文献
8.
都江堰地区灌丛内迺栎橡子的捕食和搬运(英文) 总被引:4,自引:0,他引:4
从 2 0 0 0年 9月至 2 0 0 2年 1 2月 ,以四川都江堰常绿阔叶林灌丛内的优势种———栎 (Quercusserrata)为研究对象 ,研究了昆虫、鼠类和真菌对栎橡子的捕食和搬运。结果表明 :(1 )取食橡子的鼠类的群落结构和数量在年间差异较小 ,这可能与三年间栎橡子的产量相对稳定有关 ;(2 )栎橡子的虫蛀率在三年间存在显著性差异 ,范围在 1 4 1 7% - 32 4 9%之间 ;(3)鼠类的就地取食和搬运是影响种子库内橡子命运的主要因素 ;(4 )橡子虫蛀率的变化影响鼠类的觅食活动。鼠类对饱满橡子和虫蛀橡子的选择性取食和搬运可能影响许多坚果植物 (栎树 )的自然更新过程 相似文献
9.
Perceived predation risk and competition for acorns are expected to affect scatter-hoarding decisions by Algerian mice (Mus spretus). We manipulated both factors by means of predator fecal scents and ungulate exclosures. We hypothesized that high-risk perception and ungulate presence would promote acorn dispersal. In the former case, it would stimulate acorn mobilization to safe microhabitats rather than in situ consumption. In the latter, increased competition for acorns would promote their storage for later consumption. We also expected that mice would adapt their foraging behavior to previous experience modulating the strength of these effects.In the presence of ungulates, mice focused their foraging activities on food acquisition at the expenses of vigilant behaviors. However, a more efficient foraging did not entail enhanced dispersal services. Lack of anti-predatory cover in tree surroundings may have deterred mice from transporting seeds outside canopies. Increased risk interacted with previous experience. In control trees (no predator odor), mice confidence increased throughout the night resulting in decreased vigilance and enhanced acorn mobilization rates. In contrast, in risky conditions (trees with predator odor) mice maintained a base-line vigilant behavior. Contrary to our expectations, increased risk did not result in higher acorn mobilization, but the opposite. Again, the scarcity of safe microhabitats for mobilization may have been the underlying cause of this behavior.Our results show that successful acorn dispersal depends, at least partly, on plant-animal relationships that are beyond the oak-rodent mutualism. Thus, any conservation policy aimed at restoring natural regeneration of oaks should take into account the interaction network in which oak-rodent encounters are embedded. In addition, they suggest that mice incorporate direct and indirect cues of risks (habitat structure) through recent experience. A better understanding of this process will improve our ability to incorporate such temporal and spatial variability in models of acorn dispersal. 相似文献
10.
Walter D. Koenig Douglas J. Schaefer Stefania Mambelli Todd E. Dawson 《Journal of Field Ornithology》2008,79(3):280-285
ABSTRACT The diet of Acorn Woodpeckers (Melanerpes formicivorus) in central coastal California consists of a mixture of high‐quality (insects) and low‐quality (stored acorns) food during the spring breeding season. We used stable isotope ratios obtained from blood samples to estimate possible differences in the proportion of these items being fed to nestlings and being consumed by breeding adults, as well as the extent to which the diet of nestlings shifts between insects and acorns during the nestling period. Based on both feeding observations and items recovered from nestlings, older nestlings were fed 28% acorns. Using this value as a baseline for the isotope analyses, the diet of breeding adults was estimated to consist of 90% acorns. Based on repeated samples from the same nestlings over time, the estimated proportion of acorns in their diet increased from 19% in 9‐ to 12‐d‐old nestlings to 42% in 23‐ to 26‐d‐old nestlings. There was a significant correlation between the isotope values of adults and the nestlings they fed, indicating that different groups of Acorn Woodpeckers have significantly different diets. Although important for successful reproduction in this species, stored acorns are not the primary food resource used to feed young. Instead, the availability of stored acorns allows adult Acorn Woodpeckers to provide nestlings with more protein‐rich insects while maintaining themselves on relatively protein‐poor, low‐quality acorns. Differences in the diets of adults and their nestlings are likely widespread among species that feed, at least in part, on low‐quality foods, such as fruit and seeds, during the breeding season. 相似文献