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311.
Vegetation, temperature and hydrology are major factors controlling wetland methane (CH4) dynamics. In order to test their importance, we measured CH4 emissions and environmental characteristics over 2 years from five mires representing a successional sequence, ranging in
age from 178 to 2,520 years. We hypothesized CH4 emissions to be higher from the sedge-dominated fens than from the older bog stage. The more constant hydrological conditions
at later successional stages as a consequence of the thicker peat layer appeared to result in lower temporal variation in
CH4 emissions. Accordingly, the other controls, temperature and vegetation, had an effect on CH4 emissions only when the water table was sufficiently high. The seasonal variation in CH4 emissions was controlled by temperature only at the oldest study site, which had the lowest variation in water table. Within-season
variation in emissions related to plant phenology was highest at the fen stage, which was dominated by aerenchymatous plants
with a strong seasonal pattern, namely sedges and forbs. In contrast to our hypothesis, CH4 emissions increased with mire age towards the bog stage. However, the trend did not emerge during a rainy growing season,
due to a rise in CH4 emissions at the younger stages. The results may imply two different mechanisms during mire succession: while old mires are
able to avoid the perturbation associated with variation in the water table and maintain their function as CH4 emitters, young mires are exposed to perturbation but are able to recover their function. 相似文献
312.
313.
Life history theory predicts a trade-off between fitness benefits and costs of delaying age at first reproduction (AFR). In many human populations, maternal AFR has been increasingly delayed beyond sexual maturity over the past decades, raising a question of whether any fitness benefits accrued outweigh costs incurred. To investigate the cost–benefit trade-off concerning AFR in women, we construct a theoretical model and test its predictions using pedigree data from historical Finnish mothers. The model predicts that the probability of reproductive failure (no offspring produced reaching breeding) will increase with AFR if the benefit with delaying in terms of improvement to offspring quality (i.e., breeding probability) cannot offset the cost from decline in offspring quantity. The data show that offspring quantity declined significantly with delayed reproduction, while offspring quality remained initially constant before declining when AFR was delayed beyond 30. Consistent with the theoretical model's predictions, reproductive failure probability increased markedly with delaying AFR after 30, independently of maternal socioeconomic status. Our study is the first to investigate the associations between delay in AFR after sexual maturity and changes in not only offspring quantity but also offspring quality and suggest a significant evolutionary disadvantage of delayed AFR beyond 30 for lineage persistence in a predemographic transition society. 相似文献
314.
315.
Jianing Yang Di Wang Hui Liu Lin Wang Ling Jin Virpi Ahola Chongren Xu Rongjiang Wang 《Insect Science》2023,30(3):758-770
Temperature is one of the most important environmental factors that affect organisms, especially ectotherms, due to its effects on protein stability. Understanding the general rules that govern thermostability changes in proteins to adapt high-temperature environments is crucial. Here, we report the amino acid substitutions of phosphoglucose isomerase (PGI) related to thermostability in the Glanville fritillary butterfly (Melitaea cinxia, Lepidoptera: Nymphalidae). The PGI encoded by the most common allele in M. cinxia in the Chinese population (G3-PGI), which is more thermal tolerant, is more stable under heat stress than that in the Finnish population (D1-PGI). There are 5 amino acid substitutions between G3-PGI and D1-PGI. Site-directed mutagenesis revealed that the combination of amino acid substitutions of H35Q, M49T, and I64V may increase PGI thermostability. These substitutions alter the 3D structure to increase the interaction between 2 monomers of PGI. Through molecular dynamics simulations, it was found that the amino acid at site 421 is more stable in G3-PGI, confining the motion of the α-helix 420–441 and stabilizing the interaction between 2 PGI monomers. The strategy for high-temperature adaptation through these 3 amino acid substitutions is also adopted by other butterfly species (Boloria eunomia, Aglais urticae, Colias erate, and Polycaena lua) concurrent with M. cinxia in the Tianshan Mountains of China, i.e., convergent evolution in butterflies. 相似文献
316.
An extract of a pancreatic carcinoid tumor obtained at autopsy from a patient who had suffered from Cushing's syndrome was found to have the ability to release thyrotropin (but not any other pituitary hormones) from cultured rat anterior pituitary cells, and to bind to a specific thyrotropin-releasing hormone (TRH) antiserum. The tumor contained 2.2 and 3.9 nmol/g of TRH bio- and immunoreactivity, respectively. The active material was purified and its amino acid composition and chromatographic properties were found to be identical with those of synthetic ovine/porcine TRH. This represents the first isolation of human TRH and the first established case of a 'TRHoma', a TRH-producing tumor. 相似文献
317.