Environmental signals: Synthetic humic substances act as xeno-estrogen and affect the thyroid system of Xenopus laevis

According to outdated paradigms humic substances (HS) are considered to be refractory or inert that do not directly interact with aquatic organisms. However, they are taken up and induce biotransformation activities and may act as hormone-like substances. In the present study, we tested whether HS can interfere with endocrine regulation in the amphibian Xenopus laevis. In order to exclude contamination with phyto-hormones, which may occur in environmental isolates, the artificial HS 1500 was applied. The in vivo results showed that HS 1500 causes significant estrogenic effects on X. laevis during its larval development and results of semi-quantitative RT-PCR revealed a marked increase of the estrogenic biomarker estrogen receptor mRNA (ER-mRNA). Furthermore, preliminary RT-PCR results showed that the thyroid-stimulating hormone (TSH beta-mRNA) is enhanced after exposure to HS1500, indicating a weak adverse effect on T3/T4 availability. Hence, HS may have estrogenic and anti-thyroidal effects on aquatic animals, and therefore may influence the structure of aquatic communities and they may be considered environmental signaling chemicals. (c) 2005 Elsevier Ltd. All rights reserved.

Margulis' theory on division of labour in cells revisited

Division of labour is a marked feature of multicellular organisms. Margulis proposed that the ancestors of metazoans had only one microtubule organizing center (MTOC), so they could not move and divide simultaneously. Selection for simultaneous movement and cell division had driven the division of labour between cells. However, no evidence or explanation for this assumption was provided. Why could the unicellular ancetors not have multiple MTOCs? The gain and loss of three possible strategies are discussed. It was found that the advantage of one or two MTOC per cell is environment-dependent. Unicellular organisms with only one MTOC per cell are favored only in resource-limited environments without strong predatory pressure. If division of labour occurring in a bicellular organism just makes simultaneous movement and cell division possible, the possibility of its fixation by natural selection is very low because a somatic cell performing the function of an MTOC is obviously wasting resources. Evolutionary biologists should search for other selective forces for division of labour in cells.

印象形成中同化和对比效应研究

Impression formation is an important aspect of person perception and has important interpersonal consequences. There are assimilation and contrast effects in impression formation and is still considerable debate regarding the best way to account for them. This present research used trait-implying sentences as priming materials, trait inferences sever as self-generated primes, examined the effect of different trait knowledge in assimilation and contrast effects. Experiment 1 determined the priming and target stimuli of this research by pretest. In experiment 2, participants read trait-implying sentences and resulted in trait inference as self-generated primes, examined the influence of trait activation on impression formation. The results indicated that participants instructed to memorize trait-implying sentences showed assimilation effect, whereas participants instructed to form impression from trait-implying sentences showed contrast effect. Difference to previous studies that emphasized the impact of awareness of the prime in impression formation, this research paid attention to the impact of different trait knowledge that resulted from trait inference. Experiment 3 studied the influence of actor salience on impression formation. The results indicated that when trait-implying sentences that described actors with names and were accompanied with photos of the actors, participants showed contrast under both memorization and impression instructions. Experiment 4 studied the influence of attribution context on assimilation and contrasts. The results showed that contrast ensued when trait-implying sentences were accompanied with the information that suggested a person attribution, whereas assimilation ensued when that information suggested a situation attribution, independent of processing goals. Experiment 5 made a direct test of the effect of different trait knowledge in impression formation. The results discovered that when abstract trait concepts were activated they act as a general interpretation frame in encoding stage, whereas when specific actor-trait links were activated, the activated information is likely to be used as a comparative standard in judgment stage. All studied indicated that there are two types of activated trait knowledge in trait inference: abstract trait concepts versus specific actor-trait links. When trait inference activated abstract trait concepts, the activated information serves as interpretation frame and lead to assimilation effect during impression formation, when trait inference activated specific actor-trait links, the activated information is more likely to be used as a comparative standards and resulted in contrast effects. These findings have important implications for understanding the mechanism of impression formation and practical values for interpersonal communication.