Temperature shock during development fails to increase the fluctuating asymmetry of a sexual trait in stalk-eyed flies.

The fluctuating asymmetry (FA) of bilateral traits is claimed to be a general indicator of environmental stress. Exaggerated sexual ornaments are thought to show elevated levels of FA and a greater response to stress than other traits. Previous work with stalk-eyed flies (Cyrtodiopsis dalmanni) has shown that the FA of the sexual trait (male eye stalks), wing length and wing width were unaffected by a continually applied food stress. Here we tested whether a transient stress (24-h heat shock at 31 degrees C during development) affected the FA of these traits. A second experiment tested the combined stresses of transient heat shock at 31 degrees C with continuous exposure to desiccation. In each experiment, temperature shock reduced the trait size, confirming that the treatments were stressful. However, stress had no effect on the FA of individual traits or the FA summed across all traits. Exposure to the combined stresses significantly elevated mortality and reduced trait size compared to the single-stress regime. However, FA did not differ significantly between flies from the two experiments. We found no evidence that FA in sexual and non-sexual traits reflects transient stress during the development of C. dalmanni

Elucidation of toxicity of organic acids inhibiting growth of Escherichia coli W

The toxic effects of 3-hydroxypropionic acid (3-HP) at high concentrations on cell growth and cellular metabolism are a great challenge to its commercial production. This study has examined and compared the toxic effects of 3-HP on cell growth with other similar weak acids, especially lactic acid, under various concentrations, temperatures and pH using Escherichia coli W as the test strain. 3-HP was approximately 4.4-times more toxic than lactic acid due to the 4.4-fold weaker acidity or 0.64 higher pKa value. The two acids presented no appreciable difference when the growth inhibition was correlated with the undissociated or protonated free acid concentration calculated by the Henderson-Hasselbalch equation. The growth inhibition by other small organic acids, such as acetic acid, pyruvic acid, propionic acid, 2-hydroxybutyric acid (2-HB) and 3-hydroxybutyric acid (3-HB), was also well correlated with their pKa values or protonated free acid concentrations. This study suggests that the growth inhibition by small weak acids is mainly caused by the socalled proton effect (rather than the anion effect), i.e., an increase in the intracellular proton concentration. An appropriate increase in the medium pH was suggested to alleviate the acid toxicity by reducing the free acid concentration in the culture medium