Turkey feeding regimes with different ages of introduction of a choice of foods

An experiment was carried out to investigate five feeding regimes for the turkey which involve introducing a choice of wheat grain and a higher-protein food at 1, 14, 28, 56 and 77 days of age. Broken wheat grains were used from days 1 to 14, and whole grains thereafter. Protein intakes per bird, calculated from standard tables of feed composition, were 39.1, 43.0, 41.8, 35.5 and 36.0 g/day, respectively, from 14 to 98 days. Further groups of birds on a complete diet regime consumed a significantly lower 33.3 g/day. Only two comparisons were significantly different for body weight at 98 days: birds which received the choice at 14 days had a significantly higher weight (5.7 kg/bird) than those which received the choice at 56 days (5.5 kg) and than those on the complete diet regime (5.5 kg). $\text{P}$resentation of the wheat and higher-protein food during the period of protein over-consumption, according to a fixed ratio schedule, might reduce protein intake.     

Time – size tradeoffs: a phylogenetic comparative study of flowering time, plant height and seed mass in a north-temperate flora

Parents face a timing problem as to when they should begin devoting resources from their own growth and survival to mating and offspring development. Seed mass and number, as well as maternal survival via plant size, are dependent on time for development. The time available in the favorable season will also affect the size of the developing juveniles and their survival through the unfavorable season. Flowering time may thus represent the outcome of such a time partitioning problem. We analyzed correlations between flowering onset time, seed mass, and plant height in a north-temperate flora, using both cross-species comparisons and phylogenetic comparative methods. Among perennial herbs, flowering onset time was negatively correlated with seed mass (i.e. plants with larger seeds started flowering earlier) while flowering onset time was positively correlated with plant height. Neither of these correlations was found among woody plants. Among annual plants, flowering onset time was positively correlated with seed mass. Cross-species and phylogenetically informed analyses largely agreed, except that flowering onset time was also positively correlated with plant height among annuals in the cross-species analysis. The different signs of the correlations between flowering onset time and seed mass (compar. gee regression coefficient=−7.8) and flowering onset time and plant height (compar. gee regression coefficient=+30.5) for perennial herbs, indicate that the duration of the growth season may underlie a tradeoff between maternal size and offspring size in perennial herbs, and we discuss how the partitioning of the season between parents and offspring may explain the association between early flowering and larger seed mass among these plants.     

Mechanism of metal-promoted catalysis of nucleic acid hydrolysis by Escherichia coli ribonuclease H

 Catalytic activation of Escherichia coli ribonuclease H by a series of inert chromium complexes [Cr(NH₃)_6-x(H₂O)_x]³⁺ (x = 0–6) that bear water and ammine ligands in well-defined geometries in the inner coordination shell has been examined. Such complexes are observed to function by transition state stabilization. The importance of hydrogen bonding and electrostatics to catalytic activation of this reaction were quantitatively evaluated. The availability of [Cr(NH₃)_6-x(H₂O)_x]³⁺ complexes of varying coordination geometry also affords a probe of the preferred structural arrangement for hydrogen-bonding interactions. Under the solution conditions employed, a facial array of bound water molecules is required to promote catalysis, as expected from comparison with the ligation of the enzyme-bound Mg²⁺–cofactor. These results exclude a structural role for the essential metal cofactor. Hydrogen bonding appears to be the dominant stabilizing interaction. In the absence of bound water ligands (for example, in the specific cases of Cr(NH₃)₆ ³⁺ and Co(NH₃)₆ ³⁺), hydrogen bond stabilization is precluded: however, catalysis is observed as a result of the increased positive charge on the complex. Apparently the trivalent charge offsets the poorer hydrogen bonding abilities of the ammine ligands. Received: 11 June 1996 / Accepted: 31 July 1996