Measuring fluctuating asymmetry in fattening rabbits: a valid indicator of performance and housing quality?

Fluctuating asymmetry (FA) has been advocated as the preferred measure of developmental instability and a reliable indicator of the quality of an animal (performance/fitness) and of its environment during its growing life. Empirical studies, however, are too scant or equivocal to consider this assumption adequately validated, which is partly due to the lack of a robust methodological framework for collecting and analyzing FA data. Therefore, we conducted an experiment in which 306 weaned rabbits were housed either in welfare-friendly pens (n = 6) or barren pens (n = 6). The size of both types of pen was similar (1.91 m(2)), but the welfare-friendly pens were equipped with suitable enrichment material (gnawing stick, elevated platform, and hiding box) and were stocked with one-half of the number of rabbits compared with the barren pens (17 vs. 34 rabbits per pen). Performance data (BW gain, ADFI, and G:F) were collected every 14 d. After slaughter (d 63 to 72), we measured twice the left- and right-hand side of 11 presumed bilateral traits on intact carcasses and 50 traits on fleshed bones. Using a stringent decision process, an optimal combination of morphological traits for estimating FA in fattening rabbits was determined. This combination consisted of five traits (fleshed bones) that showed no directional asymmetry or antisymmetry and showed a high level of FA relative to the measurement error; also, these traits were not correlated in their signed FA values. Measurements on intact carcasses seemed inappropriate for estimating FA. Using this robust FA measuring protocol, rabbits housed in the welfare-friendly pens were less asymmetric than were rabbits from the barren pens. Except for a greater daily BW gain in the welfare-friendly pens during the first 14 d after weaning, there were no effects of housing conditions on performance traits. The FA was negatively correlated with BW gain in rabbits from the barren pens, whereas in the welfare-friendly pens, there was no correlation. These results support the application of FA as an indicator of animal welfare and performance; however, FA seems to be a more reliable estimator of the underlying developmental instability when living conditions are suboptimal

Edge-versus vertex-inversion at trigonal pyramidal ge(II) centers-a new aromatic anchimerically assisted edge-inversion mechanism

Theoretical calculations reveal that the model phosphagermylenes {(Me)P(C6H4-2-CH2NMe2)}GeX [X = F (1F), Cl (1Cl), Br (1Br), H (1H), Me (1Me)], which are chiral at both the phosphorus and pyramidal germanium(II) centers, may be subject to multiple inversion pathways which result in interconversion between enantiomers/diastereomers. Inversion via a classical vertex-inversion process (through a trigonal planar transition state) is observed for the phosphorus center in all compounds and for the germanium center in 1H, although this latter process has a very high barrier to inversion (221.6 kJ mol?1); the barriers to vertex-inversion at phosphorus increase with decreasing electronegativity of the substituent X. Transition states corresponding to edge-inversion at germanium (via a T-shaped transition state) were located for all five compounds; for each compound two different arrangements of the substituent atoms [N and X axial (1XN?X) or P and X axial (1XP?X)] are possible, and two distinct transition states were located for each of these arrangements. In the first of these (1XN?XPlanar and 1XP?XPlanar), inversion at germanium is accompanied by simultaneous planarization at phosphorus; these transition states are stabilized by p??p? interactions between the phosphorus lone pair and the vacant pz-orbital at germanium. In the alternative transition states (1XN?XFolded and 1XP?XFolded), the phosphorus atoms remain pyramidal and inversion at germanium is accompanied by folding of the phosphide ligand such that there are short contacts between germanium and one of the ipso-carbon atoms of the aromatic ring. These transition states appear to be stabilized by donation of electron density from the ?-system of the aromatic rings into the vacant pz-orbital at germanium. The barriers to inversion via 1XP?XPlanar and 1XP?XFolded are rather high, whereas the barriers to inversion via 1XN?XPlanar and 1XN?XFolded are similar to those for inversion at phosphorus, clearly suggesting that the most important factor in stabilizing these transition states is the ?-withdrawing ability of the substituents, rather than ?-donation of lone pairs or donation of ?-electron density from the aromatic rings into the vacant pz-orbital at germanium