Genetic diversity of the tropical tree Terminalia amazonia (Combretaceae) in naturally fragmented populations.

The effect of long-term fragmentation on the genetic diversity of populations of the neotropical tree species, Terminalia amazonia, was studied using random amplified polymorphic DNA (RAPD) analysis. Leaf material from 104 trees was collected from three naturally fragmented gallery forest patches and three plots in nearby continuous forest in the Mountain Pine Ridge, Belize. In total, 30 RAPD bands generated by five decamer primers were used to compare the genetic diversity of the six populations in the two groups. Genetic variation within the populations (H0), as estimated by the Shannon diversity index, ranged from 0.32 to 0.38, with an overall diversity of 0.38 (Hspecies). Analysis of molecular variation revealed that most (94.4%, P<0.001) of the variation was attributable to differences among individuals within populations. Population differentiation was significantly (P=0.038) lower among the fragmented populations than among continuous forest populations. On average, the fragmented populations also had slightly, but statistically significant (P=0.046) lower levels of genetic diversity. However, one gallery forest site had a higher level of genetic diversity than two of the continuous forest sites. We suggest that the long-term effect of fragmentation on the genetic diversity of tropical trees will depend upon the amount of local forest cover in proximity to the fragmented populations.

Symmetry in chemistry from the hydrogen atom to proteins.

The last 2 decades have seen discoveries in highly excited states of atoms and molecules of phenomena that are qualitatively different from the "planetary" model of the atom, and the near-rigid model of molecules, characteristic of these systems in their low-energy states. A unified view is emerging in terms of approximate dynamical symmetry principles. Highly excited states of two-electron atoms display "molecular" behavior of a nonrigid linear structure undergoing collective rotation and vibration. Highly excited states of molecules described in the "standard molecular model" display normal mode couplings, which induce bifurcations on the route to molecular chaos. New approaches such as rigid-nonrigid correlation, vibrons, and quantum groups suggest a unified view of collective electronic motion in atoms and nuclear motion in molecules.

Structure-activity relationships of KNEFIRFamide (AF1), a nematode FMRFamide-related peptide, on Ascaris suum muscle.

Analogues of KNEFIRFamide (Lys-Asn-Glu-Phe-Ile-Arg-Phe-NH2; AF1), an FMRFamide-related peptide (FaRP) originally isolated from Ascaris suum, were characterized in an A. suum muscle tension assay. AF1 had biphasic effects on this preparation, inducing a brief relaxation followed by excitation and spastic paralysis. Activity of AF1 in this assay was eliminated by N-terminal deletions and by deamidation of the carboxy-terminus. The potency of AF1 was greatly reduced by alanine substitution for any residue. Peptides that retained activity did not show the biphasic response observed with AF1, suggesting that the inhibitory and excitatory phases seen with AF1 may be due to activation of distinct receptors. The basis for the marked differences in potency observed between AF1 and the structurally related nematode FaRP, AF2 (KHEYLRFamide) was also tested. AF2 is approximately 1000-fold more potent than AF1 in this assay, but has physiological effects that are otherwise indistinguishable. KNEYIRFamide and KNEFLRFamide induced characteristic AF1/AF2 responses, but were much less potent than the native peptides. In contrast, KHEYIRFamide resembled AF1 in potency and pattern of responses. These data suggest that AF1 and AF2 act at distinct receptors, and hypothesis supported by the observation that KNEFIAFamide antagonized the effects of AF1 but not of AF2.

Algebraic methods in spectroscopy.

At present, two main types of algebraic methods are employed for analysis of molecular spectra. The first goes back to the early days of molecular spectroscopy. The second, developed recently by Iachello and coworkers, grew out of nuclear physics and makes use of classical Lie algebras such as SU(4). In this review, the standard spectroscopic fitting Hamiltonian for molecular vibrations, including resonance interactions, is first described. Then, new developments in the application of the standard approach are surveyed. In particular, the question of how one determines the true nature of molecular motions in highly excited spectra is investigated. Next, the recent algebraic approach of Iachello and coworkers is discussed. Application of ideas of molecule-like modes and algebraic methods to the analysis of the electronic spectra of atoms is discussed. Finally, prospects for future development of algebraic methods are discussed.