Revised methodology for a blood-clotting response test for identification of warfarin-resistant Norway rats (Rattus norvegicus)

A blood-clotting response test for warfarin resistance in Norway rats ( Rattus norvegicus ) was developed by our laboratory in the late 1970s, based on knowledge of biochemical mechanisms available at that time. That test used warfarin, its the free base which is not watersoluble, and vitamin K₁ 2,3-epoxide as an antidote for warfarin-resistant rats only. We have modified the above test to use a water-soluble salt of vitamin K₃ (1 mg kgg⁻¹ body weight), which is an antidote in a wider range of warfarin-resistant rat strains than vitamin K₁ 2,3- epoxide, and a water-soluble salt of warfarin (5.4 mg kg⁻¹ body weight). Sodium warfarin and vitamin K₃ are administered by oral gavage, and the blood-clotting response measured 24 h later. In a series of validation tests there were no significant differences between results obtained by either method. The new method, however, uses materials which are commercially available, and eliminates the possibility of misclassifying warfarin-resistant rats as susceptible because vitamin K₁ 2,3-epoxide was not an antidote in those strains. We also present evidence that measuring blood-clotting response to feeding on a vitamin K-free diet for 4 days is not a reliable method for determining the genotype of warfarin-resistant rats.     

Germination of Chromolaena odorata (L.) K. & R. achenes: effect of storage, harvest locality and the pericarp

The percentage germination of achenes of Chromolaena odorata (L.) K. & R. stored dry in the dark at 25°C for 7 months was markedly higher than that of freshly harvested achenes. This is indicative of an after-ripening requirement that may be of benefit to the species by ensuring temporal distribution of germination. Germination of freshly harvested achenes from various sites differed. However, after 7 months of dry, dark storage at 25°C no differences were present, thus, confirming the after-ripening requirement. Although the total number of achenes per capitulum did not vary from site to site, there were distinctive differences in the number of filled (presumably viable) achenes. It is suggested that this is a reflection of the environmental conditions prevailing at the sites. Puncturing of the achene pericarp did not influence dark germination but its removal increased percentage germination significantly. Natural degradation of the pericarp in the field may, therefore, permit germination of buried achenes in the absence of a suitable light stimulus.     

Costs and the diversification of exaggerated animal structures

Sexual selection can favor production of extravagant ornaments and weapons in the contest for access to the opposite sex. Existing explanations for the diversity of sexually selected structures focus on reproductive benefits conferred by particular ornament or weapon morphologies. Here, I show that costs of weapon production also may drive patterns of weapon evolution. In beetles, production of horns reduces the size of neighboring morphological structures (antennae, eyes, or wings, depending on the location of the horns), and these tradeoffs reveal unexpected functional associations between ecology and horn morphology. This study illustrates a critical but overlooked role of costs in sexual selection and has implications for understanding the evolution of animal morphology.     

A microscopic basis for the global appearance of energy landscapes

It is shown that the appearance of a multidimensional potential energy surface, or potential energy landscape, can be related to the form of the interatomic or intermolecular potential. Catastrophe theory enables us to describe how the geometry of the surface changes with parameters in the potential, and provides universal scaling relations that explain, for example, the asymmetric reaction profiles observed for systems bound by long-range forces. The principal result is an unexpected connection between barrier heights, path lengths, and vibrational frequencies, with applications to a wide variety of problems in chemical physics, ranging from Hammond's postulate in organic chemistry, to the relaxation dynamics of complex systems such as glasses and biomolecules.