THE ISSUE OF ANTIBIOTIC USE IN THE LIVESTOCK INDUSTRY: WHAT HAVE WE LEARNED?

It is generally believed that it is better to use medicinal products as therapeutics to treat disease situations, using high doses for short periods of time, rather than as prophylactics, when low doses are fed continuously. It is therefore the continuous use of low levels of medicinal products as growth promoters in farm animals that has been brought into question, as it is thought that this may increase the risk of development of bacterial resistance to antibiotics used as therapeutic drugs to treat disease in humans.     

MORPHOLOGICAL STUDIES OF THE NYMPHAEACEAE. V. DOES NELUMBO HAVE VESSELS?

The examination of the primary xylem of roots of Nelumbo has revealed the presence of vessel elements with intra-face, transversely-rowed to obliquely-rowed bordered pitted side walls and scalariformly perforated end walls. Whole mounts of macerated xylem, serial sections of roots, and cells through which a water suspension of India ink particles under slight or no pressure was passed, were the means of investigation. It is our opinion that this discovery does not support theories which derive monocotyledons from the Nymphaeaceae. A discussion leading to this conclusion is presented.     

DO TRADE‐OFFS HAVE EXPLANATORY POWER FOR THE EVOLUTION OF ORGANISMAL INTERACTIONS?

The concept of a trade-off has long played a prominent role in understanding the evolution of organismal interactions such as mutualism, parasitism, and competition. Given the complexity inherent to interactions between different evolutionary entities, ecological factors may especially limit the power of trade-off models to predict evolutionary change. Here, we use four case studies to examine the importance of ecological context for the study of trade-offs in organismal interactions: (1) resource-based mutualisms, (2) parasite transmission and virulence, (3) plant biological invasions, and (4) host range evolution in parasites and parasitoids. In the first two case studies, mechanistic trade-off models have long provided a strong theoretical framework but face the challenge of testing assumptions under ecologically realistic conditions. Work under the second two case studies often has a strong ecological grounding, but faces challenges in identifying or quantifying the underlying genetic mechanism of the trade-off. Attention is given to recent studies that have bridged the gap between evolutionary mechanism and ecological realism. Finally, we explore the distinction between ecological factors that mask the underlying evolutionary trade-offs, and factors that actually change the trade-off relationship between fitness-related traits important to organismal interactions.