Contributions of space experiments to the study of gravitropism

The study of gravitropism in space has permitted the discovery that statoliths are not completely free to sediment in the gravisensing cells of roots. These organelles are attached to actin filaments via motor proteins (myosin) which are responsible for their displacement from the distal pole of the cell toward the proximal pole when the seedlings are transferred from a 1g centrifuge in space to microgravity. On the ground, the existence of the link between the statoliths and the actin network could not be established because the gravity force is much greater than the force exerted by the motor proteins. This finding led to a new hypothesis on gravisensing. It has been proposed that statoliths can exert tensions in the actin network which become asymmetrical when the root is stimulated in the horizontal position on the ground. The space experiments have confirmed to some extent the results obtained on gravisensitivity with clinostats, although these devices do not simulate microgravity correctly. Reexamination of the means of estimating gravisensitivity has led to the conclusion that the perception and the transduction phases could be very short (that is, within a second). This data is consistent with the fact that the statoliths are attached to the actin filament and do not have to move a long distance to exert forces on the actin network. It has also been demonstrated that gravity regulates the gravitropic bending in order to avoid the overshooting of the vertical direction on the ground. The roots, which are stimulated and placed in microgravity, are not subjected to this regulation and curve more than roots stimulated continuously. However, the curvature of roots or of coleoptiles that takes place in microgravity can be greatly reduced by straightening the extremity of the organs.     

The contribution of afferent signals from the liver to metabolic regulation during exercise

The crucial role of the liver as the only organ to produce glucose used by skeletal muscle during exercise is well known. Since hepatic glucose production is central to blood glucose homeostasis during exercise, it has been postulated that the liver may inform the central nervous system and other organs of its diminishing capacity to produce glucose from glycogen, before blood glucose falls. The sensory role of the liver during exercise would be similar to its role in the control of food intake. As a consequence, the experimental approaches used to test the hypothesis that afferent signals from the liver contribute to metabolic regulation during exercise are inspired by those used to test the same hypothesis in the regulation of food intake. In the present review, two questions are addressed. The existing evidence for the liver's sensory influence on metabolic adjustments to exercise is first reviewed; the nature of the initiating stimuli for the afferent contribution of the liver to physical exercise is discussed thereafter. The hypothetical construct upon which rests the contribution of the liver's afferent signals to metabolic regulation during exercise is that a decrease in liver glycogen or a related metabolic intermediate is sensed by the liver, and the signal is transduced to the central nervous system, most likely through the afferent activity of the hepatic vagus nerve, where it contributes to the orchestration of the metabolic and hormonal responses to exercise. Support in favour of this construct comes mainly from the demonstration that sectioning of the hepatic vagus nerve attenuates the normal hormonal response to exercise. It seems that the liver-glucagon axis is particularly responsive to this reflex activation. In other respects, the hepatic mechanism responsible for linking the metabolic activity in the liver to an afferent signal capable of regulating the metabolic response to exercise remains speculative. Substrates or derivatives of substrate oxidation, energy-related compounds (ATP and Pi), or changes in cell volume may all be related to changes in transmembrane potential in the liver cell, which according to the "potentiostatic" theory would determine the afferent vagal activity.     

Contributions of blastocyst micromanipulation to the study of mammalian development

This is a personal account of why the author chose to focus on devising techniques for micromanipulating the blastocyst stage conceptus as a way of investigating early development in mammals. Its aim is to provide insight into what such technical innovations entailed and how they have contributed to present understanding of both embryology and the analysis of gene function in mammals. The ability to dissect and reconstitute mouse blastocysts, and to inject cells or tissue into them, enabled genes to be harnessed as markers for elucidating the lineage of cells and interactions between tissues from the stage when differentiation is first evident. Most importantly, it made it possible to apply clonal analysis to the study of cell fate in mammals. The scope of blastocyst micromanipulation was further enhanced when embryonal carcinoma (EC) cells and, particularly, embryonic stem (ES) cells were found to be able to participate in normal development and contribute to the germ line following injection into the blastocyst. BioEssays 20:168–180, 1998. © 1998 John Wiley & Sons, Inc.     

Contributions of Jeffrey Harborne and co-workers to the study of anthocyanins

Jeffrey Harborne and his co-workers have played a unique role in the over-all study of plant pigments and of anthocyanins in particular through their many publications and through Jeffrey's editorial work with Phytochemistry. Jeffrey has made important contributions to our understanding of the separation and structural identification of anthocyanins; to co-pigmentation; and to the role of anthocyanins in systematics and ecology in both reproductive and vegetative tissues. This work has had considerable influence on much of the current research on the genetics and regulation of anthocyanin biosynthesis.     

Applying evolutionary models to the laboratory study of social learning

Cultural evolution is driven, in part, by the strategies that individuals employ to acquire behavior from others. These strategies themselves are partly products of natural selection, making the study of social learning an inherently Darwinian project. Formal models of the evolution of social learning suggest that reliance on social learning should increase with task difficulty and decrease with the probability of environmental change. These models also make predictions about how individuals integrate information from multiple peers. We present the results of microsociety experiments designed to evaluate these predictions. The first experiment measures baseline individual learning strategy in a two-armed bandit environment with variation in task difficulty and temporal fluctuation in the payoffs of the options. Our second experiment addresses how people in the same environment use minimal social information from a single peer. Our third experiment expands on the second by allowing access to the behavior of several other individuals, permitting frequency-dependent strategies like conformity. In each of these experiments, we vary task difficulty and environmental fluctuation. We present several candidate strategies and compute the expected payoffs to each in our experimental environment. We then fit to the data the different models of the use of social information and identify the best-fitting model via model comparison techniques. We find substantial evidence of both conformist and nonconformist social learning and compare our results to theoretical expectations.     

A popular misapplication of evolutionary modeling to the study of human cooperation

To examine the evolutionary basis of a behavior, an established approach (known as the phenotypic gambit) is to assume that the behavior is controlled by a single allele, the fitness effects of which are derived from a consideration of how the behavior interacts, via life-history, with other ecological factors. Here we contrast successful applications of this approach with several examples of an influential and superficially similar line of research on the evolutionary basis of human cooperation. A key difference is identified: in the latter line of research the focal behavior, cooperation, is abstractly defined in terms of immediate fitness costs and benefits. Selection is then assumed to act on strategies in an iterated social context for which fitness effects can be derived by aggregation of the abstractly defined immediate fitness effects over a lifetime. This approach creates a closed theoretical loop, rendering models incapable of making predictions or providing insight into the origin of human cooperation. We conclude with a discussion of how evolutionary approaches might be appropriately used in the study of human social behavior.