Epigamic selection by males as evidenced by courtship partner preferences in the checkered white butterfly (Pieris protodice)

Free-flying males of the checkered white butterfly, Pieris protodice, were presented with tethered females that varied with respect to both size (as measured by forewing length) and age (as measured by wing wear). Because males make a substantial investment in their offspring through nutrients passed to the female during copulation, they were expected to court young and large females for longer times than older and smaller females, and they did so. Additional experiments further suggest that size discriminations are made on the basis of apparent wing area and age discriminations are made on the basis of an age-related increase in ultraviolet reflectance that occurs in females. The discussion examines the adaptive value of these discriminations.     

Studies on plant growth-regulating substances

3-(3,5-Dichlorophenoxy)butyric acid and 2-(3,5-dichlorophenoxy)ethylamine were both shown to exert pronounced dwarfing effects on tomato seedlings. Examination of extracts of the treated plants revealed the conversion of these compounds to 3,5-dichlorophenoxyacetic acid (3,5-D) and it is concluded that the physiological activity shown in each case depends on such a conversion to 3,5-D within the tissues.     

CAUSES OF DECREASES IN PRODUCTIVITY IN UNDISTURBED TALL GRASS PRAIRIE

There is abundant evidence that protection of the tall grass prairie from grazing, mowing, or burning for even a few years results in accumulation of much litter and reduced productivity. This reduced productivity has been attributed primarily to either the insulating effect of the litter, a lowered rate of mineral recycling, or a presence of toxins in the litter. Considerable evidence exists in the literature concerning the first suggestion, but no studies have been reported concerning the last two in grasslands. A comprehensive project was conducted during the growing season of 1977 in a tall grass prairie in Oklahoma to investigate the three suggestions. It was clear from our data that increased productivity as a result of mowing and burning was not due to the elimination of toxins nor to an increased rate of turnover of organic matter. Soil moisture stress was greater in the mowed and burned plots than in the controls. Thus, the single factor examined which was consistently different, and likely to explain the increased productivity, was the higher soil temperature in the burned and mowed plots early in the growing season. The four dominant grasses in the study plots are non-Festucoid species which are known to have high optimum temperatures for growth.