Observations on the biology of the trochid gastropod Austrocochlea constricta (Lamarck) (Prosobranchia). II. The effects of available food on shell-banding pattern

The trochid gastropod Austrocochlea constricta (Lamarck) shows a variable pattern of shell banding. The concentration of the major shell pigment, uroporphyrin I, has been shown to differ between stripe-classes and, within each stripe-class, between shores. This paper describes the relation between amount of available food and shell pigmentation on six shores.Qualitative and quantitative methods were used to determine the concentrations of chlorophyll pigments in the substratum of each shore. Thin-layer chromatography showed differences in the type of microalgae present. Quantitative, spectrophotometric determinations of the chlorophyll concentrations of acetone extracts of scrapings of the substratum showed significant differences in total chlorophyll between the six shores. A uroporphyrin index gives an estimate of the total amount of uroporphyrin/unit area on each shore, and enables the wet wt/animal, density/area, and proportions of the population in different stripe-classes to be related to the concentrations of uroporphyrin/g shell within the stripe-classes. There was a highly significant linear regression of the uroporphyrin index on total chlorophyll concentration. This provides evidence for the effect of amount of available food on shell pigmentation. The mean concentration of pigment/g shell increased as the chlorophyll content of the substratum increased.A hypothesis is proposed to explain the observed differences in banding-pattern frequencies between shores; this represents the frequency distribution of animals with different concentrations of pigment/g shell as a normal distribution, with increasing mean and standard deviation as the concentration of chlorophyll in the substratum increases. Theoretical distributions are given to show that similar banding pattern frequencies to those observed on the six shores can be produced under this hypothesis. Neither a more complex hypothesis, nor selective nor genetic mechanisms are necessary to explain the observed distributions of banding pattern in Austrocochlea.     

Parameters of brown-headed cowbird Molothrus ater egg discrimination in warbling vireos Vireo gilvus

We examined which egg parameters warbling vireos Vireo gilvus use to discriminate brown-headed cowbird Molothrus ater eggs and, by comparing our results to other studies, tested the prediction that ejecter species with eggs more similar in appearance to cowbird eggs will be less tolerant of foreign eggs. In addition, we tested the hypothesis that egg characteristics influence the cost of ejection and probability of committing ejection errors. Warbling vireos ejected 100% of eggs with a cowbird spot pattern and only spot pattern significantly influenced the probability of ejecting a foreign egg, whereas size and nest stage did not. Foreign eggs that differed in two parameters were not ejected significantly more than those that differed in one parameter. Thus, warbling vireos appear to be less tolerant of foreign eggs than species with eggs more divergent from cowbird eggs. There was no significant difference in the number of vireo eggs that were damaged when foreign eggs of different sizes and spot patterns were ejected, which is counter to the assumptions of the evolutionary equilibrium hypothesis. Similarly, foreign egg characteristics did not significantly influence the probability of ejection errors. Finally, egg discrimination in warbling vireos appears to have evolved directly to counter cowbird parasitism because all conspecific eggs switched into their nests were accepted.     

Pineal melatonin rhythms in the lizard Anolis carolinensis: II. Photoreceptive inputs

The pineal organ of the lizard Anolis carolinensis acts as a transducer of photoperiodic information, since light can affect the pineal melatonin rhythm (PMR). The synthesis and secretion of melatonin may be a major mechanism whereby a circadian pacemaker within the pineal can control circadian clocks located elsewhere. An investigation into potential routes by which light could affect the PMR showed that (1) removal of the photosensory parietal eye did not affect the PMR as compared to controls under either a light-dark (LD) 12:12 cycle and a constant temperature (32 degrees C) or an LD 12:12 cycle and a daily temperature cycle (32 degrees C/20 degrees C); (2) removal of both the parietal eye and the lateral eyes did not affect the PRM of anoles held in LD 12:12 (constant 32 degrees C); (3) the PMR of blinded anoles re-entrained to a 10-hr shift in the phase of the LD cycle as rapidly as that of sighted anoles; (4) blocking light penetration to the brains of anoles, but leaving the lateral eyes exposed, blocked the ability of anoles to re-entrain to a 10-hr shift in the phase of an LD cycle. The data support the hypothesis that light directly affects the PMR in Anolis and that other potential photic inputs (parietal eye, lateral eyes) play little or no role. This conclusion is supported by previous neurophysiological and ultrastructural studies showing that the lizard pineal possesses functional photoreceptors.     

Supply-side ecology and benthic marine assemblages

Many marine invertebrates have a planktonic stage of their life history during which widespread dispersal and much mortality occur. The numbers surviving to recruit into habitats occupied by adults are therefore very variable in time and space. Models for the structure and dynamics of benthic assemblages tend to focus on processes causing death - often assuming consistent arrivals of recruits. Supply-side ecology is a newly fashionable term to describe recent interest in the long-realized consequences of variations in recruitment. Such variations have important influences on theory and empirical research in these assemblages.     

Substituted piperidin-2-one biphenyltetrazoles as angiotensin II antagonists

A novel series of substituted piperidine-2-ones has been identified as antagonists of angiotensin II. These compounds showed high affinity for the receptor in bovine adrenal cortex binding assays with IC₅₀'s as low as 20nM. They are potent inhibitors of angiotensin II induced contractions in rabbit aortic rings, with pA₂ values as high as 9. A number of these compounds are also orally active as antihypertensives in spontaneously hypertensive rat preparations.