Culture and Progress. DISTINGUISHED LECTURE-1975

This paper is the text of the sixth Distinguished Lecture, delivered in San Francisco at the 74th annual meeting of the American Anthropological Association, December 1975. The Lectureship was established in 1969 to honor outstanding scholars in the profession. Colson, a social anthropologist and ethnographer of wide experience, has worked in both the New and the Old Worlds, with American Indian and central African cultures. She is currently Fairchild Fellow, California Institute of Technology, on leave from her professorship at the University of California, Berkeley. Her interest in both the history and the future of our profession is reflected in her talk. The first five Distinguished Lectures—by Joseph H. Greenberg, Robert J. Braidwood, Georges Condominas, John W. M. Whiting, and Miguel León-Portilla—were published in the Association's Annual Reports (1970–74). The Lecture will now appear each year in the American Anthropologist.     

Fractionation of Sporogonial Stages of the Microsporidian Encephalitozoon cuniculi by Percoll® Gradients

Microsporidia are obligate intracellular parasites that are increasingly recognized as a cause of opportunistic infections in immunocompromised individuals. Encephalitozoon cuniculi has been identified in humans with AIDS and infects a wide range of mammalian hosts. Little is known about the metabolic processes that regulate growth and replication of microsporidia. Examination of the individual stages of development will facilitate such studies and reveal possible targets for drug therapy. The purpose of this study was to fractionate and purify stages of the microsporidian life cycle. Encephalitozoon cuniculi were cultured in RK-13 cells. The tissue supernatants containing multiple parasite stages, empty microsporidial husks and host cell debris were collected, washed, and subjected to differential centrifugation in 80% stock isotonic Percoll. Transmission electron microscopy and SDS-polyacrylamide gel electrophoresis were used to compare the content and purity of each fraction. Mature spores formed a band at a density of approximately 1.138 g/ml. Sporoblasts were found at densities between 1.102 g/ml and 1.119 g/ml. A mixture of sporonts, sporoblasts, microsporidial husks, and cell debris remained at the top of the gradient and additional centrifugation in 30% and 50% Percoll resulted in separation of these stages. These results represent the first step toward fractionating stages of microsporidia infecting humans.     

Limited effects of dominant ants on assemblage species richness in three Amazon forests

1. Ants are highly interactive organisms and dominant species are considered to be able to control the species richness of other ants via competitive exclusion. However, depending on the scale studied, inter‐specific competition may or may not structure biological assemblages. To date, ant dominance–richness relationships have only been studied in small sample units, where a few dominant colonies could plausibly control most of the sample unit. 2. We conducted a comprehensive survey of terrestrial ant assemblages using bait, pitfall, and litter‐sorting methods in three sites in Brazilian Amazonia. Using a spatially structured rarefaction approach, based on sampling units with linear dimensions ranging from 25 to 250 m, the mesoscale patterns of ant dominance–richness relationships (sampling units covering hundreds of meters separated by kilometers) were investigated. 3. Interference–competition models (parabolic or negative linear relationships between species richness and the abundance of dominant ants) tended to be more frequent in smaller sample units or in assemblages sampled with interactive methods, such as baits. Using more inclusive sampling methods, the relationship was generally asymptotic rather than parabolic, with no reduction in species diversity because of the presence of dominants. Random co‐occurrence patterns of species within sites support the interpretation of a limited role for present‐day competition in structuring these assemblages. 4. Competition from dominant species may reduce species richness in small areas, especially when artificial baits are used, but appears to be less important than environmental constraints in determining ant species richness across scales of hectares and greater in these Amazon forests.     

Genetic variation and local adaptation at a cheatgrass (Bromus tectorum) invasion edge in western Nevada

Cheatgrass ( Bromus tectorum ) is an invasive weed in western North America found primarily growing at elevations less than 2200 m. We asked whether cheatgrass is capable of becoming adapted to a marginal habitat, by investigating a population at a high elevation invasion edge. We used a combination of methods, including reciprocal field transplants, controlled environment studies and molecular analysis. High levels of SSR gene diversity (0.50 vs. 0.43) and comparable variation in phenotypic traits were observed at both the invasion edge and a low elevation, high-density population. Three heterozygotes were observed in the edge population, which is unusual in this predominantly self-pollinating plant. Plants from high elevations germinated more slowly in a growth chamber and had slower seedling growth rates. Survivorship was low at the edge (13%), compared with the low elevation site (55%), but surviving plants were of similar size and had equivalent reproductive output. Seed size positively affected survival and plant performance in the field and this trait was inherited. Emergence timing affected survival at the low elevation site and germination timing was also inherited. Local adaptation was seen in the low, rather than in the high elevation site, because of differential survival. While there was no evidence for local adaptation to the high elevation site observed in the field, family level and genotype-level differences in traits that affected field performance, high genetic diversity at the invasion edge, and evidence of outcrossing in this highly selfing species indicates that the potential for adaptation to a marginal habitat exists within this population.     

The colonization of ball-clay ponds by macroinvertebrates and macrophytes

SUMMARY. 1. The rate and nature of colonization of ball-clay ponds by aquatic macrophytes and macroinvertebrates were studied by comparing communities present in a scries of ten ponds of similar dimensions, but of different ages, ranging from 6 months to 15 years.
2. Multivariate analyses of the biotic data distinguished between'neutral'and'acid'ponds; further analyses concentrated on the former type.
3. Initial colonization of neutral ponds was rapid with a predictable sequence of species arrival, probably reflecting short dispersal distances. Variations in macroinvertebrate invasion times were related to dispersal strategy and ability. As the pond aged, successional changes, linked with macrophyte colonization, produced a shift in dominance from algivores and predators towards epiphyton grazers and detritivores. Some evidence of succession of species within invertebrate orders was found.
4. Low pH affected colonization principally by preventing the establishment of acid-intolerant immigrant species, but also by retarding succession.
5. It is concluded that non-interactive models of insular colonization, with constant immigration and extinction rates, are of limited applicability to pond colonization in temperate areas.     

Inflammatory Responses in Annelids

The cellular inflammatory responses of annelids, which includechemotaxis, phagocytosis, encapsulation, and various phasesof wound healing, are effected by coelomocytes, particularlythe hyaline amoebocytes. Coelomic epithelial cells and specializednephridial cells also participate in phagocytosis. A numberof factors related to inflammation in vertebrates have beenidentified in annelids, i.e., histamine, kallikrein, lysosomalenzymes, agglutinins, lysins and antibacterial substances. However,their precise function in annelid inflammatory responses hasyet to be determined.     

Evolutionary contrasts in insects: nutritional advantages of holometabolous development

ABSTRACT. Two insects, one holometabolous and one hemimetabolous, are compared and contrasted in respect to feeding efficiency, growth and respiration. An examination of cuticle production in these and other species leads to the conclusion that the nutritional burden of cuticle production in hemimetabolous forms has a significant effect on efficiency, and it is speculated that greater nutritional efficiency in holometabolous forms has been an important evolutionary advantage.