Gastric cancer: an epidemiological review

An attempt is made to synthesize the epidemiological literature and identify salient factors from the multitude of potential antecedents of gastric cancer, factors which to a greater or lesser degree create nonrandom variations in the distribution of the disease. Implicit in this approach is the notion that observation of spatial variations in the incidence of gastric cancer may lead to hypotheses relating to the biological, personal and physical environmental factors. An extensive bibliography accompanies the text.Formerly of the Department of Town Planning, University of Wales, College of Cardiff, PO Box 906, Cardiff CF1 3YN, Wales.     

Biochemical determination of parental uncertainty in white-fronted bee-eaters

Summary Maternity and paternity uncertainty represent important costs to breeders among white-fronted bee-eaters (Merops bullockoides) in Kenya. Analysis of enzyme polymorphisms reveals that between 9% and 12% of all offspring are genetically unrelated to one or both of their putative parents. These bastards are the result of three different sources of parental uncertainty: Extrapair copulation, intraspecific egg parasitism, and quasi-parasitism (parasitism by a female who was fertilized by the male attending the parasitized nest). The first two represent costs to males, who rear offspring that are not genetically their own; the latter two produce the same costs for females. Genetic relatedness plays an important role in defining the social structure of M. bullockoides populations. In order to predict patterns of parental investment and the choice of recipients for helping behavior, one would like to know the relative frequency of maternity vs paternity uncertainty. The possible use of maximum likelihood techniques to separate the sources of non-kin is discussed. Unfortunately, the sample size of detected non-kin in the present study was not large enough to allow constructive use of the technique for bee-eaters. A comparison of estimates from biochemical and behavioral analyses indicates that both methods can produce misleading results. Behavioral data can be used to test underlying assumptions of biochemical analyses, and vice-versa. Used together, the two approaches reinforce one another and strengthen the reliability of conclusions drawn from either one alone.     

Growth of zinc granules in the barnacleElminius modestus

The growth of insoluble, membrane-limited spherical granules has been studied in the barnacleElminius modestus Darwin, collected on 26 March 1983 from the shore of the Huon River, Tasmania. X-ray microprobe analysis of these granules using a non-aqueous fixation method established their elemental composition (in order of abundance) to be phosphorus, zinc, potassium, sulphur and chlorine. Formation of granules is initiated on exposure to high zinc levels in the ambient seawater. Granules were first detected in barnacles transplanted from an area of low seawater zinc levels to one with high levels after 12 d exposure. Over a period of 5 mo, granules increased both in numbers and diameter and were concentrated in specialized cells around the gut, the stratum perintestinale. Barnacles positioned at mid-tide level in high ambient zinc levels, developed greater numbers of larger granules than those positioned below low-tide level. Rate of uptake of zinc was higher in the former group during the first month, after which similar rates were observed in the two groups. Barnacles transplanted from an area of high to one of low seawater zinc concentration, lost zinc slowly (0.3% body load per day over an 11 wk period). There was no evidence to suggest that zinc granules are excreted intact across the gut. We conclude that zinc granules represent a detoxification mechanism for surplus zinc.     

Age-specific social dominance affects habitat use by breeding American redstarts (Setophaga ruticilla): a removal experiment

Summary By removing older males from their breeding territories, we tested the hypothesis that age-related dominance behavior influenced the pattern of habitat selection by breeding American redstarts Setophaga ruticilla (Aves: Parulinae). Fifteen older male redstarts removed in five experimental replicates during three breeding seasons were replaced by ten yearling and five older males; no redstart males of either age colonized the control sites during the same time periods, although two yearlings disappeared. Significantly more yearling males (67%, n=9) colonized the vacated areas than were present in the redstart population at large (26.8%, n=209). We reject the alternative hypothesis that yearling male redstarts occupy different habitats from older males because of age-related (innate) habitat preferences. Redstarts that colonized the territories made vacant by our removals (i.e., floaters) were a behaviorally heterogeneous group of animals. The presence of both yearling and older male floaters indicates that suitable habitat is limiting for this species and that intraspecific competitive interactions are important in habitat distribution, and potentially in population regulation.     

The functional organization of resin work in honeybee colonies

Resin is an important building material in the nests of honeybees, but little is known about how it is handled within the nest and how its collection is controlled. We studied the functional organization of resin work to better understand how a colony adaptively controls its intake of resin. Two hypotheses have been proposed for how resin collectors stay informed of the need for additional resin: (1) the unloading difficulty hypothesis (resin need is sensed indirectly by the unloading delay) and (2) the caulking activity hypothesis (resin need is sensed directly while engaged in using resin). A falsifiable prediction of the latter hypothesis, but not of the former, is that resin collectors not only gather resin outside the hive but also regularly handle resin inside the hive (taking it from other bees and using it to caulk crevices). Consistent with this prediction are our findings that in the resin sector of a colony’s economy, unlike in the pollen, nectar, and water sectors, there is no strict division of labor between the collectors and the users of a material. Over the course of a day, bees seen collecting resin were also commonly seen using resin. Moreover, we found that the unloading locations of resin collectors are unlike those of water and nectar collectors, being deep inside the hive (at the sites of resin use) rather than at the hive entrance. This arrangement facilitates the engagement in resin use by resin collectors. We conclude that the caulking activity hypothesis is well-supported, but that the unloading difficulty hypothesis also remains viable, for we found that resin collectors experience variable delays in getting rid of their loads, from less than 15 min to more than an hour, consistent with this hypothesis. The stage is now set for experimental tests of these two hypotheses. Both may be correct, which if true will imply that social insect workers, despite their small brains, can acquire and integrate information from multiple sources to improve their knowledge of conditions within the colony.