Biased parental investment and reproductive success in Gabbra pastoralists

Demographic data from 848 Gabbra households are used to examine the relationships between herd size and reproductive success in relation to sex, in a traditional, pastoralist population. The number of camels in the household herd has a significant positive effect on the reproductive success of both men and women, although the effect of wealth is greater for men, as predicted from evolutionary theory. The greater the number of elder brothers a man has, the lower his reproductive success, as a result of a smaller initial herd and a later age at marriage. This is not true for women –number of elder sisters does not have a measurable effect on a woman’s fertility, although it does have a small, negative effect on the size of her dowry. These results are interpreted as competition between same-sex siblings for parental investment, in the form of their father’s herd, which is more intense between sons than daughters as parental investments are greatest in males. Received: 30 June 1995/Accepted after revision: 23 October 1995     

Great tits choose between food and proximity to a mate

Summary These experiments test for time of day differences in the attentiveness of territorial, paired, male and female great tits (Parus major) to their mates, by requiring them to choose between feeding and being in sight of their partner. There was a strong time of day effect favouring proximity to a mate early in the day for both males and females. A difference in male and female behaviour that would have suggested that this was male mate guarding was not found. Three independent measures show that this temporal effect is not owing to foraging being more important in the afternoon. There was a significant within-pair correlation in the strength of this proximity effect, which was strongest early in the day. Possible functional explanations are discussed. When females moved out of sight of males, male vocal behaviour increased and this increase was much greater when females moved out of sight earlier in the day than later on. These effects were not observed among females. This result is consistent with the hypothesis that male mate guarding is most important early in the day.     

A graduate level course: Teaching stress management skills to occupational health physicians and practitioners

The WHO Study Group on Training and Evaluation in Occupational Medicine has recently emphasized the importance of incorporating theoretical and practical aspects of stress prevention and management in the professional training of occupational health practitioners. Such a course was developed for the Tel-Aviv University Medical School graduate program in occupational health. The course objectives are consistent with the current call for improved training in psychosocial issues in medical care. Twenty-three occupational health practitioners (physicians, nurses, hygienists and social workers) participated in a bi-semester course. The first part included a stress management and prevention program based on the RET (Rational-Emotive Training) model. The second involved developing and implementing a field project on primary and secondary prevention of stress and its outcomes. Pre-, mid-and post-course questionnaires showed significantly improved psychosocial ability and reduced irrational/dysfunctional thinking, considered a causal factor in stress and burnout. Acquiring such anti-stress resources may benefit practitioners and clients/patients, both potential victims of occupational stress alike. We recommend the inclusion of such extended courses to the professional training of occupational health practitioners.     

Who's not driving among U.S. high school seniors: A closer look at race/ethnicity,socioeconomic factors,and driving status

Objectives: We examined associations among race/ethnicity, socioeconomic factors, and driving status in a nationally representative sample of >26,000 U.S. high school seniors.

Methods: Weighted data from the 2012 and 2013 Monitoring the Future surveys were combined and analyzed. We imputed missing values using fully conditional specification multiple imputation methods. Multivariate logistic regression modeling was conducted to explore associations among race/ethnicity, socioeconomic factors, and driving status, while accounting for selected student behaviors and location. Lastly, odds ratios were converted to prevalence ratios.

Results: 23% of high school seniors did not drive during an average week; 14% of white students were nondrivers compared to 40% of black students. Multivariate analysis revealed that minority students were 1.8 to 2.5 times more likely to be nondrivers than their white counterparts, and students who had no earned income were 2.8 times more likely to be nondrivers than those earning an average of ≥$36 a week. Driving status also varied considerably by student academic performance, number of parents in the household, parental education, census region, and urbanicity.

Conclusions: Our findings suggest that resources—both financial and time—influence when or whether a teen will learn to drive. Many young people from minority or lower socioeconomic families who learn to drive may be doing so after their 18th birthday and therefore would not take advantage of the safety benefits provided by graduated driver licensing. Innovative approaches may be needed to improve safety for these young novice drivers.     

Non-host organisms affect transmission processes in two common trematode parasites of rocky shores

The transmission of free-living trematode stages is mediated by various environmental factors, of which the presence of ambient organisms within the host space is a potential major determinant. In two laboratory mesocosm experiments, we investigated the influence of four intertidal rocky shore species on transmission success of cercariae of the digenean trematodes Echinostephilla patellae (encysting in the tissue of blue mussels Mytilus edulis) and Parorchis acanthus (encysting on mussel shells). Encystment success of both parasite species was significantly lower in the presence of test organisms when compared to controls. Observations revealed that barnacles Austrominius modestus actively filtered cercariae, whereas the larvae were obstructed by the seaweeds Corallina officinalis and Fucus serratus. Anemones Actinia equina both physically disturbed and consumed cercariae. In a further laboratory experiment, grazing gastropods (Littorina littorea, Patella vulgata, and Gibbula umbilicalis) were found to significantly reduce the numbers of P. acanthus metacercariae in artificially prepared dishes by ingestion of cysts. Our results suggest that non-host organisms may play a key role in regulating the transmission of free-living trematode stages in rocky shore ecosystems, which is especially important with regard to the relative diversity and density of species in these habitats. The findings also emphasize the need to include parasites into marine food webs, since cercariae seem to be consumed by certain organisms to a considerable extent and could possibly represent an important energy source.     

The role of habitat heterogeneity in structuring the community of intertidal free-living marine nematodes

The role of habitat complexity has been widely neglected in the study of meiofaunal community patterns. We studied the intertidal nematode community of a structurally complex macrotidal beach exhibiting contrasting microhabitats (sandbars and runnels) to understand the influence of environmental gradients and habitat heterogeneity in the community structure. We tested whether topographical complexity affected (1) the zonation pattern in terms of abundance and diversity, and (2) local diversity by promoting compartmentalization into distinct faunal groups. Our analyses revealed three major faunal assemblages along the exposure gradient associated to differences in mean grain size and chlorophyll a. Diversity patterns involved a mid-intertidal peak, consistent with the intermediate disturbance hypothesis, and another peak at the limit with the subtidal region, consistent with the transition zone. These results highlight the predominance of environmental gradients in establishing intertidal zonation. However, microhabitats differed in environmental conditions and possessed significantly distinct nematofaunal communities. Runnels featured higher levels of taxonomic and functional diversity, many unique genera, and the community differed from the assemblage at the limit to the subtidal, stressing their role as distinct microhabitats. The nematofauna of the structurally complex beach was more diverse than the one from a homogeneous beach nearby, supporting the hypothesis that structural heterogeneity promotes diversity by compartmentalization and highlighting the importance of microhabitats in the assessment of biodiversity. Contrary to previous predictions, our results indicate potentially high regional marine nematode diversity in the Upper Gulf of California.     

Monitoring individual exposure. Measurements of volatile organic compounds in breathing-zone air, drinking water, and exhaled breath

Methods for determining individual exposure to volatile organic compounds (VOC) during normal daily activities were field tested on university student volunteers in Texas and North Carolina. The equipment tested included a personal monitor employing Tenax GC® to collect organic vapors for later analysis by GC-MS, and a specially designed spirometer for collecting samples of expired human breath on duplicate Tenax cartridges. The personal monitor and spirometer proved feasible for collecting abundant quantitative data on most of the 15 target organics. Air exposures to many VOC varied widely, sometimes over three orders of magnitude, among students on the same campus who had been monitored over the same time period and day. A log-linear relationship between breathing-zone air exposures and concentrations in exhaled breath was suggested for three chemicals: tetrachloroethylene, 1,1,1-trichloroethane, and vinylidene chloride. Air was the main route of exposure for all target compounds except the two trihalomethanes (chloroform and bromodichloromethane), which were transmitted mainly through water. Estimated total daily intake through air and water of the target organics ranged from 0.3 to 12.6 mg, with 1,1,1-trichloroethane at the highest concentrations in both geographic areas.     

FLUME CONDITION ASSESSMENT IN COLORADO1

ABSTRACT: A study was conducted in which 66 Parshall flumes used for agricultural flow measurement were assessed for physical integrity, settlement, and submergence. A total of 292 physical defects was documented. A flow measurement error analysis was performed indicating that 52 percent of the flumes measured flow beyond ±3 percent of the correct value and 41 percent of the flumes measured flow beyond ±5 percent. The findings indicate that the infrastructure is aging. The flow measurement system comprised of flumes no longer provide an accurate accounting of water through the distribution network.     

Nomadic pastoralists adopt subsistence strategies that maximise long-term household survival

Summary Optimality approaches have been used to investigate the adaptiveness of human subsistence strategies mainly in hunter-gatherer societies. However the static optimality models used are not suitable for investigating the long-term costs and benefits of decisions, especially in societies where wealth is accumulated and hence resources gained in one year have an influence on future years. Here I use dynamic optimality modelling to investigate the adaptiveness of a subsistence strategy in the Gabbra, a nomadic pastoralist group. I show that herders forego short-term gain in favour of long-term household survival. This is done by herders sometimes manipulating the life histories of their sheep. In herds where the breeding rate has been slowed, by restricting ewes access to males, females have greater longevity, but fewer offspring per year, than in unmanipulated herds. Models maximising offtake from the herd predict that herd breeding-rate should never be slowed. Models maximising short-term household survival predict herd-breeding rate should always be slowed. Models of long-term household survival predict that herd-breeding rate should be slowed only by relatively wealthy households. This is the behaviour observed. Poor and wealthy house-holds adopt different behaviours, yet all are following optimal strategies for their own level of wealth, that maximise their long-term survival. This is the behaviour that would be predicted on the basis of evolutionary theory, given that a family takes many years to be raised. Correspondence to: R. Mace