On rocks and hard places.

In susceptible persons emotional stress results in immediate sympathetic stimulation, with a vasomotor response that results in a high-output state and elevated blood pressure; the vasopressor response seems to be transient. There seems to be no longitudinal epidemiologic validation of the attractive hypothesis that transiently elevated blood pressures are the prelude to fixed hypertension, however. The acquisition of hypertension by populations abandoning their traditional mode of living has been attributed to the sociocultural stress inherent in westernization, but these studies usually have not taken into account concomitants of this type of acculturation, such as dietary changes and increased body weight. The inverse relationship of blood pressure levels to education could explain the development of hypertension when aspiration to upward mobility is thwarted. The severity of perceived occupational stress relates inversely to blood pressure, suggesting that familiarity with a job renders the demands made by the work environment more predictable and less threatening in terms of vasopressor response.     

Habitat effects on resource tracking ability: do wintering Blackcaps Sylvia atricapilla track fruit availability?

If resource availability shapes population distribution, changes in resource abundance should cause parallel changes in population numbers. However, tracking ability may be disrupted by different environmental and behavioural factors that act at different spatial and temporal scales. Here we analyse the ability of wintering Blackcap Sylvia atricapilla populations to track spatio-temporal variation in fruit availability in southern Spain in two habitats (forests and shrublands) with different population structure. Former studies had shown that forests are equally used by both adult migrant and local Blackcaps, whereas shrublands are nearly monopolized by juvenile migrants. These differences might affect resource tracking: it should be disrupted in forests, as local birds remain over winter in their breeding territories, but not in shrublands where similarly competitive juvenile migrants can freely track the spatial distribution of fruits. We analysed the fruit-tracking ability of Blackcap populations among sites and years in both habitat types using a habitat-matching model, which predicts spatio-temporal changes in population abundance proportional to changes in resource availability. We counted Blackcaps and fruiting shrubs (dominated by Lentiscs Pistacia lentiscus and Wild Olives Olea europaea sylvestris ) during four winters in forest and shrubland patches. The abundance of fruits was always higher in shrublands than in forests. In shrublands, Blackcaps seemed to move freely across fruit-rich habitat patches, tracking changes in fruiting-shrub abundance among sites and years. However, such tracking was not observed in forests. This supports the view that fruit-tracking ability may be constrained by local factors, such as the social structure of populations occurring in different habitat types, which introduces spatio-temporal variation in the way fruit availability shapes the abundance distribution of these birds in their Mediterranean wintering grounds.     

Biological affinities between migrant and parental populations of fishermen on the east coast of India.

We examined biological affinities between the migrant groups of fishermen in Puri and their parental counterparts using 3 sets of variables: genetic markers, anthropometric measurements, and quantitative dermatoglyphics. Results of both univariate and multivariate analyses suggest a significant migration effect, diversifying migrants from their parental populations, although the distance configurations based on each set of variables resemble each other. The migration effect is particularly remarkable for the anthropometric measurements. The plot of group centroids based on the discriminant analysis of the 7 populations depicts a clear segregation of migrants from the parental populations. Because of relatively large effective population sizes and short history of these populations in Puri, the role of genetic drift can be safely ruled out. However, a founder effect is a plausible reason for the observed differentiation of the migrants from their parental groups, especially given that certain rare variants that were not observed in the parental populations appear in the migrants. That the founders were a select group of fishermen with respect to body dimensions, not a random group, can be inferred from the occupational differences among the migrant groups, which in turn suggests phenotypic plasticity in the observed differentiation. Regression of mean phenotypic variance and heterozygosity on the distance from the centroid suggests a strong possibility of external gene flow into the migrant populations in Puri.     

Genetic aspects of migration in a rhesus monkey population

Gene frequency distributions in subdivided populations are affected by migration of individuals between groups. This paper considers the effects of such migration on blood protein allele frequency distributions in social groups of the Cayo Santiago rhesus macaque colony. Gene frequencies for complete social groups and their migrant and natal segments were analyzed at four points within a four year period in the colony's history. Gene frequencies varied between the migrant segments of different groups. Gene frequencies of migrant segments of particular groups also varied substantially with time. Usually, but not always, the presence of migrants in groups reduced the levels of inter-group gene frequency differentiation. We suggest that our findings are explained by a model in which the recruitment of immigrants into social groups is largely random with respect to individual genotypes. Such a model implies that migration contributes to both stochastic and directed changes in gene frequencies in rhesus and similarly substructured populations.     

Psychosocial factors in blood pressure variation: A comparative study of young Samoans

Abstract

Traditional peoples contacting modern cultures frequently experience increased levels of blood pressure. The aim of this investigation was to identify some acculturation‐related psychosocial factors which might contribute to those elevations. Young Samoans living in a traditional village, in modernizing American Samoa, and as migrants in Hawaii were studied. Casual blood pressure, anthropometric measurements, and extensive interview data were collected. The most important factor predicting variation in blood pressure was body mass (BMI). This finding was particularly evident among the acculturated and migrant Samoans. In those locations women's abandonment of breast feeding may contribute to their higher BMI. Among acculturated and migrant women, measures of social support favored lower blood pressures. Among men in all locations a greater number of close social ties was linked to higher blood pressures with the exception of ties with parents. Parental ties were linked to substantially lower blood pressures. A knowledge of Samoan traditions favored lower blood pressure among migrant men, while knowledge of American culture favored higher pressures. Coping strategies and complaint behavior were also significant contributors in all locations.     

Consequences of the settlement of migrant European Robins Erithacus rubecula in wintering habitats occupied by conspecific residents

In wintering areas where migrant birds meet sedentary conspecifics, early settlement of local residents in the best habitat patches might reduce the availability of suitable sites for arriving migrants. We studied how sympatric migratory and sedentary European Robins Erithacus rubecula occupy two wintering habitats of different quality (forests and shrublands) in southern Spain, and how such a distribution affects individuals of each population sector. In September, before migrants arrived, Robins were only found in forests, and they had already saturated these habitats, so that rather than increasing Robin abundance in these habitats, the arrival of migrants caused a massive occupation of the previously vacant shrublands. During the winter, we captured Robins and identified them as migrants or residents using a discriminant function based on morphological traits. Residents always predominated in forests, and migrants in shrublands, but through the winter around 35% of residents (mainly juveniles) moved to shrublands, having been replaced by some migrants in forests. Although food was more abundant in shrublands, Robins had better body condition in forests, suggesting that other factors determined habitat preferences (e.g. shelter availability or food diversity, which were higher in forests). In addition, we observed a greater variance in body mass relative to body size in forests, suggesting that energy management was less constrained in this habitat (for example owing to a lower exposure to predators or a higher food predictability). Our results suggest that sedentary Robins benefit from an early occupation of the best habitats in the wintering grounds, forcing migrants to colonize apparently less suitable sites. This would explain the persistence of these small southern populations despite the yearly flooding of the area by huge numbers of migrant conspecifics.     

Obesity, hypertension, and migration: a meta-analysis of populations of the South Asian diaspora

The effects of migration on human health have been a topic of interest for demographers and human biologists. Even if migrants to a new region achieve a higher standard of living in their new place of residence, their improved living conditions may not be associated with better health. Part of the difficulty of understanding the health consequences of migration is the complications in trying to control for variables that may affect health, such as gender, age, and urban or rural environment of migrants and nonmigrants. In this paper we report results of a meta-analysis of the body mass index (BMI) and blood pressure (BP) of people of South Asian descent, by comparing nonmigrants who inhabit the subcontinent, with migrants who moved to various places around the globe. Our results indicate that BMI almost always increases to a significant level upon migration and that an increase in BMI is most pronounced in female migrants. Our results also show that BP does not always increase in migrant communities and that it is actually lower in some migrant samples than it is in comparable nonmigrant groups. Therefore, our results show that BP and the BMI do not behave in the same manner following a migration event. We propose that the BMI changes experienced by migrants are likely to reflect different activity levels and diet in the new homeland. However, the BP changes experienced by migrants are likely to reflect stress broadly defined. Such stress may be increased or decreased, depending on the specific migration experience. We propose that the BMI and BP measure two different dimensions of the migration experience.     

Ethnic differences in atherosclerosis, cardiovascular disease and lipid metabolism

PURPOSE OF REVIEW: Comparison of risk factors and cardiovascular disease among racial and ethnic groups is a powerful approach to study genetics and lifestyle, or environmental interactions. RECENT FINDINGS: Most, mean or median, cardiovascular risk factor levels are similar among black and white people. There are much greater differences in the distribution of risk factor level within a specific race and ethnic group than between US populations. There are also very large differences in levels of risk factors for coronary heart disease between specific ethnic migrant populations such as comparing black people in Africa with those in the US, or Japanese people in Japan with those in Hawaii and California. Differences in distribution of risk factors and disease between race and ethnic group are a function of the frequency of specific genotypes and interaction with environmental factors. Several of the most important differences between racial groups are higher blood pressure, lower triglycerides and higher HDL cholesterol among blacks, higher prevalence of diabetes and insulin resistance among Mexican Americans and American Indians, and higher triglyceride levels among the Japanese. SUMMARY: Further studies of racial and ethnic differences should focus on unique phenotypes and genotypic differences, international and migrant studies and large enough sample sizes to provide robust results. The sprinkling of a percentage of minority participants in each study is worthless. The study of racial and ethnic differences in disease and detection of risk factor levels must be based on solid hypotheses that can evaluate the interaction of lifestyle and possible genetic attributes. Many of the reported ethnic differences in risk factors and disease in US populations are primarily a function of differences in education, socioeconomic variations, and utilization of preventive and clinical treatments.     

A comparison of sex ratio,birth periods and calf survival among Serengeti wildebeest sub‐populations,Tanzania

Although adaptation and environmental conditions can easily predict demographic variation in most savannah ungulates, no study on demographic consequences arising from natural and anthropogenic factors among Serengeti wildebeest (Connochaetes taurinus) sub‐populations in Tanzania has been carried out. Here, I report estimates of annual sex ratio, calf and yearling survival rate and birth seasonality between resident and migratory sub‐populations to explore demographic patterns arising from the different age and sex structure. The results indicate significantly higher female‐biased sex ratios in the resident and almost even sex ratios among individual migrants. The calf recruitment estimated as mother: offspring ratios indicate a more synchronous birth in the migrant than the resident sub‐population. Also, birth seasonality in the migratory sub‐population coincided with seasonal variability of rainfall and the timing of the birth peak was more variable in the migrants than the resident sub‐population. The migratory sub‐population had a higher annual proportional mean calf survival estimate (0.84) than that of the residents (0.44) probably due to higher mortality resulting from predation in the western corridor. However, the proportion of yearling survival estimates was much lower (0.31) in the migrants and relatively higher (0.39) in the residents. Different demographic outcomes resulting from environment, predation, movements and ecological factors including resource competition have conservation implications for the two sub‐populations.     

Trends in migrant and ethnic minority voting in Australia: findings from the Australian election study

A review of the research literature on migrant voting in Australia shows that the “ethnic vote” has almost disappeared now that migrants tend to vote in a similar way to the rest of the population according to traditional class cleavages. In addition, it is argued that migrants in Australia predominantly reside in safe Labor seats that are represented by cabinet or shadow cabinet ministers. As such their group-based interests are often neglected by the major parties. Using findings from the ABS census and the 1993–2013 AES, this article re-examines whether there is a migrant vote, and if so, the extent to which migrant voting patterns have changed since the 1990s when the migrant and ethnic vote reached its peak. This study reveals patterns of migrant voting among certain birthplace subgroups that are more volatile than in previous decades but at the same time distinctive.     

Avian population consequences of climate change are most severe for long-distance migrants in seasonal habitats

One consequence of climate change is an increasing mismatch between timing of food requirements and food availability. Such a mismatch is primarily expected in avian long-distance migrants because of their complex annual cycle, and in habitats with a seasonal food peak. Here we show that insectivorous long-distance migrant species in The Netherlands declined strongly (1984–2004) in forests, a habitat characterized by a short spring food peak, but that they did not decline in less seasonal marshes. Also, within generalist long-distance migrant species, populations declined more strongly in forests than in marshes. Forest-inhabiting migrant species arriving latest in spring declined most sharply, probably because their mismatch with the peak in food supply is greatest. Residents and short-distance migrants had non-declining populations in both habitats, suggesting that habitat quality did not deteriorate. Habitat-related differences in trends were most probably caused by climate change because at a European scale, long-distance migrants in forests declined more severely in western Europe, where springs have become considerably warmer, when compared with northern Europe, where temperatures during spring arrival and breeding have increased less. Our results suggest that trophic mismatches may have become a major cause for population declines in long-distance migrants in highly seasonal habitats.     

HIV and Latino migrant workers in the USA

Abstract

Migrant workers from Latin America are an essential source of economic development in the US agricultural industry. A majority of migrants are from Mexico and are undocumented and they represent a vulnerable and marginalized group in American society. There is a growing concern for HIV disease in the migrant community. The HIV prevalence rate among migrants is higher than the average rates in USA and in countries of Latin America. There are many behavioural, social, cultural, and health care risk factors and barriers that place migrants at increased risk for HIV infection. Many migrant workers contract HIV while working and living in the USA, which has contributed to rising HIV infection rates in Mexico. In order to prevent an increasing epidemic of HIV disease in Latino migrant workers, there is an urgent call for new and improved health care policies at the international, federal, state, and local levels.     

Winter habitat use by Loggerhead Shrikes (Lanius Ludovicianus) in Mexico: separating migrants from residents using stable isotopes

Several species of migrant birds overlap in range on their wintering grounds with non-migrant conspecifics or other species that occupy a similar niche. Very little is known whether such overlap results in competition and subsequent habitat segregation since it is usually impossible to separate resident from migrant individuals. The Loggerhead Shrike (Lanius ludovicianus) is a declining grassland species in North America that winters in the southern United States and Mexico. Using stable-hydrogen isotope (δD) analysis of feathers, we identified resident and migrant shrikes wintering in northeastern Mexico based on a latitudinal gradient in precipitation and feather δD values. Indicator species analyses showed that migrants occupied areas where bare ground was less available than those occupied by residents, a pattern which held when a more restricted set of birds from the extremes of the δD distribution were considered. This provides evidence for conspecific habitat segregation. Habitat differences were also found between sites occupied by shrikes and apparently suitable but unoccupied sites. Shrikes occupied more open sites that contained shorter tall shrubs and huisache (Acacia farneasiana) and fewer tall shrubs, mesquite (Prosopsis glandulosa) and huisache than unoccupied sites. The availability of suitable winter habitat and the potential competition between migrants and residents may be factors that influence the population dynamics of migrant shrikes in North America.     

HIV-related high-risk behaviors among Chinese migrant construction laborers in Nantong, Jiangsu

Background

HIV transmission in rural areas of China is being fueled in part by migrant workers who acquire HIV outside of their hometowns. Recent surveillance statistics indicate that HIV prevalence among returning migrants has increased significantly.

Methods

We conducted a community-based cross-sectional study to assess HIV-related knowledge, attitudes and behaviors among migrant returnees in Nantong, Jiangsu Province, one of the largest exporters of migrant laborers.

Results

A total of 1625 subjects were enrolled with a response rate of 89%. All participants were male and of the majority Han ethnicity. The mean age was 39.0 years (SD = 6.7; range: 18 to 63), and most had a stable partner (N = 1533, 94.3%). Most correctly identified the major modes of HIV transmission (68.9%–82.0%), but fewer were able to identify ways that HIV cannot be transmitted. Nearly one-third of participants held positive attitudes toward having multiple sex partners, and nearly half believed that sex work should be legalized. Multiple logistic regression analysis indicated that risky sexual behavior (defined as sex with a casual or commercial sex partner) was associated with no stable partner; working abroad; correct condom use; age <22 at first sex; higher coital frequency; and having a positive attitude towards multiple sex partners.

Conclusions

We found high levels of reported sex with a casual or commercial sex partner and low levels of consistent condom use. HIV prevention interventions among migrant workers need to focus on younger migrants, migrants without stable partners, and migrants who travel abroad for work.     

Are temporary migrants escapees of the one-child-per-family population policy: a revisit to the detachment hypothesis

Using Hubei province as a case study, this paper retests the detachment hypothesis against the three conventional hypotheses regarding migration-fertility linkage (i.e., selectivity, disruption, and adaptation hypotheses) in explaining migrant and non-migrant fertility differentials in China. The analysis of yearly order-specific birth probabilities suggests that temporary migrants exhibit a significantly higher probability of having a second or higher order birth than comparable permanent migrants and non-migrants. This higher fertility among temporary migrants occurs after migration; temporary migrants actually do not differ from non-migrants in fertility before migration. But permanent migrants experience no significant change in their fertility after migration. The results lend a strong support to the detachment hypothesis, which best explains the fertility differentials between migrant and non-migrant populations in contemporary China; the separation of temporary migrants' actual residence from their official one does lead to a greater likelihood among temporary migrants to have unplanned births.     

Modeling tails for collinear data with outliers in the English Longitudinal Study of Ageing: Quantile profile regression

Research has shown that high blood glucose levels are important predictors of incident diabetes. However, they are also strongly associated with other cardiometabolic risk factors such as high blood pressure, adiposity, and cholesterol, which are also highly correlated with one another. The aim of this analysis was to ascertain how these highly correlated cardiometabolic risk factors might be associated with high levels of blood glucose in older adults aged 50 or older from wave 2 of the English Longitudinal Study of Ageing (ELSA). Due to the high collinearity of predictor variables and our interest in extreme values of blood glucose we proposed a new method, called quantile profile regression, to answer this question. Profile regression, a Bayesian nonparametric model for clustering responses and covariates simultaneously, is a powerful tool to model the relationship between a response variable and covariates, but the standard approach of using a mixture of Gaussian distributions for the response model will not identify the underlying clusters correctly, particularly with outliers in the data or heavy tail distribution of the response. Therefore, we propose quantile profile regression to model the response variable with an asymmetric Laplace distribution, allowing us to model more accurately clusters that are asymmetric and predict more accurately for extreme values of the response variable and/or outliers. Our new method performs more accurately in simulations when compared to Normal profile regression approach as well as robustly when outliers are present in the data. We conclude with an analysis of the ELSA.     

Arterial Blood Pressure and Modernization in Brazil

The relationship between individual modernization and elevated arterial blood pressure was examined in a study in urban Brazil. We hypothesized that elevated blood pressure would result from the discrepancy between an individual's style of life and his or her economic resources; specifically, we suggested that when modern life-style acquisition exceeded economic resources, a circumstance referred to as "life-style stress," blood pressure would be elevated. This factor was related to diastolic, but not systolic, blood pressure, independently of a variety of biologic, dietary, and sociocultural confounding factors. The perceived change associated with life events also predicted diastolic, but not systolic, blood pressure. Other predictors of diastolic blood pressure were calcium intake, fat intake, race, age, and the body mass index. We argue that sociocultural risk factors emerge in the modernization process as a result of social structural imbalances generated by economic development and represent independent risk factors for elevated arterial blood pressure.     

The Kenyan Luo migration study: observations on the initiation of a rise in blood pressure.

OBJECTIVE--To demonstrate the magnitude, timing, and cause of changes in blood pressure that occur in migrants from a low blood pressure population on moving to an urban area. DESIGN--A controlled longitudinal observational study of migrants as soon after migration as possible and follow up at three, six, 12, 18, and 24 months after migration. A cohort of controls living in a rural area who were matched for age, sex, and locality were also observed at the same periods. SETTING--35 Villages on the northern shores of Lake Victoria in western Kenya and Nairobi. PARTICIPANTS--325 Members of the Luo tribe aged 15 to 34 years who had migrated to Nairobi and 267 controls living in villages. The numbers of both groups reduced during follow up such that only 63 migrants and 143 controls were followed up for two years. MAIN OUTCOME MEASURES--A medical questionnaire and three 24 hour diet histories were completed by migrants and controls. Height, weight, pulse, and blood pressure were measured. Three 12 hour overnight urine samples were collected from all participants and analysed for sodium, potassium, and creatinine concentrations. RESULTS--The mean systolic blood pressure of migrants was significantly higher than that of controls throughout the study, and the distribution of blood pressure was shifted to the right compared with controls. The mean diastolic blood pressure of the two groups diverged over time. Blood pressure differences were not due to selective migration. The migrants'' mean urinary sodium:potassium ratio was higher than that of controls (p less than 0.001) throughout, and weight and pulse rate were also higher among migrants, although differences diminished with time. CONCLUSIONS--Urinary sodium:potassium ratio, pulse rate, and weight are important predictors of increased blood pressure among migrants from a low blood pressure community and may also be implicated in the initiation of essential hypertension.     

The equilibrium population size of a partially migratory population and its response to environmental change

A partially migratory population consists of non‐migrant and migrant individuals that share a common site during one period of the annual cycle. In this paper, we derive the expected equilibrium population sizes of migrants and non‐migrants and show how the abundance of one type is dependent on the other because their dynamics are coupled through density‐dependent effects. We present an approach for developing hypotheses about how changes in the environment will influence partially migratory populations and for formulating testable predictions about the effects of future changes on the proportions of migrants and non‐migrants. We apply this approach to a hypothesis put forward by Berthold that improved environmental conditions at the shared site will generally increase the number of non‐migrants and decrease the number of migrants, and to a study by Nilsson et al. which observed an increase in the number of migrants in a partially migratory blue tit Cyanistes caeruleus population in Sweden, but an overall maintenance of the proportion of migrants.     

Response of birds to climatic variability; evidence from the western fringe of Europe

Ireland’s geographic location on the western fringe of the European continent, together with its island status and impoverished avifauna, provides a unique opportunity to observe changes in bird migration and distribution patterns in response to changing climatic conditions. Spring temperatures have increased in western Europe over the past 30 years in line with reported global warming. These have been shown, at least in part, to be responsible for changes in the timing of life cycle events (phenology) of plants and animals. In order to investigate the response of bird species in Ireland to changes in temperature, we examined ornithological records of trans-Saharan migrants over the 31-year period 1969–1999. Analysis of the data revealed that two discrete climatic phenomena produced different responses in summer migrant bird species. Firstly, a number of long-distance migrants showed a significant trend towards earlier arrival. This trend was evident in some species and was found to be a response to increasing spring air temperature particularly in the month of March. Secondly, (1) a step change in the pattern of occurrences of non-breeding migrant bird species, and (2) an increase in the ringing data of migrant species were found to correlate with a step change in temperature in 1987–1988. These results indicate that, for migrant bird species, the impact of a sudden change in temperature can be as important as any long-term monotonic trend, and we suggest that the impact of step change events merits further investigation on a wider range of species and across a greater geographical range.