Migrations and gradations : reappraising the health profile of immigrants to Canada

New immigrants to Canada typically have a more favourable health profile than the non-immigrant population. This phenomenon, known as the 'healthy immigrant effect', has been attributed to both the socioeconomic advantage (ie. educational attainment, occupational opportunity) of non-refugee immigrants and existing screening protocols that admit only the healthiest of persons to Canada. It has been suggested that this health advantage diminishes as the time of residence in Canada increases, due in part to the adoption of health-risk behaviours such as alcohol and cigarette use, an increase in excess body weight, and declining rates of physical activity. However, the majority of health research concerning immigrants to Canada has been limited to cross-sectional studies (Dunn & Dyck, 2000; Newbold & Danforth, 2003), which may mask an immigrant-specific cohort effect. Furthermore, the practice of aggregating foreign-bom persons by geographical regions or treating all immigrants as a homogeneous group may also obfuscate intra-immigrant differences in health. Accordingly, this study uses the Canadian National Population Health Surveys (NPHS) and data from the United Nations Development Program (UNDP) to prospectively evaluate factors that predict health status among immigrants to Canada. Each immigrant in the NPHS was linked to the UNDP Human Development Index of their country of birth, which uses a combined measure of health, education, and per capita income of the populace. The six-year change in health function, psychological distress, and self-rated health were considered from a population health perspective (Evans, 1994), using generalized-estimating equations (GEE) to examine the compounding effect of past and recent predictors of health. Demographic

Influence of temperature and photoperiod upon ionic regulation in rainbow trout Salmo gairdneri

Interactions of photoperiod and temperature upon waterelectrolyte balance were examined in rainbow trout acclimated to six combinations of two photoperiods {18h light: 6h dark, o 6h light: l8h dark) and three temperatures (2, 10 and 18 C). The influence of temperature and photoperiod upon plasma, skeletal muscle, cardiac muscle and liver levels of sodium, potassium, magnesi.um, calcium, chloride, water content, water distribution and cellular ion concentrations was determined by a one way analysis of variance. Significant (p < 0.05 or better) temperature effects at common photoperiods were observed in 70% of the analyses performed, showing no bias toward either photoperiod. Significant photoperiod effects occured in 57% of the analyses performed at common temperatures. The influence of photoperiod was most prevalent at reduced temperatures. Potassium and magnesium appeared to be particularly thermosensitive, while sodium and calcium were the most photosensitive of the electrolytes. The ionic composition of all tissues studied were relatively thermosensitive, with liver apparently being the most sensitive. On the other hand; the ionic composition of skeletal and cardiac muscle appear to be the mos.t photosensitive of the tissues examined. Water content and distribution in skeletal muscle and liver were significantly influenced by temperature in 50% of the analyses performed showing a very strong bias toward UwinterU animals. Photoperiod effects were significant in 56% of the water parameters measured with a strong bias toward the two lower temperatures. Body weight was of significant influence in 16% of the 174 analyses performed. These data are discussed in terms of the effect of temperature upon ionregulatory mechanisms and the possible impact of photoperiod variations on endocrine systems influencing water-electrolyte metabolism.

Sexual selections in the northern fall field cricket, Gryllus pennsylvanicus: a manipulation of the adult sex ratio

The operational sex ratio has long been considered an important constraint on the structure of mating systems. The effects of an experimentally manipulated sex ratio on mating behavior and selection were investigated in a polygynous species, Gryllus pennsylvanicus, where the potential exists for spatial/temporal fluctuations in sex ratio of field populations. Four different sex ratios (males: females, 5:0, 5:2, 5:5, 5:10) were investigated. Observations were conducted in late summer over two field seasons, from 2400 h , to 1000 h EST. Several male characters thought to be associated with male reproduc.tive success were studied: calling duration, searching distance, weight, fighting behavior, courtship frequency, and mating success. Variance in male mating success was used as the indicator for the opportunity for sexual selection. Total selection was estimated as the univariate regression coefficient between relative fitness and the character of interest, while direct selection was estimated as standardized partial regression coefficients generated from a multiple regression of relative fitness on each character. The opportunity for sexual selection was highest at 5:2 and lowest at 5:10. The frequency of fighting behavior was highest at 5:2 and 5:5. Fighting ability (% wins) was determined to be an important correlate of male body weight. Direct selection for increased male body weight was detected at 5:2, while total selection for body weight was seen at 5:5. Selection on male body weight was not detected at 5: 10. Calling duration decreased as sex ratio became more female-biased. Total and direct selection were detected for increased calling at 5:2, only total selection for calling was seen at 5:5, whereas direct selection against calling was detected at 5: 10. Searching distance also decreased as sex ratio became more female-biased, however no form of selection was detected for searching at any of the sex ratios. Data are discussed in terms of sexual selection on male reproductive tactics, the mating system and maintenance of genetic variation in male reproductive behavior.