Arctic hot and CO2 springs: Natural models of impact of climate change on terrestrial ecosystems (scientific paper)

The main purpose of this research was to investigate the carbon cycle in tundra ecosystems in the vicinity of hot springs as natural models of Global Warming and elevated atmosphere CO_2. Empirical data on ecosystem CO_2 fluxes, plant photosynthesis and respiration, vegetation and soil composition were obtained during field expeditions on the Chukotskiy Peninsula (Russia) in 1997 (Chaplino hot springs, 64°26′N, 172°30′W) and 1998 (Ioni hot and CO_2 springs, 65°48′N, 173°22′W). It was found that the influence of naturally increased temperature on carbon exchange considerably depends on the ecosystem type. Under elevated soil temperatures wet sedge ecosystems tend to increase their production, plant biomass, and, to some extent, soil carbon storage. Both species composition and carbon cycle parameters in more drained shrub ecosystems are less sensitive to elevated temperature in the immediate vicinity of the hot springs. Natural CO_2 enrichment of canopy air near the hot springs promotes reduction of photosynthetic efficiency in the studied plant species

Androgen Receptor Gene Polymorphism, Aggression, and Reproduction in Tanzanian Foragers and Pastoralists

<div><p>The androgen receptor (<i>AR</i>) gene polymorphism in humans is linked to aggression and may also be linked to reproduction. Here we report associations between <i>AR</i> gene polymorphism and aggression and reproduction in two small-scale societies in northern Tanzania (Africa)—the Hadza (monogamous foragers) and the Datoga (polygynous pastoralists). We secured self-reports of aggression and assessed genetic polymorphism of the number of CAG repeats for the <i>AR</i> gene for 210 Hadza men and 229 Datoga men (aged 17–70 years). We conducted structural equation modeling to identify links between <i>AR</i> gene polymorphism, aggression, and number of children born, and included age and ethnicity as covariates. Fewer <i>AR</i> CAG repeats predicted greater aggression, and Datoga men reported more aggression than did Hadza men. In addition, aggression mediated the identified negative relationship between CAG repeats and number of children born.</p></div

Goodness of model fit.

<p>CMIN/DF—chi square/degree of freedom ratio; CFI–Confirmatory Fit Index; RMSEA–the Root Mean Square Error of Approximation; PCLOSE—the p-value for a test of close fit.</p><p>Goodness of model fit.</p

Sample sizes of age groups and mean number of children (± <i>SE</i>) per age group in Hadza and Datoga men.

<p>Note: * these are probability values obtained in <i>post hoc</i> test using Scheffe’s modification as the most conservative among all others. Age group: 1 = 17–19 years; 2 = 20–29; 3 = 30–39; 4 = 40–49; 5 = 50–60+ years</p><p>Sample sizes of age groups and mean number of children (± <i>SE</i>) per age group in Hadza and Datoga men.</p

The association between the number of children and fathers’ age in Hadza and Datoga separately represented by five age groups (1 –fathers younger than 20 years of age; 2 –fathers from 20 to younger than 30 years of age; 3 –fathers from 30 to younger than 40 years of age; 4 –fathers from 40 to younger than 50 years of age; 5 –fathers from 50 years of age and older).

<p>The association between the number of children and fathers’ age in Hadza and Datoga separately represented by five age groups (1 –fathers younger than 20 years of age; 2 –fathers from 20 to younger than 30 years of age; 3 –fathers from 30 to younger than 40 years of age; 4 –fathers from 40 to younger than 50 years of age; 5 –fathers from 50 years of age and older).</p

The associations between age group (Age, manifested exogenous variable), number of CAG repeats of <i>AR</i> gene (CAGn, manifested exogenous variable), ethnic group (Ethnicity, manifested exogenous variable) and number of children (NC, dependent variable), mediated by total aggression (TA, endogenous mediating variable) scores based on structural equation modeling; asterisks designate significance level: *- 0.01

<p>The associations between age group (Age, manifested exogenous variable), number of CAG repeats of <i>AR</i> gene (CAGn, manifested exogenous variable), ethnic group (Ethnicity, manifested exogenous variable) and number of children (NC, dependent variable), mediated by total aggression (TA, endogenous mediating variable) scores based on structural equation modeling; asterisks designate significance level: *- 0.01</p

Standardized regression weights according to the model with lower and upper limits of the 95% confidence interval.

<p>S.E.–standard error of regression weights, C.R.–critical ratio, P–probability value.</p><p>Standardized regression weights according to the model with lower and upper limits of the 95% confidence interval.</p

The distributions of allele frequencies at the <i>AR</i> CAG locus in Hadza and Datoga men.

<p>The x-axis reflects the number of CAG repeats at the <i>AR</i> locus. Whisker plots represent 95% confidence intervals.</p

Results of the test for mediation.

<p>Results of the test for mediation.</p