maenas (intertidal zone) and Segonzacia mesatlantica - Station ...
maenas (intertidal zone) and Segonzacia mesatlantica - Station ... maenas (intertidal zone) and Segonzacia mesatlantica - Station ...
192 CHAPITRE 5. ADAPTATIONS RESPIRATOIRES DE S. MESATLANTICA TAB. 5.2 – Summary of the forward selection results for the choice of covariables. Exp4 , Exp2 and Exp3 are the experimental groups ; Site is the collection site. Since the power of the forward selection is reduced for the small number of control crabs (18), variables with a p-value up to 0.10 were chosen as covariables. Variables R 2 Cumulative R 2 Cumulative adjusted R 2 p-value Exp4 0.1625 0.1625 0.1102 0.0048 Size 0.1447 0.3073 0.2149 .0114 Site 0.0909 0.3982 0.2693 0.0674 Exp2 0.0457 0.4440 0.2729 0.3638 Exp3 0.0333 0.4773 0.2595 0.5637 Sex 0.0369 0.5142 0.2493 0.4845 the imbalance of the experimental design, it was not quite orthogonal to Interaction (correlation r = 0.06). For the same reason, Oxygenation was not quite orthogonal to Temperature (r = -0.09), and the Interaction variable was not quite orthogonal to the main factors (r(Oxygenation, Interaction) = -0.06, r(Temperature, Interaction) = 0.04). Lack of orthogonality means that the test of significance of the Interaction term will be based upon type III sums-of-squares, which will result in slightly reduced power for the test, due to a small interference from the two main factors whose sums-of-squares will be taken into account in the analysis before computing that of the interaction. The following variables represent conditions that may affect the physiological response of the crabs to the experimental conditions : hydrothermal field of origin of the animals (site, binary variable : Lucky Strike or Rainbow), sex (binary variable : male or female), width of the cephalothorax (quantitative variable : size in mm), and whether or not the hemolymph had been unfrozen prior to our measurement of the response variables for study on oxydative stress (binary variable : unfrozen). The four experimental groups (exp1 to exp4) may also explain part of the variation in the response variables. Forward selection of these variables against the 11 hemolymph response variables showed that the variables site, size, and exp4 explained significant amounts of the variation in the table of response variables (Table 5.2). These three variables were used as covariables (matrix W) during the tests of the interaction and main factors. The interaction was tested by performing an RDA on the 11 hemolymph response variables (Y), with the interaction term as the explanatory variable (X) and temperature and oxygen added to the other covariables (W). The interaction was found to be significant (R2=0.04, p-value=0.027) ; so, the effect of each factor had to be tested separately in each of the classes of the other factor. Both factors had very significant effects in both classes of the other factor. Oxygenation had an effect at low (R2=0.12, p-value=0.028) and high (R2=0.12, p-value=0.005) temperature, and temperature had an effect at low (R2=0.12, p-value=0.003) and high (R2=0.16, p-value=0.008) oxygenation
5.4. MANUSCRIT : RESPIRATORY ADAPTATIONS OF S. MESATLANTICA 193 FIG. 5.7 – Biplot graphs of the canonical redundancy analyses (RDA) performed between hemolymph composition (descriptive variables Y) and acclimation conditions (explanatory variables X) along the two first canonical axis. See the text for details on statistical analyses. Graphs were produced from an RDA performed without covariable in order to avoid distortion of the explanatory variables by the covariables. Dotted arrows, explanatory variables ; full lines, response variables. The analysis was made for each factor separately in each class of the other factor since the interaction term was significant. (a) Oxygenation effect under low temperature, (b) oxygenation effect under high temperature, (c) temperature effect under low oxygenation, (d) temperature effect under high oxygenation, (e) example graph. See the text for an interpretation of the example graph.
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192 CHAPITRE 5. ADAPTATIONS RESPIRATOIRES DE S. MESATLANTICA<br />
TAB. 5.2 – Summary of the forward selection results for the choice of covariables. Exp4 , Exp2 <strong>and</strong><br />
Exp3 are the experimental groups ; Site is the collection site. Since the power of the forward selection<br />
is reduced for the small number of control crabs (18), variables with a p-value up to 0.10 were chosen<br />
as covariables.<br />
Variables R 2 Cumulative R 2 Cumulative adjusted R 2 p-value<br />
Exp4 0.1625 0.1625 0.1102 0.0048<br />
Size 0.1447 0.3073 0.2149 .0114<br />
Site 0.0909 0.3982 0.2693 0.0674<br />
Exp2 0.0457 0.4440 0.2729 0.3638<br />
Exp3 0.0333 0.4773 0.2595 0.5637<br />
Sex 0.0369 0.5142 0.2493 0.4845<br />
the imbalance of the experimental design, it was not quite orthogonal to Interaction (correlation r =<br />
0.06). For the same reason, Oxygenation was not quite orthogonal to Temperature (r = -0.09), <strong>and</strong> the<br />
Interaction variable was not quite orthogonal to the main factors (r(Oxygenation, Interaction) = -0.06,<br />
r(Temperature, Interaction) = 0.04). Lack of orthogonality means that the test of significance of the<br />
Interaction term will be based upon type III sums-of-squares, which will result in slightly reduced<br />
power for the test, due to a small interference from the two main factors whose sums-of-squares will<br />
be taken into account in the analysis before computing that of the interaction.<br />
The following variables represent conditions that may affect the physiological response of the<br />
crabs to the experimental conditions : hydrothermal field of origin of the animals (site, binary variable<br />
: Lucky Strike or Rainbow), sex (binary variable : male or female), width of the cephalothorax<br />
(quantitative variable : size in mm), <strong>and</strong> whether or not the hemolymph had been unfrozen prior to<br />
our measurement of the response variables for study on oxydative stress (binary variable : unfrozen).<br />
The four experimental groups (exp1 to exp4) may also explain part of the variation in the response<br />
variables. Forward selection of these variables against the 11 hemolymph response variables showed<br />
that the variables site, size, <strong>and</strong> exp4 explained significant amounts of the variation in the table of<br />
response variables (Table 5.2). These three variables were used as covariables (matrix W) during the<br />
tests of the interaction <strong>and</strong> main factors.<br />
The interaction was tested by performing an RDA on the 11 hemolymph response variables (Y),<br />
with the interaction term as the explanatory variable (X) <strong>and</strong> temperature <strong>and</strong> oxygen added to the<br />
other covariables (W). The interaction was found to be significant (R2=0.04, p-value=0.027) ; so, the<br />
effect of each factor had to be tested separately in each of the classes of the other factor.<br />
Both factors had very significant effects in both classes of the other factor. Oxygenation had an<br />
effect at low (R2=0.12, p-value=0.028) <strong>and</strong> high (R2=0.12, p-value=0.005) temperature, <strong>and</strong> temperature<br />
had an effect at low (R2=0.12, p-value=0.003) <strong>and</strong> high (R2=0.16, p-value=0.008) oxygenation