maenas (intertidal zone) and Segonzacia mesatlantica - Station ...

188 CHAPITRE 5. ADAPTATIONS RESPIRATOIRES DE S. MESATLANTICA
(Sigma), or buffered at a different pH with HCl or NaOH solutions. All experiments were performed
at 15°C ; the pH of an identical sample was simultaneously determined using a microelectrode
(Orion, Thermo Corporation). Saturation of the sample for each PO2 step was determined from the
absorbance measurement at 340 nm and the P 50 (P O2 for half-saturation) and n 50 (Hill coefficient)
were determined using the Hill plot log(
S
(1−S) ) = f(log(P O2)) where S is the fractional saturation of
the pigment.
Statistical analyses
Multivariate analysis methods must be used to carry out analyses of the whole data sets of hemolymph
variables and of subunit compositions. Parametric multivariate analysis of variance (MA-
NOVA) could not be used since the number of individuals for each experimental condition or control
set was low (from 3 to 20 individuals). Canonical redundancy analysis (RDA) was used as a form of
MANOVA, as proposed by Legendre and Anderson (Legendre et Anderson, 1999). RDA uses permutation
tests of significance, which remain valid for small samples and non-normally distributed data.
We used RDA to test the significance of the effect of the experimental conditions and obtain biplot
graphs which present interesting representations of the relationships between the response variables
and the experimental conditions. The functions rdaTest and graph.rdaTest, written in the R language
by P. Legendre and S. Durand, were used for our analyses. See :
http ://www.bio.umontreal.ca/legendre/indexEn.html
5.4.3 Results
Hemolymph composition
Segonzacia mesatlantica hemolymph has a high protein content with an average value of 117 µg/µl
± 44 % for all crabs (standard deviation calculated for all crabs). A high variability exists between
crabs and values are comprised between 23 µg/µl and 200 and 282 µg/µl for the crabs with the highest
protein content. Hc is always the main hemolymph protein in all crabs and accounts for approximately
80 % of all proteins in the hemolymph (Figure 5.5a). This result is confirmed when samples are
analyzed by FPLC.
For all measured inorganic ions, concentrations are in the range of those observed for the shallow
water species Carcinus maenas (Robertson, 1960). For monovalent cations, sodium content is quite
stable with an average value of 490 mM ± 7 %. Potassium levels remain low but show a higher
variability than sodium with an average value of 10.7 mM ± 15 % (Figure 5.5b). These low potassium
levels confirm that the cellular integrity of individuals is conserved at the end of the experiments and