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

5.4. MANUSCRIT : RESPIRATORY ADAPTATIONS OF S. MESATLANTICA 197
FIG. 5.10 – Relative abundances of the 16 subunits in Segonzacia mesatlantica whole hemolymph
samples and purified complexes. Bars are average values ± standard deviation. Asterisks mark the
dodecamer specific subunits.
plexes. Purified dodecamers and hexamers from 24 crabs were analyzed and for 23 of these crabs
whole hemolymph samples were also analyzed. A very high subunit diversity exists for Segonzacia
mesatlantica, with 16 subunits identified (Figure 5.9). This diversity is higher than previously described
(Chausson et al., 2004). Two subunits were detected in dodecamer samples but never in hexamer
samples and are thus dodecamer-specific (75 749 Da and 75 870 Da, Figure 5.9). It was not determined
whether each detected subunit corresponds to a different polypeptide chain or if some subunits
are identical polypeptide chains with different post-translational modifications.
Relative abundances of the subunits were determined by measuring peak heights in the deconvoluted
spectra and by normalizing them with respect to the highest peak height. These values do not
reflect with certainty the abundances in solution since different subunits can be ionized with different
efficiencies in the ESI source. However, these values can be used for relative comparisons between
samples ; their use for statistical analysis is thus relevant. There was a very high inter-individual variability
in subunit abundances (Figure 5.10).
The 23 observations on whole hemolymph were used to test the effect of oxygenation and temperature
on subunit composition. The canonical analyses (RDA) were conducted as described above for
the effect of acclimation conditions on hemolymph composition. The 16 different subunits were used
for the analysis as response variables (Y). A forward selection was performed to determine which
explanatory variables among size, sex, site, and experimental groups were to be used as covariables.