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

200 CHAPITRE 5. ADAPTATIONS RESPIRATOIRES DE S. MESATLANTICA
FIG. 5.12 – Biplot graph of the canonical redundancy analysis (RDA) of the hemolymph composition
effect on complex proportions along the two first canonical axis. Dotted arrows, explanatory
variables ; full lines, response variables.
to L-lactate. Lactate curves were calculated with the assumption that lactate did not modify the Bohr
effect, even if lactate can alter the Bohr effect in some species. A second order polynomial was used
to fit P 50 values vs pH without lactate (log(P 50 ) = 0.9088pH 2 − 15.781pH + 67.625, r2=0.9847) and
the second and first order coefficients were kept for fitting with the data points with lactate, resulting
in a change in the third constant only. From these curves a L-lactate effect was calculated ( ∆log(P 50)
∆log[lactate] )
and had a value of -0.276 and -0.174 in another experiment (average = 0.225), compared to -0.095
for C. maenas (Figure 5.13). The cooperativity of S. mesatlantica Hc is quite low (1.28-2.58), which
could be due to the freezing and storage at -80°C (Morris, 1988).
When the urate effect was studied, no effect could be observed up to 333 µM urate (Figure 5.14).
The Bohr effect was not affected either. This is in contrast with the data for C. maenas ( ∆log(P 50)
∆log[urate] =-
0.22, (Lallier et Truchot, 1989)).
The magnesium effect was tested simultaneously on S. mesatlantica and C. maenas Hc. For both
species, affinity increased with increasing concentrations of Mg 2+ ; however the magnesium effect
was more pronounced for S. mesatlantica than for C. maenas ( ∆log(P 50)
=-0.24 vs -0.14, respectively)
(Figure 5.15). It was also clear during these experiments that C. maenas Hc had a much
∆log[Mg 2+ ]
higher
cooperativity than S. mesatlantica Hc (4.74-5.54 vs 1.83-2.06, respectively).