4.4| Distinct response of C. dehaani to ambient
minor cations
The response of C. dehaani to ambient minor cations is different
from that of H. tridens and M. japonicus. First, under
isosmotic conditions, the decrease of survival rate of C. dehaaniin 513.3 mmol/L NaCl was less drastic (Fig. 1). Consistent with
this result, there was no significant difference in hemolymph
Na+ and K+ concentrations between
crabs bathed in 513.3 mmol/L NaCl and 513.3 mmol/L NaCl+MCK solutions
(Fig. 3C, F). In addition, NKA expression was enhanced but less drastic
compared to H. tridens and M. japonicus , and CAc
expression was not activated in 513.3 mmol/L NaCl solution (Fig. 5).
Furthermore, ambient minor cations did not affect the survival rate
(Fig. 7C) and hemolymph Na+ and K+concentrations under hypo-osmotic conditions (Fig. 8C, G). These results
strongly indicate that C. dehaani is less susceptive to ambient
minor cations compared to H. tridens and M. japonicus.Compared to H. tridens and M. japonicus , C. dehaaniis adaptive to fresh water and habitats of this species is not
restricted within estuaries but extends more upstream regions (Irawan
and Kijima, 1993; Kobayashi, 2000). Susceptibility to ambient minor
cations would be less adaptive for such species and lost in C.
dehaani. Alternatively, the difference of sensitivity to ambient minor
cations is due to phylogenetic difference of these species. Comparative
studies using other fresh water–adaptive crabs, such as Eriocheir
japonica and E. sinensis (Varunidae), will elucidate the
relationship between sensitivity to ambient minor cations and adaptation
to fresh water.