Thermal shocks induce
changes in the nuclear phenotypes that correspond to survival (heterochromatin
decondensation, nuclear fusion) or death (apoptosis, necrosis) responses in the
Malpighian tubules of
Panstrongylus megistus
. Since thermal
tolerance increased survival and molting rate in this species following sequential
shocks, we investigated whether changes in nuclear phenotypes accompanied the
insect survival response to sequential thermal shocks. Fifth instar nymphs were
subjected to a single heat (35 or 40°C, 1 h) or cold (5 or 0°C, 1 h)
shock and then subjected to a second shock for 12 h at 40 or 0°C, respectively,
after 8, 18, 24 and 72 h at 28°C (control temperature). As with specimen
survival, sequential heat and cold shocks induced changes in frequency of the
mentioned nuclear phenotypes although their patterns differed. The heat shock
tolerance involved decrease in apoptosis simultaneous to increase in cell survival
responses. Sequential cold shocks did not involve cell/nuclear fusion and even
elicited increase in necrosis with advancing time after shocks. The temperatures
of 40 and 0°C were more effective than the temperatures of 35 and 5°C
in eliciting the heat and cold shock tolerances, respectively, as shown by cytological
analysis of the nuclear phenotypes. It is concluded that different sequential
thermal shocks can trigger different mechanisms of cellular protection against
stress in
P. megistus, favoring the insect to adapt to various ecotopes.
