Cold tolerance and cold shock response in wild type and TPI mutant fruit flies

The TPI sugarkill (SGK) mutation causes profound metabolic deficits in adult D. melanogaster that increase stress sensitivity and shorten lifespan; however, nothing is known about cold sensitivity in these mutants.  Acute low temperatures may cause insects to experience their incipient lethal temperature (ILT), but this effect is mitigated by recent prior exposure to moderate cold (i.e. cold shock).  We measured ILTs for three age groups (3, 10, and 25 days) of mutant and wild type (WT) flies, exposing them to -2.5, -5.0 and -7.5 C for 1 and 2 h.  Both genotypes had nearly equivalent levels of survival following the various treatments of 1 and 2 h at -2.5 C.  Both genotypes also survived similarly when exposed to -5.0 C for 1 or 2 h; however, mortality increased as the flies aged showing significance as survivorship decreased.  No flies survived exposure to -7.5 C.  Shock was induced by exposing flies to 1 h at -2.5 C and then allowing recovery for 1 h at 23 C.  Upon subsequent exposure to -5.0 C for 2 h,  WT (37%) and SGK (21%) had survival rates that greatly exceeded their baseline survival under this condition (near 0%).  Older flies of both genotypes showed almost complete intolerance of the shock treatment.  Therefore, D. melanogaster with TPI mutation are fully capable of dealing with cold stress comparably to WT flies, and they possess only a modest reduction in the ability to develop cold hardening responses versus the WT flies.