The demography of slow aging in male and female Drosophila mutant for the insulin-receptor substrate homologue chico

Hypomorphic mutants affecting the Drosophila insulin/IGF signal pathway are reported to increase longevity in females but not in males. To understand this sex-difference, we conducted a large-scale demographic study with three new isogenic strains of alleles at chico, the insulin-receptor substrate homologue. We verify that female dwarf homozygotes (ch(1)/ch(1)) and normal-sized heterozygotes (ch(1)/+) are long-lived, as originally reported. We find for the first time that male heterozygotes are long-lived relative to wildtype, by about 50%. The life span of male ch(1)/ch(1) is similar to that of wildtype but these dwarf males age at a slow demographic rate. The levels of demographic frailty and of age-independent mortality are elevated in ch(1)/ch(1) males, counteracting the effect of slow aging upon life expectancy. Mortality deceleration occurs amongst the oldest-old wildtype adults, as seen in many organisms. Remarkably, in similarly sized cohorts of male and female ch(1)/ch(1) and of male ch(1)/+ mortality deceleration is absent. Mortality deceleration is a phenotype of chico.