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

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Abstract
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 (ch1/ch1) and normal‐sized heterozygotes (ch1/+) 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 ch1/ch1 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 ch1/ch1 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 ch1/ch1 and of male ch1/+ mortality deceleration is absent. Mortality deceleration is a phenotype of chico.