Table 223

Extrinsic factors that affect lifespan in Drosophi/a

Factors

Condition

Effects

Pre-adult development

Parental age Fecundity

Ambient temperature

Mild stress

Diet

Physical activity

Higher larval density

Lower ambient temperature

Older parents

Higher reproductive activity

Lower ambient temperature

Heat shock, cold stress, hypergravity, low levels of radiation

Dietary restriction

Reduced flight activity

Prolongs the duration of development time and extends adult lifespan; results in smaller adult size Prolongs the duration of development time and extends adult lifespan; results in larger adult size Fewer viable eggs and offspring have shorter lifespan Shortens lifespan; Virgins live longer than mated flies in both sexes, but the magnitude of increase in lifespan is greater in females

Extends lifespan; Flies cultured at 18°C live more than twice as long as those at 25°C Extends lifespan

Extends lifespan Extends lifespan been used as experimental manipulations to extend lifespan in order to elucidate factors that affect longevity. However, a mechanistic explanation of these factors is still unclear (see below).

Probably the strongest environmental stimulus that affects lifespan is environmental temperature. Adult flies cultured at 18°C live more than twice as long as those cultured at 25°C. Various mild stressors, including heat shock (37°C for less than 1 hour), cold stress, hyper-gravity, and low levels of irradiation, have been shown to extend lifespan. It has been proposed that mild stressors may induce protective systems that will be beneficial for forthcoming events. However, the effects could be secondary in some cases, as some stressors such as irradiation have negative effects on reproduction, which alone can extend lifespan.

Dietary yeast is important in survival and reproduction in adult Drosophila. In the absence of yeast, Drosophila arrest reproduction and increase mortality in both males and females (Good and Tatar, 2001). Dietary restriction extends lifespan in a variety of organisms including Drosophila. The females have greater responses to dietary restriction, even in sterile or ovaryless females (Mair et al., 2004). The maximum extension of lifespan in females is achieved at a less severe level of dietary restriction than in males (Magwere et al., 2004).

Prevention of flight activity has been shown to extend lifespan in blowflies (Yan and Sohal, 2000) as well as in Drosophila (Tapi Magwere, personal communications). In accord with this, mutant flies that move more than normal (shaker mutants) have shorter lifespan (Trout and Kaplan, 1970). Thus levels of physical activity in flies appear to negatively correlate with lifespan

(see the ''Drosophila in Aging Studies'' section for further discussion).

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