A replaceable soma enables negative senescence in harvester ants.

In the western harvester ant Pogonomyrmex occidentalis, a 34-year dataset of 3,285 age-known colonies shows negative senescence: mortality decreases and reproduction increases with age.

• Why it matters: Senescence typically links aging to rising mortality and falling reproduction, but theory predicts negative senescence can evolve when growth is indeterminate and reproduction has little cost.
• What they did: The authors analyzed colony growth and reproduction across lifetime, testing for tradeoffs and correlations, and compared yearly reproduction with subsequent colony recruitment under temporally variable conditions.
• The result: They found no growth–reproduction tradeoff, with growth and reproduction positively correlated, and showed that higher reproduction in 1 year did not increase new colonies the next year, implying environmental unpredictability decouples reproduction from recruitment.

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