Kin‑Benefit Senescence: A Conserved Extracellular Signal That Links Older Individuals to Reproductive Suppression in Younger Conspecifics

Aging may persist not as a passive byproduct but as an actively maintained signal that benefits kin by tempering competition for resources. We hypothesize that older individuals release a specific class of extracellular vesicles enriched in miR‑34a and miR‑128 that transiently inhibit germline stem cell proliferation in younger conspecifics. This vesicular signal would be conserved across metazoans, detectable in serum or hemolymph, and its activity would scale with the proportion of post‑reproductive individuals in a population. If true, experimentally reducing vesicle uptake in young animals should lift the reproductive suppression without shortening their lifespan, whereas overexpressing the vesicles in young animals should mimic the reproductive decline seen in older cohorts. Such a mechanism would represent a form of group‑selected senescence that evades the classic cheater problem because the signal’s effect is conditional on the presence of older individuals, making non‑responding mutants vulnerable when older conspecifics are abundant.

To test this, we will use Drosophila melanogaster lines engineered to fluorescently label exosome‑like vesicles and to conditionally knock down the vesicle‑associated Rab‑GTPase Sec15 in the fat body of older flies. First, we will isolate hemolymph from young and old flies and quantify vesicle concentration and miRNA cargo via small‑RNA sequencing. We predict a significant increase in miR‑34a/miR‑128 load in vesicles from old flies compared with young flies (see [3] for baseline vesicle profiling methods). Second, we will generate young flies that express a dominant‑negative Rab‑GTPase specifically in their germline stem cells to block vesicle uptake. These flies should show elevated germline proliferation and increased early‑life fecundity relative to controls, without a detectable change in overall lifespan, indicating that the vesicular signal specifically modulates reproduction rather than somatic aging. Third, we will overexpress the vesicle‑loading enzyme nSMase2 in the fat body of young flies to raise circulating vesicle levels; we expect these young flies to display reduced germline stem cell activity and lower fecundity, phenocopying the reproductive suppression normally associated with age.

Parallel experiments in Caenorhabditis elegans will use transgenic reporters for exosome release (RAB‑11::GFP) and miRNA sensors for miR‑34a and miR‑128 in the distal tip cartilage. Manipulating exosome release from the intestine of old worms should alter germline mitotic index in young worms in a dose‑dependent fashion. If the vesicular signal is conserved, similar manipulations in vertebrate models (e.g., zebrafish serum transfer assays) should reproduce the effect.

A falsifiable outcome would be that altering vesicle levels fails to change germline stem cell activity or early fecundity in young individuals, or that lifespan extensions accompany the fecundity changes, suggesting the vesicles affect somatic aging rather than a dedicated reproductive checkpoint. Positive results would support the idea that evolution has preserved a molecular mechanism that actively shapes age‑dependent reproductive output to benefit kin, reframing aging as a regulated, selectable trait rather than solely a constraint-driven deterioration.