Sex-specific growth and lifespan effects of germline removal in the dioecious nematode Caenorhabditis remanei

Abstract

Germline regulates the expression of life-history traits and mediates the trade-off between reproduction and somatic maintenance. However, germline maintenance in itself can be costly, and the costs can vary between the sexes depending on the number of gametes produced across the lifetime. We tested this directly by germline ablation using glp-1 RNA interference (RNAi) in a dioecious nematode Caenorhabditis remanei. Germline removal strongly increased heat-shock resistance in both sexes, thus confirming the role of the germline in regulating somatic maintenance. However, germline removal resulted in increased lifespan only in males. High costs of mating strongly reduced lifespan in both sexes and obliterated the survival benefit of germline-less males even though neither sex produced any offspring. Furthermore, germline removal reduced male growth before maturation but not in adulthood, while female growth rate was reduced both before and especially after maturation. Thus, germline removal improves male lifespan without major growth costs, while germline-less females grow slower and do not live longer than reproductively functional counterparts in the absence of environmental stress. Overall, these results suggest that germline maintenance is costlier for males than for females in C. remanei.

Keywords: germline; glp‐1; heat‐shock; lifespan; sex‐specific.

FIGURE 1

DAPI staining of female and male L4 offspring of mothers injected with either gfp (control treatment) or glp‐1. Germline is lost in offspring where mothers are injected with glp‐1.

FIGURE 2

Sex‐specific heat shock survival (proportion surviving) of control (purple) of germline‐less glp‐1 treated (orange) worms. Error bars represent mean ± SE. Females were exposed to 40°C for 90 min, while the more heat‐shock resistant males were exposed for 95 min, therefore the sexes should not be directly compared.

FIGURE 3

Lifespan for females and males, that were (a) virgin, (b) mated and treated with kanamycin (to combat infection), or (c) mated and not treated with kanamycin. Color represent control (purple) or germline‐less glp‐1 treated (orange) worms.

FIGURE 4

Development time (a), size at maturity (b), and adult size at day 4 of adulthood (c) for females and males. Color represent control (purple) or germline‐less glp‐1 treated (orange) worms. Error bars represent mean ± SE.