Abstract
Daphnia magna is a keystone species of freshwater ecosystems, and its life-history traits have long been studied from an environmental perspective; however, the genetic determinants of these traits remain poorly defined. We asked whether genome maintenance pathways shape life-history traits such as growth, fecundity, and lifespan. Using CRISPR–Cas9, we generated loss-of-function mutants of ku70 and lig4 , two core components of non-homologous end-joining (NHEJ), a major DNA double-strand break repair pathway, as well as a ku70:lig4 double mutant. The ku70 mutants showed reduced somatic growth and shortened lifespan relative to the parental line, while fecundity was unchanged. The lig4 mutants showed a similar reduction in growth and, in addition, showed reduced fecundity; lifespan was comparable to that of ku70 and shorter than that of the parental line. The ku70:lig4 double mutant revealed a trait-specific genetic interaction: growth was more severely impaired than in either single mutant, whereas its fecundity and lifespan did not decline further from single-mutant levels (fecundity comparable to lig4−/− ; lifespan comparable to both ku70−/− and lig4−/− ). These findings suggest NHEJ contributes to life-history variation in D. magna and support incorporating DNA repair pathways when dissecting the genetic basis of life-history strategies.