Sexual dimorphism in life history traits and their trade-offs is widespread among sexually reproducing animals, and is strongly influenced by the differences in reproductive strategies between the sexes. We investigated how intrasexual competition (pre- and postcopulatory) acted on specific life history traits, important to fitness, and their trade-offs in the outcrossing nematode Caenorhabditis remanei. Here, we imposed strong sex-specific selection through experimental evolution with increased potential for intrasexual competition by skewing the adult sex ratio towards either males or females (1:10 or 10:1) over 30 generations, and subsequently measured the phenotypic response to selection in three traits related to fitness; body size, fecundity and tolerance to heat stress. We observed a stronger response to selection in females for body size and peak fitness, suggesting that females may experience stronger net selection and potentially harbour higher amounts of standing genetic variance compared to males. Our study highlights the importance of investigating direct and indirect effects of intrasexual competition in both sexes in order to capture sex-specific responses and understand the evolution of sexual dimorphism in traits expressed by both sexes.