Fig. 1

Illustration of the experimental design. Ninety-four male and 470 female house flies (Musca domestica) were joined in 94 mating jars (1:5 mating ratio). After 30 h, the female flies were isolated in oviposition vials. Eggs were collected every 12 h. Either zero, 20, 40 or 60 eggs were collected from a female depending on the size of her first egg clutch. Only eggs from the first oviposition event were used in the experiment. Two hundred and fifty-six females oviposited enough eggs for either one, two or three groups of full-siblings. Offspring were reared together in vials with maximum 20 offspring (density was dependent on mortality in the vials). One vial of full-siblings was reared until day seven, where larval traits were recorded. Another vial was reared until adult flies eclosed from the pupae and adult traits were recorded. The final vial with full-siblings was not included in the results of this study. Phenotypes were collected from 200 full-sib families. The illustration was created with BioRender.com