The repeatable opportunity for selection differs between pre‐ and postcopulatory fitness components

Abstract In species with multiple mating, intense sexual selection may occur both before and after copulation. However, comparing the strength of pre- postcopulatory is challenging, because (i) processes are generally difficult to observe (ii) often-used opportunity for (I) metric contains deterministic stochastic components. Here, we quantified male fitness components simultaneously hermaphroditic flatworm, Macrostomum lignano. We did this by tracking fluorescent sperm—using transgenics—through transparent body sperm recipients, enabling in vivo. Moreover, sequentially exposed focal worms three independent mating groups, each assessed their success, sperm-transfer efficiency, fertilizing partner fecundity. Based on these measures, could, component, combine variance repeatability (R) individual success assess amount repeatable success—a measure call (IR). found higher efficiency compared which clearly suggests that stronger than precopulatory selection. Our study demonstrates a can be disentangled from often large provide better estimate