Data from: No support for cryptic choice by ovarian fluid in an external fertilizer

Whether the ovarian fluid represents a selective environment influencing cryptic female choice was tested using an external fertilizer experiencing intense sperm competition and large effects of ovarian fluid on sperm swimming behaviour - the Arctic charr (Salvelinus alpinus). We physically separated the ovarian fluid from the eggs of reproductively active females and reintroduced either their own ovarian fluid or fluid from another female to the eggs. The eggs were then fertilized in vitro in a replicated split-brood design with sperm from two males under synchronized sperm competition trials, while also measuring sperm velocity of the individual males in the individual ovarian fluids. We found large effects of males, but no effect of females (i.e., eggs) on paternity, determined from microsatellites. More important, we found no effect of ovarian fluid treatments on the relative paternity of the two competing males in each pair. This experimental setup does not provide support for the hypothesis that ovarian fluid plays an important role as medium for cryptic female choice in charr. Power-analyses revealed that our sample size is large enough to detect medium sized changes in relative paternity (medium-sized effect-sizes), but not large enough to detect small changes in relative paternity. More studies are needed before a conclusion can be drawn about ovarian fluid’s potential influence on paternity under sperm competition - even in charr.