Male-derived copulatory plugs enhance implantation success in female Mus musculus

Abstract

Among a wide diversity of sexually reproducing species, male ejaculates coagulate to form what has been termed a copulatory plug. A number of functions have been attributed to copulatory plugs, including the inhibition of female remating and the promotion of ejaculate movement. Here we demonstrate that copulatory plugs also influence the likelihood of implantation, which occurs roughly 4 days after copulation in mice. Using a bead transfer method to control for differences in ejaculate retention and fertilization rates, we show that implantation rates significantly drop among females mated to genetically engineered males incapable of forming plugs (because they lack functional transglutaminase 4, the main enzyme responsible for its formation). Surprisingly, this result does not correlate with differences in circulating progesterone levels among females, an important hormone involved in implantation. We discuss three models that connect male-derived copulatory plugs to implantation success, including the hypothesis that plugs contribute to a threshold amount of stimulation required for females to become receptive to implantation.

Keywords: bead transfer method; copulatory plug; implantation; progesterone; pseudopregnancy.

Figure 1

Permutation based χ² test demonstrates that females receiving an ejaculate from TGM4−/− (KO) males are significantly less likely to implant than females mating to TGM4+/+ (WT) males.

Figure 2

Boxplot of progesterone levels estimated across 98 females from five different groups; Mated vs. Unmated indicates whether ejaculation was scored within 4 h of pairing. All male mates were vasectomized. WT = females paired with a TGM4+/+ male, KO = females paired with a TGM4−/− males. Control = females never paired with males. Numbers in parentheses indicate number of females per group. Gray hash marks indicate individual observations. Vertical line separates the two different groups (homogeneous within each group) identified with Tukey HSD tests.