Figure 2. pH measurements obtained from fluids collected from the female reproductive tracts of Peromyscus mice species with naturally varying mating systems. In both the uterus and the oviduct, reproductive fluids have a significantly greater pH in the polyandrousP. maniculatus (red dots) than its monogamous sister species,P. polionotus (blue dots). Small dots denote values measured for individual females; large dots represent the mean values for each species.