Sperm investment in male meadow vole is affected by presence of other male meadow vole.
The male meadow voles inseminate females with more sperm when they smell another male competitor nearby. Sperm competition occurs when 2 or more males copulate with a particular female during the same reproductive cycle, and their sperm compete to fertilize the female’s available eggs. One strategy that male voles use to assess the risk and intensity of sperm competition involves responding to the presence of scent marks of conspecific males found near a sexually receptive female.
They do not increase the frequency of their ejaculate, but actually produce more sperm within each ejaculate, as a way to increase the chances that their sperm, rather than a rival’s will impregnate the female.