polyandrous relationships benefit females "d. pseudoobscura". in males "d. pseudoobscura", the variation in number of sperms shows the difference in benefits between polyandrous and monandrous females. males "d. pseudoobscura" ejaculate more sperm than any other "drosophila" species, and it provides important nourishing factors to females and their offspring. the offspring viability benefits are increased by multiple and variable sperms through ejaculates. there are no additional costs to polyandrous females, because there are not big differences in life expectancy between monandrous female experiencing multiple copulations and polyandrous female experiencing multiple copulations.