Polyandry increases offspring viability and mother productivity but does not decrease mother survival in Drosophila pseudoobscura.

Polyandrous mating is common, but the benefits for females of polyandry remain controversial. To test whether mating with multiple males affects female fitness, we compared lifetime components of fitness of three experimental sets of Drosophila pseudoobscura females: monogamous females allowed to copulate one time (MOC); monogamous females held with a male over her entire life and experiencing many copulations (MMC); and polyandrous females with a different male over each day of their lives and also experiencing many copulations (PMC). Consistent with previous studies in this species, females in treatments in which multiple copulations occurred, MMC and PMC, had offspring with significantly higher egg-to-adult survival (i.e., offspring viability) and higher numbers of adult offspring (i.e., productivity) than MOC females, showing that multiple inseminations enhance offspring and mother fitness. In addition, although MMC females laid significantly more eggs than polyandrous (PMC) females, percent egg-to-adult survival and number of adult offspring were higher for PMC than MMC females, showing that polyandrous mating enhances the fitness of females more than multiply mating with only one male. Inconsistent with the cost of reproduction, lifespan was not significantly longer for MOC females than for MMC or PMC females. To our knowledge, this is the first study to examine simultaneously in outbred WT Drosophila pseudoobscura the lifetime costs and benefits to females of polyandry, monogamy with a single copulation, and monogamy with repeat copulations.