Sperm viability varies with buffer and genotype in .

Sperm quality, an important male fitness trait, is commonly compared between studies. However, few studies consider how genetic and environmental variation affect sperm quality, even in the genetic model . Here we show that sperm viability, the proportion of live sperm, differed across the genotypes Oregon-R, Dahomey, and Canton-S by more than 15%, and across buffers (phosphate-buffered saline (PBS), Grace's Medium and Ringer solution) by more than 20%. In terms of genotype-buffer pair comparisons, nearly half of the comparisons would produce significant differences in sperm viability (15 in 36), or its temporal decrease in a stress medium (19 in 36). Grace's medium produced the longest-lived sperm and the smallest differences between genotypes, Ringer Solution produced the shortest lifespan and the largest differences. Our results suggest that fly and other sperm researchers would benefit from a standardized protocol of measuring sperm viability.