Ejaculate Tailoring and Sperm Storage in Drosophila Melanogaster

Abstract

In this thesis, I use transgenic fruit flies that have sperm labeled with Green Fluorescent Protein to investigate sperm competition and cryptic female choice in three populations of Drosophila melanogaster adapted to markedly different life cycles by long term laboratory evolution. To do this, I analyze male ejaculate tailoring and female sperm storage in relation to female and male quality, respectively. I discuss the life history strategies of three populations: a FAST stock selected for early reproductive maturity, an intermediate BASELINE stock and a SLOW stock selected for late-life reproductive fitness. Using a full-factorial experimental design, I show evidence for ejaculate tailoring and selective sperm storage over 30 d after mating. In all three stocks, males ejaculate significantly more sperm cells into the bigger SLOW females. However, SLOW females store more SLOW sperm than BASELINE or FAST sperm. Likewise, FAST females store a higher proportion of SLOW and BASELINE sperm than FAST male sperm. Overall, FAST sperm disappear from the female reproductive tract more rapidly than other male-sperm types over 30 d of storage. My results also suggest that the spermathecal organs are responsible for long-term sperm storage. It is evident that female type plays a strong role in determining how much sperm will be ejaculated and ultimately stored, but it also appears that males are self-referrent in allocating ejaculate; body size is likely to play a major role in this plasticity.