Sperm metabolism is altered during storage by female insects: Evidence from two-photon auto-fluorescence lifetime measurements in bedbugs

Abstract

We explore the possibility of characterizing sperm cells without the need to stain them using spectral and fluorescence lifetime analyses after multiphoton excitation in an insect model. The autofluorescence emission spectrum of spermof the common bedbug, Cimex lectularius,was consistent with the presence of flavins andNAD(P)H. The mean fluorescence lifetimes showed smaller variation in sperm extracted from the male (tau m, τm = 1.54-1.84 ns) than in that extracted from the female sperm storage organ (tau m, τm = 1.26-2.00 ns). The fluorescence lifetime histograms revealed four peaks. These peaks (0.18, 0.92, 2.50 and 3.80 ns) suggest the presence ofNAD(P)Hand flavins and show that sperm metabolism can be characterized using fluorescence lifetime imaging. The difference in fluorescence lifetime variation between the sexes is consistent with the notion that female animals alter the metabolism of sperm cells during storage. It is not consistent, however, with the idea that sperm metabolism represents a sexually selected character that provides females with information about the male genotype.