Meeting Abstract
Current research suggests that unconjugated steroids excreted in the urine of male mice alter the reproductive behaviour and physiology of female conspecifics. These observations support the notion that steroids can act as pheromones in mammals. Using tritium (3H)-labelled estradiol (E2) as a radioactive tracer, we have shown that female big brown bats (Eptesicus fuscus) readily absorb exogenous 3H-E2 applied via cutaneous and intranasal exposure, with radioactivity measured throughout neural, peripheral, and reproductive tissues 1 hour after exposure. Additional experiments with 3H-E2 have shown the reliable transfer of estradiol from male E. fuscus to cohabitating female conspecifics during the Autumn mating season. Here we explore seasonal variation in estradiol transfer between male and female E. fuscus at three relevant time points: Autumn (mating season), Spring (female ovulation, ovum fertilization, and implantation), and Summer (maternity colony formation, parturition, and maternal care). We found substantial seasonal variation in the amount of 3H-E2 transferred from males to a variety of female tissues, including the frontal cortex, heart, liver, uterus, and blood serum, with a number of other tissues approaching statistically significant differences among seasons. We present data demonstrating the presence of unconjugated and bioactive estradiol in male urine across the mating cycle, with the peak concentration occurring during reproductively relevant times. We concluded that estradiol is a likely vector for steroid transfer between individuals. Seasonal variation in estradiol transfer could influence sexual behaviour and reproductive physiology of female bats during critical reproductive periods, as transferred steroids were found in both neural and reproductive tissues.
