Steroid Transfer Among Cohabitating Female Big Brown Bats

Abstract

In addition to their conventional role as hormones, studies have shown that steroids can act as pheromones in mammals. Emphasis has been placed on evaluating the physiological and behavioural effects of male, urinary 17β- estradiol (E2) exposure in pheromone phenomena including the prevention of embryo implantation and induced precocious puberty in females. Steroids have also been observed to transfer between female mice, leading to changes in the duration of their estrous cycle. Progesterone (P4), a crucial female sex steroid, promotes pro-social sexual reproductive behaviour and the growth of the endometrium in preparation for ovum implantation. Few studies have investigated the effects of P4 in a pheromonal context. Big brown bats (Eptesicus fuscus) are ideal models for pheromone research because they are evolutionarily distinct from rodents, live in highly social and sexually-competitive harems, and are regularly exposed to conspecific secretions in the close confines of their roost. Experimental analysis revealed absorption of tritium-labeled progesterone (3H-P4) (10 μCi) 1 h after cutaneous and intranasal application to adult females. Additionally, radioactivity was observed in mature female bats caged for 48 h with an adult female conspecific that had been intraperitoneally-injected with 3H- P4 (50 μCi). Using the same paradigm, 3H-E2 transfer was not observed between females. Enzyme-linked immunosorbent assays revealed measurable levels of unconjugated P4 and E2 present in the urine of female bats, suggesting urine as one likely vector for P4 transfer. Given corroborative findings in mice, progesterone transfer during cohabitation is likely a mammalian-wide phenomenon that could have evolved to prime conspecifics—and more specifically kin—for sexual reproduction.