Androgens and masculinization of genitalia in the spotted hyaena (Crocuta crocuta). 1. Urogenital morphology and placental androgen production during fetal life

Abstract

According to common understanding of sexual differentiation, the formation and development of a penile clitoris in female spotted hyaenas requires the presence of naturally circulating androgens during fetal life. The purpose of the present study was to determine potential source(s) of such fetal androgens by investigating the timing of urogenital development and placental production of androgen during early and mid-gestation. Fetuses determined to be female by molecular techniques (lack of SRY gene) at days 33 and 48 of gestation had undifferentiated gonads, but the clitoris was already 'masculinized' and was generally similar to the phallus of a 50-day-old male fetus. Wolffian and Müllerian ducts terminated at the urogenital sinus in both sexes and a urethra was present along the entire length of the clitoris and penis. The adrenal gland was large and histologically differentiated at 33 days. Steroid gradients across the uterus (a drop in delta 4-androstenedione, with increases in oestrogen and androgen), and high androstenedione in ovarian veins indicated that ovarian androstenedione was metabolized and secreted as testosterone by the placenta throughout gestation. In vitro, whole or homogenized placentae at days 48 and 58 of gestation (110 days total) metabolized radiolabelled androstenedione into testosterone and oestradiol; the specific enzymatic activity of early placental tissues was higher than at later stages. A human placental homogenate had higher aromatase activity but did not produce testosterone unless aromatase was inhibited. Infusion of labelled androstenedione into the uterine arteries of hyaenas demonstrated the conversion of this substrate into testosterone and oestradiol and their secretion into the fetal circulation. Evidently, androgen is produced by the placenta and secreted into the fetal circulation from early in pregnancy when masculinization is first evident, before differentiation of the fetal ovary.

Structure of the Midterm Placenta of the Spotted Hyena, <i>Crocuta crocuta, </i>with Emphasis on the Diverse Hemophagous Regions

“…Pregnant female hyenas were immobilized with an intramuscular injection of ketamine (4-6 mg/kg) and xylozine (1 mg/kg) administered by blow darts. Sterile surgical hysterotomy for removal of the fetus and placenta was performed after pregnant hyenas had been anesthetized with isoflurane as previously described [Licht et al, 1998;Cunha et al, 2005]. Procedures were approved by the Animal Care and Use Committee of the University of California at Berkeley.…”

Adaptation, Exaptation, and Constraint: A Hormonal Perspective

“…For example, chemical treatment of pregnant spotted hyenas with antiandrogens produces a shorter, thicker clitoris in their offspring, but the modified structure is nevertheless large and erectile and quite unlike the clitoris of a typical mammal ). This finding implies that full development of the peniform clitoris involves not simply early androgen exposure but also the action of steroid-independent mechanisms in the target tissue (Foster et al 1996;Drea et al 1998;Glickman et al 1998;Licht et al 1998). If so, and if the genes responsible for elaboration of the clitoris came to be favored after the penile form originated, then Gould and Vrba's (1982) conclusion that the penile clitoris of the female spotted hyena is simply an unselected indirect effect of selection for other masculine traits might require reexamination (West-Eberhard 1992a).…”

Non-invasive measurement of fecal estrogens in the spotted hyena (Crocuta crocuta)

“…Studies of the endocrinology of spotted hyenas to date have focused on androgenic hormones, so a great deal is known about circulating and excreted androgens in Crocuta (Dloniak et al, 2006;Dloniak et al, 2003;Glickman et al, 1998;Glickman et al, 1992;Goymann et al, 2001;Licht et al, 1992;Licht et al, 1998;Van Jaarsveld and Skinner, 1991). By contrast, little is known about estrogenic hormones in this species.…”