The annual cycle of the testis of the elephant seal (Mirounga leonina) at Macquarie Island

Testosterone levels in hair of free-ranging male northern fur seals (Callorhinus ursinus) in relation to sampling month, age class and spermatogenesis

Information about the reproductive status of free-ranging pinnipeds provides useful insight into their population dynamics, which is essential to their management and conservation. To determine the reproductive status of individual animals, blood sampling is often required despite being impractical to collect in open water. Hair as an endocrine marker has been used to less invasively assess the reproductive status of terrestrial animals. However, it is unknown whether pinniped reproductive status can be assessed from hair samples. Here, we examine testosterone levels in hair obtained from 57 male northern fur seals and used it to compare their age class and spermatogenesis during the non-breeding season off Hokkaido. We isolated testosterone from the samples using gas chromatography and measured testosterone levels using time-resolved fluoroimmunoassay. Testosterone levels in hair increased towards the breeding season. In May, testosterone levels were the highest in seals aged between 4 and 7 years, followed by those over the age of 8 years and under the age of 4 years. Spermatids, the final phase of spermatogenesis, were present in the seals sampled between April and June, even though testosterone levels were low in April. The seals with spermatids in May showed the highest testosterone levels. Our results demonstrate that seals with higher testosterone levels in May are likely to be mature males (≥4 years). Since hair can be collected using biopsy darts in the field, it will be possible to less invasively determine testosterone levels of male seals in the future.

Normal morphology and hormone receptor expression in the male California sea lion (Zalophus californianus) genital tract

Histomorphology and estrogen alpha (ER alpha), and progesterone receptor (PR) expression were evaluated in free-ranging stranded male California sea lions (Zalophus californianus). Hormone receptor expression was evaluated using an immunohistochemical technique with monoclonal antibodies. Estrogen and PRs were identified in the efferent ductules, prostate gland, corpus cavernosa, corpus spongiosium, penile urethra, and in the epithelium and stroma of both the penis and prepuce. In some tissues, ER alpha expression was more intense in the stroma, emphasizing the importance of the stroma in hormone-mediated growth and differentiation of reproductive organs. To our knowledge, this is the first study to localize ER alpha and PR to the epithelium of the glans penis. The results of this investigation add to the general knowledge of male California sea lion reproduction and suggest that estrogens could have a role in the function of the male reproductive tract.

Faecal testosterone concentrations and the acoustic behaviour of two captive male Australian fur seals

Seasonal changes in reproductive and acoustic behaviour are potentially affected by hormonal fluctuations; however, as it is difficult to routinely sample marine mammals, these associations are mostly inferred. Australian fur seals are vocal marine mammals that have a highly synchronous breeding season. The present study collected information on the testosterone concentration in faeces, vocalisations and behaviour of two captive male Australian fur seals to determine whether there are any associations between these variables. Positive associations were evident between the non-interactive agonistic behaviours (Head sway, Lay down and Head up) and an increase in calling rate of the bark calls in males. Barks were highest during August through to October, corresponding to the breeding period, while faecal testosterone levels peaked in September, coinciding with the high frequency in the calling rates of barks. Guttural threat calls were rarely heard throughout the year, but peaked in August. This call was not frequently heard but was associated with specific behaviours that were produced during more intense fighting interactions. This study presents preliminary information on the vocalisations, behaviour and hormone profiles for two captive Australian fur seals. Future studies with increased sample sizes from both wild and captive animals would clarify the intricate association between these factors.

Estradiol and Testosterone Concentrations Increase with Fasting in Weaned Pups of the Northern Elephant Seal (Mirounga angustirostris)

Although neonatal development is generally associated with increased levels of circulating testosterone (T) and estradiol (E2), food deprivation may inhibit steroidogenesis. Therefore, these potentially conflicting stimuli were examined in fasting weaned northern elephant seal (Mirounga angustirostris) pups by measuring serum concentrations of T, E2, progesterone (P4), and luteinizing hormone (LH) by either radioimmunoassay (P4, LH) or enzymeimmunoassay (T, E2). Blood samples were obtained from 20 male and 20 female pups at both early (<1 wk postweaning) and late (6-8 wk postweaning) periods during their natural postweaning fast. T in males (early: 2.9 +/- 0.4 ng/mL; late: 16 +/- 2 ng/mL; P < 0.0001) and E2 in females (early: 42 +/- 6 pg/mL; late: 67 +/- 5 pg/mL; P < 0.01) increased between the two measurement periods, while P4 (early: 2.5 +/- 0.3 ng/mL; late: 2.1 +/- 0.3 ng/mL; P > 0.05) did not. LH increased (early: 46 +/- 4 pg/mL; late: 65 +/- 6 pg/mL; P < 0.05) in males but not in females (early: 69 +/- 9 pg/mL; late: 65 +/- 6 pg/mL; P > 0.05). Increases in LH and T suggest that LH may stimulate T secretion. Alternatively, relatively low concentrations of LH in both males and females may reflect negative feedback inhibition imposed by elevated T and E2 concentrations. Despite the inherent postweaning fast, concentrations of T and E2 increased, suggesting that they may be critical for the continued development of pups. Therefore, compensatory mechanisms may exist that alleviate the fasting-induced inhibition of gonadal steroidogenesis during neonatal development in elephant seal pups.

Adenohypophysis of the elephant seal (Mirounga leonina): morphology and seasonal histological changes

Changes in adenohypophyseal cell populations over a 12-month period were studied in the seasonally breeding elephant seal (24 adult males, 3 adult females, and 5 neonates) at Macquarie Island. The glands were weighed and fixed in formol sublimate. Selected sections were stained with the oxidation-alcian blue-periodic acid Schiff-orange G technique. Gonadotropic, thyrotropic, lactotropic, and somatotropic cells were readily identifiable; whilst corticotropes, inactive secretory cells of all types, and stellate cells were not stained and were counted collectively as chromophobic cells. Hypophyseal weight was low throughout autumn and winter, but increased significantly during the spring breeding season and the summer. Thyrotropes were distributed evenly throughout the pars distalis, but the other secretory cells showed areas of concentration. Acidophils were common peripherally, particularly lactotropes, while gonadotropes were largely confined to the 'basophilic wedge,' a narrow, central superior zone. In males, lactotropic and gonadotropic cells showed significant seasonal changes in number. Gonadotropes were more common in sexually active males than sexually quiescent ones, while lactotrope numbers were much greater at midsummer than midwinter. This lactotrope cycle appeared to be related to photoperiod but unrelated to breeding.