Serum immunoglobulin G concentration in Southern elephant seal, Mirounga leonina (Linnaeus, 1758), from Elephant island (Antarctica): sexual and adrenal steroid hormones effects

Abstract

Serum immunoglobulin G (IgG; indirect enzyme-linked immunosorbent assay), as well as sexual and adrenal steroid hormones’ concentrations (radioimmunoassay) were determined in 63 (male and female) Southern elephant seals (Mirounga leonine) at different developmental stages (weaned pups, juveniles and adults). In females, IgG values (mean _ S.D.) were higher (P < 0.05) in adults (15.9 _ 6.5 mg ml_1) than in juveniles (7.9 _ 4.0 mg ml_1), but similar to weaned pups (12.0 _ 5.0 mg ml_1). Estrogen concentration was higher (P < 0.05) in adults than in the weaned pups. In females, a significant (P < 0.05) correlation (R = 0.4) between serum IgG level and progesterone concentration was observed. In males, testosterone concentration was higher (P < 0.05) in adults than in the juveniles and weaned pups. Aldosterone and cortisol concentrations were higher (P < 0.05) in weaned pups (1056.0 _ 643.1 pmol l_1 and 272.7 _ 110.0 nmol l_1, respectively) than in the juveniles (638.6 _ 579.7 pmol l_1 and 152.9 _ 97.3 nmol l_1, respectively) and adults (386.5 _ 209.1 pmol l_1 and 145.7 _ 67.3 nmol l_1, respectively). These findings indicate that weaned pups are subjected to a higher natural stressful condition in the field. Despite this, humoral immunity, measured through IgG concentration, is not impaired in weaned pups.