Sex Differences in Steroid Hormones and Parental Effort across the Breeding Cycle in Amphiprion ocellaris
While it has traditionally been viewed that high androgens are a hindrance to male parental care, recent studies in several vertebrate taxa have shown the opposite pattern, where high androgens either co-occur with, or are necessary for high parental investment. These inconsistencies suggest that in order to develop a complete understanding of the role sex steroids play in parental care, it is important to study multiple species with varying life-history characteristics. Anemonefishes of the genus Amphiprion provide a useful complement to more classically studied systems within vertebrate, and more specifically teleost models of parental care. Therefore, parental behaviors and blood plasma levels of 11-ketotestosterone (11-KT), estradiol (E2), and cortisol were measured in five breeding pairs at three points in the spawning cycle. Males displayed 5.6-fold more parental behaviors and spent 67% of their time in the nest as compared to 12% in females, along with significantly higher levels of 11-KT (males = 0.75±0.076; females = 0.02±0.005 ng/ml). Alternatively, females displayed higher levels of E2 (males = 0.09±0.009; females = 3.65±0.655 ng/ml), and E2 fluctuated across the breeding cycle with low levels on the day eggs were laid and higher levels as eggs developed. Cortisol tended to be higher in males, and higher in breeders than non-breeders, though these differences were not significant (males = 35.8±11.01; females = 16.9±3.58 ng/ml). Results suggest A. ocellaris may be a useful model for studying paternal behavior in the presence of high androgens.
Males display greater parental effort than females. (A) Average total number of combined nips and fans displayed by females (black bars) and males (white bars). (B) Average duration spent in the nest expressed as a percentage of total sample time. Standard error bars shown. Letters ‘a' and ‘b' denote significant differences.
Validation of EIA kits. Percent bound as measured by the kits is plotted against the natural logarithm of the dilution ratio (expressed as a percentage, i.e., 1:4 = 0.25). The standard dilutions are shown as open circles, whereas the pooled sample dilutions are shown as filled circles. Simple linear regression lines are shown. (A) 11-KT kit. (B) E2 kit. (C) Cortisol kit.
Sex differences in circulating steroid hormone levels. (A) Average concentration of cortisol in the plasma of females (n = 5; black bars) and males (n = 5; white bars). (B) Same as A for E2. (C) Same as A for 11-KT. Standard error bars for males and females reflect individual variation. Standard error bars for the pooled sample reflect technical replication. Letters ‘a' and ‘b' denote significant differences.
Rising and falling E2 levels across the breeding cycle. Concentration of E2 plotted against days after spawning for each of five separate females. Each female is represented by a different symbol. A loess smoothing function was applied to connect the data points separately for each female to facilitate differentiating the individuals.
Contributor Notes
Associate Editor: K. Martin.