Female Japanese quail visually differentiate testosterone-dependent male attractiveness for mating preferences

Biased mating due to female preferences towards certain traits in males is a major mechanism driving sexual selection, and may constitute an important evolutionary force in organisms with

sexual reproduction. In birds, although the role of male ornamentation, plumage coloration, genetic dissimilarity, and body size have on mate selection by females have been examined

extensively, few studies have clarified exactly how these characteristics affect female mate preferences. Here, we show that testosterone (T)-dependent male attractiveness enhances female

preference for males of a polygamous species, the Japanese quail. A significant positive correlation between female mating preference and circulating T in the male was observed. The cheek

feathers of attractive males contained higher levels of melanin and were more brightly colored. The ability of females to distinguish attractive males from other males was negated when the

light source was covered with a sharp cut filter (cutoff; 8 weeks of age) maintained under LD conditions (Fig. 2e, P = 4.9 × 10−2). Importantly, no significant difference was observed in the

melanin content of feathers from SD and LD birds immediately after sexual maturation (8 weeks, P = 0.88); however, an increase in melanin content was observed after 12 weeks (Fig. 2f, P = 

0.02). In addition, the recovery of attractiveness in castrated birds required 4 weeks of consecutive T injections (Supplementary Fig. S2c). These results indicate that full-term expression

of male attractiveness in feather color requires several weeks after sexual maturation for a sufficient amount of melanin to accumulate. Indeed, the finding that the melanin content of cheek

feathers was significantly correlated with both cloacal size (r = 0.62, P = 2.8 × 10−3) and female mate preference (r = 0.51, P = 0.03) corroborated this assumption (Supplementary Fig. S4).

We therefore consider that the T-dependent color changes in male cheek feathers are an important trait for attracting females, and males must maintain this higher level throughout the

breeding season by upregulating the tyrosinase expression and melanin deposition.

Attractive males possess more brightly colored cheek feathers. (a) Relationship between male cloacal size and colorimeter L* value (n = 32). (b) Relationship between male cloacal size and

colorimeter a* value (n = 32). (c) Relationship between male cloacal size and colorimeter b* value (n = 32). (d) Appearance of intact male (right) and castrated male (left) at 13 weeks old.

Asterisks indicate cheek area. (e) Tyrosinase gene expression in skin of males maintained for 4, 8 and 12 weeks under long-day (LD) and short-day (SD) conditions (mean ± SEM, n = 4, P = 0.79

at 4 W, P = 4.9 × 10−2 at 8 W and P = 3.4 × 10−2 at 12 W). (f) Melanin contents in the feathers of males maintained for 4, 8 and 12 weeks under long-day (LD) and short-day (SD) conditions

(mean ± SEM, n = 5, P = 0.88 at 4 W, P = 0.88 at 8 W and P = 1.8 × 10−2 at 12 W).

How do females distinguish between attractive and unattractive males? To address this question, we performed mating preference tests using a light source that was covered with a sharp cut

filter (SC64; cutoff