Plumage colour in nestling blue tits: sexual dichromatism
, condition dependence and genetic effects.
In labroids, Robertson & Hoffman (1977) suggested that epigamic selection plays a much more important role than intra-sexual selection in the development of sexual dichromatism (though not for species possessing strictly haremic mating systems), and reasoned that despite being more costly to maintain than permanent dichromatism, natural selection would favor the development of ephemeral dichromatism in environments where continuous display of conspicuous signals would increase the risk of predation.
Thresher (1984), in his review of the occurrence of sexual dichromatism in coral reef fishes, noted that although conspicuous permanent sexual dichromatism most often coincides with polygamous species, temporary dichromatism is not clearly related to a particular mating system but rather is an intraspecific communication channel to express readiness to mate.
A few cases of putative permanent sexual dichromatism have been reported but consisting in rather minor variations in color or pattern.
Temporary sexual dichromatism seems not to be common either.
Color patterns and associated behaviors of temperate serranines are poorly understood, although brief descriptions of sexual dichromatism have been reported in the genus Paralabrax.
Adult Paralabrax clathratus exhibited a pattern of seasonal sexual dichromatism, where most males collected and observed from May to early October had a conspicuous orange color on the snout region of their heads (Figure 2a, OS phase).
Adult Paralabrax clathratus exhibited seasonal sexual dichromatism during the spawning season.
Analyses of plumage mono- or dichromatism of known-sex individuals are limited to a handful of studies in this and the other two congeneric species (e.
We used molecular sexing to identify males and females, and employed reflectance spectrometry to characterize the color properties and degree of sexual dichromatism in the rusty head plumage (Fig.
Because of the fine filamentous structure of the rusty feathers, the measurement with the highest brightness score was taken for each head feather for the analyses of sexual dichromatism.
Given the evident seasonality of the gray pelage, it seems to us that the gray color phase of the spotted ground squirrel often referred to in the literature results from individual cases of seasonal dichromatism
, with some (but not all) cinnamon-colored animals molting into a gray winter pelage.
Variation in melanin-based dichromatism in birds is positively associated with extent of gender bias in passive brood defense (Owens and Hartley 1998).
Further studies analyzing preference of females for coloration of males, and the association between coloration of males and parental quality may help in understanding the function of sexual dichromatism in this group.
Twelve specimens--5 males and 7 females--exhibited similar plumage, with no sexual dichromatism