Sexual traits

Bertrand, S., Faivre, B., and Sorci, G. 2006. Do carotenoid-based sexual traits signal the availability of non-pigmentary antioxidants /. Exp. Biol. 209 4414—4419. 

Birkhead, T. R., Fletcher, F., and Pellatt, E. J. 1999. Nestling diet, secondary sexual traits and fitness in the zebra finch. Proc. R. Soc. Lond. B 266 385-390. 

Eraud, C., Devevey, G., Gaillard, M., Prost, J., Sorci, G., and Faivre, B. 2007. Environmental stress affects the expression of a carotenoid-based sexual trait in male zebra finches. J. Exp. Biol. 210 3571-3578. 

The aim of this chapter is to review genetic variation underlying exaggerated sexual traits. At first sight this has nothing to do with the nature of intelligence. However, there is one question in intelligence research that data and theory on... 

Before addressing these arguments about how selection alters the level of additive genetic variation, it is instructive to examine the data. A recent literature search was carried out of studies that measured the heritability of sexual traits (Pomiankowski Moller 1995). A comparison was made of the additive genetic variation in sexual and similar non-sexual traits from the same species. Ideally the same trait from the female (or the non-sexually selected sex) was used for comparison. When this was not available, another non-sexually dimorphic trait was used. 

A similar logic can be applied to sexual traits. Pomiankowski Moller (1995) suggested that persistent directional selection caused by female mate preferences disproportionately favours individuals with higher trait values. Such selection favours increased phenotypic variance and so selects for an increase in the... 

W e can follow the logic of this argument with a quantitative genetic model of the size of a sexual trait (Iwasa Pomiankowski 1994),... 

The genetic contribution to size of the sexual trait (/) has two parts, one that is condition independent f) and the other that is condition dependent [f v), where condition is denoted by v. The genetic variance of s can be estimated as (Rowe Houle 1996),... 

Given that Gt<, the genetic variation in the rule for converting condition into sexual trait size, is likely to be small,... 

So if condition-dependence is strong (i.e., / >0), genetic variation in the sexual trait will largely depend on genetic variation in condition, as for most traits... 

To some extent all traits show condition-dependent expression. For example, most traits scale with body size. The important question is whether we expect condition-dependence to be greater in sexual traits We can study this by... 

Where costs of sexual trait exaggeration strongly depend on condition (large k), we expect condition-dependence (f) to be large as well. 

In the first experiment (David et al 1998), condition was experimentally manipulated by allowing larvae to develop at different food densities (a 20-fold spread, from low density to very high density). As predicted, male eyespan showed a marked decrease in size as larval density increased (Fig. 2). But so did the non-sexual traits (Fig. 2). This revealed that condition-dependence was a general feature of sexual and non-sexual traits in insects. 

These experiments show that the sexual trait (male eyespan) in stalk-eyed flies is a unique character. Both sexual and non-sexual traits decreased in size under... 

FIG. 2 Decreases in male and female eyespan in stalk-eyed flies subject to increasing larval density (David et al 1998). Male eyespan (sexual trait) is more sensitive to larval density than female eyespan (non-sexual trait). 

Pomiankowski I think it was naive to believe the lek paradox as formulated— that there will be no genetic variance. This has been shown to be wrong. What explains the existence of variance and if it happens to be higher in sexual traits is a matter for experimental investigation. The fact that both sexual traits and g may share high additive variance may have no significance, since these may have completely different explanations. 

Secondary sexual traits Estrogens (estradiol, zearalenone)... 

---