Positive effect of dietary lutein and cholesterol on the undirected song activity of an opportunistic breeder

Song is a sexually selected trait that is thought to be an honest signal of the health condition of an individual in many bird species. For species that breed opportunistically, the quantity of food may be a determinant of singing activity. However, it is not yet known whether the quality of food plays an important role in this respect. The aim of the present study was to experimentally investigate the role of two calorie-free nutrients (lutein and cholesterol) in determining the expression of a sexually selected behavior (song rate) and other behaviors (locomotor activity, self-maintenance activity, eating and resting) in male zebra finches (Taeniopygia guttata). We predicted that males supplemented with lutein and cholesterol would sing at higher rates than controls because both lutein and cholesterol have important health-related physiological functions in birds and birdsong mirrors individual condition. To control for testosterone secretion that may upregulate birdsong, birds were exposed to a decreasing photoperiod. Our results showed that control males down-regulated testosterone in response to a decreasing photoperiod, while birds treated with lutein or cholesterol maintained a constant singing activity. Both lutein-and cholesterol-supplemented groups sang more than control groups by the end of the experiment, indicating that the quality of food can affect undirected song irrespective of circulating testosterone concentrations. None of the other measured behaviors were affected by the treatment, suggesting that, when individuals have full availability of food, sexually selected song traits are more sensitive to the effect of food quality than other behavioral traits. Overall the results support our prediction that undirected song produced by male zebra finches signals access to high-quality food. Song is a sexually selected trait that is thought to be an honest signal of the health condition of 19 an individual in many bird species. For species that breed opportunistically, the quantity of food 20 may be a determinant of singing activity. However, it is not yet known whether the quality of 21 food plays an important role in this respect. The aim of the present study was to experimentally 22 investigate the role of two calorie-free nutrients (lutein and cholesterol) in determining the 23 duration of undirected song (type of song not directed toward a female) singing activity and 24 other behaviors (locomotor activity, self-maintenance activity, eating and resting) in male zebra 25 finches (Taeniopygia guttata). We predicted that males supplemented with lutein and cholesterol 26 would sing at higher rates than controls because both lutein and cholesterol have important 27 health-related physiological functions in birds and birdsong can mirror individual condition. To 28 control for testosterone (T) secretion that may upregulate birdsong, birds were exposed to a 29 decreasing photoperiod. Our results showed that control males down-regulated singing activity in 30 response to a decreasing photoperiod, while birds treated with lutein or cholesterol maintained a 31 constant singing activity. Both lutein-and cholesterol-supplemented groups sang more than 32 control groups by the end of the experiment, indicating that the quality of food can affect 33 undirected song irrespective of circulating T concentrations. None of the other measured 34 behaviors were affected by the treatment, suggesting that, when individuals have full availability 35 of food, sexually selected song traits are more sensitive to the effect of food quality than other 36 behavioral traits. Overall the results support our prediction that undirected song produced by 37 male zebra finches signals access to high-quality food. 40 Introduction 41 Individuals of different species have evolved a wide array of traits to signal their condition to 42 perspective potential mates or rivals 6