Condition- and parasite- dependent expression of a male-like trait in a female bird Martínez Padilla, Jesús Vergara, Pablo Pérez-Rodríguez, Lorenzo Casas Arenas, Fabián Ludwig, Sonja Haines, Jessica Zeineddine, M. Redpath, Steve Female Comb size Trichostrongylus tenuis This study was funded by a Natural Environment Research Council grant (NE/D014352/1). In many species, females display brightly coloured and elaborate traits similar to those that males use in intra- and inter-sexual selection processes. These female characters are sometimes related to fitness, and might function as secondary sexual characteristics that have evolved through sexual selection. Here, we used descriptive data from 674 females in 10 populations and an experimental removal of Trichostrongylus tenuis parasites in four populations, to examine the effects of season, age, condition, and parasites on the size of supraorbital combs displayed by female red grouse Lagopus lagopus scoticus. We found that comb size (i) was greater during the breeding than the non-breeding season, (ii) was greater in adult than in young females, (iii) was positively correlated with body condition, and (iv) negatively correlated with parasite abundance. Experimentally, we showed that comb size increased proportionally to the number of worms removed after parasite dosing. Our findings provide a better understanding of proximate mechanisms behind the expression of a male-like trait in females, and we discuss its possible function as a female ornament. 2026-02-20T09:29:58Z 2026-02-20T09:29:58Z 2011-01-19 journal article Published version: Martinez-Padilla, J., Vergara, P., Pérez-Rodríguez, L. [et al]. (2011). Condition- and parasite- dependent expression of a male-like trait in a female bird. Biology Letters, vol. 7 (3): pp. 364–367. http://doi.org/10.1098/rsbl.2010.0991 1744-957X https://hdl.handle.net/10481/111296 10.1098/rsbl.2010.0991 eng http://creativecommons.org/licenses/by-nc-nd/4.0/ open access Attribution-NonCommercial-NoDerivatives 4.0 Internacional Royal Society