Commentary on Kehl et al. “Young male mating success is associated with sperm number but not with male sex pheromone titres”

Caroline Marie Nieberding, Marie-Jeanne Holveck

Over the last years, several studies suggested that male courtship activity is more important than female preference for male secondary sexual traits in determining male mating success in the butterfly Bicyclus anynana. We use Kehl et al. (Front Zool 12, 2015)'s study and related publications, to highlight three methodological and conceptual aspects of laboratory experiments that distort the social environment compared to natural conditions. We argue that such experimental biases prevent the expression of female mate choice and artificially inflate the role of male activity in determining mating success. We really want to stress that any work performed in laboratory conditions using extreme cage densities or sizes impedes female mate choice and promotes male-male competition when sexual conflict occurs about mating decisions. Hence, such studies, and the derived conclusions, are only applicable to ecologically-irrelevant conditions and cannot be extrapolated to more natural laboratory or field conditions. Our concerns may be relevant to many behavioural studies quantifying sexual selection across taxa. This commentary adds to the increasing scientific awareness that: i) mating outcome is, across taxa, the result of a sexual conflict whose outcome is under female, and not male, control; ii) the social environment used to quantify mating success is of utmost importance to produce reliable estimates of the strength and the direction of sexual selection on sexually-selected traits, as they evolve in nature.