Reliability of yellow bodies as indexes of egg laying activity in the primitively eusocial wasp Polistes dominula


Understanding the evolution of asymmetric access to reproduction requires reliable tools to measure individual reproductive share. In social insects, reproductive skew is usually evaluated by measuring the degree of ovarian development. However, this approach has been recently shown to reliably estimate only the physiological investment in reproduction, while it is rather inconsistent regarding the individual egg laying rate. Here, I assess the reliability of other physiological traits, the presence and size of yellow bodies, i.e. the remains of nurse cells deposited at the base of the ovarioles whenever an egg is laid. Their usefulness in indicating previous egg laying activity has been recognized since decades, but a formal assessment of their reliability has never been performed. By combining behavioural observations and physiological measurements in the social wasp Polistes dominula I determined whether yellow bodies presence and size reliably track previous reproductive activity. Despite the presence of yellow bodies is associated with egg laying, the classification of individuals to egg layer/non egg layer categories is not completely reliable, inducing in a relevant rate of false positive and false negatives. Moreover, size of yellow bodies is poorly correlated with egg laying and does not allow to properly infer the relative reproductive activity. Overall, yellow bodies do not precisely track small differences in egg laying and their use is thus recommended only when moderate to big differences are expected. Prudence is especially suggested in primitively eusocial species, where the short reproductive period and the distributed totipotency may result in small differences in individual reproduction.


ovarian development; paper wasps; reproduction; reproductive skew; corpora lutea; fitness

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