No evidence for adaptive suppression of joint laying by dominant female Seychelles warblers:an experimental study

Several theoretical frameworks exist for explaining variation in reproductive allocation between same-sex individuals living within social groups. To determine this adequately, we need to know which party is more able to manipulate reproduction of the other. Theoretical models often sidestep this problem by making the assumption that dominants either have complete or partial control of reproduction by subordinates. This Study clearly indicates that in the cooperatively breeding Seychelles warbler (Acrocephalus sechellensis) this assumption is not met. Seychelles warblers occupy year-round territories of different quality (measured as amount of insect food available). Joint laying, in which the dominant and subordinate females lay eggs in the same nest, decreases the fitness of primary females on low-quality territories, but not oil high-quality territories. This study found good experimental evidence that dominant females on low-quality territories have no modes to Suppress or prevent subordinate females from joint laying: (i) The frequency of joint laying in multi-female groups is independent of territory quality; (ii) There is no aggression among females at the nest around the time of egg laying at either low- or high-quality territories; (iii) Dominant females do not remove the other female's egg or experimentally introduced eggs, before or after laying their own. (iv) Dominant females do not reject an experimentally introduced egg through nest desertion. Given the absence of reproductive control, increased attention to alternative models of reproductive partitioning in vertebrate societies is needed and a realistic model has to take into account interactions within the sexes.