Intracolonial patterns of reproduction in the queen-size dimorphic ant Leptothorax rugatulus

Animals that live in genetically heterogeneous groups are faced with a combination of cooperation and conflict. Reproductive skew theory aims to provide a unified theory of the partitioning of reproduction in animal societies by combining genetic, demographic, and environmental factors. Although theoretical elaborations abound, empirical data are rare. Specifically, explicit intraspecific tests are scarce and have provided conflicting results. We present data on reproductive partitioning among queens in the ant Leptothorax rugatulus with special emphasis on relatedness and body size. Relatedness was negatively correlated to skew in sexual offspring and uncorrelated to skew in total offspring. Body size was not correlated to a queen's reproductive share. Thus, we did not find any support for the classic optimal skew models that are based on concessions. In artificial colonies, composed of randomly selected, unrelated workers and queens, reproductive skew was higher than in natural colonies, which suggested that unequal reproduction among queens could arise without nepotism by workers. Again, a queen's body size was not a good indicator of her reproductive share, but egg laying rate was. In colonies that contained large and small queens, small queens produced proportionally more sexual offspring. Although this result is in accordance with the kin conflict over caste determination hypothesis, it is more plausibly explained by an adaptation of the caste ratios to alternative dispersal tactics.