Social evolution in ground and twig-nesting bees

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Altruism is behaviour in which an individual sacrifices its own reproduction in order to help other individuals reproduce. How do genes for altruism spread through populations when they are at a fitness disadvantage? The puzzle is often explained by kin selection: altruists do sacrifice personal reproduction, but more than make up for it by helping to raise close relatives which share their genes. Kin selection suggests that altruism can spread through populations when altruists target their cooperative behaviour towards raising relatives, which, like their own offspring, also carry the altruist's genes. Altruistic animals live in societies, and some of the best known are those of social insects, including many species of bees. In two bee groups, the sweat bees and carpenter bees, behaviour is highly variable, from bees that are completely solitary and raise their young with no help from other bees, to egalitarian or 'communal' societies where all individuals are equally cooperative, to caste-based societies composed of selfish queens and altruistic workers. My research is geared towards explaining this variation in bee societies. I am also studying why some individual females are more likely to be altruistic than others. I am testing several theories to explain both altruism and the forms of bee societies. These theories include kin selection, the female quality hypothesis, which suggests that small, weak or infertile females are more likely to become helpers than breeders, and the environmental quality hypothesis, which suggests that bees are more likely to form societies in environments where colonies are more productive if adults cooperate. For more than 50 years, biologists have been accumulating observations on bee social diversity. The studies proposed here will allow me and my students to address important questions about animal social behaviour, questions that have preoccupied evolutionary biologists for decades, but which until recently, have not been amenable to study.