Queen and worker influence on sex allocation patterns in the honeybee, Apis mellifera.

摘要

Since Darwin, biologists have sought to understand the ways in which natural selection shapes the ability of organisms to adjust their investment in the sexes. A social insect colony, comprised of many individuals, faces the challenge of coordinating its individuals to achieve an adaptive allocation to the sexes. In this dissertation, I focus on the ways in which sex allocation in honeybee colonies is shaped by the actions and interactions of the queen and workers.;Previously, attempts to understand how colony members shape colony sex allocation patterns have generally focused on social insect species in which the queen and workers favor different colony sex allocation optima. This queen-worker conflict over sex allocation is expected to be minimal or absent in species with a highly polyandrous queen, including the honeybee. In these species, understanding how the queen and workers influence colony sex allocation might provide important insights into how colonies efficiently and flexibly respond to environmental conditions. To better understand how queens and workers shape colony sex allocation patterns when conflict is expected to be minimal or absent, I conducted experiments using the honeybee.;The queen lays nearly all of the eggs in her colony and might therefore play a key role in her colony's investment in males (drones). To test whether the queen's egg-laying decisions impact colony sex allocation patterns, I manipulated the previous egg-laying experiences of queens and examined their subsequent tendency to lay worker or drone eggs. My results indicate that the queen has the ability to regulate her production of drone eggs, and in turn has the ability to influence her colony's regulation of investment in male reproductive function. More generally, this work reveals that the honeybee queen and workers share control over their colony's sex allocation.;After the queen lays eggs, the workers rear the eggs to adulthood. However, workers occasionally eliminate a portion of their colony's immature males. To better understand how brood rearing decisions by workers impact colony patterns of sex allocation, I manipulated the abundance of older male brood in colonies and quantified the tendency of workers to rear young larvae. Workers eliminated a greater proportion of young male larvae when I increased the abundance of older male brood than when I decreased it. While earlier studies suggest that male elimination reflects conflict between the queen and workers, my results raise the possibility that male elimination might sometimes reflect adaptive adjustment of male reproductive function, potentially increasing colony efficiency in the interests of all colony members.;Historically, biologists have primarily investigated sex allocation theory through the study of offspring sex ratios. I suggest that our understanding of sex allocation will be aided by applying analyses that use the raw numbers of males and females, rather than the ratio of males to females, as the primary variables of interest. To illustrate this point, I examine existing datasets of offspring production and demonstrate that analyzing sex allocation behavior can lead to fundamentally different biological conclusions than those drawn from analyzing sex ratio behavior.