Bumblebee size polymorphism and worker response to queen pheromone

Queen pheromones are chemical signals produced by reproductive individuals in social insect colonies. In many species they are key to the maintenance of reproductive division of labor, with workers beginning to reproduce individually once the queen pheromone disappears. Recently, a queen pheromone that negatively affects worker fecundity was discovered in the bumblebee Bombus terrestris, presenting an exciting opportunity for comparisons with analogous queen pheromones in independently-evolved eusocial lineages such as honey bees, ants, wasps and termites. I set out to replicate this discovery and verify its reproducibility. Using blind, controlled experiments, I found that n-pentacosane (C₂₅) does indeed negatively affect worker ovary development. Moreover, the pheromone affects both large and small workers, and applies to workers from large, mature colonies as well as young colonies. Given that C₂₅ is readily available and that bumblebees are popular study organisms, I hope that this replication will encourage other researchers to tackle the many research questions enabled by the discovery of a queen pheromone.

Queen Control or Queen Signal in Ants: What Remains of the Controversy 25 Years After Keller and Nonacs' Seminal Paper?

Ant queen pheromones (QPs) have long been known to affect colony functioning. In many species, QPs affect important reproductive functions such as diploid larvae sexualization and egg-laying by workers, unmated queens (gynes), or other queens. Until the 1990s, these effects were generally viewed to be the result of queen manipulation through the use of coercive or dishonest signals. However, in their seminal 1993 paper, Keller and Nonacs challenged this idea, suggesting that QPs had evolved as honest signals that informed workers and other colony members of the queen's presence and reproductive state. This paper has greatly influenced the study of ant QPs and inspired numerous attempts to identify fertility-related compounds and test their physiological and behavioral effects. In the present article, we review the literature on ant QPs in various contexts and pay special attention to the role of cuticular hydrocarbons (CHCs). Although the controversy generated by Keller and Nonacs' (Anim Behav 45:787-794, 1993) paper is currently less intensively debated, there is still no clear evidence which allows the rejection of the queen control hypothesis in favor of the queen signal hypothesis. We argue that important questions remain regarding the mode of action of QPs, and their targets which may help understanding their evolution.

Reproductive Dominance Strategies in Insect Social Parasites

In eusocial insects, the high cost of altruistic cooperation between colony members has favoured the evolution of cheaters that exploit social services of other species. In the most extreme forms of insect social parasitism, which has evolved multiple times across most social lineages, obligately parasitic species invade the nests of social species and manipulate the workforce of their hosts to rear their own reproductive offspring. As alien species that have lost their own sociality, these social parasites still face social challenges to infiltrate and control their hosts, thus providing independent replicates for understanding the mechanisms essential to social dominance. This review compares socially parasitic insect lineages to find general trends and build a hypothetical framework for the means by which social parasites achieve reproductive dominance. It highlights how host social organization and social parasite life history traits may impact the way they achieve reproductive supremacy, including the potential role of chemical cues. The review discusses the coevolutionary dynamics between host and parasite during this process. Altogether, this review emphasizes the value of social parasites for understanding social evolution and the need for future research in this area.

Pheromones Regulating Reproduction in Subsocial Beetles: Insights with References to Eusocial Insects

Beetles have evolved diverse strategies to cope with environmental challenges. Although parents of the vast majority of beetle species do not take care of their offspring, there are some species, in which parents provide elaborate post-hatching care and remain temporarily associated with their offspring to defend them from competitors or to provision them with food. Usually, socially induced reproductive "control" is a core feature of eusocial societies, but here we highlight that already in small family groups, socially induced reproductive regulation can play a fundamental role. By discussing the family life of burying beetles, we illustrate the mechanisms behind such a reproductive "control" and show that - similar to eusocial insects - pheromones can be an important regulating factor. However, apart from burying beetles, our knowledge of pheromones or other signals mediating reproductive regulation is surprisingly rudimentary for social beetles. More data are required to broaden our currently patchy picture.