Workers influence royal reproduction

Abstract

Understanding which parties regulate reproduction is fundamental to understanding conflict resolution in animal societies. In social insects, workers can influence male production and sex ratio. Surprisingly, few studies have investigated worker influence over which queen(s) reproduce(s) in multiple queen (MQ) colonies (skew), despite skew determining worker-brood relatedness and so worker fitness. We provide evidence for worker influence over skew in a functionally monogynous population of the ant Leptothorax acervorum. Observations of MQ colonies leading up to egg laying showed worker aggressive and nonaggressive behaviour towards queens and predicted which queen monopolized reproduction. In contrast, among-queen interactions were rare and did not predict queen reproduction. Furthermore, parentage analysis showed workers favoured their mother when present, ensuring closely related fullsibs (average r ¼ 0.5) were reared instead of less related offspring of other resident queens (r 0.375). Discrimination among queens using relatedness-based cues, however, seems unlikely as workers also biased their behaviour in colonies without a mother queen. In other polygynous populations of this species, workers are not aggressive towards queens and MQs reproduce, showing the outcome of social conflicts varies within species. In conclusion, this study supports non-reproductive parties having the power and information to influence skew within cooperative breeding groups.

Behavioral Plasticity in Ant Queens: Environmental Manipulation Induces Aggression among Normally Peaceful Queens in the Socially Polymorphic Ant Leptothorax acervorum

“…Our finding also contrasts with previous studies in L. acervorum : dissections and population genetic analyses suggest that the level of skew is more or less fixed within populations, and that colonies maintain their social phenotype when kept under standardized laboratory conditions [18], [19], [25], [26]. Therefore, different levels of reproductive skew have been suggested to be an evolved rather than a behavioral response [19], [49]. This discrepancy might mean that ants from different populations have evolved different thresholds for fighting and dominance behavior, leading to more or less fixed local social organization.…”

Worker demography and behavior in a supercolonial ant colony: The case of the desert antCataglyphis niger

“…Queen number has also been shown to negatively affect aggression levels toward non-nestmates (Starks, Watson, Dipaola, & Dipaola, 2010), which perhaps suggests a lower threshold of recognition cues in such high-polygynous nests. Indeed, to date the hypothesis of positive nepotism in eusocial insects, specifically in ants, has mostly been refuted (DeHeer & Ross, 1997;Friend & Bourke, 2012;Holzer, Kummerli, Keller, & Chapuisat, 2006;Zinck, Châline, & Jaisson, 2009), except for Formica fusca (Hannonen & Sundström, 2003), but see the criticism by Holzer, Kummerli, et al (2006); e.g., selective brood mortality rather than preferential brood rearing), and Leptothorax acervorum ants (Gill & Hammond, 2011). Boomsma and d'Ettorre (2013) suggested that within-colony kin discrimination might be maintained in a secondary polygyny where there are a high queen turnover and fluctuating relatedness in the colony.…”

Absence of Within‐Colony Kin Discrimination in a Multiple‐Queen Ant, Leptothorax acervorum

“…Previous studies of facultatively polygynous L. acervorum failed to find within-colony kin discrimination during either egg cannibalism by queens (Bourke 1994) or colony fission . In their functionally monogynous study population, Gill & Hammond (2011) found that workers favoured their mother queen as the colony reproductive, although workers may not have used relatedness-based cues to do so. However, potentially nepotistic interactions of workers with queens within facultatively polygynous colonies have not previously been investigated in L. acervorum.…”

“…If they are nepotistic, workers in the study population are especially likely to use care (as opposed to aggression) to favour a particular queen, because they rarely exhibit aggression towards nestmate queens or interfere with queens' egg‐laying (Bourke ). By contrast, in a population of L. acervorum with functionally monogynous colonies, that is, ones in which there are several mated queens but only one lays eggs at any one time, workers frequently exhibit aggression towards queens (Gill & Hammond ). Previous studies of facultatively polygynous L. acervorum failed to find within‐colony kin discrimination during either egg cannibalism by queens (Bourke ) or colony fission (Heinze et al.…”

“…). In their functionally monogynous study population, Gill & Hammond () found that workers favoured their mother queen as the colony reproductive, although workers may not have used relatedness‐based cues to do so. However, potentially nepotistic interactions of workers with queens within facultatively polygynous colonies have not previously been investigated in L. acervorum .…”