Global network structure of dominance hierarchy of ant workers

Abstract

Dominance hierarchy among animals is widespread in various species and believed to serve to regulate resource allocation within an animal group. Unlike small groups, however, detection and quantification of linear hierarchy in large groups of animals are a difficult task. Here, we analyse aggressionbased dominance hierarchies formed by worker ants in Diacamma sp. as large directed networks. We show that the observed dominance networks are perfect or approximate directed acyclic graphs, which are consistent with perfect linear hierarchy. The observed networks are also sparse and random but significantly different from networks generated through thinning of the perfect linear tournament (i.e. all individuals are linearly ranked and dominance relationship exists between every pair of individuals). These results pertain to global structure of the networks, which contrasts with the previous studies inspecting frequencies of different types of triads. In addition, the distribution of the out-degree (i.e. number of workers that the focal worker attacks), not in-degree (i.e. number of workers that attack the focal worker), of each observed network is right-skewed. Those having excessively large out-degrees are located near the top, but not the top, of the hierarchy. We also discuss evolutionary implications of the discovered properties of dominance networks.

A Simple Behavioral Model Predicts the Emergence of Complex Animal Hierarchies

“…In this genus, subordinate workers are physically mutilated to prevent reproduction, which is similar to strong policing in our model (but mutilation is performed by the unmutilated alpha worker against her subordinates in Diacamma). In one Diacamma species, most workers remain unmutilated and develop despotic hierarchies with policing and dominance biting involved (Cournault and Peeters 2012), while there are other cases where workers establish a linear hierarchy before an unmutilated alpha is produced (Sommer et al 1993;Shimoji et al 2014). Despite the diversity of dominance structures described in Diacamma, the presence of standard dominance behaviors and policing always leads to despotic or linear hierarchies, similar to our model outcomes.…”

Social dominance and reproductive differentiation mediated by dopaminergic signaling in a queenless ant

“…After 9 days of individual rearing, their ovaries were dissected and oocyte sizes (represented by largest oocyte) were measured by dissection microscope (Olympus, SZX7, Tokyo, Japan). Although most mutilated workers are not aggressive (Peeters and Higashi, 1989), gamergate-right colonies sometimes contain a few aggressive mutilated workers that contrive to lay eggs (beta, gamma and delta, Nakata and Tsuji, 1996;Shimoji et al, 2014). These potential high rankers were identified by 30 min of observation for two consecutive days before the experiment and were not used.…”

Community detection in directed acyclic graphs

“…As a final example, we examine DAGs induced by dominance hierarchies in ant colonies using the data in reference [18]. The data set contains aggression-based hierarchy among workers in six ant colonies of species Diacamma sp.…”

“…DAGs have been common as a tool for statistical inference for decades [15,16]. Equally importantly, we find various instances of DAGs in the real world such as some food webs [17], some dominance hierarchy networks [18,19], citation networks [20][21][22][23], family trees [24], and phylogenetic networks [25]. Temporal networks can be mapped to DAGs in at least two ways.…”