SFB-TRR 212

Proximate and ultimate mechanisms of social niche choice and construction during colony founding in the ant Pogonomyrmex californicus

All ants live in societies and the constant interactions between members of these societies determine its social organisation, e.g. colony size or numbers of reproductive individuals. Minute, individual behavioural differences can have large and long-lasting effects on colony organisation. In particular, variations in terms of clustering/avoidance and tolerance/aggression of colony founding queens can lead to fundamentally different colony organisations with far reaching proximate and ultimate effects. We aim to study the evolution and genetic and regulatory mechanisms that determine individual differences in aggression and clustering behaviour in the socially variable ant species Pogonomyrmex californicus that underlie to social niche choice and construction.

We will use individual and population wide differences in founding behaviour of queens between and within populations of P. californicus to understand the underlying molecular mechanisms and evolution of two notoriously complex behaviours, aggression and social organisation. P. californicus founding queens have to first make a choice in either founding a colony alone or in a group (social niche choice) and later, once queens have joined, whether to cooperate or escalate aggression and kill or expel other co-foundresses (social niche construction). These differences in colony founding (haplometrotic (alone) or pleometrotic (in groups)) in P. californicus have a strong genetic basis that manifests itself in significant differences in aggression and conflict escalation during the first 48 hours of colony founding. However, the expression of aggressive behaviour is also dependent on social context, i.e., who is/are the interacting partner/s. Hence, the propensity for aggression is phenotypically plastic and both direct and indirect genetic and epigenetic mechanisms could be involved and decide which trajectory an individual founding queen and colony will follow. These behavioural differences and variations between founding queens have significant fitness effects both at the individual (queen survival) and colony level (colony survival, division of labour, colony growth, and production of reproductive individuals).

Although I am using population differences in founding behaviour as a tool to elucidate the molecular mechanisms underlying differences in social niche construction and choice, I consider these two founding types as the extreme endpoints of a continuum in which both environmental and genetic factors determine the social niche a queen chooses and how interactions with other queens lead to the construction of a variety of social niches. This proposal tries to better understand how complex interactions within and between multiple organisational levels (DNA modifications, genotypes, transcription, translation, physiology, behaviour and societies) can explain individual variation in behaviour and social organization at the individual and colony level.

Following up on our previous work we propose

1. (Aim 1) a comparative and population genomics approach to understand the genetic and genomic population differences and evolutionary mechanisms leading to the differences between haplo- and pleometrotic populations/queens. Additionally, we will determine candidate genes or genomic regions that are linked to the observed phenotypic differences and explore the evolutionary mechanisms (drift versus selection) that lead to these population and behavioural differences between individuals/populations. Consecutively, we will test four intrinsic mechanisms that could individually or in conjunction with each other form the proximate molecular basis of the observed differences in niche choice and niche construction.
2. Aim 2 will test whether queens differ in their DNA methylation and how this affects transcription.
3. Aim 3 will characterise and examine expression differences of small non-coding RNA between aggressive and non-aggressive queens.
4. Aim 4 will target a hormonal factor (juvenile hormone titer) and its variation as candidate for the differences between haplo- and pleometrotic founding queens.
5. Aim 5 will investigate the link between variation in metabolic rates of queens, aggressive behaviour and colony founding type. All four mechanisms have previously been shown to be linked to variation or modulation of aggressive and social behaviour in eusocial insects.