Manfredini | Fire ant foundresses

BACKGROUND. One of the fundamental questions in biology is how altruistic behaviour, in which individuals help others at a cost to their own reproduction evolved. The majority of studies seeking to identify the genes regulating altruistic behaviour have been performed in systems where behavioural and physiological differences between sterile and reproductive individuals are relatively fixed, such as in the honey bee. Colony founding in the monogyne (one queen per colony) social form of the fire ant Solenopsis invicta is a primitively social system where newly-mated queens that are anatomically, physiologically and genetically very similar may start a new colony individually (haplometrosis) or in groups (pleometrosis). However, only one queen (the ‘winner’) in pleometrotic associations survives and takes the lead of the young colony while the others (the ‘losers’) are executed. Thus, this is an excellent system in which to examine the genes underpinning altruistic behaviour, and examine how social environment may shape expression of these genes.

Multi-level analysis of the evolution of cooperative behaviour in social insects

This is a research project that I initiated when I was a postdoc in the Grozinger Lab at Penn State. This project led to a Marie Curie Fellowship (IIF) that supported my work at Royal Holloway from 2014 to 2016. The analysis of data associated with this project is still undergoing at the moment. Current collaborators on the project are Prof Mark Brown (Royal Holloway) and Dr DeWayne Shoemaker (University of Tennessee)

AIM OF THE PROJECT. This project is a follow-up of my microarray studies where I explored the patterns of global gene expression associated with haplometrosis vs. pleometrosis in fire ants (Manfredini et al. 2013 PLoS Gen). Here I adopt an RNAseq approach to identify the molecular mechanisms that regulate cooperative colony founding in S. invicta. I focus on two key moments of the founding process and address the following questions:

1) INITIATION OF COOPERATION

How is cooperative breeding initiated in fire ants?
What are the genes involved in the regulation of this complex social behaviour?

2) THE EFFECT OF SOCIAL ENVIRONMENT ON BRAIN FUNCTIONS

How is the brain modelled by cooperative breeding in fire ants?
What genes respond to the different social environment that founding queens experience?
How are these genes affected by the different social complexity associated with each founding syndrome?

Heatmaps of expression values for the fire ant transcripts that are putatively involved in aging (left) and immunity (right). * = gene that extends lifespan when its activity is increased; ∧ = gene that extends lifespan when its activity is decreased (Manfredini et al. 2013 - PLoS Gen).

Top: 1) virgin winged queens, mated wingless queen and workers of S. invicta (left, photo by Romain Libbrecht); 2) queens sampled immediately after a mating flight (right). Bottom: 3) claustral colony founding in lab conditions, showing both haplometrotic and pleometrotic queens; 4) cofoundresses after the emergence of the first workers.

Colony founding in fire ants. (a) Mating flight. (b) Claustral phase. (c) Adult workers hatch. (d) Queens fight until only one survives (from Bernasconi and Strassmann 1999 TREE).