Professor Stuart West

Abstract Division of labour, where cooperating individuals specialise to perform complementary tasks, plays a fundamental role at all levels of biological complexity, from genes to complex animal societies. Different labour-dividing species employ different mechanisms to determine how tasks are allocated between individuals, including coordinated, random, and genetic determination of phenotype (caste). It is not clear if this diversity is adaptive—arising because different mechanisms are favoured in different environments—or is merely the result of non-adaptive, historical artifacts of evolution. We analyse theoretically the relative advantages of the two dominant mechanisms employed for reproductive division of labour in social microorganisms: coordinated and random specialisation. We show that coordinated specialisation is more likely to evolve over random specialisation when: (i) social groups are small; (ii) cooperation has a greater relative impact on fitness (i.e., it is more “essential”); and (iii) there is a low cost to coordination. We also show how a fully coordinated group of cells can evolve step-wise from less precise forms of coordination. Our predictions are in broad qualitative agreement with empirical patterns across microorganism species that divide labour. More generally, our results show how evolutionary theory can help explain both why between-individual coordination evolves, and why there is mechanistic variation between species.

Bacteria eliminate competitors via 'chemical warfare' with bacteriocins. Some species appear to adjust bacteriocin production conditionally in response to the social environment. We tested whether variation in the cost and benefit of producing bacteriocins could explain such conditional behaviour, in the bacteria Lactobacillus plantarum. We found that: (a) bacterial bacteriocin production could be upregulated by either the addition of a synthetic autoinducer peptide (PLNC8IF; signalling molecule), or by a plasmid which constitutively encodes for the production of this peptide; (b) bacteriocin production is costly, leading to reduced growth when grown in poor and, to a lesser extent, in rich media; (c) bacteriocin production provides a fitness advantage, when grown in competition with sensitive strains; and (d) the fitness benefits provided by bacteriocin production are greater at higher cell densities. These results show how the costs and benefits of upregulating bacteriocin production can depend upon abiotic and biotic conditions.

Fields such as behavioural and evolutionary ecology are built on the assumption that natural selection leads to organisms that behave as if they are trying to maximise their fitness. However, there is considerable evidence for selfish genetic elements that change the behaviour of individuals to increase their own transmission. How can we reconcile this contradiction? Here we show that: (1) when selfish genetic elements have a greater impact at the individual level, they are more likely to be suppressed, and suppression spreads more quickly; (2) selection on selfish genetic elements leads them towards a greater impact at the individual level, making them more likely to be suppressed; (3) the majority interest within the genome generally prevails over 'cabals' of a few genes, irrespective of genome size, mutation rate and the sophistication of trait distorters. Overall, our results suggest that even when there is the potential for considerable genetic conflict, this will often have negligible impact at the individual level.