Professor Stuart West

Research Interests

I am an evolutionary biologist whose main interest is adaptation, and especially the evolution of social behaviours, such as cooperation, altruism, spite, mutualism, and how these can influence major evolutionary transitions. I use a mixture of techniques including theory, experiment and across species comparative studies.

My empirical work has utilised a range of organisms, including bacteria, protozoa, insects (especially parasitoid wasps), fish, birds and mammals. 

WATCH now: What caused life's major evolutionary transitions?

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Publications

  • Cooperative interactions among females and even more extraordinary sex ratios

    2020
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    Journal article
    Abstract Hamilton’s local mate competition theory provided an explanation for extraordinary female biased sex ratios in a range of organisms. When mating takes place locally, in structured populations, a female biased sex ratio is favoured to reduce competition between related males, and to provide more mates for males. However, there are a number of wasp species where the sex ratios appear to more female biased than predicted by Hamilton’s theory. We investigated theoretically the extent to which cooperative interactions between related females can interact with local mate competition to favour even more female biased sex ratios. We found that: (i) cooperative interactions between females can lead to sex ratios that are more female biased than predicted by local competition theory alone; (ii) sex ratios can be more female biased when the cooperative interactions are offspring helping parents, rather than cooperation between siblings. Our results can be applied to a range of organisms, and provide an explanation for the extreme sex ratio biases that have been observed in Sclerodemus and Melittobia wasps.

  • Dividing labour in social microorganisms: coordinated or random specialisation?

    2020
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    Journal article
    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 microogranisms: 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.

  • Kin discrimination, negative relatedness, and how to distinguish between selfishness and spite.

    2020
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    Journal article
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    Evolution letters
    Spiteful behaviors occur when an actor harms its own fitness to inflict harm on the fitness of others. Several papers have predicted that spite can be favored in sufficiently small populations, even when the harming behavior is directed indiscriminately at others. However, it is not clear that truly spiteful behavior could be favored without the harm being directed at a subset of social partners with relatively low genetic similarity to the actor (kin discrimination, causing a negative relatedness between actor and harmed recipient). Using mathematical models, we show that (1) the evolution of spite requires kin discrimination; (2) previous models suggesting indiscriminate spite involve scenarios where the actor gains a direct feedback benefit from harming others, and so the harming is selfish rather than spiteful; (3) extreme selfishness can be favored in small populations (or, more generally, under local competition) because this is where the direct feedback benefit of harming is greatest.

  • The cost and benefit of quorum sensing-controlled bacteriocin production in Lactobacillus plantarum.

    2020
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    Journal article
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    J Evol Biol
    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.
    bacteriocins, benefits, costs, fitness, quorum sensing

  • The social coevolution hypothesis for the origin of enzymatic cooperation.

    2020
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    Journal article
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    Nature ecology & evolution
    At the start of life, the origin of a primitive genome required individual replicators, or genes, to act like enzymes and cooperatively copy each other. The evolutionary stability of such enzymatic cooperation poses a problem, because it would have been susceptible to parasitic replicators that did not act like enzymes but could still benefit from the enzymatic behaviour of other replicators. Existing hypotheses to solve this problem require restrictive assumptions that may not be justified, such as the evolution of a cell membrane before the evolution of enzymatic cooperation. We show theoretically that, instead, selection itself can lead to replicators grouping themselves together in a way that favours cooperation. We show that the tendency to physically associate with others and cooperative enzymatic activity can coevolve, leading to the evolution of physically linked cooperative replicators. Our results shift the empirical problem from a search for special environmental conditions to questions about what types of phenotypes can be produced by simple replicators.
    Genome

  • Adaptation is maintained by the parliament of genes.

    2019
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    Journal article
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    Nature communications
    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.
    Adaptation, Physiological, Repetitive Sequences, Nucleic Acid, Quantitative Trait, Heritable, Genes, Models, Genetic, Genome Size

  • Honest signaling and the double counting of inclusive fitness.

    2019
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    Journal article
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    Evolution letters
    Inclusive fitness requires a careful accounting of all the fitness effects of a particular behavior. Verbal arguments can potentially exaggerate the inclusive fitness consequences of a behavior by including the fitness of relatives that was not caused by that behavior, leading to error. We show how this "double-counting" error can arise, with a recent example from the signaling literature. In particular, we examine the recent debate over whether parental divorce increases parent-offspring conflict, selecting for less honest signaling. We found that, when all the inclusive fitness consequences are accounted for, parental divorce increases conflict between siblings, in a way that they can select for less honest signaling. This prediction is consistent with the empirical data. More generally, our results illustrate how verbal arguments can be misleading, emphasizing the advantage of formal mathematical models.

  • Transmission, relatedness, and the evolution of cooperative symbionts.

    2019
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    Journal article
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    Journal of evolutionary biology
    Cooperative interactions between species, termed mutualisms, play a key role in shaping natural ecosystems, economically important agricultural systems, and in influencing human health. Across different mutualisms, there is significant variation in the benefit that hosts receive from their symbionts. Empirical data suggest that transmission mode can help explain this variation: vertical transmission, where symbionts infect their host's offspring, leads to symbionts that provide greater benefits to their hosts than horizontal transmission, where symbionts leave their host and infect other hosts in the population. However, two different theoretical explanations have been given for this pattern: firstly, vertical transmission aligns the fitness interests of hosts and their symbionts; secondly, vertical transmission leads to increased relatedness between symbionts sharing a host, favouring cooperation between symbionts. We used a combination of analytical models and dynamic simulations to tease these factors apart, in order to compare their separate influences and see how they interact. We found that relatedness between symbionts sharing a host, rather than transmission mode per se, was the most important factor driving symbiont cooperation. Transmission mode mattered mainly because it determined relatedness. We also found evolutionary branching throughout much of our simulation, suggesting that a combination of transmission mode and multiplicity of infections could lead to the stable coexistence of different symbiont strategies.
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Graduate Students
Contact Details

E: stuart.west@zoo.ox.ac.uk 
T: 01865 (2) 81998
  http://zoo-web02.zoo.ox.ac.uk/group/west/index.html