Disruptive selection as a driver of evolutionary branching and caste evolution in social insects

AbstractAs social insects, ants represent extremely interaction-rich biological systems shaped by tightly integrated social structures and constant mutual exchange with a multitude of internal and external environmental factors. Due to this high level of ecological interconnection, ant colonies can harbour a diverse array of parasites and pathogens, many of which are known to interfere with the delicate processes of ontogeny and caste differentiation and induce phenotypic changes in their hosts. Despite their often striking nature, parasite-induced changes to host development and morphology have hitherto been largely overlooked in the context of ecological evolutionary developmental biology (EcoEvoDevo). Parasitogenic morphologies in ants can, however, serve as “natural experiments” that may shed light on mechanisms and pathways relevant to host development, plasticity or robustness under environmental perturbations, colony-level effects and caste evolution. By assessing case studies of parasites causing morphological changes in their ant hosts, from the eighteenth century to current research, this review article presents a first overview of relevant host and parasite taxa. Hypotheses about the underlying developmental and evolutionary mechanisms, and open questions for further research are discussed. This will contribute towards highlighting the importance of parasites of social insects for both biological theory and empirical research and facilitate future interdisciplinary work at the interface of myrmecology, parasitology, and the EcoEvoDevo framework.

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Evolution of dispersal in a spatially heterogeneous population with finite patch sizes

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1915881117 ◽

2020 ◽

Vol 117 (13) ◽

pp. 7290-7295

Author(s):

Kalle Parvinen ◽

Hisashi Ohtsuki ◽

Joe Yuichiro Wakano

Keyword(s):

Spatial Heterogeneity ◽

Reproductive Potential ◽

Life History Strategies ◽

Disruptive Selection ◽

Evolutionary Branching ◽

Homogeneous Case ◽

Kin Competition ◽

Dispersal Traits ◽

Dispersal Evolution ◽

Reproduction Efficiency

Dispersal is one of the fundamental life-history strategies of organisms, so understanding the selective forces shaping the dispersal traits is important. In the Wright’s island model, dispersal evolves due to kin competition even when dispersal is costly, and it has traditionally been assumed that the living conditions are the same everywhere. To study the effect of spatial heterogeneity, we extend the model so that patches may receive different amounts of immigrants, foster different numbers of individuals, and give different reproduction efficiency to individuals therein. We obtain an analytical expression for the fitness gradient, which shows that directional selection consists of three components: As in the homogeneous case, the direct cost of dispersal selects against dispersal and kin competition promotes dispersal. The additional component, spatial heterogeneity, more precisely the variance of so-called relative reproductive potential, tends to select against dispersal. We also obtain an expression for the second derivative of fitness, which can be used to determine whether there is disruptive selection: Unlike the homogeneous case, we found that divergence of traits through evolutionary branching is possible in the heterogeneous case. Our numerical explorations suggest that evolutionary branching is promoted more by differences in patch size than by reproduction efficiency. Our results show the importance of the existing spatial heterogeneity in the real world as a key determinant in dispersal evolution.

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Kin selection, genomics and caste-antagonistic pleiotropy

Biology Letters ◽

10.1098/rsbl.2013.0309 ◽

2013 ◽

Vol 9 (6) ◽

pp. 20130309 ◽

Cited By ~ 8

Author(s):

David W. Hall ◽

Soojin V. Yi ◽

Michael A. D. Goodisman

Keyword(s):

Social Insects ◽

Kin Selection ◽

Multiple Mating ◽

Genomic Data ◽

Single Locus ◽

Antagonistic Pleiotropy ◽

Important Process ◽

Caste Evolution ◽

Worker Caste ◽

Social Behaviours

Kin selection is a fundamentally important process that affects the evolution of social behaviours. The genomics revolution now provides the opportunity to test kin selection theory using genomic data. In this commentary, we discuss previous studies that explored the link between kin selection and patterns of variation within the genome. We then present a new theory aimed at understanding the evolution of genes involved in the development of social insects. Specifically, we investigate caste-antagonistic pleiotropy, which occurs when the phenotypes of distinct castes are optimized by different genotypes at a single locus. We find that caste-antagonistic pleiotropy leads to narrow regions where polymorphism can be maintained. Furthermore, multiple mating by queens reduces the region in which worker-favoured alleles fix, which suggests that multiple mating impedes worker caste evolution. We conclude by discussing ways to test these and other facets of kin selection using newly emerging genomic data.

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Adaptive Diversification Due to Resource Competition in Sexual Models

Adaptive Diversification (MPB-48) ◽

10.23943/princeton/9780691128931.003.0004 ◽

2011 ◽

Author(s):

Michael Doebeli

Keyword(s):

Reproductive Isolation ◽

Sexual Reproduction ◽

Assortative Mating ◽

Resource Competition ◽

Disruptive Selection ◽

Evolutionary Branching ◽

Adaptive Diversification ◽

Intermediate Phenotypes ◽

Branching Point ◽

Adaptive Speciation

This chapter examines evolutionary branching in sexual populations. As sexual populations converge to what would be a branching point in clonal models, splitting obviously becomes a problem, because mating between different marginal phenotypes generally creates intermediate phenotypes. Through segregation and recombination, sexual reproduction can prevent the establishment of diverging phenotypic clusters in randomly mating populations. To allow for a phenotypic split, mating needs to be assortative with respect to the ecological trait that is under disruptive selection. Thus, the question of evolutionary branching in sexual populations, that is, of adaptive speciation, is intimately tied to questions about the evolution of assortative mating. If evolutionary branching occurs in sexual populations due to the presence of assortative mating mechanisms, the diverging phenotypic clusters will show prezygotic reproductive isolation at least to some extent, and hence they can be viewed as representing incipient species.

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