One of the most striking patterns in biology is the formation of animal aggregations. Classically, aggregation has been viewed as an evolutionarily advantageous state, in which members derive the benefits of protection, mate choice, and centralized information, balanced by the costs of limiting resources. Consisting of individual members, aggregations nevertheless function as an integrated whole, displaying a complex set of behaviors not possible at the level of the individual organism. Complexity theory indicates that large populations of units can self-organize into aggregations that generate pattern, store information, and engage in collective decision-making. This begs the question, are all emergent properties of animal aggregations functional or are some simply pattern? Solutions to this dilemma will necessitate a closer marriage of theoretical and modeling studies linked to empirical work addressing the choices, and trajectories, of individuals constrained by membership in the group.

https://science.sciencemag.org/content/sci/284/5411/99.full.pdf

Complexity, pattern, and evolutionary trade-offs in animal aggregation.

Evidence for the formation of cell aggregates by chemotaxis in the development of the slime mold Dictyostelium discoideum

Conditions were established in which Legionella pneumophila, an intracellular bacterial pathogen, could replicate within the unicellular organism Dictyostelium discoideum. By several criteria, L. pneumophila grew by the same mechanism within D. discoideum as it does in amoebae and macrophages. Bacteria grew within membrane-bound vesicles associated with rough endoplasmic reticulum, and L. pneumophila dot/icm mutants, blocked for growth in macrophages and amoebae, also did not grow in D. discoideum. Internalized L. pneumophila avoided degradation by D. discoideum and showed evidence of reduced fusion with endocytic compartments. The ability of L. pneumophila to grow within D. discoideum depended on the growth state of the cells. D. discoideum grown as adherent monolayers was susceptible to L. pneumophila infection and to contact-dependent cytotoxicity during high-multiplicity infections, whereas D. discoideum grown in suspension was relatively resistant to cytotoxicity and did not support intracellular growth. Some known D. discoideum mutants were examined for their effect on growth of L. pneumophila. The coronin mutant and the myoA/B double myosin I mutant were more permissive than wild-type strains for intracellular growth. Growth of L. pneumophila in a Gβ mutant was slightly reduced compared to the parent strain. This work demonstrates the usefulness of the L. pneumophila-D. discoideum system for genetic analysis of host-pathogen interactions.

https://iai.asm.org/content/iai/68/5/2939.full.pdf

Intracellular Growth of Legionella pneumophila in Dictyostelium discoideum, a System for Genetic Analysis of Host-Pathogen Interactions

Publisher Summary This chapter discusses experiments on the control of cell differentiation and pattern formation in a simple multicellular system. Aggregation patterns and mechanisms of Dictyostelium cells have been used as a model for these studies. The aggregation patterns are formed through self-organization; whereas the establishment of polarity in the conus is under the control of influences provided by exposure of a cell group to a liquid-air interphase. In the aggregation in D. minutum, pattern results from control of the number of cells that found aggregation centers, and also from the activity of a simple chemotactic system. In contrast, D. discoideum involves more complicated cell functions and interactions, particularly oscillation of the center's activity and transmission of stimuli. The chapter discusses how these phenomena in D. discoideum may be useful as models when pattern formation in other developmental systems is considered.

Chapter 6 Cell Aggregation and Differentiation in Dictyostelium

This review attempts to survey in a uniform manner the available evidence concerning the generation and behaviour of several well-investigated cellular oscillators. Members of two broad classifications are contrasted: (i) cytoplasmic oscillations, where the periodic phenomena is generated by an instability pathway and (ii) membrane oscillators in which a membrane potential rhythm is generated at the membrane. Interactions between the cytoplasmic and membrane compartments are considered and the effects of these interactions on oscillatory behaviour is discussed. Because of their biological importance and the greater body of experimental results, particular attention is directed to a study of membrane potential oscillations. These systems can be approximately classified in two groups: (i) systems in which a periodic potential results from oscillatory changes in permeability and (ii) systems in which potential oscillations result from the periodic activity of an electrogenic pump. The examples considered include the glycolytic oscillator, oscillations in vein contraction in the slime mould Physarum polycephalum, rhythmic aggregation in Dictyostelium discoideum, neural oscillators, the periodic potential in Purkinje fibres and the sino-atrial node and rhythmic behaviour in smooth muscle. Questions considered include the generation of periodic activity, the modulation of the oscillation by drugs and other metabolic and membrane effectors and the question of the functional role of these oscillations.

/pdf/a-comparative-survey-of-the-function-mechanism-and-control-c5vk60iz9e.pdf

John T. Bonner

Papers

A descriptive study of the development of the slime mold dictyostelium discoideum