Complex third-party effects in the symbiosis: prey bacteria that are eaten, carried or left behind.

Symbiotic interactions may change depending on third parties like predators or prey. Third-party interactions with prey bacteria are central to the symbiosis between social amoeba hosts and bacterial symbionts. Symbiosis with inedible allows host to carry prey bacteria through the dispersal stage where hosts aggregate and develop into fruiting bodies that disperse spores.

Unpredictable soil conditions can affect the prevalence of a microbial symbiosis.

The evolution of symbiotic interactions may be affected by unpredictable conditions. However, a link between prevalence of these conditions and symbiosis has not been widely demonstrated. We test for these associations using social amoebae and their bacterial endosymbionts.

In the social amoeba , shortened stalks may limit obligate cheater success even when exploitable partners are available.

Cooperation is widespread across life, but its existence can be threatened by exploitation. The rise of obligate social cheaters that are incapable of contributing to a necessary cooperative function can lead to the loss of that function. In the social amoeba , obligate social cheaters cannot form dead stalk cells and in chimeras instead form living spore cells.

Costs of being a diet generalist for the protist predator .

Consumers range from specialists that feed on few resources to generalists that feed on many. Generalism has the clear advantage of having more resources to exploit, but the costs that limit generalism are less clear. We explore two understudied costs of generalism in a generalist amoeba predator, , feeding on naturally co-occurring bacterial prey.

Reduced social function in experimentally evolved implies selection for social conflict in nature.

Many microbes interact with one another, but the difficulty of directly observing these interactions in nature makes interpreting their adaptive value complicated. The social amoeba forms aggregates wherein some cells are sacrificed for the benefit of others. Within chimaeric aggregates containing multiple unrelated lineages, cheaters can gain an advantage by undercontributing, but the extent to which wild has adapted to cheat is not fully clear.

Predation-resistant Pseudomonas bacteria engage in symbiont-like behavior with the social amoeba Dictyostelium discoideum.

The soil amoeba Dictyostelium discoideum acts as both a predator and potential host for diverse bacteria. We tested fifteen Pseudomonas strains that were isolated from transiently infected wild D. discoideum for ability to escape predation and infect D.

Parallel evolution of the G protein-coupled receptor GrlG and the loss of fruiting body formation in the social amoeba Dictyostelium discoideum evolved under low relatedness.

Aggregative multicellularity relies on cooperation among formerly independent cells to form a multicellular body. Previous work with Dictyostelium discoideum showed that experimental evolution under low relatedness profoundly decreased cooperation, as indicated by the loss of fruiting body formation in many clones and an increase of cheaters that contribute proportionally more to spores than to the dead stalk. Using whole-genome sequencing and variant analysis of these lines, we identified 38 single nucleotide polymorphisms in 29 genes.

Symbiotic bacteria, immune-like sentinel cells, and the response to pathogens in a social amoeba.

Some endosymbionts living within a host must modulate their hosts' immune systems in order to infect and persist. We studied the effect of a bacterial endosymbiont on a facultatively multicellular social amoeba host. Aggregates of the amoeba contain a subpopulation of sentinel cells that function akin to the immune systems of more conventional multicellular organisms.

symbionts isolated from induce bacterial carriage in other species.

The social amoeba engages in a complex relationship with bacterial endosymbionts in the genus , which can benefit their host by imbuing it with the ability to carry prey bacteria throughout its life cycle. The relationship between and has been shown to take place across many strains and a large geographical area, but little is known about 's potential interaction with other dictyostelid species. We explore the ability of three species to stably infect and induce bacterial carriage in other dictyostelid hosts.

The social amoeba Dictyostelium discoideum rescues Paraburkholderia hayleyella, but not P. agricolaris, from interspecific competition.

Bacterial endosymbionts can provide benefits for their eukaryotic hosts, but it is often unclear if endosymbionts benefit from these relationships. The social amoeba Dictyostelium discoideum associates with three species of Paraburkholderia endosymbionts, including P. agricolaris and P.

Reduced and Nonreduced Genomes in Symbionts of Social Amoebas.

The social amoeba Dictyostelium discoideum is a predatory soil protist frequently used for studying host-pathogen interactions. A subset of D. discoideum strains isolated from soil persistently carry symbiotic , recently formally described as , , and .

Context dependence in the symbiosis between and .

Symbiotic interactions change with environmental context. Measuring these context-dependent effects in hosts and symbionts is critical to determining the nature of symbiotic interactions. We investigated context dependence in the symbiosis between social amoeba hosts and their inedible bacterial symbionts, where the context is the abundance of host food bacteria.

Novel Chlamydiae and Amoebophilus endosymbionts are prevalent in wild isolates of the model social amoeba Dictyostelium discoideum.

Amoebae interact with bacteria in multifaceted ways. Amoeba predation can serve as a selective pressure for the development of bacterial virulence traits. Bacteria may also adapt to life inside amoebae, resulting in symbiotic relationships.

Inference of symbiotic adaptations in nature using experimental evolution.

Microbes must adapt to the presence of other species, but it can be difficult to recreate the natural context for these interactions in the laboratory. We describe a method for inferring the existence of symbiotic adaptations by experimentally evolving microbes that would normally interact in an artificial environment without access to other species. By looking for changes in the fitness effects microbes adapted to isolation have on their partners, we can infer the existence of ancestral adaptations that were lost during experimental evolution.

Loss and resiliency of social amoeba symbiosis under simulated warming.

Anthropogenic global change is increasingly raising concerns about collapses of symbiotic interactions worldwide. Therefore, understanding how climate change affects symbioses remains a challenge and demands more study. Here, we look at how simulated warming affects the social ameba and its relationship with its facultative bacterial symbionts, and .

The Ecology and Evolution of Amoeba-Bacterium Interactions.

Amoebae are protists that have complicated relationships with bacteria, covering the whole spectrum of symbiosis. Amoeba-bacterium interactions contribute to the study of predation, symbiosis, pathogenesis, and human health. Given the complexity of their relationships, it is necessary to understand the ecology and evolution of their interactions.

Low Base-Substitution Mutation Rate but High Rate of Slippage Mutations in the Sequence Repeat-Rich Genome of .

We describe the rate and spectrum of spontaneous mutations for the social amoeba , a key model organism in molecular, cellular, evolutionary and developmental biology. Whole-genome sequencing of 37 mutation accumulation lines of after an average of 1,500 cell divisions yields a base-substitution mutation rate of 2.47 × 10 per site per generation, substantially lower than that of most eukaryotic and prokaryotic organisms, and of the same order of magnitude as in the ciliates and Known for its high genomic AT content and abundance of simple sequence repeats, we observe that base-substitution mutations in are highly A/T biased.

Endosymbiotic adaptations in three new bacterial species associated with : sp. nov., sp. nov., and sp. nov.

Here we give names to three new species of that can remain in symbiosis indefinitely in the spores of a soil dwelling eukaryote, . The new species sp. nov.

The gene's eye view, the Gouldian knot, Fisherian swords and the causes of selection.

The biological units-of-selection debate has centred on questions of which units experience selection and adaptation. Here, I use a causal framework and the Price equation to develop the gene's eye perspective. Genes are causally special in being both replicators and interactors.

Wild social amoebae show plastic responses to the presence of nonrelatives during multicellular development.

When multiple strains of microbes form social groups, such as the multicellular fruiting bodies of , conflict can arise regarding cell fate. Both fixed and plastic differences among strains can contribute to cell fate, and plastic responses may be particularly important if social environments frequently change. We used RNA-sequencing and photographic time series analysis to detect possible conflict-induced plastic differences between wild .

Cooperation and conflict in the social amoeba Dictyostelium discoideum.

The social amoeba Dictyostelium discoideum has provided considerable insight into the evolution of cooperation and conflict. Under starvation, D. discoideum amoebas cooperate to form a fruiting body comprised of hardy spores atop a stalk.

Long-term evolutionary conflict, Sisyphean arms races, and power in Fisher's geometric model.

Evolutionary conflict and arms races are important drivers of evolution in nature. During arms races, new abilities in one party select for counterabilities in the second party. This process can repeat and lead to successive fixations of novel mutations, without a long-term increase in fitness.

Fitness costs and benefits vary for two facultative symbionts of the social amoeba, .

Unlabelled: Hosts and their associated microbes can enter into different relationships, which can range from mutualism, where both partners benefit, to exploitation, where one partner benefits at the expense of the other. Many host-microbe relationships have been presumed to be mutualistic, but frequently only benefits to the host, and not the microbial symbiont, have been considered. Here, we address this issue by looking at the effect of host association on the fitness of two facultative members of the microbiome ( and ).

Pleiotropy and synergistic cooperation.

Some forms of stable cooperation can evolve though pleiotropy with a beneficial private trait. This Formal Comment addresses a recent challenge to this idea, arguing that for synergistic, frequency-dependent cooperation, pleiotropy can raise the frequency up to a point where cooperation is favoured on its own.