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Microbes providing public goods are widespread in nature despite running the risk of being exploited by free-riders. However, the precise ecological factors supporting cooperation are still puzzling. Following recent experiments, we consider the role of population growth and the repetitive fragmentation of populations into new colonies mimicking simple microbial life-cycles. Individual-based modeling reveals that demographic fluctuations, which lead to a large variance in the composition of colonies, promote cooperation. Biased by population dynamics these fluctuations result in two qualitatively distinct regimes of robust cooperation under repetitive fragmentation into groups. First, if the level of cooperation exceeds a threshold, cooperators will take over the whole population. Second, cooperators can also emerge from a single mutant leading to a robust coexistence between cooperators and free-riders. We find frequency and size of population bottlenecks, and growth dynamics to be the major ecological factors determining the regimes and thereby the evolutionary pathway towards cooperation.

This article is from Frontiers in Plant Science , volume 4 . Abstract The rhizosphere is a hotbed of microbial activity in ecosystems, fueled by carbon compounds from plant roots. Basic questions about the location and dynamics of plant-spurred microbial growth in the rhizosphere are difficult to answer with standard, destructive soil assays mixing a multitude of microbe-scale microenvironments in a single, often sieved, sample. Soil microbial biosensors designed with the luxCDABE reporter genes fused to a promoter of interest enable continuous imaging of the microbial perception of (and response to) environmental conditions in soil. We used the common soil bacterium Pseudomonas putida KT2440 as host to plasmid pZKH2 containing a fusion between the strong constitutive promoter nptII and luxCDABE (coding for light-emitting proteins) from Vibrio fischeri. Experiments in liquid media demonstrated that high light production by KT2440/pZKH2 was associated with rapid microbial growth supported by high carbon availability. We applied the biosensors in microcosms filled with non-sterile soil in which corn (Zea mays L.), black poplar (Populus nigra L.), or tomato (Solanum lycopersicum L.) was growing. We detected minimal light production from microbiosensors in the bulk soil, but biosensors reported continuously from around roots for as long as six days. For corn, peaks of luminescence were detected 1–4 and 20–35 mm along the root axis behind growing root tips, with the location of maximum light production moving farther back from the tip as root growth rate increased. For poplar, luminescence around mature roots increased and decreased on a coordinated diel rhythm, but was not bright near root tips. For tomato, luminescence was dynamic, but did not exhibit a diel rhythm, appearing in acropetal waves along roots. KT2440/pZKH2 revealed that root tips are not always the only, or even the dominant, hotspots for rhizosphere microbial growth, and carbon availability is highly variable in space and time around roots.

This article is from Scientific Reports , volume 2 . Abstract Microbes providing public goods are widespread in nature despite running the risk of being exploited by free-riders. However, the precise ecological factors supporting cooperation are still puzzling. Following recent experiments, we consider the role of population growth and the repetitive fragmentation of populations into new colonies mimicking simple microbial life-cycles. Individual-based modeling reveals that demographic fluctuations, which lead to a large variance in the composition of colonies, promote cooperation. Biased by population dynamics these fluctuations result in two qualitatively distinct regimes of robust cooperation under repetitive fragmentation into groups. First, if the level of cooperation exceeds a threshold, cooperators will take over the whole population. Second, cooperators can also emerge from a single mutant leading to a robust coexistence between cooperators and free-riders. We find frequency and size of population bottlenecks, and growth dynamics to be the major ecological factors determining the regimes and thereby the evolutionary pathway towards cooperation.

This article is from Scientific Reports , volume 2 . Abstract Microbes providing public goods are widespread in nature despite running the risk of being exploited by free-riders. However, the precise ecological factors supporting cooperation are still puzzling. Following recent experiments, we consider the role of population growth and the repetitive fragmentation of populations into new colonies mimicking simple microbial life-cycles. Individual-based modeling reveals that demographic fluctuations, which lead to a large variance in the composition of colonies, promote cooperation. Biased by population dynamics these fluctuations result in two qualitatively distinct regimes of robust cooperation under repetitive fragmentation into groups. First, if the level of cooperation exceeds a threshold, cooperators will take over the whole population. Second, cooperators can also emerge from a single mutant leading to a robust coexistence between cooperators and free-riders. We find frequency and size of population bottlenecks, and growth dynamics to be the major ecological factors determining the regimes and thereby the evolutionary pathway towards cooperation.

1Harbor

By Ernest Poole

<em>The Harbor</em> was written in 1915 by Ernest Poole. The novel is considered by many to be one of Poole’s best efforts even though his book, <em>The Family</em> won a Pulitzer Prize. <em>The Harbor</em> is a fictional account of life on a Brooklyn waterfront through the eyes of Billy as he is growing up. The novel starts with Billy the child, living on the harbor with his father, mother, and sister, Sue. During this time he also meets Eleanor who, at that time, he considers to be strange. She later becomes an important character in the novel. His father owns a shipping business, is hard-working, and can think of little else. As a young man, Billy begins to detest the harbor and longs for escape to pursue his lifelong dream of becoming a writer and avoiding his father’s business. With his mother’s blessing, he takes flight to Paris to hone his trade. While in Paris, he meets Joe Kramer (J.K.) and a sometimes stormy relationship begins. J.K. forces him to confront human situations that Billy would prefer to close his eyes to. Billy eventually returns to the harbor after some years and recognizes changes are taking place in the harbor, and in his life. The harbor becomes a subject for his writing and his personal relationships. His attitude about the harbor begins to evolve. Throughout the novel, J.K. continues to make appearances in Billy’s life, challenging him to write about things as they really are and not as Billy’s world of comfort shows them to be. Billy’s life is changed when the harbor goes on strike and he becomes involved in the labor movement. What more can be said about a book that starts with the words, “You Chump!”? (Summary by Tom Weiss)

2His Family

By Ernest Poole

The 1910s is historically considered the decade of greatest social change in history. It saw the advent and proliferation of the automobile, electricity, lighting, radio, telephone and cinema. Our present time of change is actually quite tame in comparison, though also breathless. <i>His Family</i> is a tale of a widowed father, working to manage this decade of change as it affects his family in New York City. <i>His Family</i> was the first winner of the Pulitzer Prize for literature in 1919. (Summary by JCarson)