Biology subjects

Richter, X.-Y. L.

Publications and source records attributed to Richter, X.-Y. L..

4 recordsLinked to original sources

bioRxiv2022

Ecology shapes the cyclic dominance games between Escherichia coli strains

Evolutionary game theory has provided various models to explain the coexistence of competing strategies, one of which is the rock-paper-scissors (RPS) game. A system of three Escherichia coli strains--a toxin-producer, a resistant, and a sensitive--has become a classic experimental model for studying RPS games. Previous experimental and theoretical studies, however, often ignored the influence of ecological factors such as nutrients and toxin dynamics on the evolutionary game dynamics. In this work, we combine experiments and modeling to study how these factors affect competition dynamics. Using 3D-printed mini-bioreactors, we tracked the frequency of the three strains in different culturing media and under different flow regimes. Although our experimental system fulfilled the requirements of cyclic dominance, we did not observe clear cycles or long-term coexistence between strains. We found that both nutrients and flow rates strongly impacted population dynamics. In our simulations, we explicitly modeled the release, removal and diffusion of toxin. We showed that the amount of toxin that is retained in the system is a simple indicator that can predict competition outcomes across broad parameter space. Moreover, our simulation results suggest that high rates of toxin diffusion might have prevented cyclic patterns from emerging in our experimental system.

evolutionary biology↗

bioRxiv2022

Design and construction of 3D-printed devices to investigate active and passive bacterial dispersal on hydrated surfaces

To disperse in water-unsaturated environments, such as the soil, bacteria rely on the availability and structure of water films forming on biotic and abiotic surfaces, and, especially, along fungal mycelia. Dispersal along such "fungal highways" is driven both by mycelial physical properties and by interactions between bacteria and fungi. To understand the role of abiotic elements, we designed and 3D-printed two devices establishing stable liquid films that support bacteria dispersal in the absence of biotic interactions. The thickness of the liquid film determined the presence of hydraulic flow capable of carrying non-motile cells. In the absence of flow, only motile cells can disperse in the presence of an energy source. Non-motile cells could not disperse autonomously without flow, but dispersed when co-inoculated with motile cells. By teasing apart the abiotic and biotic dimensions, these 3D-printed devices will stimulate further research on microbial dispersal in soil and other water-unsaturated environments.

microbiology↗

bioRxiv2022

Spatial scales of competition and a growth-motility tradeoff interact to determine bacterial coexistence

1.The coexistence of competing species is a long-lasting puzzle in evolutionary ecology research. Despite abundant experimental evidence showing that the opportunity for coexistence decreases as niche overlap increases between species, bacterial species and strains competing for the same resources are commonly found across diverse spatially heterogeneous habitats. We thus hypothesized that the spatial scale of competition may play a key role in determining bacterial coexistence, and interact with other mechanisms that promote coexistence, including a growth-motility tradeoff. To test this hypothesis, we let two Pseudomonas putida strains compete at local and regional scales by inoculating them either in a mixed droplet or in separate droplets in the same Petri dish, respectively. We also created conditions that allow the bacterial strains to disperse across abiotic or fungal hyphae networks. We found that competition at the local scale led to competitive exclusion while regional competition promoted coexistence. When competing in the presence of dispersal networks, the growth-motility tradeoff promoted coexistence only when the strains were inoculated in separate droplets. Our results provide a mechanism by which existing laboratory data suggesting competitive exclusion at a local scale is reconciled with the widespread coexistence of competing bacterial strains in complex natural environments with dispersal.

ecology↗

bioRxiv2021

Who takes care of the kids at when? Variation of sex-role patterns across different parental care forms in passerine birds

Parental care in birds consists of many elaborate forms, including nest building, incubation, and offspring provision, but we still do not know how much each parent contributes to the different forms. Furthermore, the variations, relationships, and potential drivers of sex differentiation in providing care across different care stages remain largely unknown. Here, we surveyed species in birds and uncovered remarkable differences in the sex role patterns across different care forms. This result implied that parental care should not be treated as a unitary trait but as a composite of integrated features with great variations. Further analyses revealed moderate correlations of the sex roles between care forms, indicating the existence of shared intrinsic drivers. We tested the effects of sexual selection, certainty of paternity, predation risk, and offsprings life history traits in driving sex role variations. Results showed that species with strong sexual selection on males or uncertainty of paternity tend to have female-biased care.

evolutionary biology↗