Inertial effect on evasion and pursuit dynamics of prey swarms: the emergence of a favourable mass ratio for the predator-prey arms race.

We show, based on a theoretical model, how inertia plays a pivotal role in the survival dynamics of a prey swarm while chased by a predator. With the varying mass of the prey and predator, diverse escape patterns emerge, such as circling, chasing, maneuvering, dividing into subgroups, and merging into a unitary group, similar to the escape trajectories observed in nature. Moreover, we find a transition from non-survival to survival of the prey swarm with increasing predator mass. The transition regime is also sensitive to the variation in prey mass. Further, the analysis of the prey group survival as a function of predator-to-prey mass ratio unveils the existence of three distinct regimes: (i) frequent chase and capture leading to the non-survival of the prey swarm, (ii) an intermediate regime where competition between pursuit and capture occurs, resembling an arms race, and (iii) the survival regime without the capture of prey. Interestingly, our study demonstrates the existence of a favourable predator-prey mass ratio for coexistence of both prey and predator in an ecosystem, which agrees well with the field studies.

Cholate-conjugated cationic polymers for regulation of actin dynamics.

Cytoskeletal movement is a compulsory necessity for proper cell functioning and is largely controlled by actin filament dynamics. The actin dynamics can be fine-tuned by various natural and artificial materials including cationic proteins, polymers, liposomes, and lipids, although most of the synthetic substrates have toxicity issues. Herein, we show actin nucleation and stabilization with a synthetic family of cholic acid (CA)-conjugated cationic macromolecules. Architectural conjugation of CA is designed by attaching it to the polymer chain end, as well as to the side chain of the polymer. The side-chain cholate content is also varied in the copolymer, which results in self-aggregation in aqueous media above a certain critical aggregation concentration (CAC). Below the CAC, the in vitro actin dynamics modulation behaviour is studied using a pyrene actin fluorescence assay, actin co-sedimentation assay, dynamic light scattering (DLS), and transmission electron microscopy (TEM). These polymers are nontoxic to HeLa cells, and the 2% cholate conjugated cationic copolymer showed maximum enhancement of G-actin nucleation, as well as F-actin stabilization. We further develop a theoretical model to elucidate the underlying dynamics of the actin polymerization process under the influence of cationic copolymers with cholate pendants. Finally, we proposed macromolecular self-aggregation as a unique tool for modulating actin dynamics, as revealed from the experimental findings and theoretical modelling.