Biological Coevolution

Abstract: Generalist bacterial predators are likely to strongly shape many important ecological and evolutionary features of microbial communities, for example by altering the character and pace of molecular evolution, but investigations of such effects are scarce. Here we report how predator-prey interactions alter the evolution of fitness, genomes and phenotypic diversity in coevolving bacterial communities composed of Myxococcus xanthus as predator and Escherichia coli as prey, relative to single-species controls. We show evidence of reciprocal adaptation and demonstrate accelerated genomic evolution specific to coevolving communities, including the rapid appearance of mutator genotypes. Strong parallel evolution unique to the predator-prey communities occurs in both parties, with predators driving adaptation at two prey traits associated with virulence in bacterial pathogens—mucoidy and the outer-membrane protease OmpT. Our results suggest that generalist predatory bacteria are important determinants of how complex microbial communities and their interaction networks evolve in natural habitats. Predator-prey coevolution is expected to hasten evolutionary rates, but this is difficult to test in long-lived species. Here, the authors report consequences of experimental coevolution between bacterial predators and prey, including accelerated molecular evolution and parallel genomic and phenotypic adaptation.

Abstract: Trade-offs play an important role in evolution. Without trade-offs, evolution would maximize fitness of all traits leading to a “master of all traits”. The shape of trade-offs has been shown to determine evolutionary trajectories and is often assumed to be static and independent of the actual evolutionary process. Here we propose that coevolution leads to a dynamical trade-off. We test this hypothesis in a microbial predator–prey system and show that the bacterial growth-defense trade-off changes from concave to convex, i.e., defense is effective and cheap initially, but gets costly when predators coevolve. We further explore the impact of such dynamical trade-offs by a novel mathematical model incorporating de novo mutations for both species. Predator and prey populations diversify rapidly leading to higher prey diversity when the trade-off is concave (cheap). Coevolution results in more convex (costly) trade-offs and lower prey diversity compared to the scenario where only the prey evolves. How a trait evolves depends on the shape of its fitness trade-off. Here, Huang et al. demonstrate evolution of trade-off shape in an experimental predator-prey system and develop a mathematical model of trait evolution when the underlying trade-off can also evolve.

Abstract: Ecosystems are complex food webs in which multiple species interact and ecological and evolutionary processes continuously shape populations and communities. Previous studies on eco-evolutionary dynamics have shown that the presence of intraspecific diversity affects community structure and function, and that eco-evolutionary feedback dynamics can be an important driver for its maintenance. Within communities, feedbacks are, however, often indirect, and they can feed back over many generations. Here, we studied eco-evolutionary feedbacks in evolving communities over many generations and compared two-species systems (virus-host and prey-predator) with a more complex three-species system (virus-host-predator). Both indirect density- and trait-mediated effects drove the dynamics in the complex system, where host-virus coevolution facilitated coexistence of predator and virus, and where coexistence, in return, lowered intraspecific diversity of the host population. Furthermore, ecological and evolutionary dynamics were significantly altered in the three-species system compared with the two-species systems. We found that the predator slowed host-virus coevolution in the complex system and that the virus' effect on the overall population dynamics was negligible when the three species coexisted. Overall, we show that a detailed understanding of the mechanism driving eco-evolutionary feedback dynamics is necessary for explaining trait and species diversity in communities, even in communities with only three species.

Abstract: Male intromittent organs are exceedingly diverse, yet we know comparatively little about female genital diversity. However, the most direct mechanical interaction between males and females occurs during copulation, and therefore, genital coevolution is expected to be widespread. This means that diversification of male structures must influence diversity of female genital features and vice versa. As we expand our understanding of coevolutionary interactions between the sexes, we need to expand our knowledge of three basic areas: First, we need quantitative data, on morphological variation of female genitalia. Second, we need to study the mechanics of copulatory interactions, and third, we need to use this understanding to determine which features of genital morphology are under selection, and how their variable morphology and function may affect fitness. Though studying coevolution is certainly difficult, this knowledge is crucial to our understanding of diversity in morphology of the male intromittent organ.