Evolution in interacting species alters predator life-history traits, behaviour and morphology in experimental microbial communities

Abstract

Predator–prey interactions heavily influence the dynamics of many ecosystems. An increasing body of evidence suggests that rapid evolution and coevolution can alter these interactions, with important ecological implications, by acting on traits determining fitness, including reproduction, anti-predatory defence and foraging efficiency. However, most studies to date have focused only on evolution in the prey species, and the predator traits in (co)evolving systems remain poorly understood. Here, we investigated changes in predator traits after approximately 600 generations in a predator–prey (ciliate–bacteria) evolutionary experiment. Predators independently evolved on seven different prey species, allowing generalization of the predator's evolutionary response. We used highly resolved automated image analysis to quantify changes in predator life history, morphology and behaviour. Consistent with previous studies, we found that prey evolution impaired growth of the predator, although the effect depended on the prey species. By contrast, predator evolution did not cause a clear increase in predator growth when feeding on ancestral prey. However, predator evolution affected morphology and behaviour, increasing size, speed and directionality of movement, which have all been linked to higher prey search efficiency. These results show that in (co)evolving systems, predator adaptation can occur in traits relevant to foraging efficiency without translating into an increased ability of the predator to grow on the ancestral prey type.

Effects of phenotypic variation on consumer coexistence and prey community structure

“…In our experiment, high trait variability increased the median prey clearance of the ciliate while also increasing the relative variability of prey clearance. For example, the HTV ciliate was a less efficient forager than the LTV ciliate for some key species (e.g., Myroides odoratus 1923), which likely reflects foraging trade-offs resulting from specific evolved responses in the HTV ciliate consumer[27]. However, high trait variability increased ciliate foraging efficiency for other abundant (> 1%) prey species that were also preferentially grazed by the nematode.…”

“…S6). The most defended prey species were less abundant with the HTV ciliate than with the LTV ciliate, presumably because the HTV ciliate was better adapted to consume these prey species[17, 27]. However, biofilm-forming prey species were more abundant with the HTV ciliate, potentially because it was poorly adapted to consuming prey biofilms.…”

“…These competitive differences likely reflect consumer foraging specificity, but may also be related to other life history traits. For example, ciliate individuals from the HTV populations were, on average, 40 μ m larger, 1.25× faster, and turned less often than isogenic, LTV ciliate individuals[27]. These offensive traits likely altered the sensitivity of both consumers to interspecific competition which altered mean competitive differences.…”

“…Only one of the bacterial species from the co-evolution experiment ( Comamonas testosterone 0403) was included in the experimental prey community. These HTV ciliate populations each displayed altered phenotypic traits related to predation, including increased swimming speed, straighter swimming trajectories, and increased body size [27].…”

“…Clones were then grown in 5% King’s Broth (KB) until mid-log phase and cell densities (colony forming units) determined via plating on 50% PPY agar. Ciliates were revived from liquid nitrogen and cultured axenically at room temperature in PPY as described before[27, 57]. 50 ml of each revived ciliate culture was harvested by centrifugation (8 minutes, 3300 rpm, 4°C), then the cell pellet was resuspended in 25 ml M9 buffer.…”