Laakso, J. | Search bioRxiv

bioRxiv2021

Infective prey leads to a partial role reversal in a predator-prey interaction

An infective prey has the potential to infect, kill and consume its predator. Such a prey-predator relationship fundamentally differs from the classical Lotka-Volterra predator-prey premise because the prey can directly profit from the predator as a growth resource. Here we present a population dynamics model of partial role reversal in the predator-prey interaction. We parametrize the model to represent the predator-prey interaction of sea cucumber Apostichopus japonicus and bacterium Vibrio splendidus. We observe that two major factors stabilize the predator-prey interaction. First, the partial role reversal in the predator-prey community stabilizes the predator-prey interaction. Second, if the predator is a generalist and follows the type I functional response in attacking the prey, the predator-prey interaction is stable. We also analysed the conditions for species extinction. The extinction of the prey, V. splendidus, may occur when its growth rate is low, or in the absence of infectivity. The extinction of the predator, A. japonicus, may follow if either the infectivity of the prey is high or a moderately infective prey is abundant. We conclude that partial role reversal is an underestimated subject in predator-prey studies.

ecology↗

bioRxiv2020

Rich resource environment of fish farms facilitates phenotypic variation and virulence in an opportunistic fish pathogen

Phenotypic variation allows adaptation of opportunistic pathogens to variable conditions in the outside-host environment with strong effects on their epidemiology and pathogenicity in hosts. Here we found that the isolates of an opportunistic fish pathogen Flavobacterium columnare from fish farming environment had higher phenotypic variation between two morphotypes in growth, as compared to the isolates from the natural water environment. The rough morphotypes had higher growth rate than the rhizoid morphotypes especially in the higher resource concentrations and in the higher temperature, but only if the isolate was originating from the fish farms. Rhizoid morphotype was more virulent than the rough type regardless of their origin. However, the virulence of the rough type increased sharply with the size of the fish, and the bacterial isolates from the gills of diseased fish were rhizoid type, indicating a reversal of the rough morphotype into rhizoid in contact with the fish. The high growth rate of the rough morphotype combined with the morphotype reversibility could increase the probability of columnaris epidemics at fish farms. Our findings suggest that intensive farming imposes different selection pressures on bacterial survival in the outside-host environment and its transmission compared to the natural water environment.

microbiology↗