Analysis of self-overlap reveals trade-offs in plankton swimming trajectories

Abstract

Movement is a fundamental behaviour of organisms that not only brings about beneficial encounters with resources and mates, but also at the same time exposes the organism to dangerous encounters with predators. The movement patterns adopted by organisms should reflect a balance between these contrasting processes. This trade-off can be hypothesized as being evident in the behaviour of plankton, which inhabit a dilute three-dimensional environment with few refuges or orienting landmarks. We present an analysis of the swimming path geometries based on a volumetric Monte Carlo sampling approach, which is particularly adept at revealing such trade-offs by measuring the self-overlap of the trajectories. Application of this method to experimentally measured trajectories reveals that swimming patterns in copepods are shaped to efficiently explore volumes at small scales, while achieving a large overlap at larger scales. Regularities in the observed trajectories make the transition between these two regimes always sharper than in randomized trajectories or as predicted by random walk theory. Thus, real trajectories present a stronger separation between exploration for food and exposure to predators. The specific scale and features of this transition depend on species, gender and local environmental conditions, pointing at adaptation to state and stage-dependent evolutionary trade-offs.

Distinctive diffusive properties of swimming planktonic copepods in different environmental conditions

“…The reduction of D b with the concentration of food may be considered as a metabolic energy-saving mechanism that, coupled with the swimming dependent encounter rate with prey 41 , supports the successful development of C. furcatus populations in oligotrophic conditions 18 . In addition, the plateau in the MSD (localized regime) parallels the transition in the number of crossovers occurring at scales typical of the shift from prey/mates to predator encounter 26 . The volume of the localization region may be related to the concentration of food through a conservative mechanism, such as (ρ f λ 3 p ) α const.…”

“…We speculate that in the presence of food, C. furcatus explores a limited region by continuous looping (mostly in the horizontal plane) 6 , reducing path crossovers at the small scale to increase the encounter with prey 26 . By contrast, the diffusive behaviour at the large scale associates with high crossovers 26 , likely ensuring reduced encounters with predators.…”

“…We speculate that in the presence of food, C. furcatus explores a limited region by continuous looping (mostly in the horizontal plane) 6 , reducing path crossovers at the small scale to increase the encounter with prey 26 . By contrast, the diffusive behaviour at the large scale associates with high crossovers 26 , likely ensuring reduced encounters with predators. The reduction of D b with the concentration of food may be considered as a metabolic energy-saving mechanism that, coupled with the swimming dependent encounter rate with prey 41 , supports the successful development of C. furcatus populations in oligotrophic conditions 18 .…”

Turbulence triggers vigorous swimming but hinders motion strategy in planktonic copepods

“…In copepods, they reflect an optimized trade-off between beneficial encounters with resources and mates and dangerous meetings with predators [49]. Therefore, we investigated the extent to which copepods can maintain the optimal diffusive properties of their behaviour in the presence of unpredictable, turbulence-imposed constraints on their movement.…”

Motilidade da associação entre uma diatomácea cêntrica e um ciliado peritríquio e suas possíveis consequências ecológicas

“…O deslocamento de um organismo é definido como a mudança de sua posição espacial em um intervalo de tempo (Schmitt & Seuront, 2001;Nathan, 2008). A capacidade de movimento é um fenômeno que influencia as interações entre os indivíduos, incluindo a probabilidade de acasalamento, a interação presapredador, assim como amplia a probabilidade de os organismos encontrarem condições adequadas, como alimento, temperatura e luminosidade (Crenshaw, 1996, Nathan, 2008, Bianco et al, 2014.…”