Adaptive phenotypic plasticity in juvenile Scyphomedusae facilitates effective animal-fluid interaction

Abstract

Phenotypic plasticity enables animals to respond rapidly to environmental changes. Predictions of ecosystem dynamics in times of perturbation, such as climate change, need to take into account the varying capacity for such short-term adaptations among species. However, it is often difficult to evaluate whether morphological change in response to external factors has a functional benefit or merely constitutes abnormal growth. This is because modifications in animal shape might affect a range of behaviors and thus impede straightforward conclusions on overall fitness. Further, the physical impact of environmental change on a given organism can be difficult to establish. We investigate phenotypic plasticity in juvenile Scyphomedusae ("jellyfish"), as these animals display stereotypic swimming and feeding behaviors enabling us to assess fitness based on their performance. Further, the radial bauplan facilitates the use of methods adapted from fluid dynamics to visualize changes in animal-fluid interaction. We report that ontogenetic morphogenesis in Scyphomedusae responds to changes in water temperature in a way that facilitates effective animal-fluid interaction. In particular, altered proportional growth was found to exploit the increased viscosity of colder water by utilizing adhering water boundary layers as "paddles", effectively replacing tissue. This effect was documented by flow field visualization and further confirmed by behavioral assays of swimming performance. Our study suggests that phenotypic plasticity in juvenile Scyphomedusae allows for functional adaptation to ambient water temperature, a potential mechanism leading to robustness of Scyphozoan jellyfish populations to altered ocean temperature distributions.

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