Metabolic Activation and Scaling in Two Species of Colonial Cnidarians
Almegbel, Maram Nasser . 2019
Abstract. Metabolic activation can have a profound impact, for instance, by more than compensating for the lower resting metabolic rates of large organisms compared to smaller ones. In some animals, activity can easily be judged by the rate of muscle-driven movement. In sessile organisms, however, judging activity is less straightforward, although feeding often results in metabolic activation. Two colonial cnidarians were examined in this context, using entirely lab-grown material to remove any artifactual effects of experimental manipulations. Hydractinia symbiolongicarpus is a carnivorous hydroid that uses active muscular contractions to drive its gastrovascular fluid. Sympodium sp., on the other hand, is an octocoral that hosts photosynthetic Symbiodinium and uses cilia to propel its gastrovascular fluid. Measures of oxygen uptake indicated that feeding activated metabolism in H. symbiolongicarpus. While lighttreatmenthadnoeffecton subsequent dark metabolism in Sympodium sp., stress activated metabolism to an extent comparable to H. symbiolongicarpus. In both taxa, different individual size measures or synthetic size measures derived from principalcomponent analysis produced different scaling relationships between metabolism and size. On balance, the data suggest that scaling was negatively allometric in Sympodium sp. and nearly isometric in H. symbiolongicarpus; yet metabolic activation was comparable in the two species. Regardless of the size measure used, active and resting colonies of H. symbiolongicarpus exhibited similar scaling relationships. Colonial animals may lack the large difference between resting and active metabolic rates found in Received 1 October 2018; Accepted 29 March 2019; Published online 24 June 2019. * To whom correspondence should be addressed. Email: neilb@niu.edu. Abbreviations: PC1, first principal component; PCA, principal component analysis; SDA, .specific dynamic action. 63 highly active animals, and this may be related to how their metabolism scales with size
Abstract. Metabolic activation can have a profound impact, for instance, by more than compensating for the lower resting metabolic rates of large organisms compared to smaller ones. In some…