Nutrient Distribution and Absorption in the Colonial Hydroid Podocoryna carnea Is Sequentially Diffusive and Directional

Abstract

The distribution and absorption of ingested protein was characterized within a colony of Podocoryna carnea when a single polyp was fed. Observations were conducted at multiple spatial and temporal scales at three different stages of colony ontogeny with an artificial food item containing Texas Red conjugated albumin. Food pellets were digested and all tracer absorbed by digestive cells within the first 2–3 hours post-feeding. The preponderance of the label was located in the fed polyp and in a transport-induced diffusion pattern surrounding the fed polyp. After 6 hours post-feeding particulates re-appeared in the gastrovascular system and their absorption increased the area over which the nutrients were distributed, albeit still in a pattern that was centered on the fed polyp. At later intervals, tracer became concentrated in some stolon tips, but not in others, despite the proximity of these stolons either to the fed polyp or to adjacent stolons receiving nutrients. Distribution and absorption of nutrients is sequentially diffusive and directional.

Long-term aquaria study suggests species-specific responses of two cold-water corals to macro-and microplastics exposure

“…Alternatively, the M. oculata polyps facing away from the obstacle could share their nutritional resources and/or energy with the other polyps in a more efficient way than does L. pertusa. Colonial organisms have been shown to share their proteins between adjacent and sometimes remote polyps (Buss et al, 2015). However, M. oculata polyps, contrary to L. pertusa, do not exhibit a physical link at the polyp basis, inside the skeleton (Lartaud et al, in press), which opens additional questions regarding the pathways of resource and energy sharing between polyps of a same branch or colony.…”

The Selective Myosin II Inhibitor Blebbistatin Reversibly Eliminates Gastrovascular Flow and Stolon Tip Pulsations in the Colonial Hydroid Podocoryna carnea

“…The pace of recovery was surprising, since recovery in studies of bilaterian systems is rapid [ 26 ]. We suspect this finding reflects the fact that stolon tips in athecate hydroids are not continuously active [ 11 , 35 ], which implies the existence of a mechanism governing whether a tip is active or inactive. We hypothesize that a tip once silenced may require some latency period before resuming activity.…”

“…The observation that gastrovascular flow was observed in the isolated stolon experiments is of importance for a second reason. In intact colonies gastrovascular flow is driven by the contractions of polyps [ 6 , 8 , 11 ]. The fact that severed stolons, which lack polyps, can also drive gastrovascular flow and that the onset of this flow follows the onset of tip pulsations is consistent with prior suggestions that tip pulsations trigger stolonal axial muscles [ 11 , 24 ].…”

“…In intact colonies gastrovascular flow is driven by the contractions of polyps [ 6 , 8 , 11 ]. The fact that severed stolons, which lack polyps, can also drive gastrovascular flow and that the onset of this flow follows the onset of tip pulsations is consistent with prior suggestions that tip pulsations trigger stolonal axial muscles [ 11 , 24 ]. Communication between tips and axial muscles is presumably neuronal, as nerves have recently been localized to proximal regions of the stolonal tip gastroderm [ 24 ].…”

“…Two movements with different functions are known. When fed, a polyp begins a series of contractions that act to drive fluids into the gastrovascular system where nutrients are subsequently absorbed [ 7 – 11 ]. Another set of movements characterize stolon tips and polyp buds.…”