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.
Highlights
Studies of the growth and form of animal colonies often come to focus on the topic of colony integration [1,2,3]
We developed an artificial food item which can be laced with fluorescent tracers and use to track nutrient absorption
We developed an artificial food pellet that is consumed by P. carnea polyps, largely solubilizes in the gastric cavity of the fed polyp, and can be laced with fluorescent tracer molecules
Summary
Studies of the growth and form of animal colonies often come to focus on the topic of colony integration [1,2,3]. A principal concern is the physiological mechanisms that govern nutrient distribution amongst the tissues of a colony. Polyps capturing food must distribute nutrients to unfed tissues and, in a growing colony, to sites of growth at the colony periphery. The same distribution system must direct nutrients to reproductive polyps. While these problems are shared by all colonial organisms, hydrozoans have been favorable subjects for study of colony integration by virtue of the relative ease with which they can be maintained, and experimented upon, in the laboratory. Our understanding of how nutrients are distributed within hydroid colonies remains incomplete, as the available data are seemingly contradictory
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