Energetic costs of loss and regeneration of arms in stellate echinoderms.

Loss of arms has energetic consequences for stellate echinoderms (crinoids, ophiuroids, and asteroids). The energetic cost of losing an arm includes loss of investment, decrease in ability to obtain nutrients and allocation of nutrients to regeneration of the lost arms at a cost to other body compartments. The cost to other body compartments is low when food availability is very low or very high. The cost becomes apparent when food availability is sufficient to support production but not high enough that the cost of regeneration has no effect on production of other body compartments. Loss of investment is greater in asteroids than in crinoids and ophiuroids because of greater development of the body wall and presence of gonads and pyloric caeca in the arms. The cost of regeneration of organic matter in an arm can be estimated from the amount of organic matter present in intact arms and the cost of anabolism. Protein production is the primary cost of regeneration of an arm because of the high concentration of protein in the regenerated arm and the high anabolic cost of protein production. A major energetic cost of loss of arms that affects regeneration is decrease in food consumption. It is necessary to separate cost of decrease in consumption from cost of regeneration. Comparison of intact and regenerating individuals requires they consume the same amount of food. The cost of regeneration will also be affected by the quality of food because of the nutrient requirements for growth. Because the quantity and quality of the food ingested is not known, it is not possible to quantify the cost of regeneration in the field. Asteroids appear to be a good model for the study of regeneration in the laboratory because it is possible to control the quantity and quality of food they ingest. They are also a good model for the study of the evolutionary significance of regeneration by comparing individuals that have lost arms and are regenerating them to those that have lost arms and are not. The difference in the frequency of loss of arms of species is related to the difference in availability of food and the ability to feed that affect the capacity for re-investment in the lost arm. This is important in considering life-history strategies.