Thermal acclimatization and acclimation in the echinoid, Strongylocentrotus droebachiensis (O.F. Müller, 1776).

Percy, J. A. (1971) Thermal acclimatization and acclimation in the echinoid, Strongylocentrotus droebachiensis (O.F. Müller, 1776). Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Thermal adaptation in the sea urchin, Strongylocentrotus droebachiensis, is described both in regard to seasonal acclimatization in the natural habitat, and experimental acclimation in the laboratory under summer-like and winter-like thermal regimes. Intact-animal respiration, in vitro tissue respiration, and righting reflex serve as indicators of physiologic performance. -- Three thermal compensation coefficients, useful for comparative purposes, are proposed. These permit quantitative description of both the magnitude and specific pattern of a given adaptation response. Assumptions, limitations, and potential difficulties associated with use of the coefficients are discussed. -- Regression equations of respiration on weight are presented for summer- and winter-acclimatized urchins. Respiration rates, measured at 0°, 5°, and 10°C, are higher in winter than in summer, indicating substantial acclimatization, but at 15°C summer and winter rates are similar. -- Seasonal acclimatization is also detectable in the respiratory metabolism of several excised tissues, suggesting that increased intact-animal respiration in winter is attributable to augmentation of cellular metabolism, rather than to limitations of oxygen transport in the water vascular system in summer, or to increased efficiency of transport in winter. -- An activity coefficient, based on the righting reflex, is defined and shown to maintain a relatively high rate of activity through the winter. Laboratory studies indicate that acclimation of activity requires 4-5 weeks for completion. -- Acclimatization permits gonad development in autumn and winter, in preparation for spawning in early spring. -- Food consumption has two maxima: in spring and again in autumn. A decline in food consumption in winter appears to be at least partially offset by an increase in feeding efficiency. -- S. droebachiensis exhibits seasonal resistance acclimatization; in summer urchins are able to tolerate short-term exposer to temperature extremes several degrees higher than in winter. -- That annual temperature fluctuations are primarily responsible for inducing seasonal acclimatization is indicated by the demonstration of a compensatory adjustment in the respiration of both intact animals and excised tissues of urchins acclimated for 4-6 weeks in the laboratory at summer-like and winter-like temperatures. -- Ability of S. droebachiensis to adapt to low temperatures is inversely proportional to size. This is demonstrated for metabolism both of intact urchins and of excised tissues. The importance of considering animal size in adaptation studies is stressed. -- In general, metabolism of both intact urchins and excised tissues increases with rising temperature in accordance with the Q₁₀ rule. -- It is concluded that S. droebachiensis exhibits partial adaptation, involving primarily a translation of rate-temperature relationships; as such the response corresponds to Prosser’s (1961) pattern IIa. -- The water content of stomach tissue increases, and that of intestine decreases on cold-acclimation. -- The acclimation of metabolism demonstrable in cell-free intestine homogenates is similar in magnitude and pattern to that observed in relatively undamaged tissue slices. -- The hexosemonophosphate shunt enzyme G-6-P dehydrogenase is present in intestine tissue, although the shunt may not be a major metabolic route in this tissue. The activity of G-6-P dehydrogenase increases on cold-acclimation. Cold-acclimation also results in an increase in sensitivity to the glycolysis inhibitor, iodoacetic acid. These results are consistent with the mechanism of adaptation suggested by the adaptation patterns; namely, that the increase in metabolism is primarily brought about by general augmentation of enzyme activity, with little or no change in the relative contributions of alternate metabolic pathways. -- The possible adaptive significance of both capacity and resistance adaptation in the life of S. droebachiensis is discussed. -- It is suggested that thermal adaptation of S. droebachiensis may be explained by the origin and genetic history of the species.

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