Recent developments concerning the nature of bivalve filter feeding are reviewed and interpretations of data are examined. No convincing evidence was found for: (1) a function of mucus in the normal feeding mechanism; (2) sorting of suspended particles according to food value; (3) low rates of water processing in nature; (4) physiological control of water pumping and filtration efficiency according to nutritional needs. Recent findings are consistent with the view that the capacity for water processing is evolutionarily adapted to the concentrations of suspended food, primarily phytoplankton. that prevail in the biotope during the productive seasons of the year. 'Scope for growth', computed from measurements of the energy balance parameters, is extensively used to assess effects of environmental factors, including pollutants, on the physiology and energetlcs, particularly of mussels. Estimates tend, however, to underrate the values they are believed to reflect due to neglect of negative effects of the experimental conditions on the filter-pump. Possible effects of the experimental conditions on filtration rates should therefore be established before a calculated 'scope for growth' can be extrapolated to the habitat whlch the experiment simulates.
The relations between nutritional state and vitellogenic growth of oocytes were studied in 87 sexually mature female toads Bufo bufo during the postbreeding season before initiation of the next annual ovarian cycle. Recruitment of small oocytes to vitellogenic growth was correlated with resumption of food uptake and the restoration of a positive energy balance in the toads that had become depleted of energy reserves during hibernation and breeding. Treatment with exogenous gonadotropin (hCG) immediately initiated vitellogenic growth, independently of the nutritional state. But the hCG-induced vitellogenic growth was faster in toads that ate more than the maintenance ration than in those that ate less. hCG also maintained rapid vitellogenic growth in toads that starved after an initial period of feeding during which vitellogenic growth had been resumed. The results support the hypothesis that the period of ovarian quiescence, which normally follows breeding in Bufo bufo, and other anurans from the northern range of distribution of the species, results from inactivation of the hypothalamic-hypophysial gonadotropic system, and that reactivation of the system depends upon reestablishment of a proper nutritional state of the organism.
Summary.
When frogs in water are transferred from room temperature to low temperatures, e.g. 2–3° C, the body water increases rapidly in amount until a new equilibrium is established within some few days. Further weight increase, e.g. increase in body water may occur at a low rate. This slow working part of the water retention goes parallel to a salt accumulation brought about by active uptake of NaCl through the skin from the surrounding water.
Injected water is also rapidly eliminated by the kidneys in frogs living at low temperatures. Salt administered in form of hypertonic solution of NaCl is, however, not eliminated by the kidneys. The water and salt accumulation demonstrated in frogs at low temperatures is therefore probably caused by an inability of the kidney to excrete the salt taken up through the skin, the resulting hypertonicity of the blood being counteracted by retention of some of the water entering through the skin.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.