Lewis Greenwald

Sparrows and a brushpile: Foraging responses to different combinations of predation risk and energy cost

Abstract Our observations of wintering house sparrows ( Passer domesticus ) feeding on cracked corn at feeders placed at different distances from a brushpile and in positions differentially exposed to the wind supported the hypothesis that where food patches are equal in net energy return, foragers use the one furnishing the most protection from predation. Results reinforced the hypothesis that when food sources furnish equal protection from predators, homeotherms below their lower critical temperature use the one providing the largest net energy return. When the sparrows had available both a colder, safer feeding site and a warmer, riskier one, they frequented both over the course of the winter and, as predicted, their use of the colder, safer site was negatively correlated with wind velocity and positively related to temperature and solar radiation. In this last case, it appeared the birds decided where to feed on the basis of some threshold difference between metabolic rates at the colder, safer site and the warmer, riskier location.

Energetics and osmoregulation in the catfish, Ictalurus nebulosus and I. Punctatus

1. 1. Groups of brown bullhead catfish (Ictalurus nebulosus) and channel catfish (I. punctatus) were acclimated to different concentrations (6, 120, 200 mOsm/kg) of either diluted artificial seawater (DASW) or MgSO4 solutions in order to derive the metabolic costs of osmotic and ionic regulation in fresh water. 2. 2. Oxygen consumption declined when the osmotic and/or ionic gradient between the external medium and internal body fluids decreased. In the DASW solutions the reductions were 16.8% and 28.6% in the 120 and 200 mOsm/kg solutions, whereas in MgSO4 solutions the reductions were 13.2% and 27.1%, respectively, indicating that the cost of living in a dilute medium is largely that of osmotic regulation. 3. 3. Both urine flow rate and glomerular filtration rate (GFR) decreased greatly (83 % and 93 % in the 200 mOsm/kg DASW amd MgSO4 solutions, respectively) as the medium concentration decreased. 4. 4. We propose that the major portion of the measured decreases in oxygen consumption is a result of the reduction in the active reabsorption of Na+ and K+ by the kidney due to the reduced GFR.

The structure of the chambered nautilus siphuncle: The siphuncular epithelium

The siphuncle of the chambered nautilus (Nautilus macromphalus) is composed of a layer of columnar epithelial cells resting on a vascularized connective tissue base. The siphuncular epithelium taken from chambers that have not yet begun to be emptied of cameral liquid has a dense apical brush border. The great number of apical cell junctions (zonula adherens) compared to the number of nuclei suggests extensive interdigitation of these cells. The perinuclear cytoplasm of these preemptying cells is rich in rough endoplasmic reticulum. The siphuncular epithelium of both emptying and “old” siphuncle (which has already completed emptying its chamber) both show little rough endoplasmic reticulum but do contain extensive systems of mitochondria‐lined infoldings of the basolateral plasma membranes. Active transport of NaCl into the extracellular space of this tubular system probably entrains the water transport involved in the chamber‐emptying process. Both emptying and old siphuncular epithelium also show large basal infoldings (canaliculi) continuous with the hemocoel, which appear to be filled with hemocyanin. The apical cell junctions of emptying and old siphuncular epithelium contain septate desmosomes that may help to prevent back‐flow of cameral liquid into the chambers.

Chamber refilling in Nautilus

Freshly captured Nautilus macromphalus were observed to place new cameral liquid into emptied or partially emptied chambers, both at the surface and at 250 m, in response to sudden buoyancy increase. The sudden addition of buoyancy was accomplished either through removal of cameral liquid from chambers, removal of shell material from the apertural region of the body chamber, or by cementing buoyant corks on the sides of the shell. A maximal refilling rate of 100 μ l/h was observed. The osmolality of refilled cameral liquid was observed to match closely the osmolality of the original cameral liquid. The refilling mechanism allows Nautilus to regain neutral buoyancy after sudden buoyancy gain, such as could be expected to occur from shell loss due to predatory attack on the Nautilus , or from shell breakage.

Effects of dehydration on the urine concentration and salt gland secretion of the green sea turtle

Abstract 1. 1. Urine of normally hydrated green turtles was isosmotic relative to plasma (320 mOsm/kg). 2. 2. Green turtles kept out of water for 10–20 days produced urine with a mean concentration of 450 mOsm/kg; plasma concentration for these animals was 390 mOsm/kg. 3. 3. Mean urine composition of dehydrated animals was 16 mmol/1 Na + , 38 mmol/l K + , 2.4 mmol/1 Ca 2+ , 74 mmol/1 NH 3 , 5.8 mmol/1 Cl − and 34 mmol/1 urea. The balance of the urine composition presumably consists of unknown organic anions. 4. 4. Salt gland secretions were composed primarily of sodium and chloride ions and had a mean concentration of 1845 mOsm/kg for dehydrated animals; normally hydrated animals had a mean concentration of 768 mOsm/kg.

Physiological Responses of Lake Erie Freshwater Drum to Capture by Commercial Shore Seine

Abstract Physiological changes associated with pronounced capture stress in freshwater drum (Aplodinotus grunniens) were studied. Increasing the exposure of exercised freshwater drums to low-oxygen water resulted in increasing degrees of skin reddening and partial hemolysis in blood samples. Artifacts associated with blood sampling by heart puncture did not cause hemolysis, nor did a loss of Na+ and Cl− ions or an influx of water into the blood. Blood from freshwater drums that were severely distressed by seine capture showed no significant changes in hematocrit and plasma Na+ and Cl− concentrations, compared to fish that were exercised to near exhaustion by capture but were only briefly exposed to low oxygen. After 40 minutes of forced exercise in a low-oxygen aquarium freshwater drums lost equilibrium and had extensive skin reddening, symptoms also observed in freshwater drums that were captured in a commercial shore seine. Blood from cannulated freshwater drums that were exhausted in the laboratory sho...