Intra- and Interspecific Prey Theft in Cicada Killers (Hymenoptera: Apoidea: Sphecius).

We studied prey theft in two cicada killer aggregations: Ruby, Arizona (Sphecius convallis Patton) and Easton, Pennsylvania (Sphecius speciosus Drury). Many prey (Tibicen parallelus Davis [Hemiptera: Cicadidae]) were stolen from S. convallis by kingbirds and Greater Roadrunners at Ruby. Seventy percent of kingbird attacks on provisioning wasps were successful. Using sand-filled trap nests baited with a cicada, we tested the hypothesis that conspecific females might kleptoparasitize by laying an egg on the cicada and closing the nest cell. At Ruby, 45% were so appropriated, and at Easton, 52%. Easton data showed that the longer a nest cell was left open, the higher the rate of kleptoparasitism. Hence, intraspecific kleptoparasitism likely occurs at high rates in both populations. Not needing to dig a burrow, or to hunt, capture, and carry a paralyzed cicada favors intraspecific kleptoparasitism in cicada killers. Low cicada availability and intense avian kleptoparasitism of cicada killers may intensify selection pressure for this behavior at the Arizona site. Pirating cicadas may be the only viable reproductive outlet for females that are small or in environments with few prey. We suggest that provisioned nest cell kleptoparasitism may have evolved in cicada killers as an alternative strategy to standard provisioning, given the dual uncertainties of adult body size and prey availability.

High Ammonia and Low pH in the Urine of the Ghost Crab, Ocypode quadrata.

Nitrogen excreted into the urine (<1 mM) has generally been considered a negligible component of total nitrogen output of crustaceans. But concentrations of ammonia >100 mM were found in the urine of laboratory-held Ocypode quadrata, suggesting that this notion might not be applicable to all crustaceans. To address this issue, hemolymph and urine were removed from freshly captured O. quadrata and analyzed for nitrogenous catabolites and major ions. Hemolymph composition was similar to that of other crustaceans, but the urine was acidic ({Xbar} pH = 5.50) and contained ammonia, often at >100 mM. Other nitrogenous catabolites in the urine (urea, amino acids, and uric acid) were much less concentrated: totaling <12 mM on average. The ionic composition of the urine was similar to that of other crustaceans, with the exception that Na was much less concentrated than Cl-. Total osmolality of hemolymph and urine was similar. The Na+/K+ ATPase activity was greater in the antennal glands than in the posterior gills of O. quadrata, suggesting that this enzyme is important for ammonia concentration and Na resorption. This pattern of enzyme activity was not present in two terrestrial brachyurans whose urine contains little ammonia. The evolutionary significance of high ammonia concentrations in the urine of ghost crabs is unclear.

Organic cation secretion by Cancer borealis urinary bladder.

In the crab, Cancer borealis, initial clearance studies showed a potent renal excretory system for the model organic cation, tetraethylammonium (TEA). TEA clearance averaged 145 +/- 32 ml/day, which was 18 times the paired polyethylene glycol clearance. TEA uptake by slices of urinary bladder was concentrative, saturable, inhibitable by N1-methylnicotinamide chloride, and dependent on glycolytic, but not oxidative, metabolism. When mounted in flux chambers, bladders exhibited a large net secretory flux. For 0.1 mM TEA, the ratio of secretory to reabsorptive fluxes was 65. Urinary bladders from another crab, Cancer irroratus, and a lobster, Homarus americanus, also exhibited net TEA secretion. In C. borealis bladder, secretory transport was concentrative, saturable, and nearly abolished by addition of 1 mM quinine to the serosal bath. Reabsorptive transport was not concentrative and was not reduced by luminal quinine. The data are consistent with a secretory pathway that is transcellular and mediated by carriers at both the serosal and luminal membranes.

PAH excretion in two species of cancroid crab Cancer irroratus and C. borealis.

To determine the characteristics of p-aminohippuric acid (PAH) excretion in Cancer irroratus and C. borealis, crabs were given a single injection of radiolabeled PAH and polyethylene glycol (PEG), and serum, urine, tissue, and seawater concentrations of each were measured over the next 6 days. In both species, PEG clearances averaged 5-10 ml serum/day; serum PAH concentrations fell exponentially after a 1-day equilibration period. In C. irroratus, urine PAH rose over the first 2 days and then fell; during days 2-6, mean urine PAH averaged two to four times mean serum PAH. In C. borealis, urine-to-serum ratios for PAH were 20-40 during days 2-6. PAH-to-PEG clearance ratios exceeded unity in both species, with ratios in C. borealis about three to six times those in C. irroratus. Tissue distribution data showed that C. irroratus midgut gland accumulated up to 50% of injected PAH, with gland-to-serum concentration ratios of 15-45; in this species, stomach fluid-to-serum PAH concentration ratios averaged 87, and nonurinary routes accounted for more than half of excreted PAH. In C. borealis, midgut gland-to-serum ratios never exceeded 2, and the urinary routes accounted for all excreted PAH. Thus, in C. irroratus, injected PAH accumulated in the midgut gland, with slow excretion through renal and nonrenal routes; in C. borealis, PAH remained in hemolymph, and only the renal route of excretion was utilized.

PAH secretion in the urinary bladder of a crab Cancer borealis.

Uptake of 10 microM p-aminohippuric acid (PAH) by sections of Cancer borealis urinary bladder was concentrative, saturable (Km 67 microM, Vmax 1.7 nmol.mg tissue-1.h-1), inhibitable by other organic anions, and dependent on medium Na and glycolytic metabolism. Bladders mounted in flux chambers exhibited net secretory transport of PAH, with serosa-to-lumen fluxes (Js leads to l) being about 4 times lumen-to-serosa fluxes (Jl leads to s). In 60-min flux chamber studies, tissue-to-medium ratios exceeded unity with serosal, but not luminal, PAH. Initial (10 min) fluxes and tissue accumulations (Ac) were measured in the absence and presence of 1-5 mM BCG (bromocresol green; competitor organic anion). With serosal PAH, serosal BCG (1 mM) reduced serosa-to cell flux (Js leads to c), Ac, and Jc leads to l by 60-75%. With luminal PAH, luminal BCG (1 mM) had no effect on Jl leads to c, Ac, or Jc leads to s; increasing the luminal BCG concentration to 5 mM reduced Jl leads to c, Ac, and Jc leads to s by 40-50%. The data are consistent with a model featuring an inwardly directed pump on the serosal membrane, cellular accumulation, and a facilitated carrier on the luminal membrane.

PAH transport in rock crab urinary bladder. II. Luminal and serosal steps.

To characterize the organic anion transport properties of the luminal (1) and serosal (s) membranes of crab urinary bladder, initial (10 min) fluxes (J) and tissue accumulations (Ac) of 10 microM PAH were measured in the absence and presence of 1 mM BCG (nontransported, high-affinity competitor). Control bladders exhibited net reabsorptive transport with a mean Jl leads to s/Js leads to 1 of about 7; concentrative transport of p-aminohippuric acid (PAH) occurred only across the luminal cell (c) membrane. With luminal PAH, luminal bromocresol green (BCG) reduced Jl leads to c, Jc leads to s, and Ac by about 85%; serosal BCG reduced Jc leads to s, increased Ac but had no effect on Jl leads to c. With serosal PAH, serosal BCG reduced Js leads to c, Jc leads to l, and Ac; luminal BCG had no effects on either fluxes or tissue accumulation. When bladder sheets were loaded with radiolabeled PAH, mounted in a chamber, and exposed to flowing crab Ringer solution on both sides, Jc leads to s was nearly twice as large as Jc leads to l; BCG significantly reduced Jc leads to s but not Jc leads to l. With unlabeled PAH in the efflux media, Jc leads to s was increased. The data are consistent with a model featuring an inwardly directed pump at the luminal membrane, a facilitated carrier at the serosal membrane, and nonmediated pathways at both membranes.

PAH transport in rock crab (Cancer irroratus) urinary bladder.

Crab urinary bladder appears to possess several morphological and functional similarities to vertebrate renal proximal tubule. Sections of intermolt rock crab bladder accumulated PAH by a process that was concentrative (60 min tissue-to-medium ratio (T/M) for 10 microM PAH averaged 24), Na dependent, powered by glycolytic metabolism, and inhibitable by other organic anions. Initial section uptakes exhibited saturation kinetics and a double-reciprocal plot of uptake vs. concentration yielded a single line with a Km of 70 microM and a Vmax of 5 nmol . mg tissue-1 . h-1. Chlorophenol red and bromocresol green (BCG) competitively inhibited PAH uptake. When bladder sheets were mounted in a flux chamber, they exhibited a large, net lumen-to-serosa (L leads to S) flux of 10 microM PAH that was abolished by 1 mM BCG. The small unidirectional S leads to L flux was not BCG-inhibitable. Bladder sheets exhibited PAH T/M greater than 1 after luminal, but not serosal, exposure. BCG only reduced bladder sheet T/M after luminal exposure. The data are consistent with uphill, Na-dependent, and carrier-mediated entry of PAH at the luminal membrane and nonmediated exit at the serosal membrane.