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Although most of the studies on the evolution of mimicry and warning signals in insects have considered birds as the main predators, predation by other taxonomic groups, such as insects, may far exceed avian predation at some localities. However, few studies have investigated the possibility that insect predators might facilitate selection for warning colours and mimicry in other insects. We experimentally evaluated whether prey size and/or wasp-like colours and patterns were important in deterring attacks by dragonflies, using pairwise and single presentations of both natural and artificial prey in the field. Dragonflies were more likely to attack smaller natural prey and smaller artificial prey. However, dragonflies showed no differences between attacks on prey with wasp-like colours and patterns and those on the same-sized prey that were nonmimetic. Moreover, dragonflies avoided attacking both mock-painted and black-painted wasps entirely. Overall, we found no evidence to support the hypothesis that wasp-like warning signals protect small insect prey from attack by dragonflies, although size seems to be an important cue in dragonfly prey choice.

The relationship between gregariousness and warning signals in defended species has been the subject of much debate. While previous researchers have found that predators learn to avoid conspicuous unpalatable prey faster when they are in aggregations, they have not presented solitary and aggregated unprofitable prey to predators simultaneously to directly compare their survivorship. Furthermore, no experiment has investigated the influence of profitable prey configuration on predator response to aggregation in unprofitable prey. Here we investigated the response of human, Homo sapiens, predators to profitable and unprofitable prey in a computer version of the ‘novel world’ experiments that addressed these issues. When all prey types were cryptic and all profitable prey were solitary, then aggregated unprofitable prey had higher per capita survivorship than solitary unprofitable prey. In this case, aggregation was the sole reliable distinguishing characteristic of unprofitability. By contrast, when profitable and unprofitable prey could be distinguished in terms of their conspicuousness, then aggregation did not confer a benefit to unprofitable prey. When profitable prey were simultaneously presented in solitary and aggregated configurations, aggregated profitable prey consistently had a lower per capita survivorship than solitary profitable prey, regardless of the configuration of unprofitable prey. We conclude that while aggregation can serve as a signal of unprofitability, it may not be required for the evolution of warning signals. Instead, we suggest that the common association between aggregation and distastefulness may primarily arise for a ‘negative’ reason: the vulnerability of aggregated palatable prey.

Studies of the production of the Δ resonance in hadronic charge exchange reactions show a shift in the Δ peak position. Measurements looking also at the Δ decay products give some evidence for coherent pion production. We have recently completed a new measurement of the 12 C ( p , n ) reaction leading to the Δ resonance, including a higher resolution coincidence measurement of decay π's in the forward direction. We describe the experiment and some aspects of the preliminary analysis.

Measurements of cross sections for pion double exchange (DCX) on 16O at incident pion energies of 180–292 MeV and laboratory scattering angles of 5°–35° have been obtained using EPICS at LAMPF. The angular distributions indicate a shift in the position of the first minimum from that expected for diffractive scattering as a function of energy.

Three different signatures for isoscalar spin transitions in nuclei have been tested in the 12 C( d , d ') 12 C reaction at 400 MeV. These signatures have values of close to zero for the natural parity states, and values ranging from 0.22 to 0.50 for the ΔS =1, ΔT =0, 12.7 MeV state.

Measurements of the spin-flip probability S nn for inclusive inelastic proton scattering around 300 MeV from nuclei between 12 C and 90 Zr show that an enhanced spin response near 40 MeV excitation at q ∼ 100 MeV/ c is a general feature of nuclear structure. Data for 40 Ca at 800 MeV confirm that the enhancement is not a peculiarity of 300 MeV scattering. In addition, measurements in 44 Ca up to 75 MeV show that the enhancement cannot be attributed solely to a relatively narrow resonance. Continuum RPA calculations suggest that the enhancement is due to the exhaustion of most S = 0 strength at lower energy and a shift of S = 1 strength to higher energy.

Adult bullfrogs, Rana catesbeiana , have a pair of scotopic visual pigments: a rhodopsin and a porphyropsin. Partial bleaching experiments performed on rhodopsin and porphyropsin rich retinal extracts from the bullfrog revealed that the absorbance maxima (λ max ) are 499 and 522 nm respectively. The rhodopsin absorbance maximum of 499 nm is slightly lower than the values (i.e. 500–503 nm) previously reported. After subjecting groups of bullfrogs to different light-temperature environments for 40 days, some frogs, when considering the retina as a whole, had predominately rhodopsin, whereas others possessed up to 50% porphyropsin because of the presence of porphyropsin in the dorsal part of the retina. The visual pigment composition in the dorsal (superior one third) part of the retina changed from predominately porphyropsin to predominately rhodopsin in response to specific light and temperature regimes. The ventral part of the retina of these frogs always remained rhodopsin rich. The vitamin A composition (i.e. the relative proportions of vitamin A 2 to vitamin A 1 ) of the associating pigment epithelium was, in most cases, similar to the visual pigment composition (i.e. the relative proportions of porphyropsin to rhodopsin) in both the dorsal and ventral parts of the retina. However, exceptions were found in dorsal retinas of frogs held in constant darkness (for 40 days) and in dorsal retinas which become rhodopsin rich in response to specific light and temperature treatments. In both instances, the vitamin A 2 proportions in the pigment epithelium were higher than the porphyropsin proportions in the retinas. The liver of all frogs had predominately vitamin A 1 . This article provides the first report on a successful attempt to induce changes in the visual pigment and vitamin A compositions in the eyes of an adult amphibian using specific combinations of light and temperatures.

The yellow staae of the American eel. Anguilla rostrata. from fresh and brackish water have mixtures of rhodopsin. P5011 and porphyropsin. P5232 with the latter predominating. Downstream migrants of the silver stage have mixtures of two rhodopsins. P4821 and P5011: and porphyropsin. P5232 the latter in only small amounts. Silver eels, which were more sexually mature and held in seawater. have only the two rhodopsins with P4821 predominating. The results generally agree with those reported for the European eel. A. angiuilla. The biological significance and uniqueness of the change in opsin during metamorphosis is discussed.

Among mammals, birds, most reptiles and chondrichthians, only rhodopsins are present. Among agnathans, osteichthians, amphibians and certain freshwater turtles there are species having only porphyropsins or only rhodopsins or, more interestingly, both pigments, either sequentially or together. This latter grouping represents the paired-pigment species. Associated with the presence of paired-pigments is the possibility that the proportions of rhodopsin and porphyropsin may change. Depending on the characteristics of each paired-pigment species, naturally occurring changes in visual pigment ratios are related to migrations in anadromous and catadromous teleosts and anadromous cyclostomes and to seasonal variation in several teleosts. In addition, the visual pigment composition of certain species of teleosts has been altered by the specific effects of light, temperature, diet and hormones. Of two possible mechanisms for altering spectral sensitivity, varying the proportion of rhodopsin and porphyropsin is far more common than utilizing a single chromophore and changing the opsin. In addition to the long established evidence that extractable rod pigment ratios may change during the life cycle or in response to specific exogenous factors, there is the more recent recognition from microspectrophotometry that cone pigment ratios may also change in concert. The effect of lighting conditions and temperature on the visual pigment composition of certain paired-pigment species is presented.

Microsomes and Golgi fractions were isolated from 13 human liver samples without local malignancy. Binding of insulin to microsomes (per cent per 0.5 mg protein) was 14.4 +/- 7.9% with two classes of receptors: K1 = 1.4 nM, R1 = 0.28 pmol/mg; K2 = 8.1 nM, R2 = 0.62 pmol/mg. The binding was insignificantly lower than in rats. Binding of EGF was only 3.4 +/- 1.7% with two classes of receptors: K1 = 1.4 nM, R1 = 0.06 pmol/mg; K2 = 10.8 nM, R2 = 0.22 pmol/mg; the binding was much lower than in rats (26.3 +/- 5.8%). Binding of insulin to Golgi fraction (per cent per 0.1 mg protein) was 5.5 +/- 0.4% with straight line Scatchard plot; Kd = 5.6 nM, Ro = 3.06 pmol/mg; it was only half of that found in rats. In one case of hepatoma, the binding of insulin to microsomes was normal but that of EGF very low.

This microspectrophotometric (MSP) study has confirmed that goldfish, acclimated under a certain light and temperature regimen, possess mixtures of porphyropsin and rhodopsin in their rod outer segments. Moreover, the MSP spectra from the red, green and blue cones of these acclimated goldfish also shifted to shorter wavelengths from spectra of pure 3-dehydroretinal based visual pigments. Thus, goldfish retinas may possess a total of eight visual pigments (two rod pigments and six cone pigments) instead of four (one rod pigment and three cone pigments). Possibly, a common control mechanism, governed by external conditions, regulates the utilization of retinal and 3-dehydroretinal for the biosynthesis and/or regeneration of visual pigments in both rods and cones.

Recently, the retinas of goldfish from Grassyfork Fisheries (Martinsville, Indiana 46151, U.S.A.) were reported to possess a rhodopsin with an absorbance maximum at 499 nm, in addition to the known porphyropsin. Rhodopsin and porphyropsin are visual pigments respectively derived from the conjugation of vitamin A1 aldehyde (retinal) and vitamin A2 aldehyde (3-dehydroretinal) to a species-specific opsin. In this study, goldfish from a different supplier (Ozark Fisheries, Stoutland, Missouri 65567, U.S.A.) were also confirmed to possess a rhodopsin with an absorbance maximum at 499 nm. In addition, this paper describes how external factors (photoperiod, light intensity, temperature and exogenous thyroxine) affected the composition of these visual pigments in the goldfish retinas and the vitamins A (retinol/3-dehydroretinol) in their pigment epithelium. After 50 days of acclimation, constant illumination (at 30°C with a 7·5 W incandescent light bulb) and constant darkness (at 30°C) both favored high proportions of porphyropsin (more than 85%) whereas fish held under a 16L/8D cycle (at 30°C with a 7·5 W light bulb) had predominately rhodopsin (less than 10% porphyropsin). Testing at 16L/8D and 30°C, light intensities higher and lower than the equivalent of a 7·5 W bulb (i.e. 6×1013 photons/cm2-sec, 400–750 nm, measured at water surface) both favored significantly higher proportions of porphyropsin. Lower water temperature (10°C and 20°C) or the introduction of thyroxine to the tank water (at a concentration of 100 μg l -thyroxine per liter tank water) also resulted in significantly higher proportions of porphyropsin. Despite the influence of these external factors on the visual pigment composition in the goldfish retinas, the vitamins A (retinol and 3-dehydroretinol) in their pigment epithelium remained predominately 3-dehydroretinol. Although the rhodopsin dominated retinas were always associated with pigment epithelium of slightly lowered 3-dehydroretinol proportions, these results do not agree with previous reports on other species where the proportions of retinol and 3-dehydroretinol mirrored the ratios of rhodopsin to porphyropsin.

Tetraiodothyronine ( T 4 ) or triiodothyronine ( T 3 ) injected intraperitioneally into juvenile kokanee (landlocked sockeye salmon), Oncorhynchus nerka , results in a marked increase in the percentage of the retinene 2 based visual pigment when compared to sham injected controls. Controls have predominately retinine 1 based visual pigment. Doses of 100 μg of T 4 cause nearly a complete conversion from retinene 1 to retinene 2 visual pigment i.e. from VP503 1 to VP527 2 . These results are contrary to what has been reported when thyroid hormone is injected into bullfrog tadpoles. Tadpoles have shown an increase in the amount of vitamin A 1 and presumably of the retinene 1 visual pigment when injected with thyroid hormone. The possible implications of the results are discussed in relation to visual pigment conversions that occur in a number of paired pigment species.

The first documented case of prolapse of an ectopic ureterocele and bladder trigone is presented. The differential diagnosis and therapy are discussed.

Two cases of benign bronchoesophageal fistula are presented which are representative of both congenital and acquired forms. The presentation of this relatively rare condition is characterized by recurrent cough especially after drinking liquids and is easily diagnosed by esophagogram. A high index of suspicion is required in all cases of recurrent cough and lung suppuration in order for this condition to be recognized.