Observations on myiasis by the calliphorid,Bufolucilia silvarum,in the eastern American toad (Bufo americanus americanus) from southeastern Wisconsin

Larvae of certain species of blowflies (Calliphoridae) cause myiasis in amphibians which may result in significant mortality, yet there are few reports from North America. In this study, we observed primary myiasis in a population of juvenile eastern American toads (Bufo americanus americanus) collected during May-July 1998 from southeastern Wisconsin (USA). Nine (6%) of 140 toads were infected by the green blow fly (Bufolucilia silvarum) with a mean intensity of 10.5 +/- 7.2 (range = 1-24). Weekly parasite prevalence and mean intensity remained low, ranging from 0-20% and 2 +/- 1.4 to 14 +/- 6, respectively. We found: 1) flies lay eggs on healthy toads, 2) eggs hatch with first instar maggots penetrating under the skin, 3) maggots develop to mature third instars within 5-7 days, 4) maggots leave the host and form pupa within 8-11 days of hatching, and 5) maggots pupate within 7-9 days at room temperature. All infected toads died within 1-2 wk as a result of the infection. The low prevalence observed in this study and other reports of this species from mammalian and bird carcasses indicated that B. silvarum is probably a facultative parasite of toads and other amphibians in the United States. This is the first report of B. silvarum causing myiasis in Wisconsin amphibians and the first report in eastern American toads in the United States.     

The effects of ambient pH on nitrogen excretion in early life stages of the American toad (Bufo americanus)

Acidification of breeding ponds has been identified as a potential threat to the survival and health of North American amphibian populations. The effects of acid exposure on ion and acid-balance are well known, but there is little information on how environmental water pH influences nitrogen balance in amphibians. The aim of this study was to determine the effects of moderately acidic water (pH 6.0) on nitrogen excretion in early life stages of the toad, Bufo americanus. Acid exposure (pH 6.0, 54 h) resulted in a 20–80% increase in ammonia-N excretion rates in embryos and early, middle and late tadpoles stages, whereas there was no significant effect on urea-N excretion. Tissue ammonia concentrations were significantly higher (+ 33%) in the embryos and 35–65% lower in the three groups of tadpoles exposed to water of pH 6.0 compared to control animals (pH 8.5). In embryos, ammonia excretion accounted for greater than 90% of total nitrogen excretion (ammonia-N + urea-N), but by the late tadpole stage this value had decreased to approximately 65%. These findings indicate that exposure of embryonic and larval B. americanus to moderately acidic water disrupts nitrogen balance by increasing nitrogen loss as ammonia, with no compensatory decrease in urea excretion.     

Genetic variation in the genus Bufo I. An extreme degree of transferrin and albumin polymorphism in a population of the American toad (Bufo americanus)

A population of Bufo americanus from southwestern Ohio exhibited an extreme degree of transferrin and albumin polymorphism. One hundred and eighty-five individuals were collected from this population, and their transferrin and albumin phenotypes were determined by vertical acrylamide gel electrophoresis. Thirteen transferrin alleles were present in 36 phenotypes, and 11 albumin alleles were present in 29 phenotypes. A deficiency of heterozygotes occurred at both protein loci. The possible mechanisms responsible for the polymorphism and deficiency of heterozygotes are discussed.This work was supported by grants from the following agencies to the Senior author: NSF GB23601, Society of the Sigma Xi, and the American Philosophical Society. Miami University contributed the computer and audiovisual services.     

Visual optics in toads (Bufo americanus)

Aspects of visual optics were investigated in the American toad (Bufo americanus). The development of the refractive state of the eye during metamorphosis was followed with IR photoretinoscopy. Frozen sections documented the changes in optical parameters before and after metamorphosis. There is a difference in light sensitivity between juvenile and adult toads. Binocular accommodation in adult toads was observed. 1. IR photoretinoscopic measurements showed that the refractive state of the eye changed very rapidly during metamorphosis, about 10 D/h while the animal entered the terrestrial habitat. 2. Frozen sections showed that the almost spherical lens in a tadpole eye had flattened in a just metamorphosed toad's eye while at the same time the distance of the lens to the retina had decreased. However, the morphological measurements were not sufficiently sensitive to record the relatively small changes in ocular dimensions that were responsible for the rapid changes in refractive state during metamorphosis. 3. Schematic eyes, with homogeneous and non homogeneous lenses, were constructed for tadpoles, juvenile toads, and adult toads. 4. Nonparaxial raytracing studies in schematic eyes suggested that the lenses of animals of the three developmental stages tadpole, juvenile toad, and adult are not homogeneous but have a refractive index gradient. The raytracing studies indicated that the refractive index gradient is different for the different developmental stages, being highest in the tadpole lens. 5. The observations of toads during feeding behavior at different light levels showed an increased light sensitivity in the adult nocturnal toads in contrast to the juvenile animals, which are diurnal. The increased light sensitivity could partly be explained with an increase in aperture and an increase in red rod outer segments. To fully explain the higher light sensitivity in adult toads, changes in neuronal parameters had to be assumed. 6. Retinoscopic measurements of the resting refractive state in the adult toad showed a hyperopic defocus of about +8 D. By subtracting the measurement artefact for retinoscopy, the true resting focus was found to be nearly emmetropic. 7. The amount of natural accommodation in adult toads during normal feeding behavior was investigated with IR photoretinoscopy. Binocular accommodation of about 8 D was observed.     

Microbodies (peroxisomes) in the toad,Bufo marinus

Summary Microbodies (peroxisomes), a group of cytoplasmic organelles enriched in catalase, are demonstrated in the toad, Bufo marinus, by light and electron microscopy by means of a cytochemical staining procedure that demonstrates the peroxidatic activity of catalase with diaminobenzidine (DAB). Amphibian microbodies are similar to those of other classes in their fine structure and localization in hepatocytes and kidney, where they are prominent in the proximal tubular cells. Nucleoids are present only in renal microbodies. In the proximal renal tubule an unusual group of large brown granules are identified as lysosomes by their acid phosphatase, -glucosaminidase and -glucuronidase activities.This work was supported by U.S. Public Health Service Grants Nos. NS-06856 and HD 00674. We wish to thank Dr. Richard M. Hays who generously supplied us with toads; Dr. Alex B. Novikoff for making available facilities for ultramicrotomy, Miss Betty De Prest for technical assistance; Miss Marianne Van Hooren for preparation of the photomicrographs.     

Renal vascular anatomy of the toad (Bufo marinus)

The renal vasculature of the toad, Bufo marinus, was studied mainly by means of scanning electron microscopy of vascular corrosion casts. All arterial branches terminated in a glomerulus. Each glomerulus was supplied by only one afferent arteriole. No shunts between afferent and efferent arterioles were observed. The glomerular channels appeared to be permanent capillaries. No evidence supporting the theory of freely shifting glomerular blood channels was found. Efferent arterioles radiated out towards the dorsal surface of the kidney where they connected with peritubular vessels. The renal portal veins produced an anastomosing plexus on the dorsal surface of the kidney, giving rise to the peritubular vessels. Peritubular vessels ran radially toward the ventral surface of the kidney, where they formed the roots of the renal veins. Attention is drawn to the possibility of hairpin countercurrent exchange between the capillary-like efferent arterioles and the peritubular vessels in the dorsal kidney.     

Feeding causes thermophily in the woodhouse's toad (Bufo woodhousii)

(1) We placed 12 toads (Bufo woodhousii) in linear thermal gradients with floor temperatures ranging from 10 to 40 degrees C and monitored body temperatures (T(b)'s) with chromega-alomega thermocouples interfaced with a datalogger. (2) We measured T(b)'s at 10min intervals over a 24h period in toads that had eaten an equivalent of 5% of their body mass or had fasted for 5 days. (3) The mean 24h T(b) did not differ significantly between the fed and fasted groups. (4) Hourly mean T(b)'s of fed toads differed significantly over the 24h, but those of fasted toads did not. Fed toads selected highest T(b)'s during late afternoon and evening.     

Leptospires in the marine toad (Bufo marinus) on Barbados

Leptospires were isolated from the kidneys of four of 211 toads (Bufo marinus) caught on Barbados. Two of the isolates were identified as Leptospira interrogans serovar bim in the Autumnalis serogroup (the most common cause of leptospiral illness on Barbados), and two as possibly new serovars in the Australis serogroup. Sera from 198 of the toads were examined by the leptospire microscopic agglutination test. Forty-two (21%) were positive at titers of greater than or equal to 1:100, and 54 (27%) at greater than or equal to 1:50. The predominating serogroups were Australis (50%), Autumnalis (23%) and Panama (13%). The agglutination tests on the culture-positive toads showed that serologic studies alone may be of limited value in these animals. Bufo marinus can harbor pathogenic leptospires, and it may be a significant source of the Autumnalis serogroup infections in the Caribbean.     

Innervation of the renal vasculature of the toad (Bufo marinus)

The innervation of the dorsal aorta and renal vasculature in the toad (Bufo marinus) has been studied with both fluorescence and ultrastructural histochemistry. The innervation consists primarily of a dense plexus of adrenergic nerves associated with all levels of the preglomerular vasculature. Non-adrenergic nerves are occasionally found in the renal artery, and even more rarely near the afferent arterioles. Many of the adrenergic nerve profiles in the dorsal aorta and renal vasculature are distinguished by high proportions of chromaffin-negative, large, filled vesicles. Close neuromuscular contacts are common in both the renal arteries and afferent arterioles. Possibly every smooth muscle cell in the afferent arterioles is multiply innervated. The glomerular capillaries and peritubular vessels are not innervated, and only 3-5% of efferent arterioles are accompanied by single adrenergic nerve fibres. Thus, nervous control of glomerular blood flow must be exerted primarily by adrenergic nerves acting on the preglomerular vasculature. The adrenergic innervation of the renal portal veins and efferent renal veins may play a role in regulating peritubular blood flow. In addition, glomerular and postglomerular control of renal blood flow could be achieved by circulating agents acting via contractile elements in the glomerular mesangial cells, and in the endothelial cells and pericytes of the efferent arterioles. Some adrenergic nerve profiles near afferent arterioles are as close as 70 nm to distal tubule cells, indicating that tubular function may be directly controlled by adrenergic nerves.