Atrazine increases ranavirus susceptibility in the tiger salamander, Ambystoma tigrinum

Pathogenic diseases and environmental contaminants are two of the leading hypotheses for global amphibian declines, yet few studies have examined the influence of contaminants on disease susceptibility. In this study, we examined effects of ecologically relevant doses of atrazine (0, 1.6, 16, and 160 microg/L), sodium nitrate (0, 6.8, 68 mg/L), and their interactions on susceptibility of four laboratory-bred tiger salamander families to Ambystoma tigrinum virus (ATV), a pathogen implicated in global amphibian die-offs. Salamanders were from Arizona populations where a coevolutionary history with ATV is supported, and thus cofactors rather than recent introduction may contribute to disease epizootics. Use of atrazine and nitrogenous fertilizers are ubiquitous; therefore, the impact of these cofactors on disease susceptibility is an important consideration. Atrazine and sodium nitrate significantly decreased peripheral leukocyte levels, suggesting an impact of these contaminants on the immune system. As expected from this result, atrazine significantly increased susceptibility of larvae to ATV infection. In contrast, nitrate had a marginally significant main effect and significantly decreased infection rate at the highest level. However, neither atrazine nor sodium nitrate had significant effects on viral copy number per individual. These results suggest that ecologically relevant concentrations of atrazine and nitrates have immunosuppressive effects, and atrazine may contribute to ATV epizootics, raising concerns about the influence of contaminants on diseases in general.

Corticosterone concentrations in free-living spotted salamanders (Ambystoma maculatum)

A non-lethal technique for drawing repeated blood samples from spotted salamanders (Ambystoma maculatum) was used to examine sex, seasonal, and capture technique differences in the physiological stress response under natural, undisturbed conditions. Baseline and stress-induced (30 min of handling and restraint) corticosterone (CORT) concentrations were measured at night during the spring migrations into and out of the breeding pond, as well as during the fall migration to over-wintering sites. Females had significantly higher CORT concentrations than males during the spring migration toward the breeding pond, but this difference was not present when animals emerged from the pond post-breeding or during the fall migration. CORT concentrations did not vary seasonally, but during the acute stress response, CORT concentrations nearly doubled during the spring inbound migration, exhibited a nearly significant increase during the spring outbound migration, and did not change in the fall. Allowing animals to sit overnight in the buckets in which they were captured elicited CORT concentrations that tended to be higher (although not statistically significant) than when animals were sampled on the night of capture. The ability to sample blood from spotted salamanders using a non-lethal technique offers an opportunity to better understand both amphibian physiology and ecology.

Courtship behavior and plasma levels of androgens and corticosterone in male marbled salamanders, Ambystoma opacum (ambystomatidae)

We measured plasma levels of testosterone, dihydrotestosterone (DHT), and corticosterone for male marbled salamanders (Ambystoma opacum) collected during the breeding season. Our goal was to ascertain whether steroid levels changed in response to particular reproductive behaviors or laboratory confinement. Six groups of salamanders were examined: (a) MIGRATING, males migrating toward the pond basin during the breeding season; (b) LABORATORY, males kept under confined conditions in the laboratory for 10 days; (c) LAB-FIELD, laboratory males that were later released into seminatural enclosures in the field; (d) COURTING, males from male-female pairs in which the male actively courted the female (and deposited at least one spermatophore); (e) SOLO, males that were individually isolated from conspecifics; and (f) MALE-MALE, males that were placed together in pairs, and in which one male actively courted the other male. In three groups (COURTING, SOLO, and MALE-MALE), salamanders were placed in containers for observation and each male was observed for at least 2 hr prior to a plasma sample being taken. Circulating levels of testosterone, DHT, and corticosterone did not differ significantly for males in these groups. The similarity of androgen levels among the three groups indicated a lack of behaviorally evoked change under experimental conditions designed to reveal a behavior-androgen response. Male A. opacum differ taxonomically from other amphibians showing a behavior-androgen response (three species of toads in the genus Bufo) and also lack amplexus and male-male combat during competition for mates. The effects of confinement were indicated by levels of testosterone and DHT in LABORATORY males that were significantly lower than average levels of males in the following groups: MIGRATING, LAB-FIELD, and MALE-MALE. We inferred that LAB-FIELD males, following their release to seminatural enclosures, were able to regain plasma androgen levels typical of migrating males. This increase is one of very few demonstrations for amphibians of an increase in androgen levels upon release from laboratory confinement. Levels of corticosterone did not differ significantly between males that were active in the field and males that were kept in the laboratory. The similarity of corticosterone levels among these groups differs from the typical pattern of elevated corticosterone and depressed androgen levels in captive amphibians. Maximal corticosterone levels in breeding male A. opacum may act differently than in other species in which chronic elevations inhibit the pituitary-gonadal axis.

Interrenal function in larval Ambystoma tigrinum. III. Acid-base balance responses

Larval Ambystoma tigrinum (59-199 g) were treated with the drug aminoglutethimide (6 mg/day) in order to abolish steroid hormone synthesis. Steroid deprivation prevented the increase in plasma aldosterone concentration observed in sham-infused larvae during respiratory acidosis. It also blocked the normal compensatory response to respiratory acidosis of elevated plasma [HCO3-] and inhibited cutaneous Na+ transport. Aldosterone (10 micrograms/day) and, to a lesser extent, corticosterone (240 micrograms/day) restored the compensatory response. Aldosterone replacement also stimulated cutaneous Na+ transport in AG-inhibited larvae. The results suggest that aldosterone, at about 1000 pg/ml, supports the compensatory ionic responses to respiratory acidosis in this species.

Luteinizing hormone-releasing hormone induces thyroxine release together with testosterone in the neotenic axolotl Ambystoma mexicanum

In male neotenic axolotls Ambystoma mexicanum plasma concentrations of thyroxine (T4) and testosterone were increased following intravenous injection of 10 micrograms luteinizing hormone-releasing hormone. A dose of 50 micrograms influenced only plasma T4 levels. This observation suggests for the first time that a hypothalamic hormone is capable of stimulating the thyroidal axis in the neotenic axolotl.

Trypanosoma ambystomae in Ambystoma spp. (order Caudata) in southern Ontario

Using the haematocrit centrifuge technique, Trypanosoma ambystomae was recorded from Ambystoma jeffersonianum, Ambystoma platineum, Ambystoma laterale, Ambystoma maculatum, and Ambystoma tremblayi from five areas in southern Ontario. The percentage of infected animals varied from about 5% in A. tremblayi to 27% in A. platineum and A. maculatum. This report not only expands the host range for the trypanosome, it is also the first report of it being found outside western North America. The division process of the trypanosome in the salamander is described and it is shown that it can be maintained in salamanders in the laboratory by blood inoculation.

Hemoglobins of an amphibia, the neotenous Ambystoma mexicanum. Complete amino-acid sequence of the alpha chain of the major component using automatic solid-phase Edman degradation

The primary structure of axolotl (neotenous Ambystoma mexicanum) alpha chain has been determined. NH2-terminal sequence data were performed using the solid-phase method. Complete amino acid assignments were deduced from the sequences of peptides obtained after cleavage with cyanogen bromide; the methionine-containing peptides, isolated from alpha chain tryptic digest, allowing the alignment of these fragments. All overlaps have been clearly established. Axolotl alpha chain contains 142 residues, one extra phenylalanine residue being located at its N terminus, when compared with mammalian alpha chains. The amino acid sequences of this polypeptidic chain and of an other urodele, the newt Taricha granulosa, show 44 differences with only 18 non-isopolar replacements. Homologies between various vertebrate alpha chains are briefly discussed.

[Pattern and nomenclature of serum proteins of the amphibian urodele Ambystoma dumerilii Duges]

By means of many electrophoresis techniques, the serum of Ambystoma dumerilii was studied. The pattern in cellulose acetate is different from A. mexicanum proteinogram. Direct two-dimensional analysis in acetate/polyacrylamid gel with progressively increasing concentration from 4-30%, gives us the opportunity to observe 41 proteic components. By immunological results, the fastest proteic fraction is equivalent to a globuline with alpha-mobility more than an albumin. A nomenclature for this blood serum is proposed.