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The chytrid fungus Batrachochytrium dendrobatidis (Bd) has been devastating amphibians globally. Two general scenarios have been proposed for the nature and spread of this pathogen: Bd is an epidemic, spreading as a wave and wiping out individuals, populations, and species in its path; and Bd is endemic, widespread throughout many geographic regions on every continent except Antarctica. To explore these hypotheses, we conducted a transcontinental transect of United States Department of Defense (DoD) installations along U.S. Highway 66 from California to central Illinois, and continuing eastward to the Atlantic Seaboard along U.S. Interstate 64 (in sum from Marine Corps Base Camp Pendleton in California to Naval Air Station Oceana in Virginia). We addressed the following questions: 1) Does Bd occur in amphibian populations on protected DoD environments? 2) Is there a temporal pattern to the presence of Bd? 3) Is there a spatial pattern to the presence of Bd? and 4) In these limited human-traffic areas, is Bd acting as an epidemic (i.e., with evidence of recent introduction and/or die-offs due to chytridiomycosis), or as an endemic (present without clinical signs of disease)? Bd was detected on 13 of the 15 bases sampled. Samples from 30 amphibian species were collected (10% of known United States' species); half (15) tested Bd positive. There was a strong temporal (seasonal) component; in total, 78.5% of all positive samples came in the first (spring/early-summer) sampling period. There was also a strong spatial component--the eleven temperate DoD installations had higher prevalences of Bd infection (20.8%) than the four arid (<60 mm annual precipitation) bases (8.5%). These data support the conclusion that Bd is now widespread, and promote the idea that Bd can today be considered endemic across much of North America, extending from coast-to-coast, with the exception of remote pockets of naïve populations.

During March 2001–April 2004, 164 adult anurans of 6 species (47 Rana blairi, 35 Rana catesbeiana, 31 Hyla chrysoscelis, 31 Pseudacris triseriata triseriata, 11 Bufo woodhousii, and 9 Acris crepitans blanchardi) from Pawnee Lake, Lancaster County, Nebraska, were surveyed for myxozoan parasites. Of these, 20 of 31 (65%) P. triseriata triseriata and 1 of 9 (11%) A. crepitans blanchardi were infected with a new species of Myxidium. Myxidium melleni n. sp. (Myxosporea) is described from the gallbladder of the western chorus frog, P. triseriata triseriata (Hylidae). This is the second species of Myxidium described from North American amphibians. Mature plasmodia are disc-shaped or elliptical 691 (400–1,375) × 499 (230–1,200) × 23 (16–35) μm, polysporic, producing many disporic pansporoblasts. The mature spores, 12.3 (12.0–13.5) × 7.6 (7.0–9.0) × 6.6 (6.0–8.0) μm, containing a single binucleated sporoplasm, are broadly elliptical, with 2–5 transverse grooves on each valve, and contain 2 equal polar capsules 5.2 (4.8–5.5) × 4.2 (3.8–4.5) μm positioned at opposite ends of the spore. Myxidium melleni n. sp. is morphologically consistent with other members of Myxidium. However, M. melleni n. sp. was phylogenetically distinct from other Myxidium species for which DNA sequences are available. Only with improved morphological analyses, accompanied by molecular data, and the deposit of type specimens, can the ambiguous nature of Myxidium be resolved. Guidelines for descriptions of new species of Myxidium are provided.

This study examines the use of dominant frequency for assessment of fighting ability in Blanchard's cricket frog Acris crepitans blanchardi. Like most anurans, the dominant frequency of the call is negatively correlated with size. However, unlike many anurans, dominant frequency varies within individual males, providing a less reliable signal of size. Wrestling contests between male cricket frogs were differentially won by larger males. I thus tested the hypothesis that males use dominant frequency for assessment of an opponent's fighting ability. Males retreated from, or became satellites of, broadcasts of synthetic low frequency calls, simulating the calls of a large male. In contrast, males attacked broadcasts of synthetic high frequency calls, simulating the calls of a small male. The dominant frequency of the call therefore appears to contain information about size which males use to assess the fighting ability of opponents, despite the lower degree of reliability resulting from individual variation in the signal. Individual variation in dominant frequency arises partially as a consequence of active alteration of the signal in response to social competition. Males differentially lowered their dominant frequencies in response to lower frequency broadcasts, thus in response to larger opponents. Furthermore, the higher a male's dominant frequency relative to that of an opponent, the greater was the decrease in dominant frequency. These results suggest that smaller males may conditionally lower their dominant frequencies in order to sound larger to larger opponents, thereby inflating their apparent fighting ability. Two alternative hypotheses are discussed.

One of the species of amphibians experiencing dramatic population declines is the Blanchard's cricket frog. Concentrations of several persistent organic contaminants in Blanchard's cricket frogs from Ohio were measured, showing significant differences between sites. Frogs from Williams County in northeastern Ohio had higher levels of DDE than those from southern Ohio counties. Environmental chemical contaminants may be at least partly responsible for declines in this species in northern parts of its range.

Blanchard's Cricket Frogs (Acris crepitans blanchardi) in the central portion of their range show minimal capacities for freezing tolerance and survive overwinter by using terrestrial hibernacula where they avoid freezing. However, frogs may exhibit greater freeze-tolerance capacity at high latitude range limits, where winter climate is more severe. We studied freezing tolerance, glucose mobilization during freezing, and hibernacula microclimates of cricket frogs in southeastern South Dakota, at the northwestern limit of their range. Cricket frogs from South Dakota generally survived freezing exposure at −1.5 to −2.5°C for 6-h periods (80% survival), but uniformly died when exposed to these same temperatures for 24-h freezing bouts. Hepatic glucose levels and phosphorylase a activities increased significantly during freezing, but hepatic glucose levels during freezing remained low, only reaching levels approximating those prior to freezing in freeze-tolerant species. Moreover, muscle glucose and hepatic glycogen levels did not vary with freezing, suggesting little mobilization of glucose from hepatic glycogen stores during freezing, contrasting with patterns in freeze-tolerant frogs. Temperatures in soil cracks and burrows potentially used for hibernacula were variable, with some sites remaining above the freezing point of the body fluids throughout the winter, some sites dropping below the freezing point for only short periods, and some sites dropping below the freezing point for extended periods. These data suggest that cricket frogs in South Dakota, as in other portions of their range, survive overwinter by locating hibernacula that prevent freezing, although their toleration of short freezing bouts may expand the range of suitable hibernacula. These data also suggest that overwinter mortality may be high at the northern range boundary and might limit cricket frogs from expanding their range northward.

Blanchard's Cricket Frogs (Acris crepitans blanchardi) are geographically widespread and historically common, yet they are in decline throughout much of the northern part of their range. One proposed mechanism for this decline is the negative effects of acidified precipitation on this acid-sensitive species. To test the predictions of this hypothesis, we sampled 570 randomly-selected sites along three transects in Ohio using chorusing surveys during 2004. Along these transects, we assessed pH and acid neutralizing capacity (alkalinity), as well as terrestrial and aquatic vegetation cover. Our surveys detected 53 extant Cricket Frog populations (9.3% of surveyed sites) in ponds, lakes, and streams. These sites were exclusively located in western Ohio, indicating a substantial (120 km) range contraction, compared to its historic distribution in the state. A multiple logistic regression model found no significant relationship between Cricket Frog occurrence and either pH or acid neutralizing capacity (P > 0.50). Acid neutralizing capacity and pH were also not significantly different in extant and extinct areas of the Cricket Frog's range in Ohio (P > 0.05). Cricket Frogs were found to occur significantly more frequently than expected by chance in lakes and at sites with low canopy cover (P < 0.001). While synergistic interactions with other factors cannot be ruled out, these results suggest that habitat acidification is likely not responsible for Cricket Frog declines in Ohio. Unlike other declining amphibians, where likely causal mechanism(s) have been identified, causes of Cricket Frog declines remain enigmatic.

We investigated phonotactic responses of amplexed and unamplexed females to different male calls in the Cricket Frog Acris crepitans blanchardi. A significantly higher proportion of amplexed females responded to male calls than did unamplexed females. When unamplexed females responded to male calls their phonotactic preferences did not differ from that of amplexed females. Amplexed and unamplexed females did not differ in their latency to respond to different male calls. Thus, the use of unamplexed females in phonotaxis experiments does not seem to bias any interpretation of preferences and would increase the number of testable females available.

Field observations, coupled with displacement experiments, suggest that male Acris crepitans are site specific. In two experimental manipulations, when conspecific mating calls were broadcast to resident calling males, there was a significant reduction in the number of notes produced by the test subjects. In another series of playback experiments, a subject's response call was modified by an increase in note duration. We suggest that call modification resulting from the stimulus of a conspecific mating call is a mechanism designed to spatially spread out males.

Prey may use a variety of strategies to avoid predators, including behavioral modification and inducible defenses. For an inducible defense to evolve, one necessary component is that the defense must be costly; if it is not, then the defense should evolve into one that is always expressed (i.e., a constitutive defense). However, costs of inducible defenses have not been well-documented. Using predator exposure experiments in aquatic mesocosms, we demonstrate that dark tail coloration (or lack thereof) in Blanchard's Cricket Frog (Acris blanchardi) tadpoles is an inducible defense. Specifically, Acris tadpole tail spots in treatments with dragonfly predators (Anax sp.) were significantly larger when compared to treatments with fish predators (Lepomis macrochirus). However, tadpoles in control tanks (with no predators) had tail spots that were not significantly different in area from the Anax treatment. Therefore, this defense is unique among those known because the presence of fish induces the loss (not the appearance) of this morphology. Because Acris tadpoles express the tail spot in the absence of predation risk, this phenotype also does not appear to have any substantial allocation cost. We also document predation of Acris tadpoles by a fish predator and demonstrate reduction in movement and differential habitat use in the presence of fish predator cues. Under predation risk, tadpoles became less active and occupied the shallowest regions of their habitats. This combination of plastic morphological and behavioral defenses likely allows these frogs to successfully breed in a broad range of aquatic habitats with different assemblages of predators. While likely effective in reducing vulnerability to Anax attacks, the tail spot may increase vulnerability to fish. Our results suggest that the antagonistic effects of predator-specific inducible defenses may represent another type of cost relevant to the conditions under which inducible defenses are expected to evolve.