Rana Muscosa Research Articles

Basking by Adult Boreal Toads (Bufo boreas boreas) during the Breeding Season

Basking is a thermoregulatory mechanism by which some ectothermic animals increase their body temperatures by exposing all or some of its body to direct sunlight. Posturing or changing the angle of the body in relation to the sun can increase or decrease the thermal benefits (Brattstrom, 1979). Wet skinned animals, such as toads, are not directly affected by radiant heat exchange (Tracy, 1975; Hoppe, 1979) and are best able to influence their body temperature by behaviorally choosing microhabitats receiving solar radiation (Tracy et al., 1993). While not directly warming the animal, solar radiation warms the substratum and thereby the air near the substratum such that the animal is experiencing a microhabitat warmer than the ambient air temperature. Adult and juvenile toads (Bufo boreas boreas and B. canorus) living at high elevations in western North America are active diurally and have been observed to bask in direct sunlight during mid to late summer, after the breeding season (Mullally and Cunningham, 1956; Mullally, 1958; Campbell, 1970; Lillywhite et al., 1973, Carey, 1978). Summer basking has been documented for other high-elevation anurans, such as Rana muscosa (Bradford, 1984). Daytime breeding activity in a population of B. b. halophilus in southern California has been described by Mullally (1958) and amplexed pairs of B. b. boreas are commonly observed laying eggs during daylight (Campbell, 1970; Corn and Muths, unpub. data). However, basking by adult toads during the breeding season has not been described. Basking may have several physiological benefits (Lofts, 1984; Zapata et al., 1992) but increased exposure might increase the risk of predation by birds, which has been observed in this population (Corn, 1993). We observed basking toads (completely out of the water on emergent rocks and logs) at Kettle Tarn in Rocky Mountain National Park (Larimer County, Colorado; UTM Zone 13, 2810 m elevation) early in the 1995 breeding season. On 3 June from 0955 to 1100 h, we observed 10-15 adult male and three amplexing pairs of B. b. boreas basking (Fig. 1). We observed several other males and nine additional amplexing pairs in the water. The pond was free of ice but was completely surrounded by snow. The sky was clear and temperatures were recorded by thermistor thermometer single-channel data loggers placed at Kettle Tarn on 12 May. Air temperature (measured 10-15 cm above the substratum) was 11.9 C at 1030 h and water temperature (measured at a depth of approximately 10 cm) was 12.2? at 1000 h and 13.6? at 1100 h. Wind was undetectable.

Effects of low pH and aluminum on amphibians at high elevation in the Sierra Nevada, California

At high elevation in the Sierra Nevada of California, surface waters are extremely low in acid-neutralizing capacity and thus may be vulnerable to changes in water chemistry due to acid deposition. The present study assesses the sensitivity of embryos and hatchling larvae of two Sierran amphibians, Pseudacris regilla (Pacific chorus frog) and Ambystoma macrodactylum (long-toed salamander), to low pH and an elevated level of dissolved aluminum. The populations of these two species are not known to be declining at present. These findings are compared with results for two other Sierran amphibians, Rana muscosa (mountain yellow-legged frog) and Bufo canorus (Yosemite toad), both of which reportedly have declined substantially in numbers in recent years. Embryos and hatchlings of P. regilla and A. macrodactylum were kept for 7 d in reconstituted soft water at pH 4.0–6.0 (inorganic monomeric aluminum effectively 0 or 39–80 μg/L at pH ≥ 4.9), and subsequently for a post-treatment period of up to 16 d in reconstituted soft water at pH 6.0 (no aluminum). LC50 pH values for post-treatment survival averaged 4.3 for embryos and tadpoles of both species. The estimated extreme pH for Sierra Nevada surface water, 5.0, did not cause a significant reduction in survival for either life stage of either species, and sublethal effects on body size and hatching time were not evident at pH ≥ 5.0. Aluminum also did not affect survival of either species, although sublethal effects were evident as reduced body size of A. macrodactylum larvae and earlier hatching in P. regilla. Pseudacris regilla and A. macrodactylum were not consistently more tolerant of low pH than R. muscosa and B. canorus. However, the latter two species show sublethal effects of low pH at pH ≥ 5.0, whereas the former two do not.

Isolation of remaining populations of the native frog, Rana muscosa, by introduced fishes in Sequoia and Kings Canyon National Parks, California : D. F. Bradford, F. Tabatabai & D. M. Graber, Conservation Biology, 7(4), 1993, pp 882–888

Isolation of remaining populations of the native frog, Rana muscosa, by introduced fishes in Sequoia and Kings Canyon National Parks, California : D. F. Bradford, F. Tabatabai & D. M. Graber, Conservation Biology, 7(4), 1993, pp 882–888

Acidic deposition as an unlikely cause for amphibian population declines in the Sierra Nevada, California

The Sierra Nevada of California is one of many regions worldwide that has recently experienced dramatic declines in amphibian populations. During the past two to three decades many populations of at least two species (Rana muscosa and Bufo canorus) have disappeared in national parks and designated wilderness areas at high elevation, whereas populations of a third widespread species (Pseudacris regilla) have remained stable or declined to a lesser extent. Acidification from atmospheric deposition has been suggested as a cause for these disappearances primarily because most surface waters in these areas are exceptionally low in acid neutralizing capacity (ANC), and thus are vulnerable to changes in water chemistry due to acidic deposition. We tested the hypothesis that acidification of habitats has adversely affected amphibian populations by eliminating populations from waters most vulnerable to acidification, i.e. low in pH or ANC, or from waters low in ionic strength, a condition that increases the sensitivity of amphibians to low pH. A survey of 235 potential breeding sites in 30 randomly selected survey areas failed to reveal significant differences in water chemistry parameters between sites with and sites without each of the three species. Moreover, the water chemistry parameters did not differ among sites inhabited by the three species in a manner paralleling their degrees of acid tolerance. These findings contra-indicate acidic deposition as a cause of recent amphibian population declines in the Sierra Nevada at high elevation.

Isolation of Remaining Populations of the Native Frog, Rana muscosa, by Introduced Fishes in Sequoia and Kings Canyon National Parks, California

Abstract: Rana muscosa (mountain yellow‐legged frog) was eliminated by introduced fishes early in this century in many of the lakes and streams in Sequoia and Kings Canyon National Parks, California. In waters not inhabited by fish, however, R. muscosa has disappeared from many sites within the parks during the past 30 years, and it appears to have gone extinct in some drainage systems. Fragmentation of populations may have caused or contributed to these recent extinctions, because R. muscosa populations are significantly more isolated from one another by fish at present than in prestocking conditions. A total of 312 lake‐sites in 95 drainage basins were surveyed for amphibians and fish in 1989–1990. For the 109 sites containing R. muscosa, we delineated networks of sites connected to one another via fishless streams, and we compared these present fishless networks (“present networks”) to those expected for the same sites assuming that fish had not been introduced to the parks (“former networks”). Most present networks consist of only one site (mean = 1.4), whereas the former networks average 5.2 sites. This difference represents approximately a 10‐fold difference in connectivity of populations, which is defined as the mean number of potential dispersal links (fishless streams) per network. Connectivity averages only 0.43 in present networks, in contrast to 4.15 in former ones.

Effects of Low pH and Aluminum on Two Declining Species of Amphibians in the Sierra Nevada, California

In the Sierra Nevada of California at high elevation, two species of amphibians, Rana muscosa and Bufo canorus, have dramatically declined in numbers during the past two decades. The surface waters in which these species spawn typically are extremely low in acid-neutralizing capacity, and thus may be vulnerable to changes in water chemistry due to acidic deposition. Such changes have been hypothesized to be a cause of the recent population declines. The present study assesses the sensitivity of embryos and hatchling tadpoles of these species to low pH and an elevated level of dissolved aluminum

Declining Amphibian Populations

W T tORLDWIDE DECLINES IN AMPHIBIAN POPULATIONS ATtracted wide attention following a workshop sponsored by the National Research Council (NRC) (1, 2). The declines seem to be general, but some regions and many taxa are apparently unaffected (1). Are the declines due to normal climatic fluctuations, which produce droughts and frosts that can severely reduce population size locally, or are there other, more insidious causes? The report of census data for four amphibians (three salamanders and a frog) gathered during a 12-year period of continuous (daily) monitoring at the Savannah River Site in South Carolina contributes importantly to this question (3). Substantial variation was found in breeding population sizes and juvenile recruitment. Population declines were found in some years, but these were coupled with increases; there is a complex dynamic associated with many factors, especially local moisture regimen. The new data, the most extensive available, raise the possibility that declines are the coincidental effect of population fluctuations. If so, the consequences will vary greatly from place to place. The southeastern United States is a veritable carpet of amphibians, from the abundant salamanders of the highest Appalachian peaks to dense lowland populations of both frogs and salamanders. Should populations decline to local extinction in this area, chances of recovery are high. However, local extinctions have more profound implications in other parts of the world, where species are specialists for habitats that are localized or badly fragmented; under such circumstances, opportunities for recolonization are low to nonexistent (4). It is significant that participants at the NRC workshop, who heard a brief summary of the new data, considered it unlikely that global declines were coincidental, because of the number and widespread distribution of the reports, but population fluctuations clearly must be taken into account. Concern about declines arises because amphibians are abundant, integral components ofmany diverse ecosystems. They are local top carnivores that are major consumers of invertebrates, especially insects. General declines would have widespread consequences and might indicate more general environmental problems (5). Some declines have been dramatic. Ranid frogs have all but disappeared from southern California (6). By the late 1980s a montane frog (Rana muscosa) had disappeared from 98% of the ponds in which it had been studied in the mid-1970s in SequoiaKings Canyon National Park (1, 4). In Oregon, populations ofRana cascadae, monitored since the mid-1970s, have suffered about an 80% disappearance (1, 7). The golden toad (Bufo periglenes), endemic to the Monteverde Cloud Forest Preserve in Costa Rica, has not bred in its traditional breeding sites since 1987; many other frog taxa in the region have experienced declines and local disappearance during this period (1, 8). The gastric-brooding frog (Rheobatrachus silus), which lived in rivers in relatively undisturbed regions of Queensland, Australia, has not been seen since 1979, and several other sympatric species offrogs also are thought to be extinct (9). Sometime after 1981, 8 of 13 species of frogs that had been present in Reserva Atlantica, Brazil, disappeared, including unusual diurnal hylodine frogs, whose birdlike calls were distinctive features

Mass Mortality and Extinction in a High-Elevation Population of Rana muscosa

Rana muscosa is one of several high-elevation amphibians that have recently disappeared from seemingly pristine sites. The present study documents an event of mass mortality among larval and metamorphosed R. muscosa in a lake in Kings Canyon National Park, California, and the ultimate extinction of the population. In 1979 metamorphosed individuals declined from ca. 800 individuals in early summer to nearly zero in late summer. During this time many carcasses were collected, individuals showed symp- toms of red-leg disease, and blood from an affected individual contained the bacterial pathogen charac- teristic of this disease, Aeromonas hydrophila. Also during the summer of 1979, nearly all of the approx- imately 1100 tadpoles began metamorphosis, but all metamorphosing individuals were consumed by Brewer's blackbirds (Euphagus cyanocephalus). This population of R. muscosa continued to exist until at least 1983, but was extinct by 1989. Recolonization of the site will probably never occur because streams connecting to extant populations of R. muscosa now contain introduced fishes.

Temperature Modulation in a High-Elevation Amphibian, Rana muscosa

Temperature Modulation in a High-Elevation Amphibian, Rana muscosa

Water and Osmotic Balance in Overwintering Tadpoles and Frogs, Rana muscosa

Water content, extracellular osmolality, and total solute content were measured in tadpoles and frogs of Rana muscosa submerged in the laboratory for 0, 1, 7, and 12 mo at 4 C. Edema was maintained at a constant level in both tadpoles and frogs during most of the natural overwintering period (7 mo), whereas extracellular osmolality and total solute content varied. During the first month of submergence, water content (excluding fat bodies, ovaries plus eggs, and tadpole digestive tracts) increased by 5.7% in tadpoles and 14.0% in frogs. Concomitantly, extracellular osmolality declined by 13.6% and 9.6%, respectively. The decline in osmolality was due solely to dilution in frogs, but it was due to both solute loss and dilution in tadpoles. Between 1 and 7 mo, water content in both tadpoles and frogs remained constant, whereas solutes were accumulated and extracellular osmolality increased. Between 7 and 12 mo, water content increased further, whereas solutes were lost and extracellular osmolality diminished. These findings are consistent with those for adult anurans of other species at low temperature, but the initial solute loss in tadpoles is not. The changes in water content, extracellular osmolality, and total solute content during overwintering were independent of body mass and skin surface area. Mass-specific water content was negatively related to dry body mass in both tadpoles and frogs, but tadpoles were more hydrated than frogs of the same size.

Winterkill, Oxygen Relations, and Energy Metabolism of a Submerged Dormant Amphibian, Rana Muscosa

Both larval and metamorphosed Rana muscosa (mountain yellow—legged frog) over—winter for 6—9 mo in ice—covered lakes and streams at high elevation (≤3700 m) in California and Nevada. In some winters almost all the frogs in shallow lakes (<4 m deep) die. This mortality is associated with oxygen depletion, which occurs most rapidly in shallow lakes. However, tadpoles survive for months in nearly anoxic conditions when shallow lakes are frozen to the bottom. In the laboratory at low P02, oxygen metabolism of overwintering tadpoles at 4° differed from that of frogs. The critical oxygen tension (Pc) of tadpoles (1.98 kPa) was significantly lower than for frogs (4.04 kPa). Also, when P02 was greater than Pc, the resting oxygen consumption (V02) of tadpoles partially conformed to P02, whereas the resting V02 of frogs was constant. At the atmosphere P02 of their natural environment (P02 °13.3 kPa), however, the resting V02 of tadpoles was not significantly different from that of frogs. Tadpoles apparently have two advantages over frogs during winter: (1) a greater tolerance of low P02, and (2) a reduced consumption of energy and oxygen at low P02. Unlike a number of anuran species which become dormant on land at temperatures above 4°, the resting V02 of metamorphosed R. muscosa overwintering at 4° was nearly the same as for summer—acclimated individuals in air at 4°. During 7 mo dormancy, the standard metabolic rate of both tadpoles and frogs remained constant. Resulting V02 of frogs in water at 4°, and in air at 15° was related to the 0.83—0.85 power of body mass.

Morphologic and Karyotypic Differentiations of the California Frogs Rana muscosa and R. boylii

Morphologic and Karyotypic Differentiations of the California Frogs Rana muscosa and R. boylii