Joseph Freda

Effects of Low pH and Other Chemical Variables on the Local Distribution of Amphibians

mortality caused by low pH could be responsible for the absence of the two least tolerant species from acidic ponds. Hatching of embryos of R. sylvatica was not related to pond pH while mortality of embryos of A. jeffersonianum increased significantly as pond pH declined. H. andersoni also hatched in all experimental New Jersey ponds, but embryos of B. woodhousei suffered significantly higher mortality in ponds of lower pHs. Hatching success was variable at specific pond pHs, indicating significant interaction of pH with other chemical variables. In laboratory trials, tadpoles of B. woodhousei and H. andersoni grew significantly slower when exposed to low pH. This sublethal effect on body size has important implications for dynamics of amphibian populations in acidic ponds.

Sodium Balance of Amphibian Larvae Exposed to Low Environmental pH

Sodium influx and efflux and body ionic contents of amphibian larvae were measured during acute and chronic exposures to acidic and neutral waters. Acute exposure to low pHs (2.5-4.0) depressed sodium influx and markedly accelerated sodium efflux. The resulting net loss of 50% of body sodium was fatal. Increasing the external calcium concentration extended survival time by slowing the loss of sodium. Chronic exposure to low pH caused a 21%-62% reduction in body sodium content; potassium content did not change. It also caused sodium influx to increase and efflux to decrease in comparison with fluxes measured during acute exposure at the same pH. Interspecific sensitivity differences were related to the relative magnitude of disruption in sodium balance. The three species of tadpoles studied differed in body sodium content under control conditions. Initial body sodium content was inversely correlated with acid tolerance and may represent a previously unknown mechanism for coping with physiologically stressful low-pH environments.

Field and Laboratory Studies of Ion Balance and Growth Rates of Ranid Tadpoles Chronically Exposed to Low pH

The effect of sublethal, chronic exposure of tadpoles to low environmental pH under natural conditions was investigated by making weekly measurements of various physiological variables. Rana sylvatica tadpoles from a low pH pond (pH 4.05-4.90) had lower body sodium, chloride and water concentrations in comparison with tadpoles from a nearby high pH pond (pH 5.74-6.37). Tadpoles from both ponds placed in the low pH pond also underwent higher sodium efflux than when placed in the high pH pond. These observations parallel similar studies on fish and demonstrate the effects of low environmental pH on larval anuran ionic regulatory mechanisms. Survival times of field-collected R. sylvatica tadpoles placed at pH 3.0 (H2SO4) did not change with age nor were there any differences between tadpoles from high and low pH ponds. However, survival times of laboratory raised R. pipiens tadpoles did increase with age, and animals raised at pH 4.4 grew slower than siblings at pH 5.8.

Interspecific differences in gill morphology of freshwater fish in relation to tolerance of low-pH environments

Five species of fish were chosen to approximate the range of tolerance to low pH seen in freshwater fish. On the basis of published field and laboratory information, which was confirmed by measuring ion losses at low pH (pH 4. 0 and 3.25), the five species ranked in terms of decreasing tolerance to low pH as follows: banded sunfish (Centrarchidae: Enneacanthus obesus), yellow perch (Percidae: Perca flavescens), smallmouth bass (Centrarchidae: Micropterus dolomieu), rainbow trout (Salmonidae: Oncorhynchus mykiss), and common shiner (Cyprinidae: Notropis cornutus). Gills were analyzed for various morphological and morphometric features including lamellar surface area, chloride-cell density and mucous-cell density, sialic acid content, and depth of tight junctions. We conclude from these measurements that acid tolerance is not correlated with either the overt physical dimensions of the gills (surface area, lamellar thickness, diffusion distance) or with the degree of mucification of the surface. It may, however, be correlated with chloride-cell density and branchial ion-transport activity. This relation is interpreted as indicating that sensitivity to low pH is largely a function of the intrinsic ion permeability of the gills. Measurements on trout and perch indicate that one way of reducing ion permeability is via an increase in the depth of tight junctions between adjacent gill-pavement cells.

Long term monitoring of amphibian populations with respect to the effects of acidic deposition

Amphibians breed in a variety of aquatic habitats in the United States. While the tolerance of low pH has been examined for many species of amphibians, those that breed in temporary ponds have been the most studied in terms of acidic precipitation. Some of the latter have been shown to have lethal limits for low pH that are close to or above the pHs found in many breeding ponds. Temporary ponds occur in large numbers in the areas of the country most affected by acidic precipitation. Many of these ponds are susceptible to acidification and reduced reproductive success of sensitive species of salamanders has been observed in acidic ponds. Additional practical and logistical considerations clearly make temporary ponds, and certain salamanders that breed in them, the best candidates for monitoring the long term effects of acidic precipitation on amphibian populations. We recommend a cost efficient monitoring scheme across three categories of acidic temporary ponds (low, medium, and high) that incorporates (a) chemical analyses of pond samples, (b) a census of the annual deposition of egg masses, as well as assessment of embryonic mortality in enclosed and unenclosed egg masses in the ponds, and (c) sampling of larval success. This plan offers the best opportunity for detecting changes in amphibian populations that are correlated with the acidity of precipitation, and would provide desperately needed long term data on the abundance of these amphibians.

Behavioral Response of Amphibian Larvae to Acidic Water

Five species of amphibian tadpoles (Rana clamitans, Rana sylvatica, Rana pipiens, Pseudacris crucifer, Bufo americanus) which varied in their sensitivity to low pH were exposed to a range of water pH and observed for avoidance behavior and changes in activity levels. All species tested avoided lethally acidic water and all species except Rana sylvatica avoided sublethal levels of acidity. However, the highest pH at which tadpoles avoided acidic water varied with species and appeared to be related to the acid sensitivity of the test species

Daily Movements of the Treefrog, Hyla andersoni

, AND R. A. BALLINGER. 1979. Food resource utilization during periods of low and high food availability in Sceloporus jarrovi (Sauria: Iguanidae). Southwest. Nat. 24:347-363. HEATWOLE, H. 1977. Habitat selection in reptiles. In C. Gans and D. W. Tinkle (eds.), Biology of the Reptilia. Vol. 7. Pp. 137-155. Academic Press, New York. MOERMOND, T. C. 1979a. The influence of habitat structure on Anolis foraging behavior. Behaviour 70:147-167. 1979b. Habitat constraints on the behav-

The effect of prior exposure on sodium uptake in tadpoles exposed to low pH water

SummaryBullfrog tadpoles (Rana catesbeiana) were pre-exposed (7d) to 5 different solutions which varied in ionic composition and pH. Unidirectional sodium influx was then measured over a range of sodium concentrations (50–2000 μM) and at 2 pHs (4.0 and 5.8). Tadpoles pre-treated in either distilled water or pH 4.0 soft water exhibited higher sodium influx than animals pre-treated in pH 5.8 soft water. Pre-exposure to solutions high in calcium or sodium reduced sodium influx. Tadpoles pre-treated in pH 4.0 soft water exhibited an increasedVmax for sodium transport, whileKm was unchanged relative to tadpoles pre-treated in pH 5.8 soft water. In contrast,Km was increased andVmax was unchanged in tadpoles pre-exposed to high concentrations of calcium or sodium. Within each pre-exposure treatment, influx was inhibited in pH 4.0 test water relative to pH 5.8 test water. However, the magnitude of inhibition was lessened with increasing external concentrations of sodium.

Water Permeability of the Skin of the Amphibious Snake, Agkistrodon piscivorus

The cottonmouth (A. piscivorus) is a semi-aquatic fresh water snake which is closely related to the terrestrial copperhead (A. contortrix). Despite the differences in habitat preference, both species have similarly low integumentary water permeability in the summer. Influx and efflux of water measured between tritiated distilled water and a 1 M NaCl solution were about 20-50 gtmoles/cm2 h. These are fairly typical values for terrestrial snakes, but abnormally low for fresh water species. A. piscivorus were caught soon after emergence from hibernation, and successive shed skins tested under constant conditions over a five month period showed significant declines in water permeability with a minimum of about 20 pmoles/cm2-h in June-September. Newborn A. piscivorus placed in water for three weeks had significantly lower cutaneous water permeabilities than those dehydrated by about 27% of their initial body mass in air. Thus integumentary perme- ability may vary in response to the state of body fluid hydration. Skin water permeability appears to be controlled by lipids since their extraction causes an enormous increase in influx and efflux. The lipid extracted shed skin of A. piscivorus demonstrated a marked asymmetry in downhill water diffusion, with influx exceeding efflux.