Species

Hyla regilla (sometimes listed as Pseudacris regilla) is a small frog measuring from ¾ to 2 inches with a distinctive black or dark brown eye stripe and notable toe pads (Stebbins, 1985). A darker triangle is apparent between the eyes (Wright and Wright, 1995). The dorsal colors vary from brown to green, as well as combinations of brown and green, with a series of dark spots that may be more or less distinctive depending on the color phase (Stebbins, 1985). Ventral color is cream colored and leg area may be yellowish to orange (Wright and Wright, 1995). Males have dusky, wrinkled throats (Behler and King, 2000). Eyes from the pupil rim behind and in front is broken by black; above the rim is lemon yellow, while the rest of the iris is raw sienna or antique brown (Wright and Wright, 1995).

Nesting and Status in Estuarine and Coastal Areas

The habitat of the Pacific treefrog varies from sea level to mountains (11,600 ft) and includes grassland, chaparral, woodland, forest, desert, oases and farmland (Stebbins, 1985). Pacific treefrogs breed from November to July in marshes, lakes, ponds, roadside ditches, reservoirs and slow streams (Stebbins, 1985).   The brown and yellowish eggs, in small, loose, irregular masses (10-70 eggs) are laid in quiet water beneath or sometimes at the surface, attached to vegetation; a total of 500 to 750 eggs can be deposited from a single female (Wright and Wright, 1995). Tadpoles transform after 50 to 80 days (Wright and Wright, 1995). Lifespan is unknown for the Pacific treefrog, but 2 years are required from hatching to maturity (Stebbins, 1951).

Abundance and Range

The Pacific treefrog is probably the most abundant frog found in California (Wright and Wright, 1995). Pacific treefrogs can be found from Mt. Scriven and McBride in British Columbia all the way south to the tip of Baja California, and from the Pacific coast eastward to western Montana and eastern Nevada (Stebbins, 1985). These are the only native frogs known to inhabit the Channel Islands off the coast of southern California.

Site Fidelity

Although this frog frequents ponds, springs, streams, irrigation canals and other bodies of water, it has been found as far as one-half mile from water (Stebbins, 1951).

Ease of Census

Moderate effort is required to expose and census egg masses. Census of breeding frogs entering and exiting pools or of calling frogs in the breeding season is relatively easy.

Feeding Habits

Pacific treefrogs eat a variety of small aquatic and terrestrial invertebrates. An examination of stomach contents of 18 individuals revealed a diet primarily of small leaf hoppers (jassids) and various dipterans (including midges, small crane flies, and muscoid flies), but also included ants, spiders (Erigone), parasitic hymenopterans, and small beetles (Stebbins, 1951).

Pacific Treefrog Contaminant Exposure Data

I.

Organochlorine Contaminants

A.

Concentrations in Adults and Juveniles

1.

Tadpoles were collected from two sites in California during June and July 1996 (Datta et al., 1998). The following are the composite concentrations (ng/g wet weight) found:  Sycamore Creek, Southern Sierra Nevada mountains, n = 31, June 22, (PCBs = 12 / DDE = 9.6); Sycamore Creek, Southern Sierra Nevada mountains, n = 44, July 9, (PCBs = 23.8 / DDE = 9.3);  UC Davis, n=32, July 2, (PCBs = 229.3 / DDE = 258 ).

2.

Composite samples of adults (n=48) and tadpoles (n=34) were collected at various California sites (Sparling et al., 2001). The following concentrations (ng/g) are listed as (mean / percent detected ):  Coastal California (reference site):  Endosulfans (1.8 / 28%); Lassen: Endosulfans (1.0 / 12%); Tahoe: SDDT (1 / 18), Endosulfans (4.5 / 82%); SHCH (0.8 / 5%); Yosemite:  SDDT (2.2 / 40), Endosulfans (2.1 / 67%); SHCH (0.9 / 11%);  Sequoia:   SDDT (6.9 / 30), Endosulfans (3.1 / 67%); SHCH (0.9 / 10%). Among all the pesticides tested SDDT and endosulfans had the highest frequency of occurrence across locations. For adults and tadpoles collectively the difference among locations was significant.  The contaminant HCH was only found in adults. 

3.

Pooled tadpole samples from the Sierra Nevada mountains in California were analyzed for SPCB and Stoxaphene (Angermann et al., 2002).  The following mean concentrations are listed in order of (SPCB ng/g, toxaphene ng/g): Auburn Slate Rec Area (243.75, 15.62); French Creek (12.26, 3.88);  DeLong Creek (33.91, 10.03);  California Youth Authority Pond (12.02, 7.96);  Alpha Diggings (14.51, 8.6);  Big Meadow (22.15, 2.37);  Secret Diggings (22.97, 5.76);  Miguel Meadow (6.75, 3.81);  Camp Spaulding Pond (35.28, 9.15);  Loch Lleven Pond (18.98 / NA);  Crane Flat Meadow (10.31, 2.05);  Pacific Crest Trail at I-80 (NA / 4.72);  Siesta Lake (22.77, NA);  Margery Pond (20.89, NA);  Crooked Meadow (14.70, NA);  Kaiser Pass Meadow (1.57, 2.88);  Pear Lake (5.69, 2.02);  Pond at Bennettville (7.97, 3.35);  Pond at Tioga Pass (4.36, 2.28); Sixty Lakes Basin (2.55,  1.47);  Mt. Conness Meadow (4.21, 2.23). Both toxaphene and PCB concentrations generally diminished with increasing elevations. Neither latitude nor Central Valley (a source of pesticides) to site distance correlated with PCB or toxaphene residues in multiple stepwise regression analysis, yet both were significant when regressed independently against S toxaphene residue concentrations. A comparison of sites designated within east-facing catchment basins with sites designated within west-facing (towards the central valley) catchment basins yielded significant different mean concentrations of both SPCB and S toxaphene supporting a rain-shadow model of residue disposition in mountainous zones.  West facing sites at the northern end of the sampling range, in the northern Sierra Nevada mountains, had relatively high proportions of low and moderately chlorinated congeners compared to sites in the central Sierra Nevada mountains and at the southern end of the sampling range.

B.

Concentrations in Eggs

1.

Egg masses (n = 8) were collected from Upper Meadow in the northern Sierra Nevada mountains, California on July 11, 1996 contained 9.1 ng/g wet weight PCBs (Datta et al., 1998).

II.

Cholinesterase-Inhibiting Pesticides

1.

Pacific treefrog tadpoles were collected from two sites in California during June and July 1996 (Datta et al., 1998). Mean concentrations of chlorpyrifos (ng/g wet weight) were 10.4 (June, n=31) and 17.4 (July, n=44) at Sycamore Creek, Southern Sierra Nevada mountains, and 9.2 (July, n=32) at UC Davis.  Egg masses collected from the Upper Meadow in the northern Sierra Nevada mountains contained trace amount of chlorpyrifos (July, n=8).

 2.

Tongues and brain tissue from adult Pacific treefrogs collected from various sites in California were compared for cholinesterase (ChE) activity (nmol substrate hydrolyzed/min/g tissue) after exposure to diazinon (9 mg/g) for 5 days in a laboratory setting (Sparling et al., 2001). The mean ChE activities were as follows: Tongues control group (0.934);  Tongues diazanon exposed group (0.572); Brain control group (5.723); Brain diazanon exposed group (5.95).

Whole body composites of tadpoles (n=170) taken from 23 sites in California were analyzed for ChE activity and compared by development and by site as follows: Tadpoles with joined hind limbs (2.38); tadpoles with limb bud (1.69); tadpoles with no limb (1.69).  Tadpole ChE was depressed at both Lake Tahoe and Sequoia compared with coastal sites and was less at Sequoia than at Lake Tahoe.

Composites of adults (n=48) and tadpoles (n=34) were collected from various California sites. The following concentrations (ng/g) are listed as (mean / percent detected):  Coastal California (reference site): Chloropyrifos (1 / 9%); Lassen: Chloropyrifos (1 / 29%);  Tahoe: Chloropyrifos (1.5 / 22%), Diazanon (2 / 11%);  Yosemite:  Chloropyrifos (14 / 12%), Diazanon (3 / 53%);  Sequoia:   Chloropyrifos (8 / 16%), Diazanon (2 / 9%). More than 50% of tadpoles and adults at Yosemite Park had measurable concentrations of chlorpyrifos or diazinon, both potent ChE inhibitors, while the reference site had only 9% with measurable concentrations of these compounds.   

III.

Trace Elements, Metals, and Metalloids

No residue data available

IV.

Petroleum

No residue data available

V.

Other

1.

Tadpoles were collected from two sites in California during June and July 1996 (Datta et al., 1998). Mean concentrations of chlorothalonil (ng/g wet weight) were 47.7 (June, n=31) and 33.3 (July, n=44) Sycamore Creek, Southern Sierra Nevada mountains, and 12.7 (July l, n=32) at UC Davis.  Egg masses collected from the Upper Meadow in the northern Sierra Nevada mountains contained 4.5 ng/g chlorothalonil (July, n=8).

Pacific Treefrog Contaminant Response Data

I.

Organochlorine Contaminants

No response data available

II.

Cholinesterase-Inhibiting Pesticides

1.

Three-week-old tadpoles hatched in the laboratory from egg masses collected from ponds near Concord, California were exposed to field application concentrations of five organophosphorus pesticides (Johnson, 1980). After 24 exposure periods, tadpoles were tested for thermal stress by increasing ambient water temperature until spasms were noted.  The following data are listed as (concentration in ppb, average temperature at start of spasm in degrees Centigrade, number in sample): Chloropyrifos (25, 35.3, n=36), (50, 34.1, n=30);  Methyl parathion (25, 35.7, n=27), (50, 34.3, n=34), (100, 33.6, n=36);  Temephos (25, 36.2, n=39), (50, 35.5, n=37);  Fenthion (25, 36.9, n=42), (50, 36.7, n=35), (100, 35.7, n=45);  Malathion (25, 36.9, n=28), (50, 36.4, n=31), (100, 36.4, n=35), (500, 36.1, n=27). The thermal tolerance was significantly lowered by all chemicals and concentrations tested. The most active toxicants were chloropyrifos and methyl parathion, while malathion was found to be the least toxic chemical to the tadpoles. Mortality was observed with exposure to chloropyrifos (6 dead at 50 ppb) and methyl parathion (1 dead at 50 ppb).

III.

Trace Elements, Metals, and Metalloids

No response data available

IV.

Petroleum

No response data available

V.

Other

1.

Embryos (stage 12) produced from egg masses collected within the Willamette Valley in Oregon were exposed (4 and 10 day tests) to increasing concentrations of ammonium compounds and sodium nitrate (NaNO₃) (Schuytema and Nebecker, 1999). During the 10 day test, in addition to a control set of embryos exposed only to well water, sets of embryos were also exposed to a sodium chloride (NaCl) solution with a Cl equivalent to a 100 mg/L ammonium chloride (NH₄Cl) solution and to a sulfate solution with an SO₄ equivalent to a 100 mg/L ammonium sulfate ((NH₄)₂SO₄) solution. The mortality rates (increasing concentrations in mg/L / % embryos that died) were as follows:  Four day test :   Ammonium nitrate (NH₄NO₃),  (0.3 mg/L  / 0 %, 3.3 / 0,  6.9 / 0,  13.3 / 0, 25.1 / 0,  50.9 / 80,  101.2 / 100);  NH₄Cl (0.2 / 3.3,  2.8 / 0, 7.3 / 0,  12.8 / 0,  24.9 / 6.7,  49.7 / 23.3,  102.9 / 96.7);  (NH₄)₂SO₄ (0.04 /  0,  2.6 / 0,  6.1 / 0,  11.7 / 0, 23.1 / 0, 45.4 / 0, 91.5 / 43.3);  NaNO₃ (0.1 / 0,  24.8 / 0,  56.7 / 0,  111 / 0,  230.4 / 16.7,  470.4 / 43.3,  979.2 / 56.7,  2,716 / 100).  Ten day test:  NH₄NO₃,  (0.3 mg/L  / 0 %, 3.3 / 0, 6.9 / 0,  13.3 / 6.7, 25.1 / 46.7,  50.9 / 100,  101.2 / 100);  NH₄Cl (0.2 / 3.3,  2.8 / 0, 7.3 / 0,  12.8 / 0,  24.9 / 23.3,  49.7 / 100,  102.9 / 100);  (NH₄)₂SO₄ (0.04 /  0,  2.6 / 0,  6.1 / 0,  11.7 / 3.3,  23.1 / 3.3,  45.4 / 93.3, 91.5 / 100);  NaNO₃ (0.1 / 0,  24.8 / 0,  56.7 / 0,  111 / 0,  230.4 / 20,  470.4 / 46.7,  979.2 / 63.3,  2,716 / 100).  Embryos were smaller and exhibited less spontaneous movement than controls after 2 to 3 days exposure to 50-100 mg/L (NH₄NO₃)or 1000 mg/L NaNO₃, and embryos appeared to be immobilized by 1000 mg/L NaNO₃. No embryos died when Cl and SO₄ were held at the same levels as test solutions of ammonium or chloride sulfate at 100 mg/L concentrations. No differences were found in length or weight between embryos exposed to these ions or to a well water control.

The LC50 (median lethal concentration) values (mg/L) for these embryos (4 day test / 10 day test) were:  NH₄NO₃ (41.1 / 25); NH₄Cl (60.3 / 30.3); (NH₄)₂SO₄ (>102.9 / 32.4); NaNO₃ (643 / 578). The LOAEL (lowest observed adverse effect level) and NOAEL (no observed adverse effect level) values (mg/L) using the 10 day exposure results (LOAEL / NOAEL) were:  NH₄NO₃ (6.9 / 3.3); NH₄Cl (24.9 / 12.8); (NH₄)₂SO₄ (11.7  / 6.1); NaNO₃ (111 / 56.7).

References for Pacific Treefrog

Angermann, J.E., G.M. Fellers, and F. Matsumura. 2002. Polychlorinated biphenyls and toxaphene in Pacific Tree Frog tadpoles (Hyla regilla) from the California Sierra Nevada, USA. Environ. Toxicol. Chem. 21:2209-2215. 

Behler, J.L. and F.W. King. 2000. National Audubon Society Field Guide to North American Reptiles and Amphibians. Alfred A. Knopf. New York. 743 pp.

Datta, S., L. Hansen, L. McConnell, J. Baker, J. LeNoir, and J.N. Selber. 1998. Pesticides and PCB contaminants in fish and tadpoles from the Kaweah River Basin, California. Bull. Environ. Contam. Toxicol. 60:829-836.

Johnson, C.R. 1980. The effects of five organophosphorus insecticides on thermal stress in tadpoles of the Pacific treefrog, Hyla regilla. Zoological Journal of the Linnean Society 69:143-147.

Schuytema, G.S. and A.V. Nebecker. 1999. Comparative effects of ammonium and nitrate compounds on Pacific treefrog and African clawed frog embryos. Arch. Environ. Contam. Toxicol. 36:200-206.

Sparling, D.W., G.M. Fellers, and L.L. McConnell. 2001. Pesticides and amphibian population declines in California, USA.  Environ. Toxicol. Chem. 20:1591-1595.

Stebbins, R.C. 1951. Amphibians of Western North America. University of California Press, Berkeley. 539 pp.

Stebbins, R.C. 1985. Peterson Field Guide to Western Reptiles and Amphibians. Houghton Mifflin Co. Boston. 336 pp.

Wright, A.H. and A.A. Wright. 1995. Handbook of Frogs and Toads of the United States and Canada. Comstock Publishing Associates. Ithaca, NY. 640 pp.