Chiricahua Leopard Frog

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Chiricahua Leopard Frog

Lithobates chiricahuensis (Platz & Mecham, 1979)

Adults range from 51 to 125 mm, and tadpoles metamorphose at 30 to 40 mm SUL (or a total length of about 80 mm).  Females are larger than males. They have an olive or brown dorsum with small black spots without a pale border, an incomplete or absent white lip stripe, and an interrupted dorsolateral fold. The skin is rugose with dorsal tubercles, and the throat is a mottled gray.  The species also has a distinctive salt and pepper pattern on the concealed surface of the rear of the thigh. This is also the only leopard frog in the State to have an entirely green dorsum, however, some specimens lack green in the dorsal pattern. The position of the eyes is more dorsal than lateral in this frog, suggesting it is more aquatic than other leopard frogs.

Larvae grow to > 80 mm total length prior to metamorphosis. Small tadpoles have a dark olive dorsum with lateral and ventral white to gray patches with bronze. Larger tadpoles are generally dark gray or olive dorsally with pale venter and heavy mottling on the tail fin (Scott and Jennings 1985).  Coloration distinguished tadpoles inhabiting stream and pond habitats. Jennings and Scott (1993) found tadpoles from streams had more contrasting and blotched color patterns than those from ponds. In general, stream tadpoles possessed thicker fins than pond tadpoles. Tadpoles from the stream sites had thicker dorsal fins. Tadpoles found in streams have more contrasting patterns on the tail, thicker dorsal fins, and somewhat larger tail muscles than those from ponds. Unexpected differences between tadpoles from two stream habitats might represent nonadaptive morphological variation. Alternatively, such differences may represent different morphological responses to similar selection pressures, to subtly different aquatic habitats, or different developmental responses to different environmental cues.

Distribution and Habitat. The species ranges from southeastern Arizona and southwestern New Mexico into Mexico along the eastern slopes of the Sierra Madre Occidental. Habitats used include semi-desert grassland, Madrean woodland, pinyon juniper coniferous forest, and montane coniferous forest.  It is usually associated with streams flowing through these habitats from February to September.  Hinderer et al. (2015) note that movement habits of the Chiricahua Leopard Frog and patterns of dispersal between disjunct water sources are not well understood. They attached radio transmitters to 44 frogs on the Ladder Ranch in southern New Mexico during summer 2014 and located each frog daily for up to eight weeks (mean = 29 days) during the summer monsoon. Frogs chose areas with more low-lying cover (especially aquatic vegetation and woody debris), less overstory cover, and a mud substrate.  Whether the location was far from or close to water and the amount of overstory cover did not appear to be important for selection, suggesting that frogs are able to find areas that provide habitat away from water.

The Chiricahua Leopard Frog inhabits southeastern Arizona and adjacent Sonora, Mexico, at elevations ranging from 1,219-4,023 feet, and from montane central Arizona east and south along the Mogollon Rim to montane parts of west-southwestern New Mexico, at elevations ranging from 3,500-8,040 feet. It inhabits federal, tribal, and privately-owned land. The species has been extirpated from about 80 percent of its historical localities in Arizona and New Mexico. The species is still extant in the major drainage basins in Arizona and New Mexico where it occurred historically; except for the Little Colorado River drainage in Arizona and possibly the Yaqui drainage in New Mexico. However, it was extirpated from many rivers within those major drainage basins, valleys, and mountains ranges, including: White River, West Clear Creek, Tonto Creek, Verde River mainstem, San Francisco River, San Carlos River, upper San Pedro River mainstem, Santa Cruz River mainstem, Aravaipa Creek, Babocomari River mainstem, and Sonoita Creek mainstem. No records from 1995 to the present exist for the Pinaleño Mountains or Sulphur Springs Valley. As of 2009, there were 84 sites in Arizona at which Chiricahua leopard frogs occur or are likely to occur in the wild, with an additional four captive or partially captive refuge sites. At least 33 of the wild sites support breeding.

The habitat includes oak, mixed oak, and pine woodlands, although its habitat ranges into areas of chaparral, grassland, and desert, particularly for the southern populations. This species requires permanent water sources, including streams, rivers, backwaters, ponds, and stock tanks that are free from introduced fish, crayfish, and bullfrogs. Natural aquatic systems include rocky streams with deep rock-bound pools, river overflow pools, oxbows, permanent springs, permanent pools in intermittent streams, and beaver dams. Human-influenced aquatic systems include earthen stock tanks, livestock drinkers, irrigation sloughs, mine adits, abandoned swimming pools, and ornamental backyard pools (USFWS 2007).Froglets disperse away from their natal wetlands and can move up to 800 m in two or three days (Dole, 1971) and tend to move to the edges of permanent bodies of water (Merrill 1977; Cochran 1982).  During the metamorphic period, at least a few frogs will leave wetlands every night; mass emigrations can occur following heavy rains (Bovbjerg 1965; Dole 1971).  Dole (1972a) provides evidence for celestial orientation in froglets.

Streicher et al. (2012) investigated variation in this frog in the Durango, Mexico population using morphology, as well as mitochondrial and nuclear DNA to characterize the population. Previous reports documented little mtDNA variation between populations of L. chiricahuensis in the United States (Goldberg et al. 2004; Pfeiler and Markow 2008; Hekkala et al. 2011). This coupled with the low genetic divergence between central Durango and east–central Arizona populations (Hillis and Wilcox 2005) suggest that the extant populations referred to L. chiricahuensis are collectively a young lineage. The maximum level of 12S and Tyr divergence observed was approximately equal. The individuals they examined shared haplotypes across the examined mitochondrial and nuclear loci.Reproduction. Populations at higher elevations (above 1,800 m) will reproduce later in the season than those at lower elevations.  Eggs are attached to vegetation.  Eggs hatching late in the season will have their tadpoles overwinter.

Populations. Field workers in the 1960s characterized Chiricahua Leopard Frogs as abundant in well-watered sites in southeastern Arizona.  However, most populations have declined precipitously, while they remain locally abundant at some sites.  The first report of declining Arizona leopard frogs was published in the mid-1980s. The problem seemed to be due to introduced fish and the introduced bullfrog, which preyed upon the native leopard frogs.  Also, the habitat was degraded at many locations.

Arizona surveys for this frog between 1983 and 1987 (Clarkson and Rorabaugh 1989) found Chiricahua leopard frogs at only two of 36 historical sites and at two new sites. Sredl et al. (1997) conducted 656 surveys within the range for southern populations and found frogs at 17 of 84 historical sites and at 44 new sites. In New Mexico, R.D. Jennings (1995a) found Chiricahua leopard frogs at 6 of 50 historical sites and 5 of 22 new sites.

Sredl and Jennings (2005) noted Zweifel (1968b) characterized leopard frogs as abundant in well-watered sites in valleys in southeastern Arizona. In other parts of southeastern and east-central Arizona, frogs that were likely Chiricahua Leopard Frogs were more abundant and widespread than they are at present (Wright and Wright, 1949). They (Sredl and Jennings 2005) commented these frogs can be locally abundant (10–20 frogs jump with each step along the shoreline) or can be scarce. This variation seems to be associated with environmental conditions found in different types of habitats.

Documented declines and extirpations at historical localities resulted in the Chiricahua Leopard Frogs added to the list of Category 2 candidate species (USFWS, 1991). Beginning with the 28 February 1996, candidate notice of review, the U.S. Fish and Wildlife Service discontinued the designation of multiple categories of candidates, and only those taxa meeting the definition for the former Category 1 candidate were considered candidates (USFWS 1996a). In that 28 February 1996 notice, Chiricahua Leopard Frogs were listed as a candidate species (U.S.F.W.S., 1996a). In 2000, they were proposed for Federal listing as Threatened (U.S.F.W.S., 2000a), and are now federally listed as Threatened.

The reintroduction of the Chiricahua Leopard Frog to portions of its historic range started in 2003 and was combined with an active program to remove bullfrogs from some localities.  The risk of bullfrog extinction to the re-established populations was considered low because the species has excellent dispersal abilities (Chandler et al. 2015).  Today, the leopard frog populations have improved and will likely continue to thrive, unless or until, the bullfrog returns. Howell et al. (2016) examined the survival rate of this frog at a reintroduction site and found it low (27%) compared to other reintroduced ranid frog populations. They attributed their findings to emigration of the frogs away from the study site.

Calfee and Little (2017) performed acute toxicity tests and found copper was toxic at concentrations lower than those observed in the environment. Developing tadpoles were exposed for 60 days to cadmium, copper and zinc because of the potential for long term exposure to these metals during early development. Cadmium was toxic, but at concentrations above observed environmental levels. Copper was especially toxic to this species at concentrations of about 10% of concentrations observed in their habitats. The onset of toxicity occurred within a few days of exposure, thus pulsed exposures from rain events could potentially be acutely toxic to tadpoles of this species. Zinc did not appear to have a negative impact during the acute or chronic exposures.

Conservation.  The species is listed as threatened under the Endangered Species Act of 1973. It is a closed-season species.  Collection of leopard frogs requires a scientific permit or a similar permit (Arizona Game and Fish Department, 2001). The most serious threats to the Chiricahua Leopard Frog are invasive predators (American Bullfrogs, spiny-rayed fishes, the crayfish Oronectes virilis) and the fungal skin disease (Bd), habitat fragmentation, major wetland manipulations, water pollution, and over-grazing.

The introduced crayfish has a major negative effect on native populations of frogs in North America (Kats and Ferrer 2003) and has probably contributed to the statewide decline of Chiricahua Leopard Frogs in Arizona (USFWS 2007).Recent eradication efforts of the Bullfrog in southern Arizona (Atascosa Mountains and Cienega Valley) appear to have established conditions that are favorable to the reestablishment.

Control of BD and other nonnative organisms, reduced habitat fragmentation and loss resulting from water diversion, groundwater pumping, and pollution, have meant that recovery criteria outlined in the recovery plan continue to be problems for this species.

The various aspects of climate change increases in UV radiation, drought, floods, wildfires, degradation and destruction of habitat, water diversions, groundwater pumping, disruption of metapopulation dynamics (relationships among populations of frogs) all increase the chances of extirpation and extinction.

Jarchow et al. (2016) attempted to identify corridors that would be used by Chiricahua Leopard Frogs following the eradication of invasive American Bullfrogs from most of Buenos Aires National Wildlife Refuge (BANWR). Larval Chiricahua Leopard Frogs from a private pond were reintroduced into three stock ponds. Populations became established at all three reintroduction sites followed by colonization of neighboring ponds in subsequent years. The goal was to better understand colonization patterns used by L. chiricahuensis which could help inform other reintroduction efforts. They assessed the influence of four landscape features on colonization. Using surveys from 2007 and information about the landscape, they developed a habitat connectivity model, based on electrical circuit theory, that identified potential dispersal corridors after explicitly accounting for imperfect detection of frogs. Landscape features provided little insight into why some sites were colonized and others were not, results that are likely because of the uniformity of the BANWR landscape. While corridor modeling may be effective in more complex landscapes, our results suggest focusing on local habitat will be more useful at BANWR.

Howell et al. (2016) used three years of capture-mark-recapture data from three breeding ponds and a Cormack-Jolly-Seber model to estimate annual apparent survival for reintroduced populations of the Chiricahua Leopard Frog (Lithobates chiricahuensis) at the Buenos Aires National Wildlife Refuge (BANWR), in the Altar Valley. Average apparent survival of Chiricahua Leopard Frogs at BANWR was 0.27 (95% CI [0.07, 0.74]) and average individual capture probability was 0.02 (95% CI [0, 0.05]). The apparent survival estimate for Chiricahua Leopard Frogs is lower than for most other ranids and is not consistent with recent research that showed metapopulation viability in the Altar Valley is high. They suggest that low apparent survival may be indicative of high emigration rates.

Alvarez et al. (2017) investigated the effects of exposure to CFT Legumine (5% rotenone), a piscicide that is used to remove invasive fish or tadpoles. They used multi-aged tadpoles of the federally listed Chiricahua Leopard Frog, the widespread Northern Leopard Frog, and the invasive American Bullfrog. They found at the earliest Gosner stages (GS21–25), Chiricahua Leopard Frogs were more sensitive to CFT Legumine (median lethal concentration [LC50] = 0.41–0.58 mg/L) than American Bullfrogs (LC50 = 0.63–0.69 mg/L) and Northern Leopard Frogs (LC50 = 0.91 and 1.17 mg/L). As tadpoles developed (i.e., increase in GS), their sensitivity to rotenone decreased. In a separate series of 48-h static nonrenewal toxicity tests, tadpoles (GS 21–25 and GS 31–36) of all three species were exposed to piscicidal concentrations of CFT Legumine (0.5, 1.0, and 2.0 mg/L) to assess postexposure effects on metamorphosis. In survivors of all three species at both life stages, the time to tail resorption was nearly doubled in comparison with that of controls. For example, mid-age (GS 31–36) Chiricahua Leopard Frog tadpoles required 210.7 hours to complete tail resorption, whereas controls required 108.5 hours. However, because tail resorption is a relatively short period in metamorphosis, the total duration of development (days from post hatch to complete metamorphosis) and the final weight did not differ in either age-group surviving nominal concentrations of 0.5-, 1.0-, and 2.0-mg/L CFT Legumine relative to controls. This research demonstrates that the CFT Legumine concentrations commonly used in field applications to remove unwanted fish could result in considerable mortality of the earliest stages of Lithobates tadpoles. In addition to acute lethality, piscicide treatments may result in delayed tail resorption, which places the tadpoles at risk by increasing their vulnerability to predation and pathogens.

Taxonomy. Platz and Mecham (1979:383) described Rana chiricahuensis based on the Holotype: AMNH 100372 from type locality Herb Martyr Lake (elev. 1768 m), 6 km W of Portal, Coronado National Forest, Cochise County, Arizona. Dubois (1987 “1986” :41–42 implied the combination Rana (Rana) chiricahuensis. Dubois (1992:332) used the combination Rana (Pantherana) chiricahuensis. Platz (1993:155) described Rana subaquavocalis based upon the Holotype: AMNH 136096 with the type locality Ramsey Canyon (elev. 1622 m), 7 km southwest of Sierra Vista, Cochise County, Arizona, USA. It was placed in the synonymy of L. chiricahuensis by Goldberg et al. (2004:313). Hillis and Wilcox (2005:305) used the combination Rana (Novirana, Sierrana, Pantherana, Stertirana, Lacusirana) chiricahuensis. Invalid name formulation under the International Code of Zoological Nomenclature (1999) as discussed by Dubois, 2007, Cladistics 23:395. Hillis and Wilcox (2005:305) used the combination Rana (Novirana, Sierrana, Pantherana, Stertirana, Lacusirana) subaquavocalis. Invalid name formulation under the International Code of Zoological Nomenclature (1999) as discussed by Dubois, 2007, Cladistics, 23: 395. Hillis and Wilcox, (2005:305) used the combination Rana (Novirana) subaquavocalis. Frost et al. (2006:369) placed the species in the genus Lithobates, using the combination Lithobates chiricahuensis by implication. Dubois (2006:325) used the combination Lithobates (Lithobates) chiricahuensis. Dubois (2006:325) used the combination Lithobates (Lithobates) subaquavocalis. Hillis (2007:335-336) used the combinations Rana (Lacusirana) chiricahuensis by implication. Fouquette and Dubois (2014:410) used the combination Rana (Lithobates) chiricahuensis. The populations on the western end of Mollogon Rim were assigned to this species, however its morphology, and mtDNA suggest that it is distinct from the southern populations (Hekkala et al. 2011) and the mtDNA suggest it may be Lithobates fisheri – a species thought extinct. The population on the eastern side of the Mogollon Rim also needs investigation to determine if it is conspecific with the populations in the west, conspecific with L. chiricahuensis, or distinct from both.Because this is a species complex, the morphology and the call can be expected to vary across the range.  The call is a single note that lasts 1 to 2 seconds and sounds like a snoring trill that is made while submerged, or a semi-croak or a very low croak. Multiple species appear to be covered under this name at present, some of them have been described.  The Ramsey Canyon population has been described as Lithobates subaquavocalis.  The Las Vegas Leopard Frog was originally known from the Las Vegas Valley in southern Nevada, where it has been extirpated.  The populations of leopard frogs from the western Mogollon Rim previously recognized as the Chiricahua Leopard Frog are morphologically distinct from the populations of Chiricahua Leopard Frogs in southern Arizona, New Mexico, and Mexico.  Hillis et al. (2005) suggest the Mogollon Rim populations may be conspecific with the Vegas Leopard Frog, Lithobates fisheri.  Prior to that it was considered extinct until Hekkala et al. (2011) provided evidence that the morphologically distinct Chiricahua Leopard Frog from the western Mogollon Rim was the Las Vegas Leopard Frog.  They obtained genetic information from a California Academy of Science specimen preserved in 1913 and determined that it is a member of one of the two lineages, which is extant along the western Mogollon Rim and White Mountains of central and eastern Arizona and extreme west-central New Mexico.  The Las Vegas Leopard Frog may have emerged from extinction and expanded distribution with this new knowledge.  Further investigation, however, may show it is a distinct form.

Conlan et al (2011) did a cladistic analysis based upon the amino acid sequence of known brevinin-1 peptides (antimicrobial peptides) from North American leopard frogs and produced a phylogenetic tree that generally support currently accepted evolutionary relationships. The three peptides from L. chiricahuensis form a well-defined clade that is sister-group to L. onca and L. yavapaiensis. This assemblage is distinct from the clade containing L. berlandieri, L. blairi, and L. sphenocephalus and the clade containing L. pipiens.

The status of  Lithobates cf fisheri. The Las Vegas Leopard Frog, Lithobates fisheri (Stejneger, 1893) was described based upon the holotype USNM 18957 (adult female) that was collected on March 13, 1891. Specimens collected at Vegas Valley in 1891 are in several museum collections (USNM, MVZ, CAS, LACM). Males 44-64 mm SUL; females 46-74 mm SUL (Wright and Wright 1949). Lithobates fisheri can be distinguished from Lithobates pipiens and Lithobates onca by reduced spotting on the dorsum and head.  It has shorter legs than L. onca, which in turn has smaller and fewer spots and shorter legs than L. pipiens (Linsdale 1940). Stejneger (1893) diagnosed this species as having: the heel of the extended hind limb falls short of snout tip; tympanic disc has vertical diameter greater than the eye-nostril distance; vomerine teeth between choanae and projecting beyond choanae posteriorly; hind feet about two-thirds webbed; a single small metatarsal tubercle;. paired weak dorsolateral ridges and an absence of longitudinal folds between the dorsolateral ridges; skin is granular on posterior lower aspect of femur; dorsum and flanks with numerous small dark spots bordered by lighter pigment; no black ear patch. Olive green ground color, sometimes with the anterior body a brighter green, and with dark greenish olive to green spots. Spots often reduced or indistinct on anterior body/head, especially in males. Light stripes along dorsolateral folds. Throat light green with some pinkish suffusion, clouded with dark grayish olive green. Chest and belly may have pinkish cinnamon and may be clouded like the throat. Ventral surfaces of hindlimbs honey yellow to chamois. Males have nuptial pads. Females have more spotting dorsally than males (Wright and Wright 1949, from 1925 field notes on Tule Springs specimens, collected about 16 miles from what was Las Vegas at the time). Linsdale (1940) notes that R. fisheri had a “peculiar shade of ground color” compared to R. pipiens, but the coloration is not described by that author.

This species was thought to be extinct, and if it is, its distribution is restricted to its type locality in the city of Las Vegas, Nevada, it is extinct. However, Hekkala et al. (2011), showed that the closely related species Lithobates chiricahuensis includes two genetically distinct lineages. They obtained sufficient genetic information from specimens of R. fisheri preserved in 1913 in ethanol and stored at the California Academy of Sciences to determine that it is a member of one of the two lineages, which is extant along the Mogollon Rim and White Mountains of central and eastern Arizona and extreme west-central New Mexico. The authors assigned this lineage to Rana fisheri, and accordingly, the species continues to exist. This species was placed in the genus Lithobates by Frost et al. (2006). However, Yuan et al. (2016) showed that this action created problems of paraphyly in other genera. Yuan et al. (2016) recognized subgenera within Rana for the major traditional species groups, with Lithobates used as the subgenus for the Rana palmipes group. AmphibiaWeb recommends the optional use of these subgenera to refer to these major species groups, with names written as Rana (Aquarana) catesbeiana, for example. The status of Lithobates subaquavocalis Platz (1993:155) described Rana subaquavocalis. based upon the holotype: AMNH 136096 from Ramsey Canyon, Cochise County, Arizona. It was placed in the synonymy of Rana chiricahuensis Goldberg et al. (2004: 313).