Arizona Treefrog (Hyla wrightorum)

Photo by Jim Rorabaugh

Arizona Treefrog, Mogollon Rim, AZ. Photo by Jim Rorabaugh.

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The Sierra Madre Occidental and the Sonoran and Chihuahuan deserts usually take center stage in discussions of the biogeography of southern Arizona’s herpetofauna. Surprisingly, two species found in the region, the Canyon Treefrog (Hyla arenicolor) and the Arizona Treefrog (H. wrightorum), were considered in the 1960s to have close biogeographic affinities with the herpetofauna of the Pacific coast. This was the heyday of taxonomy based on overall similarity, and there is a general resemblance of Arizona’s boulder-adapted Canyon Treefrog (H. arenicolor) to its analog, the California Treefrog (Pseudacris cadaverina) and of the vegetation adapted Arizona Treefrog (H. wrightorum) to members of the Pacific Treefrog complex (P. regilla complex). But these are recurrent ecomorphic themes among treefrogs (Hylidae).

When E. H. Taylor described the Arizona Treefrog in 1939 he considered it to be most similar to the Pacific Treefrog. In a study of geographic variation in external measurements, Jameson et al. (1966) concluded that the Arizona Treefrog was a subspecies of the Pacific Treefrog and coined the combination H. regilla wrightorum. But eight years later, genetic data entered the picture in the form of immunological distances, and Maxson and Wilson (1974) announced in the pages of Science that the similarity of the Arizona Treefrog to the Pacific Treefrog is the result of evolutionary convergence, and that its nearest relative is the Mountain Treefrog (Hyla eximia) of Mexico. Subsequent analyses using allozymes and nuclear and mitochondrial DNA sequences (Case et al. 1975, Hedges 1986, Barber 1999, Faivovich et al. 2005, Hua et al 2009, Wiens et al. 2010) have upheld this conclusion and place the Arizona Treefrog in the Hyla eximia species group that includes the Canyon Treefrog (H. arenicolor). Analyses of DNA sequences also indicate that a parallel relationship exists among the Pacific species, with the boulder-adapted California Treefrog (P. cadaverina) comprising the nearest relative of the Pacific Treefrog complex (P. regilla complex; Moriarity and Cannatella 2004, Recuero et al. 2006a, 2006b) and place these species in Pseudacris (chorus frogs) rather than Hyla (Holarctic treefrogs). The several studies of nuclear and mitochondrial markers appear to be largely congruent, reveal remarkable instances of convergent evolution, and confirm that the biogeographic affinities of the treefrogs of southern Arizona are with the herpetofauna of the Sierra Madre Occidental rather than the Pacific coast.

The advertisement call of the Arizona Treefrog was first studied by Blair (1960). He found it to be similar to that of the Squirrel Treefrog (Hyla squirella) and certain populations of the Mountain Treefrogs (Hyla eximia). He found large differences in pulse rate among populations of the Mountain Treefrog, with rates of less than 50 pulses/second (slow eximia) in the states of Jalisco, Morelos, Mexico, and Tlaxcala; and rates greater than 100 pulses/second (fast eximia) in Michoacan. He concluded that H. eximia may include more than one species and that H. wrightorum calls resemble fast eximia from Michoacan rather than slow eximia from near the type locality in Valley of Mexico. He rejected the combination Hyla eximia wrightorum listed by Schmidt (1953), and recognized Hyla wrightorum as a separate species.

In an unpublished dissertation, Renaud (1977) found that H. wrightorum differs from H. eximia of southern Mexico in body shape and size and in dominant frequency of advertisement calls, and concluded that the two represent distinct species.

Sullivan (1986) studied the advertisement calls of Hyla wrightorum at Baker Lake, Coconino Co., Arizona. He found dominant frequency to be negatively correlated with male body size. Males found in amplexus were not significantly larger than non-mating males, and there was no significant correlation between sizes of males and females for pairs in amplexus. Mating success of males appears to be unrelated to size. The advertisement calls of H. wrightorum differ from those of Hyla eximia in having a higher pulse rate and shorter call duration.

Although Duellman (1970) considered H. wrightorum to be conspecific with H. eximia based on tadpole and adult morphology and on variation in advertisement calls, more recently he concluded that the two represent separate species, mapping H. wrightorum south into southern Chihuahua separated by a distributional gap from H. eximia in southern Durango (Duellman 2001). Gergus et al. (2004) found that H. wrightorum in Arizona differed substantially in allozymes and mitochondrial sequences from H. eximia from the Distrito Federal, Mexico and concluded that they represent separate evolutionary species.

A thorough study of variation throughout the range of H. eximia is needed to determine whether it includes several cryptic species and to clarify their relationship to H. wrightorum. Additional data also may elucidate the findings by Barber (1999) that mitochondrial DNA from three populations of H. arenicolor from the Pinaleño Mts., Graham Co, have a closer phylogenetic relationship with H. eximia from Estado de Mexico than with other Canyon Treefrogs.

Geographic variation in advertisement calls, allozymes, and mitochondrial DNA sequences of the Arizona Treefrog was examined by Gergus et al. (2004). For all populations as a group, temperature significantly influenced pulse rate and call duration, whereas snout-vent length influenced dominant frequency. Size-adjusted dominant frequency and temperature-adjusted call duration differed significantly among populations. However, no significant differences were found among the populations in temperature-adjusted pulse rate, which is considered the most important call component for mate recognition. The authors conclude that over-all variation in call parameters among populations of the species probably are not biologically significant. Divergence in allozymes among the populations was found to be low, with no fixed differences. A unique cytochrome b haplotype was found to be fixed in the populations in the Huachuca Mts. and Canelo Hills, although the three population clusters (Mogollon Rim, Huachuca/Canelo, and Sonora) have approximately equal overall divergence in the cytochrome b fragment sequenced. The authors conclude that the levels of divergence in allozymes, mitochondrial DNA, and advertisement call parameters suggest that the three population clusters may have become isolated relatively recently (late Pleistocene), and they refrain from recommending that they be given formal taxonomic recognition.

Chapel (1939) found that in central Arizona the species breeds from 2 July to 9 August primarily in shallow grassy temporary ponds, but occasionally in permanent lakes. He reported that he heard the frogs calling from trees on sultry days, found several in wells 20 feet deep, and observed individuals jarred loose from felled trees, some up to 75 feet above the base. Examinations of stomach contents of 7 individuals from near Williams revealed beetles,earthworms, a fly, and a spider. Three of the seven had fed on bark beetles (Ips).

Zweifel (1961) described and illustrated larval Arizona Treefrogs hatched in the lab from an egg mass collected on 24 June in Greenlee Co. (8 mi SW Alpine, Apache Co.). The tadpoles hatched at stage 20 with a total length of 4.9 – 5.2 mm and attained a maximum total length of 38 mm and body length of 12.7 mm. Mouth parts were found to be similar to those of other North American species of Hyla. Sredl and Collins (1992) studied the effects of predation by Arizona Tiger Salamanders (Ambystoma mavortium nebulosum) on H. wrightorum tadpoles using field enclosures in a lake in Coconino County. They found when salamanders were absent, survival of treefrog larvae was nearly five times greater than when two or four salamanders were in an enclosure. Goldberg et al. (1996) examined 53 specimens of H. wrightorum and found that they harbored 3 species of helminth parasites (1 cestode, 2 nematodes). They conclude that for Arizona species, the helminth communities found in treefrogs appear to be depauperate and, with the exception of ubiquitous larval physalopterans, are mutually exclusive of those found in toads.

Gergus et al. (2005) provide a very useful summary of the literature on the species, including a number of unpublished works (Renaud 1977, Holm and Lowe 1995, Collins 1996, Gergus 1999). In Arizona the species occurs in Petran Montane Coniferous Forest from Williams (Coconino Co.) southeast along the Mogollon Rim to Alpine (Apache Co.) and Hannagan Meadow (Greenlee Co.), and in Madrean Evergreen Woodland in the Huachuca Mts. (Cochise Co.) and Canelo Hills (Santa Cruz Co.; Gergus et al. 2005; see Distribution map in the image gallery). Published distributional records for the species in Arizona include localities in the White Mts. at 8 mi SW Alpine (Zweifel 1961), 7 mi N Hannagan Meadow (Gergus et al. 2005), Greenlee Co.; 11 mi S Springerville (Taylor 1938), Bog Creek, McNary (Blair 1960), Apache Co; Pinetop (Chapel 1939), Navajo Co.; west along the base of the Mogollon Rim to Pine and Strawberry (Sullivan 1986), Gila Co.; and above the rim at Lake One (Sredl and Collins 1992), Lee Johnson Spring (Williams and Chrapliwy 1958), Baker Lake (Sullivan 1986), Hart Canyon (Chapel 1939), 12 mi N Flagstaff, Jones Crossing (Gergus et al. 2005), and Williams (Chapel 1939), Coconino Co. Isolated populations occur in the Sierra Ancha (Gergus et al. 2005), Gila Co., the Huachuca Mts (Taylor 1939), Cochise Co., and Canelo (Gergus et al. 2005), Santa Cruz Co.

The species is the official “Arizona State Amphibian”. The genus is named for Hylas, a figure in ancient Greek religion who was kidnapped by nymphs from the spring of Pegae. The species is named for Anna Allen Wright and Albert Hazen Wright, a rare herpetological combination of a matronym and patronym.

On a personal note, in August 1989 at the Southwestern Research Station, R.L.B. presented Charles Lowe with a live Arizona Treefrog from the White Mts. The frog was in a gallon bottle with a wet clump of grass from the same locality. Dr. Lowe, always fascinated with ecological relationships, pointed out that the grass was the same species found around the ponds in the Huachuca Mts. where the treefrog breeds. Waxing poetic, he said, “Bob, wherever we may be down the road of life, we will always be watching Hyla wrightorum calling from that grass.” Indeed, his predictions proved accurate, and the authors have spent many delightful hours observing, listening to, and photographing these magnificent frogs around the grassy ponds of the Huachuca Mountains.

Literature Cited

Barber, P.H. 1999. Phylogeography of the Canyon Treefrog, Hyla arenicolor (Cope) based on mitochondrial DNA sequence data. Molecular Ecology 8:547-56. Blair, W.F. 1960. Mating call as evidence of relations in the Hyla eximia group. Southwestern Naturalist 5:129-135.

Case, S.M., P.G. Haneline, and M.F. Smith . 1975. Protein variation in several species of Hyla. Systematic Zoology 24: 281-295.

Chapel, W.L. 1959. Field notes on Hyla wrightorum Taylor. Copeia 1939:225-227.

Collins, J.P. 1996. A status survey of three species of endangered/sensitive amphibians in Arizona. Arizona Game and Fish Department Heritage Program, Project Report, Number I92014, Phoenix, Arizona.

Duellman, W.E. 1970. The hylid frogs of Middle America, Volume 2. Monograph of the Museum of Natural History, University of Kansas, Lawrence, Kansas.

Duellman, W.E. 2001. The hylid frogs of Middle America. Expanded edition. Society for the Study of Amphibians and Reptiles, St. Louis, Missouri.

Faivovich, J., C.F.B. Haddad, P.C.A. Garcia, D.R. Frost, J.A. Campbell, and W.C. Wheeler. 2005. Systematic review of the frog family Hylidae, with special reference to Hylinae: a phylogenetic analysis and taxonomic revision. Bulletin of the American Museum of Natural History 294:1-240.

Gergus, E.W.A. 1999. Geographic variation in hylid frogs of southwestern North America: taxonomic and population genetic implications. Ph.D. dissertation. Arizona State University, Tempe, Arizona.

Gergus, E.W.A., T.W. Reeder, and B.K. Sullivan. 2004. Geographic variation in Hyla wrightorum: advertisement calls, allozymes, mtDNA, and morphology. Copeia 2004:758-769.

Gergus, E.W. A., J.E. Wallace, and B.K. Sullivan. 2005. Hyla wrightorum: (eximia) Taylor, 1938(a) Arizona Treefrog. Pages 461-463 in: M.J. Lannoo (ed), Amphibian Declines: The Conservation Status of United States Species. University of California Press, Berkeley, CA.

Goldberg, S.R., C.R. Bursey, E.W.A. Gergus, B.K. Sullivan and Q.A. Truong. 1996. Helminths from three treefrogs, Hyla arenicolor, Hyla wrightorum, and Pseudacris triseriata (Hylidae) from Arizona. Journal of Parasitology 82:833-835.

Hedges, S. B. 1986. An electrophoretic analysis of Holarctic frog evolution. Systematic Zoology 35:1-21.

Holm, P.A. and C.H. Lowe. 1995. Status and conservation of sensitive herpetofauna in the Madrean riparian habitat of Scotia Canyon, Huachuca Mountains, Arizona. Arizona Game and Fish Department, Technical Report, Phoenix, Arizona.

Hua, X., C. Fu, J. Li, A. Nieto Montes de Oca, and J.J. Wiens. 2009. A revised phylogeny of Holarctic Treefrogs (genus Hyla) based on nuclear and mitochondrial DNA sequences. Herpetologica 65:246-259.

Jameson, D.L., J.P. Mackey, and R.C. Richmond. 1966. The sytematics of the Pacific Tree Frog, Hyla regilla. Proceedings of the California Academy of Sciences 33:551-620.

Maxson, L.R. and A.C. Wilson. 1974. Convergent morphological evolution detected by studying proteins of treefrogs in the Hyla eximia species group. Science 185:66–68.

Moriarity, E.C., and D.C. Cannatella. 2004. Phylogenetic relationships of the North American chorus frogs (Pseudacris: Hylidae). Molecular Phylogenetics and Evolution 30:409-420.

Recuero, E., Í. Martínez-Solano, G. Parra-Olea, and M. García-París. 2006a. Phylogeography of Pseudacris regilla (Anura: Hylidae) in western North America, with a proposal for a new taxonomic rearrangement. Molecular Phylogenetics and Evolution 39: 293-304.

Recuero, E., Í. Martínez-Solano, G. Parra-Olea, and M. García-París. 2006b. Corrigendum to “Phylogeography of Pseudacris regilla (Anura: Hylidae) in western North America, with a proposal for a new taxonomic rearrangement” [Mol. Phylogenet. Evol. 39 (2006) 293-304]. Molecular Phylogenetics and Evolution 41:511.

Renaud, M. 1977. Polymorphic and polytypic variation in the Arizona treefrog (Hyla wrightorum). Ph.D. dissertation. Arizona State University, Tempe, Arizona.

Schmidt K.P. 1953. A Check List of North American Amphibians and Reptiles. Sixth edition. American Society of Ichthyologists and Herpetologists and University of Chicago Press, Illinois.

Sredl, M.J., and J.P. Collins. 1992. The interaction of predation, competition, and habitat complexity in structuring an amphibian community. Copeia 1992:607-614.

Sullivan, B.K. 1986. Advertisement call variation in the Arizona treefrog, Hyla wrightorum Taylor, 1938. Great Basin Naturalist 46:378-381.

Taylor, E.H. 1939 [“1938’]. Frogs of the Hyla eximia group in Mexico, with descriptions of two new species. University of Kansas Science Bulletin 25:421-445.

Wiens, J.J., C.A., Kuczynski, X. Hua, and D.S. Moen. 2010. An expanded phylogeny of treefrogs (Hylidae) based on nuclear and mitochondrial sequence data. Molecular Phylogenetics and Evolution 55:871-882.

Williams, K.E., and P.S. Chrapliwy. 1958. Selected records of amphibians and reptiles from Arizona. Transactions of the Kansas Academy of Sciences 61:299-301.

Zweifel, R.G. 1961. Larval development of the tree frogs Hyla arenicolor and Hyla wrightorum. American Museum Novitates 2056:1-19.

Authors: Robert L. Bezy, Natural History Museum of Los Angeles County, Los Angeles, CA, USA;

Kit B. Bezy and Kathryn Bolles, Tucson Herpetological Society

Erik F. Enderson, Drylands Institute Tucson, AZ, USA;

Originally Published in Sonoran Herpetologist 2010 24(11):110-114

For additional information on this species, please see the following volume and pages in the Sonoran Herpetologist: 2008 Mar:32-33.


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