Canyon Treefrog
Dryophytes arenicolor (Cope, 1866)

Voice. Advertisement calls are hollow, nasal, and explosive, lasting only 1-3 seconds (Behler 1979). The call has been described by Campbell (1934) as a sheep-like ba a a, a quacking duck, and a r,r,r,r. Females answer the male’s call with a lower note. Storer (1925) suggested the calls from boulder strewn streams were enhanced by the rocks.

Diet. Hyla arenicolor feeds on a variety of insects, including beetles, ants, and caterpillars (Behler 1979). Winter et al (2007) found termites and beetles were the most important prey, but volumetrically, beetles and orthopterans were most important.

Water Relationships. Preest et al. (1992) measured the combined effects of variation in body temperature and hydration state on resting and active metabolism of the Canyon Treefrog. Skin resistance, body temperature, and rates of evaporation were measured at two temperatures. There was significant individual variation and a significant effect of temperature on oxygen consumption of resting animals. Individual variation, temperature, hydration state, and a temperature/hydration state interaction affected oxygen consumption of active animals. The Canyon Treefrog had lower rates of evaporative water loss and higher body temperatures than expected for typical anurans at both test temperatures. Skin resistance was lower at higher temperatures. Reduced evaporative water loss, the lack of an effect of dehydration on resting metabolism, and the sedentary nature of this species may contribute to its ability to inhabit an environment with often stressful thermal and hydric conditions.

Reproduction. Breeding period ranges from March to July but can be extended due to insufficient rainfall (Zweifel 1961; Stebbins 2003).

Observations by Zweifel (1961) in the Chiricahua Mountains suggest that most breeding activity takes place in the spring or very early summer. In 1958 there were larvae in potholes in the South Fork of Cave Creek when he first investigated on June 22. Judging from the size of some individuals, breeding must have commenced at least a month earlier during the dry season. Although there is no rain in May, stream flow may be high owing to melting snow at higher elevations. The amount of surface water rapidly diminishes, until in late June, just prior to the first summer rains, water remains in only a few potholes. Summer rains are usually enough to keep the pools filled, though surface flow disappears at times. Some breeding probably took place along South Fork in late June and early July 1958, though direct evidence is lacking.

The largest chorus encountered was on July 1, following 13 mm of rain that day. A gravid female was found on this date. Although this chorus followed a heavy rain, other rains before and after this date elicited no such mass response from the frogs and calling on dry nights was not infrequent. Only one other gravid female was found in 1958 (June 28), and vocal activity decreased greatly after the first week in July. The situation was somewhat different in 1960. Investigation of the pools in South Fork in late June contained no tadpoles. If there was a spring breeding, all tadpoles had metamorphosed and left the water by late June. On July 17, 1960, in South Fork small tadpoles and an egg almost ready to hatch were found. A sample of tadpoles taken there on July 20 includes individuals in stages 26 through 31. The first summer rain at the nearby Southwestern Research Station in 1960, 0.70 inches, fell on July 3, and a total of slightly more than 4 inches fell by July 10. Most breeding this year took place during this period, for there was little calling later, and no females were found after July 8.

Eggs are 3.8–5.0mm in diameter and attached to debris and rocks at the bottom of rocky pools. Eggs may be single or in clumps. Tadpoles transform between 40–75 days of age and about 15–18 mm in body length. Transformation occurs from in early June mid-August. Newly transformed froglets are about 17 mm.

The period from oviposition to metamorphosis estimated by Zweifel (1961) was between 50 ̶60 days, like the range of 40 ̶75 days given by Stebbins (1951). It is curious that the pool in which the eggs were laid was the only one of several in the canyon that did not go dry later in the summer. At the time oviposition took place all pools were full and connected.

Parasites. Canyon Treefrogs are hosts for the trombiculid mites of the genus Hannemania. The larval mites present as orange-colored skin lesions about one millimeter in diameter mostly on the on ventral skin and ventral surface of the hind limbs. The larval mites had ovoid bodies approximately 44 microns in length and 240 microns in width. Three of six captive frogs with the infection died. However, it is unknown whether mite infestations directly kill or if the  mites transmit infectious diseases (Sladky et al. 2000).

Predatory Defense. The cryptic coloration is likely their primary defense, but like other anurans it likely has toxic or noxious skin secretion to deter predators. Hernández-Pérez et al. (2018) found skin secretions from D. arenicolor are rich in proteins with a molecular weight between 20 and 37 kDa. However, the skin secretions do not contain any of the typical defensive 12 to 48 amino acid-long peptides described in other members of the Hylidae. At the same time, one of the major components in the skin secretion of D. arenicolor is a 58 amino acid polypeptide that shares homology with anntoxin, a Kunitz-like protease inhibitor and neurotoxin first described in the skin secretions of H. annectans. The authors were interested in the antimicrobial potential of skin secretions from this frog based on ethnopharmacology treatment of skin infections. They tested its effects and found a small antimicrobial effect not considered significant in its ability to protection against microorganisms. They suggest arenicolor skin secretions focused primarily, but not exclusively, for defense against non-microbial threats.

Have been used in experiments to test the thermoregulation relating to how its skin manages water uptake (Snyder and Hammerson 1992).

Taxonomy & Systematics. Baird (1854:61) described Hyla affinis based upon syntypes that were not listed in the original publication but according to Cochran (1961:50) they were five specimens (USNM 11410). She designated USNM 11410a designated a lectotype by implication. The type locality given by Baird was Northern Sonora, Mexico, or likely in the Gadsden Purchase region in what is now Arizona, USA, south of the Gila River. Smith and Taylor (1950) restricted it to the Santa Rita Mts., Pima and Santa Cruz counties, Arizona. Gorman (1960) restricted it to Peña Blanca Springs, 10 miles northwest of Nogales, Santa Cruz County, Arizona. Neither of these restrictions was based on disclosed evidence and therefore invalid according to Fouquette and Dubois (2014). The name was preoccupied by Hyla affinis Spix, 1824.

Baird (1859:35 caption, and pl37, fig. 10–13). Hylarana fusca based on the holotype: figured in the original publication, possibly deposited in the USNM or ANSP.  The type locality was not given, but presumably from the United States–Mexico boundary region. Nomen oblitum, tentatively placed in this synonymy by Frost and McDiarmid based on the illustration and the presumption that the specimen came from the United States/Mexico boundary region. Junior secondary homonym of Hyla fusca Laurenti, 1768.

Cope (1866:84) proposed the name Hyla arenicolor as a replacement name for Hyla affinis Baird, 1854. Boulenger (1887:53) described Hyla copii based upon syntypes BMNH 1947.2.23.26–27 from the type locality of El Paso, Texas. The name was place in the synonymy by Cope, 1888: 80. Cope 1888:80 corrected the error with the spelling of Hyla copii to Hyla coper. Mocquard (1899:165) described Hyliola digueti based upon the syntypes: MNHNP 1898.257–258, 1901.343–345 from the type locality: Nayarit, Mexico. This name was placed in the synonymy by Kellogg (1932:152). Fouquette and Dubois (21014:333) used the combination Hyla (Dryophytes) arenicolor. Duellman et al. (2016:23) placed it in the genus Dryophytes and used the combination Dryophytes arenicolor.

Barber (1999) examined patterns of phylogeography and gene flow in the Canyon Treefrog using 973 bp of mitochondrial cytochrome b sequence data were obtained for 65 individuals from 53 populations, and he recovered 50 unique haplotypes. Interpopulation sequence variation ranged from 0.0-13.7%. Phylogenetic analysis revealed three deeply divergent mtDNA lineages. These three clades were mapped and found to represent completely concordant, nonoverlapping, geographical regions. Levels of sequence divergence between the three clades were equal to or greater than published levels of divergence found in other vertebrate species and genera. Furthermore, one clade was found to be more closely related to the outgroup D. eximia than to other.

Klymus et al. (2010) surveyed the geographical variation in male advertisement calls of the wide-ranging Canyon Treefrog and found large differences in geographically distant lineages that had been characterized by a recent phylogeographical study. To test whether these call differences were biologically relevant and could allow reproductive isolation of different lineages should they come into secondary contact, they assessed female preference in a lineage occurring in southern Utah and north-western Arizona, USA. These females exhibited a strong preference for their own lineage’s call type over the calls of two Mexican lineages, but not over the calls from the geographically nearest lineage. They also identified traits that female frogs probably use to discriminate between lineage-specific advertisement calls.

Klymus and Gerhardt (2012) used genome wide AFLP (amplified fragment length polymorphism) markers to resolve relationships within Canyon Treefrogs. As in previous studies, their inferred phylogeny not only provides evidence for repeated mitochondrial introgression between D. arenicolor lineages and D. eximia/D. wrightorum, but it also provides more resolution within the main D. arenicolor clade than was previously achieved with sequence data. However, the placement of a lineage of H. arenicolor whose distribution is centered in the Balsas Basin of Mexico remains poorly resolved, perhaps due to past hybridization with the D. eximia complex. Furthermore, the AFLP data set shows no differentiation among lineages from the Grand Canyon and Colorado Plateau despite their large mitochondrial sequence divergence. The results inferred a well-supported sister relationship between this combined Colorado Plateau/Grand Canyon lineage and the Sonoran Desert lineage, a relationship that strongly contradicts conclusions drawn from the mtDNA evidence.

Bonnie et al. (2008) looked at the genetic structure of populations in the Rincon Mountains and found no genetic structure with geography. They suggest changes in the Tucson basin in the past 100 years may play a role in their results. The populations sampled may have been more broadly connected to others in greater eastern Pima County; but they are no longer connected because of landscape changes made by humans. A larger, more recent (<100 years) population over a broader geographic area reduced to isolated foothill populations in the different mountain ranges would be consistent with their results. Such a recent event would likely not have had enough time to be revealed in mtDNA differences across the landscape. Their negative Tajima’s D value suggests recent expansion (increase in number of individuals) across all the study populations. They proposed that Hyla arenicolor populations probably experience large booms and busts consistent with variation in water availability. Monsoon weather patterns in the Tucson area drives some of this variability and may also assist in dispersal of the Canyon Treefrog; higher water levels and relatively moist environmental conditions allow them to return to habitat patches to recolonize as water returns. Thus, each canyon site historically had equal opportunity to be colonized by all possible genetic types (haplotypes) in the source population during productive years. During a bust year, those genetic types each have equal probability of being locally extirpated, thus leaving a distribution of haplotypes unrelated to geographic location. Each time this pattern occurs, it is like shuffling a genetic deck of cards. This would explain why more distantly related haplotypes might be found at the same site, as opposed to them having evolved at each specific site. Thus, the genetic structure is not tied to geography at the resolution level used in the analysis.