Hyla Cinerea Research Articles

Tadpole bullies: examining mechanisms of competition in a community of larval anurans

We examined interference competition during interspecific interactions of larval anurans to determine its importance. We conducted laboratory experiments to examine behavioral and chemical interference competition between tadpoles of the southern leopard frog (Rana utricularia) and those of the green treefrog (Hyla cinerea). Water preconditioned byR. utricularia tadpoles significantly decreased the growth and increased the mortality of H. cinerea tadpoles compared with control treatments. In addition, R. utricularia tadpoles inhibited the feeding rate ofH. cinerea tadpolesby harassing them, and these interactions significantly decreased the growth and increased the mortality of theH. cinerea tadpoles. Rana utricularia tadpoles apparently use both chemical interference and aggressive behavior in securing a competitive advantage over H. cinerea tadpoles, and the H. cinerea tadpoles suffer from these interactions. Intraspecific chemical and behavioral interference competition also significantly decreased the growth of larval H. cinerea. In natural ponds, R. utricularia tadpoles that inhibit the growth and increase the mortality of H. cinerea tadpoles may increase their own chances of survival and metamorphosis, while H. cinerea tadpoles that avoid interactions with conspecifics and with R. utricularia tadpoles may increase their own chances of survival and metamorphosis.

Spontaneous otoacoustic emissions in seven frog species

Spontaneous otoacoustic emissions were screened for in five advanced frog species (Hyla cinerea, n =10 ears; Hyla chrysoscelis, n = 10; Hyla versicolor, n = 7; Leptodactylus albilabris, n = 2; Rana pipiens pipiens, n = 8), and two primitive frog species (Xenopus laevis, n = 9; Bombina orientalis, n = 12). Emissions were found in 90% of the advanced species' ears, whereas none of the primitive species' ears had emissions. Emission frequencies ranged from 645 Hz to 1680 Hz. The absence of emissions in the primitive species correlates with (1) the absence of a tympanic membrane, and (2) a reduced length of the caudal extension of the amphibian papilla. In eight frogs, the effect of body temperature on emissions was investigated. As a function of temperature, the frequency changed at a rate between 0.009 and 0.091 oct/°C, and emission levels displayed a complex but consistent behavior. For 9 out of 15 spectral emission peaks encountered during the temperature experiments, the relation between the peak height and peak width was similar to that of an active oscillator.

Geographic Variation in the Morphology and Lateral Stripe of the Green Treefrog (Hyla cinerea) in the Southeastern United States

-Five southeastern populations of the green treefrog were examined to evaluate geographic variation in four morphological characters and lateral stripe length. Analysis of covariance demonstrated that tibio-fibula length was significantly shorter in the population from the Appalachian Plateau and Ridge and Valley regions of northern Alabama compared to that of the Piedmont and Coastal Plain populations. Body length varied significantly among some populations. Lateral stripe length was highly variable among populations with no apparent geographic pattern to this variation. The morphological differences found in northern Alabama may be attributed to genetic drift or the founder effect.

Effects of low pH and aluminum on body size, swimming performance, and susceptibility to predation of green tree frog (Hyla cinerea) tadpoles

Green tree frog (Hyla cinerea) tadpoles were exposed immediately after hatching to aluminum (nominally 0, 150, 250, 400 μg/L) at pH 4.5 or 5.5, plus a control (pH 7.0, 0 μg/L Al) for 96 h. Mortality increased with increasing Al concentration at pH 4.5 but not at pH 5.5. Among surviving tadpoles, body size was significantly reduced at higher Al concentrations at both pH 4.5 and 5.5. At pH 4.5, analysis of covariance indicated that maximal swimming speed was positively correlated with tadpole total length and differed among Al treatments; tadpoles at higher Al levels swam more slowly. Body Al and Na+concentrations also differed among treatments. In a second experiment, tadpoles exposed for 96 h to approximately 150 μg/L Al at 4.5 pH were preyed upon by dragonfly larvae (Libellulidae) at a higher rate than were tadpoles raised in pH 4.5 or 7.0 without Al. As in the first experiment, tadpoles exposed to Al were smaller and were slower swimmers. Sublethal concentrations of Al at low pH may result in lowered growth rates and hence reduced body size. Swimming performance is reduced by small body size, and size-adjusted performance is further reduced by Al and low pH, which might lead to higher predation on Al-stressed tadpoles.

Feeding kinematics of phyllomedusine tree frogs.

Previous studies have demonstrated that the phyllomedusine hylids possess highly protrusible tongues, a derived characteristic within the family Hylidae. In the present study, the kinematics of the feeding behavior of a phyllomedusine species, Pachymedusa dacnicolor, was analyzed using high-speed video (180 frames s-1). Its behavior was compared with that of Hyla cinerea, a species with a weakly protrusible tongue. P. dacnicolor exhibits a faster rate of tongue protraction, a longer gape cycle and more variable feeding kinematics than H. cinerea. In addition, the tongue is used in a unique 'fly-swatter' fashion, to pin the prey to the substratum as the frog completes the lunge. The rapid tongue protraction, extended gape cycle and fly-swatter action may have evolved in response to a diet of large, rapidly moving insects. In addition, several duration variables of the feeding cycle were greater for misses than for captures and drops, which suggests that sensory feedback rather than biomechanics controls gape cycle duration.

Rear Leg Amputation and Subsequent Adaptive Behavior During Reintroduction of A Green Tree Frog, Hyla cinerea

The left rear leg of a green tree frog, Hyla cinerea was amputated following a severe femoral fracture. After convalescence, the frog was reintroduced into the display area where volunteers monitored its locomotive abilities, successful capture of prey, and interaction with other frogs for one week. The frog adapted well and continues to be a popular and valuable feature of the exhibit.

The lung-eardrum pathway in three treefrog and four dendrobatid frog species: some properties of sound transmission.

Frequency-response curves of the tympanum and lateral body wall (lung area) were measured by laser Doppler vibrometry in three treefrog (Smilisca baudini, Hyla cinerea, Osteopilus septentrionalis) and four dendrobatid frog (Dendrobates tinctorius, D. histrionicus, Epipedobates tricolor, E. azureiventris) species. The high-frequency cut-off of the body wall response was always lower than that of the tympanum. The best response frequencies of the lateral body wall were lower than those of the tympanum in some species (S. baudini, O. septentrionalis, D. tinctorius), while in the others they were rather similar. Best tympanic frequencies and best body wall response frequencies tended to differ more with increasing body size. Stimulation of the tympanum by sound transfer through 3.14 mm2 areas of the lateral body wall showed that the lung-eardrum pathway can be in two states, depending on breathing activity within the lungs: 44% (in Smilisca), 39% (in Hyla) and 31% (in Osteopilus) of the eardrum vibrations were 2.5-8 times (8-18 dB) larger when the frogs were breathing with the lungs compared with non-breathing conditions. The vibration amplitudes of the tympanum and lateral body wall of the treefrogs followed the same dependence on sound intensity, only absolute amplitudes differed between species. Our results suggest that the lung-eardrum pathway attenuates high-frequency components of species-specific calls and enhances low-frequency components. In addition, an amplitude modulation is imposed on the low frequencies during the rhythm of breathing.

Metamorphic Responses to Changing Food Levels in Two Species of Hylid Frogs

We investigate how changes in food availability during development affected the timing of and body size at metamorphosis in two closely related species of tree frogs that use different larval habitats. We raised tadpoles of Hyla gratiosa (a temporary—pond breeder) and Hyla cinerea (a permanent—pond breeder) at two different temperatures on either constant resources or a regime in which we altered food levels at one of three different times during development. For both species, larval period was affected only by early changes in food level; early increases shortened larval period, and decreases lengthened it. The timing of metamorphosis of Hyla gratiosa showed greater plasticity than that of Hyla cinerea, because of its greater overall response to any food—level change and not because of any difference between species in the duration of the sensitive period. The two species showed comparable levels of plasticity in body size at metamorphosis; increases in food level produced larger body sizes, and decreases produced smaller sizes. However, in contrast to the pattern seen in larval period, later changes in food level had the greatest effect on body size. These results force a reexamination of current ideas about the adaptive significance of plasticity in the timing of metamorphosis in response to food availability in larval anurans. We offer a model of dynamic allocation that accommodates the extant data on this issue.

Measurement of temporal regularity of spike train responses in auditory nerve fibers of the green treefrog

This paper describes a method which we have developed for quantifying the temporal regularity of neural spike trains in the sensory nervous system. Our method relies on the use of a modified correlation approach for identifying response firing patterns. We apply the concept of an ambiguity function and related coefficients to measure the tonic/phasic character and statistical variability of spike patterns. We tested this method in recordings from auditory nerve fibers of the green treefrog ( Hyla cinerea) in response to pure tone, multi-tone, and gaussian white noise. Our results indicate that there is a great deal of variability in the trains of spike times generated by any given fiber in response to identically repeated stimulus presentations. Nevertheless, despite this statistical jitter of the pattern to repetitive stimulation, the spike response trains from a single fiber maintain a high degree of individual detectability in signal metric space. The procedures in our method can be implemented in a relatively simple way on a Macintosh computer and the speed is fast enough for real-time spike analysis. This kind of quantification may especially be useful in studying habituation and plasticity in neural spike train data, as well as in judging the selectivity within the neural code of an individual fiber for particular stimulus features.

Physiological Color Change in the Green Treefrog: Responses to Background Brightness and Temperature

In an effort to better understand the function of physiological color change in anurans, we measured color change responses of the green treefrog, Hyla cinerea, to background brightness and temperature. We used our results to compare color and color change responses of males and females and to test two hypotheses for the function of physiological color change in anurans: (1) that color change serves to prevent detection by visual predators, and (2) that color change functions in thermoregulation or water balance. We found that (1) males are generally darker than females but the sexes exhibit similar color change responses, (2) treefrogs become lighter on brighter backgrounds, (3) treefrogs become lighter at higher temperatures, and (4) there is a background-by-temperature interaction such that color change responses to one variable depend on the level of the other. Our results suggest that color change may function both in predator avoidance and in thermoregulation or water balance. However, further investigations of color change responses to differently hued backgrounds, of the magnitude and biological significance of color-induced changes in body temperature and rates of evaporative water loss, and of color change in freeranging animals are needed.

Temporal features mediating call recognition in the green treefrog, Hyla cinerea: amplitude modulation

Abstract. The male green treefrog, Hyla cinerea, has two signals in its vocal repertoire, the advertisement call and the aggressive call. These vocalizations are similar in frequency composition, but differ in their rate of amplitude modulation (waveform periodicity). The ability of male green treefrogs to respond to signals differing in modulation rate and depth was tested with an evoked-calling paradigm. Males were significantly more likely to vocalize in response to playbacks of stimuli modulated at the waveform periodicity of the conspecific advertisement call, and less likely to vocalize in response to stimuli modulated at the rate of the conspecific aggressive call, or to stimuli modulated at the rate of a heterospecific advertisement call. Male vocal responses showed similar changes with modulation rate in response to either modulated calls (containing both spectral and temporal cues) and modulated noise (containing temporal cues alone). Decreasing the modulation depth eliminated the effect of modulation rate on the males' vocal responses. Changes in responding with modulation rate were consistent across both field and laboratory conditions. These results suggest that the temporal feature of amplitude modulation plays an important role in call recognition in the natural environment.

The middle ear muscle of frogs does not modulate tympanic responses to sound

The effect of the opercularis (= middle ear) muscle on the acoustic responsiveness of the tympanic middle ear of anuran amphibians was studied using laser vibrometric measurements of tympanic responses to sound. Removal of the muscle or direct stimulation of denervated muscles had no measurable effects on tympanic responses to sound in either American bullfrogs (Rana catesbeiana) or green treefrogs (Hyla cinerea) at any frequency or at any sound-pressure level studied. These results suggest that, contrary to proposed hypotheses, the opercularis muscle of the anuran middle ear is not capable of modulating the responsiveness of the tympanic middle ear. Instead, the opercularis system most likely functions as an independent system involved in acoustic reception.

Effects of freshwater petroleum contamination on amphibian hatching and metamorphosis

AbstractThis study examined the effects of freshwater petroleum contamination on amphibian reproduction The primary objectives were to assess the potential environmental and physiological impacts of runoff petroleum products on amphibians, using the green treefrog (Hyla cinerea) as a target species and engine crankcase oil as a contaminant Egg hatching success, tadpole growth, and successful metamorphosis were measured in four concentrations of oil The effects of oil on food source was also studied Hatching success was not measurably influenced by the presence of oil Tadpole and alga growth were negatively associated with the presence of oil No tadpoles from the high concentration of oil treatments successfully metamorphosed

Efferents from the suprachiasmatic nucleus to basal forebrain nuclei in the green treefrog (Hyla cinerea).

Injections of horseradish peroxidase (HRP) into the eye, striatum, preoptic area, or ventral hypothalamus of the green treefrog (Hyla cinerea) demonstrated an indirect retinal pathway to each basal forebrain region via the suprachiasmatic nucleus (SCN). Intraocular injections resulted in HRP-filled fibers within the ventral portion of the SCN bilaterally. Apparent en passant and terminal swellings on these fibers were seen adjacent to SCN cells. Cells in both the ventral and dorsal portions of the SCN were retrogradely filled following each of the forebrain injections, but the relative distributions of filled cells were different. The striatum receives a bilateral projection mainly from cells in the ventral portion of the SCN. A small ipsilateral projection from this same SCN region reaches the ventral hypothalamus. The SCN projection to the preoptic area arises from a more uniform distribution of cells, with the majority located in the ipsilateral dorsal region of the nucleus. The striatum is believed to be involved in orientation responses, while the preoptic area and ventral hypothalamus regulate gonadal activity related to reproduction. Each of these areas receives auditory input carrying information about acoustic communication signals, social cues important for coordinating reproductive activity. Input from the SCN could provide these same basal forebrain centers with information about the photic environment, an important environmental cue regulating reproduction.

Scotopic spectral sensitivity of the optomotor response in the green treefrog Hyla cinerea

Amphibians are unusual among vertebrates in having two spectral classes of rod photoreceptors, unique amphibian "green" rods and typical vertebrate "red" rods. Although amphibians have been the subject of extensive research on visual function, it is not known whether possession of two classes of rods is a general feature of Amphibia, nor is it clear to what behaviors each class of rods contributes. The Hylidae comprise one of the largest families within Amphibia but have been little studied with respect to visual function. Here, we demonstrate the presence of green and red rods in Hyla cinerea by microspectrophotometry and provide evidence for the contribution of green rods to one visually based behavior, the optomotor response. In addition, we discuss the role of green and red rods in visually based behavior in light of apparently conflicting demands resulting from the need to maximize absolute sensitivity, visual acuity, and color sensitivity.

Perception of complex sounds by the green treefrog, Hyla cinerea: envelope and fine-structure cues.

1. The envelope periodicity of communication signals is an important feature distinguishing advertisement and aggressive calls for the green treefrog (Hyla cinerea). Envelope periodicity, a cue for periodicity pitch perception in humans, is affected by the fine-structure of the signal, a cue for timbre perception in humans. The present study examined perception of two acoustic features affecting waveform fine-structure--harmonic structure and phase structure--in male green treefrogs. 2. We analyzed evoked vocal responses of male green treefrogs living in laboratory arenas to playbacks of digitally-generated signals resembling either conspecific advertisement or aggressive calls in their first harmonic periodicity. Systematic changes in the harmonic structure of these signals were achieved by varying the harmonic relations between frequency components in the signals, and changes in phase structure were achieved by varying the starting phases of harmonically-related components. 3. Calling was significantly influenced by the first harmonic periodicity of the signals. Males vocalized more to signals with the periodicity of the advertisement than the aggressive call. There were no differences in response to harmonic and inharmonic signals with similar spectral content. Phase structure did not significantly influence vocal responses. 4. These results suggest that the fine-structure ("timbre") of complex acoustic signals is not a significant feature guiding behavior tested using a communication response in this species.

Trypanosome transmission by Corethrella wirthi (Diptera: Chaoboridae) to the green treefrog, Hyla cinerea (Anura: Hylidae).

Seventy-two percent of 215 male green tree frog, Hyla cinerea (Schneider), captured in Alachua and Levy counties, FL, between April and mid-September 1978 and 1979 were infected with an undescribed Trypanosoma sp. None of the 31 female frogs captured concurrently was infected. Periodic sampling of the peripheral blood from the infected male frogs showed that the trypanosomes were present in high numbers only at night. Conspecific trypanosomes also were found in the mid and hind guts of female Corethrella wirthi Stone flies collected on or near male frogs in the field. Transmission of the parasite to uninfected frogs was demonstrated by exposure of male and female frogs to naturally infected flies and to parasites injected subdermally. This is the first report of parasite transmission by a species of Corethrella.

Acoustic modulation of neural activity in the preoptic area and ventral hypothalamus of the green treefrog (Hyla cinerea).

Responses of neurons in the preoptic area and ventral hypothalamus to conspecific mating calls or white noise bursts were examined in male green treefrogs (Hyla cinerea) during different seasons. In the winter, 34.3% of preoptic neurons and 46.7% of ventral hypothalamic cells demonstrated significant changes in activity level during presentation of a conspecific mating call. In contrast, only 13.3% of preoptic units and 16.7% of ventral hypothalamic cells responded to the white noise. The percentage of preoptic and hypothalamic units responding to the advertisement call did not differ significantly during the summer breeding season. Type I units exhibited a dramatic increase in activity during acoustic stimulation followed by a rapid return to baseline activity levels after stimulus offset. Type II cells showed a robust activity increase during stimulation, but maintained an intermediate activity level after stimulus offset. In the preoptic area, a third response type exhibited suppressed activity during acoustic stimulation. Although seasonal condition did not alter the percentage of acoustically responsive units within either nucleus, the proportion of Type I units in the ventral hypothalamus was greatest during the summer.

Developmental abnormalities in triploid hybrids between tetraploid and diploid tree frogs (genus Hyla)

Crosses between tetraploid female grey tree frogs, Hyla versicolor, and diploid males of the same genus may provide information on developmental differences between the parental species. Crosses with Hyla cinerea males in 1988 produced a large number of vigorous offspring, but abnormalities in eye development indicated some incompatibility of the parental genomes. The degree of eye development of the hybrids varied, ranging from completely absent to fully functional. Repetition of this cross combination in 1989 resulted in similar variation in eye formation. Histological sections through developing eyes indicated that the abnormalities may be related to improper formation of the cornea, improper orientation of the lens, or lack of lens induction. This may reflect differences in the timing of development between the two parental species.

The Kinematics of Prey Capture and the Mechanism of Tongue Protraction in the Green Tree Frog Hyla Cinerea

ABSTRACT Prey capture was studied in the green tree frog (Hyla cinerea) before and after denervation of either the m. genioglossus or m. submentalis using high-speed videography and kinematic analysis. The prey capture behavior and extent of tongue protraction of several members of the subfamilies Hylinae, Pelodryadinae and Phyllomedusinae were also studied. Results show that the m. genioglossus is necessary to produce complete tongue protraction and that the m. submentalis is necessary for mandibular bending, but not necessary for complete tongue protraction in Hyla cinerea. The tongue of Hyla cinerea resembles the weakly protrusible tongues of the archaeobatrachian frogs Ascaphus and Discoglossus more than the highly protrusible tongues of other neobatrachians, such as Rana or Bufo. A weakly protrusible tongue is present in the subfamilies Hylinae and Pelodryadinae, and a highly protrusible tongue is present in the subfamily Phyllomedusinae. These results suggest that hyline and pelodryadine hylids have retained the ancestral anuran tongue morphology and that highly protrusible tongues have evolved once within the family Hylidae, in the subfamily Phyllo-medusinae.