Hyla Regilla Research Articles

Latitudinal effects on metabolic rates in the cricket frog, Acris crepitans: acutely measured rates in summer frogs.

If a poikilothermic animal could not compensate for temperature in metabolic activity, the rates of chemical reactions and the rates of various activities of the or ganism could be expected to be proportional to the temperatures to which the animal is exposed. It is, however, well documented that a great variety of poikilotherniic animals can compensate for temperature in various physiological activities (Bullock, 1955 ; Precht, Christophersen and Hensel, 1955 ; Prosser, 1964) . Northern populations of the same or closely related species often have higher rates of activity than southern populations measured at the same temperature. As a result, northern and southern populations may have similar rates of activity although they are living in very different thermal environments (Bullock, 1955; Precht, 1958 ; Vernberg, 1962). The compensation for temperature in physiological activities which may be encountered among populations from different latitudes is frequently found to be stable and the differences are assumed to be genetically determined. On the other hand, the response of an individual organism to temperature may be dependent upon the temperatures to which the animal was previously exposed. Any such acclimation effect must be ruled out before differences between geographically separated populations can be considered to have a genetic basis. Several investigators have compared the metabolic rates of latitudinally or altitudinally separated populations of the same or different species of Anura. Thus, Tashian and Ray (1957) reported differences in the rates of oxygen con sumption between adults of northern and southern species of frogs. In addition, Tashian and Ray (1957) compared northern and southern subspecies of Bufo borea-s while Packard (1971) compared montane and piedmont populations of Pseudacris trisericita. Significant differences were not found in either case. How ever, Jameson, Taylor and Mountjoy (1970) report a great deal of variability in metabolic rates between populations of the frog, Hyla regilla, from localities ex tending from British Columbia to Baja California. They found no clear-cut correlation between latitude and metabolic rate but did find that frogs from locali ties which were similar with respect to climate showed similar degrees of metabolic adjustment and tended to differ markedly from frogs from climatically different regions. In the examples cited, the possibilities that genetically fixed latitudinal and short-term acclimation effects would be confounded were reduced by comparing ani mals acclimated at the same temperature under controlled conditions in the labora tory. Nonseasonal thermal acclimation of the metabolic rate has been reported

A REAPPRAISAL OF MATING CALL DIFFERENTIATION IN HYLA CADAVERINA (= HYLA CALIFORNIAE) AND HYLA REGILLA.

Ball and Jameson (1966) in their of reproductive isolation between the broadly sympatric western North American tree frogs, Hyla cadaverina (as H. californiae; see Duellman, 1968) and H. regilla, paid particular attention to differences in mating call structure, which they presumed to be the most important of the possible premating isolating mechanisms. They described the call of H. cadaverina as strictly monophasic and lacking the compact trills (= pulse modulation) present in the usually pulsed, diphasic calls of H. regilla. But instead of concentrating on these marked differences, they selected three other call components for detailed multivariate statistical analysis: mid-point of the dominant frequency, call duration, and call repetition rate. Snyder and Jameson (1965) made a detailed of geographic variation in the mating call structure of H. regilla throughout its extensive western range, and also omitted any consideration of pulse repetition rate. Although they did not consider the presence of H. cadaverina as a possible selective influencing dominant frequency in the southern populations of H. regilla, they showed that H. regilla females could effectively discriminate between the mating calls of the two species and were attracted only to calls of conspecific males. Other monophasic signals, presumably associated with territoriality, were also described. Following a complex statistical analysis involving several samples from singlespecies (allopatric) and two-species (sympatric) breeding assemblages (all of which are from within the area of geographic overlap; see range maps in Stebbins, 1966), Ball and Jameson (1966) arrived at the following conclusions. 1) Since there is overlap in the values of all of the call components measured, one call character appears to be independently operative as the primary isolating factor (page 544). Evidently differences in the total call complex of each species is (sic) significant enough to result in interspecies isolation with no one parameter being the major selective force (page 550). 2) Little evidence of the reinforcement of morphological or call parameter differences between Hyla regilla and Hyla californiae was demonstrated in this study (page 545). Both of these statements, but more especially the first, are widely at variance with what has been reported for other sympatric hylid frogs. Blair (1958), Crenshaw and Blair (19591), Littlejohn (1959, 1965, 1969), Michaud (1964) and Ralin (1968) have drawn attention to the striking differences in pulse repetition rates in mating calls of closely related sympatric species of hylid frogs. In general, there is no overlap in ranges of variation, and means differ by a of two or more (Littlejohn, 1969). Results of two-choice female discrimination tests between sympatric hylids in which the mating calls differ principally in pulse repetition rates (Littlejohn, 1960; Littlejohn, Fouquette and Johnson, 1960; Littlejohn and LoftusHills, 1968; Michaud, 1962) showed that sexually active females could differentiate between the calls and were only attracted to those of the homospecific male. LoftusHills and Littlejohn (1971), using syn-

Canonical Correlation between Variation in Weather and Variation in Size in the Pacific Tree Frog, Hyla regilla, in Southern California

The Pacific tree frog, Hyla regilla, is known to display a great deal of intraspecies variation and occupy diverse habitats. Temperature, rainfall, and altitude following Bergmann's rule and Allen's rule were suggested as selective forces which might be related to the morphological variation. Frogs from seven localities along a transect across southern California were collected and ten morphological measurements were made. Eight weather variables were chosen and measured. Discriminant analysis showed the populations differed significantly from one another in size, p < .001. Canonical correlation was used to determine which of the measurements in the two domains contributed to

Chronological Correlation between Change in Weather and Change in Morphology of the Pacific Tree Frog in Southern California

Morphological variation in a single population of Hyla regilla was studied over a period of three years, and this variation was analyzed and correlated with environmental changes using discriminant analysis, principal component analysis and canonical correlation. A significant difference was found to exist between samples captured at different times and these differences were found to be strongly correlated with rainfall during development and high and low temperatures in the fall prior to breeding. The first year of the study was the driest on record, and the frogs taken during that year were smaller and had relatively longer fingers and shorter toes than the frogs obtained in two subsequent years. Frogs may differ allometrically at different times of the year and also, to a lesser degree, from year to year in response to fluctuations of environment. The rapidity of response in the population may indicate that initially some of the variation is non-genetic followed later by periods of genetic stabilization. The exact nature of the selective mechanism is not clear, but direct effects of heat and moisture on the frogs' abilities to retain water and dissipate heat may be important.

Osmic staining of amphibian and gastropod photoreceptors

Eyes of two species of amphibian tadpoles (Xenopus laevis and Hyla regilla) and of a pulmonate snail (Helix aspersa) were impregnated with osmium tetroxide, with or without extraction by chloroform. Amphibian rods, but not cones, stained heavily with aqueous osmium tetroxide. After extraction with chloroform, osmification (OsO4 in CCl4) did not produce heavy deposits of osmium black, but 30–45 diameter granules in the outer leaflets of rod disk membranes became visible. The granules may be stained molecules of photopigment. The pigmented epithelium of light-adapted eyes, but not of dark-adapted eyes, exhibited prominent Golgi cisternae and cytoplasmic vesicles filled with reaction product. Photosensory cells of H. aspersa exhibited osmium black in rhabdomeric microvilli and in 800 vesicles, termed photic vesicles. After extraction with chloroform, little reaction product appeared, but 30–50 diameter granules, interpreted as stained molecules of photopigment, were found in the vesicles and microvilli.

Metabolic and Morphological Adaptation to Heterogenous Environments by the Pacific Tree Toad, Hyla regilla

Metabolic and Morphological Adaptation to Heterogenous Environments by the Pacific Tree Toad, Hyla regilla

METABOLIC AND MORPHOLOGICAL ADAPTATION TO HETEROGENOUS ENVIRONMENTS BY THE PACIFIC TREE TOAD, HYLA REGULA.

Massive strides in the understanding of basic biological phenomena have been accomplished by the concentration on one or a few variables. The geneticist has considered the variable genotype in a constant environment, the ecologist a variable external environment on a constant genotype. The physiologist has emphasized the metabolic mechanisms involved in the relation between variable external and internal environments usually with a constant genotype. The developmental biologist has studied the changing phenotype in a relatively constant genotypic and external environment. These specializations have proven desirable-even necessary. The spectacular breakthroughs of the molecular biologist are indicative of the power of the method of concentration on a limited objective which ignores or standardizes or often uses as tools the other variables. The method works-a sufficient criterion for its continued use. These specialized approaches have led to naive considerations of the invariable components and, probably more important, have led to constricted visions of the whole system. Studies of the interaction of the several systems are hampered by the absence of adequate models subject to experimental test. Successful economic studies in agriculture use analysis of variance and multivariate analysis. These studies are based on the linear additive model and investigators usually are content to identify the relative magnitude of the interaction component when compared to the within-group variation. The nonlinearity of nature does not hamper this approach but may well limit its use in understanding the mechanism of interaction. A few holistic analyses have had variable successes. Birch (1960, and elsewhere) examined some aspects of the relation of genotype on numbers of organisms through the genetic variability of the components of the intrinsic rate of increase. Levins (1968, and elsewhere) used an optimum genotype and an optimum environment and analyzed the variation in terms of deviations from these optima. These models are logical outgrowths of earlier approaches including concepts presented within the terms adaptation, assimilation, stabilization, canalization, acclimatization, all of which must be considered as various ways of looking at the same phenomena. The necessity to use the holistic approach increases as the knowledge multiplies in each field and as the tools and data of other fields are required to understand the information obtained in specialized studies. This study attempts to examine the interrelation between internal and external environment and genotype in the life of the Pacific tree frog, Hyla regill. The study is subject to naive considerations and constricted vision and can merely claim to emphasize the role of these variables in the life of the frog. Prosser (1955) listed three kinds of variation of physiological and morphological characteristics: genetic, ontogenetic, and phenotypic. The genotype sets the limit for phenotypic variation. Physiological variation allows environmental limits to be set for each population of animals

Osmic Impregnation of Amphibian and Gastropod Photoreceptors

Friend and Murray found that long osmification of mouse epididymis revealed localized osmium reduction in epithelial cells; in this instance, in only the outer cisternae and vesicles of the Golgi apparatus. Although many substances reduce osmium, aldehydes and compounds with multiple double bonds are particularly active. Knowing that retinaldehyde (vitamin A aldehyde) is a highly unsaturated aldehyde we applied their technique to eyes of tadpoles of two amphibians (Xenopus laevis and Hyla regilla) and to adult eyes of one pulmonate snail (Helix aspersa). Eyes were extirpated, immersed in unbuffered 2% aqueous osmium tetroxide for two or three days at 40°C, and prepared for electron microscopy by rapid dehydration with ethanol, embedment in Epon, and examination of ultrathin sections without further staining.

Description and Life Cycle of Glypthelmins hyloreus sp. n. (Digenea: Plagiorchiidae)

Adults live in the intestine of the Pacific tree frog, Hyla regilla. Sporocysts in the pond snail, Lymnaea stagnalis, produce gymnocephalous cercariae with continuous dorsal and ventral caudal fins. Cercariae escape the snail, enter H. regilla tadpoles via the nares, and reach the coelom. There they develop as motile unencysted metacercariae which then enter and mature in the frog's intestine only after metamorphosis. Glypthelmins hyloreus most closely resembles G. pennsylvaniensis but has vitellaria which extend farther posteriorly, a larger seminal receptacle and cirrus sac, cercariae with fin folds and without stylet, and unencysted metacercariae. Separating the species of Glypthelmins on the basis of adult morphology alone is considered unsatisfactory. During a survey of Oregon amphibia for trematode infections, a plagiorchiid species was found in the intestine of the Pacific tree frog, Hyla regilla Baird and Girard. This fluke resembles other species of Glypthelmins but because of differences in morphology and life cycle it is here designated as a new species, Glypthelmins hyloreus. The taxonomy of Glypthelmins and related genera has been in confusion for many years. Stafford (1900) described Distomum quietum for which he later (1905) erected the genus Glypthelmins. Thereafter, species assigned and reassigned to this genus and the systematic position of the genus itself have posed the taxonomic difficulties which Byrd and Maples (1963) discussed in revising the genus Glypthelmins. Later, Nasir (1966) reduced Margeana Cort, 1919; Choledocystus Pereira and Cuocolo, 1941; Reynoldstrema Cheng, 1959; and Repandum Byrd and Maples, 1963 to synonymy with Glypthelmins in which he considered 20 species as valid. Leigh (1937, 1946) and Rankin (1944) independently determined the life cycle of Glypthelmins quieta. Xiphidiocercariae with caudal fins develop in species of Physa, emerge and encyst in the skin of various frogs. Metacercariae shed with the skin are ingested by the frog and develop to adults in the intestine. Cheng (1961) reported essentially the same life cycle for his Glypthelmins pennsylvaniensis except that Helisoma trivolvis Say is the intermediate host, and the cercaria lacks a caudal

Ultrastructure of amphibian melanophores after light-dark adaptation and hormonal treatment

Melanophores in dark-adapted or melatonin-treated tadpoles of Xenopus laevis and Hyla regilla are punctate with the melanosomes aggregated in the perikaryon. The processes of these melanophores are devoid of melanosomes and markedly reduced in diameter. Upon exposure to light or MSH, the evacuated processes imbibe fluid by macropinocytosis, distending the evacuated processes and allowing the melanosomes to migrate distally. When light-adapted melanophores are placed in the dark, the melanosomes migrate toward the perikaryon and the processes then collapse, the melanosomes being forced proximally. It is proposed that fluid uptake is involved in melanosome dispersion and fluid loss in melanosome aggregation. Microtubules do not appear to aid in the movement of melanosomes or to function as a cytoskeleton.

The Heat Resistance of Some Anuran Tadpoles (Hylidae and Pelobatidae)

Survival times of anuran tadpoles representing four species of two genera in the families Hylidae and Pelobatidae were determined at high temperatures. Heat resistance was studied by acclimating tadpoles to a constant temperature and determining the time to 50% survival after direct transfer to constant, high temperatures. Results indicate that thermal acclimation influences heat resistance, and that heat resistance correlates with the species' geographic distribution and breeding habits. Tadpoles of the tropical treefrog, Hyla septentrionalis, and desert spadefoot toad, Scaphiopus couchii, were the most heat resistant; tadpoles of the western spadefoot toad, S. hammondii, from California were the next most heat resistant, and tadpoles of the Pacific treefrog, H. regilla, were the least resistant.

Studies on Water Loss and Rehydration in Anurans

Studies on Water Loss and Rehydration in Anurans

An albino Pacific tree frog, Hyla regilla, from Death Valley, California

An albino Pacific tree frog, Hyla regilla, from Death Valley, California

A Comparison of the Chromosomes of Hyla regilla and Hyla californiae

Testicular mitotic chromosomes from Hyla regilla and Hyla californiae show the diploid number to be 24. No observable structural differences in the chromosomes of these species could be detected. Three distinct groups of chromosomes are identifiable in each species. Karyograms were analyzed and differences in normalized chromosome length between samples from allopatric and sympatric populations were not detected. The overall length of the chromosomes of H. regilla was greater than that of H. californiae, probably due to differential condensation of the chromosomes of the two species.

Development of Color in Chimeras of Pacific Tree Frogs

Development of Color in Chimeras of Pacific Tree Frogs

Cytoplasmic filaments and morphogenetic movement in the amphibian neural tube

Cells of the medullary plate and groove were studied with the electron microscope during neurulation in Hyla regilla and Xenopus laevis in an attempt to locate structures that might be involved in morphogenetic movement. The apices of the neural plate cells contain a thin band of filaments aligned parallel to the outer surface of the plate. As neurulation proceeds, the groove narrows and deepens; correspondingly, the cell apices narrow, the apical band becomes broader and crowded with oriented filaments, and the cell body assumes a long columnar or bottle shape. In Xenopus filaments are arranged circularly around the cell neck. The cell apices are tightly joined to one another. It is proposed that filament contraction causes the neural plate to invaginate. This theory is discussed in relation to other theories of neurulation and morphogenetic movements.

Onset of chromatophore-stimulating activity by the hypothalamus and adenohyphysis in Hyla regilla and Ambystoma tigrinum

Infundibular and adenohypophysial analagen were homoplastically transplanted to subcutaneous tissue of larvae previously hypophysectomized at the tailbud stage. Results indicate that at the stages employed in this study differentiation of the grafts proceeded at a rate reflected by the stage of development of the donor. The onset of chromatophore-stimulating activity by hypothalamic grafts from tailbud embryos of the Pacific Treefrog, Hyla regilla, occurred at post-tailbud stages 20 and 21 (Eakin's series). Adenohypophysial grafts, on the other hand, evoked initial responses in the host melanophores at young larval stages 23 and 24. Similarly in the Tiger Salamander, Ambystoma tigrinum melanostictum, initial pigment responses by hypothalamic and adenohypophysial grafts occurred at post-tailbud stages 37 and 38 and larval stages 39 and 40 (Harrison's series), respectively. By triturating individual grafts the chromatophorotropin was detected approximately one stage prior to the initial release.

Hypothalamic chromatophore-stimulating activity in the amphibians Hyla regilla and Ambystoma tigrinum

Hypothalamic grafts from embryos, larvae, and adults, of the Pacific Treefrog, Hyla regilla, and the Tiger Salamander, Ambystoma tigrinum, homoplastically transplanted to young larvae previously hypophysectomized at the tailbud stage, evoked melanin dispersion and aggregation of reflecting pigment in host chromatophores. To avoid contamination with adenohypophysial hormones hypothalamic tissue was excised from embryos prior to contact with the adenohypophysial anlage and from “albino” larvae and adults hypophysectomized at least one week previously. Sustained responses by adult brain tissue were limited to grafts from ventral parts of the post optic ventral hypothalamus. Responses by grafts from other areas of the hypothalamus and adjacent regions of the brain disappeared within a few days. Histological examination of positive and negative grafts confirmed their exclusively neural origin but did not reveal the cells responsible for the chromatophorotropic activity.

Ultrastructural studies on the developing neurohypophysis of the Pacific Treefrog, Hyla regilla

The differentiation of the hypothalamo-hypophysial neurosecretory system of the Pacific Treefrog Hyla regilla has been examined by correlated light and electron microscopy. Growing neurosecretory axons reach the diencephalic floor in close proximity to the “migrating” adenohypophysis at embryonic stage 23, approximately at the time of hatching. These axons, which already contain typical elementary neurosecretory granules and small vesicles, then grow caudad into the thin-walled infundibulum, reaching the site of the future neurohypophysis by larval stage 1. Not until active outgrowth of the nerve fibers is completed can the neurosecretory material within them be visualized with the light microscope. A striking synchrony exists between the rate of axon growth and the rate of adenohypophysial “migration.” Axons, usually containing small vesicles and small dense granules, penetrate the pars intermedia extensively, beginning with embryonic stage 24. Vascularization of the neurohypophysial area coincides with the arrival of neurosecretory axons at the site of the pars nervosa, just prior to larval stage I. As soon as these events have occurred, the pars nervosa is a miniature but ultrastructurally complete version of the adult neurohemal organ. Further development of the pars nervosa involves an increase in the number and size of axons, in number and possibly size of elementary neurosecretory granules, and in number of glial cells and capillaries. The median eminence differs from the pars nervosa in ultrastructure. Its axon terminals contain smaller neurosecretory granules (1000 A as opposed to 1500 A) and a greater abundance of small vesicles; the difference is reflected in the lesser intensity of paraldehyde fuchsin staining in the median eminence as compared to the pars nervosa. The characteristic terminals do not appear in large numbers in the median eminence until just before metamorphic climax. The observations are discussed in terms of the ontogeny of neurohypophysial function and the possibility of inductive relationships between various parts of the hypophysis.

Rate of Weight Loss of Tree Frogs at Various Temperatures and Humidities

Sixteen Hyla regilla, four each from four localities, were desiccated at each of four temperatures (10, 15, 20, 25°C); each animal was weighed five time in 23 hr. Three of the frogs maintained at 25°C died after a loss of approximately 36 to 52% of body weight during 23 hr; none died at lower temperatures. The rate of weight loss was significantly higher at high temperatures than at low temperatures and increase logarithmically with temperature. The total difference between localities was not statistically significant. Fifteen combinations of temperature (5,10, 15, 20, 25°C) and humidity (35 to 40, 50 to 55, 60 to 80% R.H.) were successively established in a plant growth chamber. The mean rate of weight loss of 6 Hyla regilla from each of 11 localities and 6 H. californiae from 1 locality was obtained at each set of conditions. The effect on rate of weight loss of a given increase in temperature is greater at low humidities than at high humidities. The rate of weight loss was adjusted by initial weight and by eigenvector values from principal component of morphological values. The adjusted rates were than analyzed by split—plot design analysis of variance. The sample means were found to differ significantly with respect to temperature, humidity and locality. The interaction of locality and temperature of humidity was not significant; temperature and humidity did have a significant interaction. Multivariate discriminant analysis separated the population into three groups. One group consisted of frogs from southern California desert and Baja California localities. The second group consisted of frogs from southern Carolina coast and mountains, and frogs from Yosemite. The third consisted of frogs from the northern part of the range. The rate of weight loss of different localities demonstrates a relation between latitude and some linear function of the first two discriminant axes. The data were reanalyzed after removal of the 25°C conditions. The split—plot design analysis of variance then indicated that the rate of weight loss of the frogs from the different localities were not significantly different. The discriminant analysis did not show a grouping as discrete as before, but the general pattern was about the same. The grand means for each locality of all frogs for all conditions were obtained and compared. A single sample (Lee's Camp) differed greatly from all samples, more than Hyla regilla differs from H. californiae. No relation between available environmental moisture and rate of weight loss was discerned. The linear arrangement of the discriminant values of the northern populations suggests some relation to the "ecogegrophical rules." This relationship is not shown in the discriminant values of the rates from southern localities.