Further scanning electron microscope studies of lizard auditory papillae

The papillae basilares of 12 species of lizards from seven different families were studied by SEM. The iguanids, Sceloporus magister and S. occidentalis, have typical “iguanid type” papillae with central short-ciliated unidirectional hair cell segments and apical and basal long-ciliated bidirectional hair cell segments. These species of Sceloporus are unique among iguanids in that the bidirectional segments consist of but two rows of hair cells. The agamids, Agama agama and Calotes nigrolabius, have an “agamid-anguid type” papilla consisting of an apical short-ciliated unidirectional hair cell segment and a longer basal bidirectional segment. Agama agama is unusual in having a few long-ciliated hair cells at the apical end of the apical short-ciliated segment. The agamid, Uromastix sp., has an “iguanid type” papilla with a central short-ciliated unidirectional segment and apical and basal bidirectional segments. The anguid, Ophisaurus ventralis, has an “iguanid” papillar pattern with the short-ciliated segment centrally located. All the short-ciliated hair cells of the above species are covered by a limbus-attached tectorial network or cap and the long-ciliated hair cells, only by loose tectorial strands. The lacertids, Lacerta viridis and L. galloti, have papillae divided into two separate segments. The shorter apical segment consists of opposingly oriented, widely separated short-ciliated cells covered by a heavy tectorial membrane. The apical portion of the longer basal segment consists of unidirectionally oriented hair cells, while the greater part of the segment has opposingly oriented hair cells. The xantusiids, Xantusia vigilis and X. henshawi, have papillae made up of separate small apical segments and elongated basal segments. The apical hair cells are largely, but not exclusively, unidirectional and are covered by a heavy tectorial cap. The basal strip is bidirectional and the hair cells are covered by sallets. The kinocilial heads are arrowhead-shaped. The papilla of the cordylid, Cordylus jonesii, is very similar to that of Xantusia except that the apical segment is not completely separated from the basal strip. The papilla of the Varanus bengalensis is divided into a shorter apical and a longer basal segment. The hair cells of the entire apical and the basal three quarters of the basal segment are opposingly oriented, not with reference to the midpapillary axis but randomly to either the neural or abneural direction. The apical quarter of the basal segment contains unidirectional, abneurally oriented hair cells. The entire papilla is covered by a dense tectorial membrane. The functional correlations of the above structural variables are discussed.     

Scanning electron microscope studies of the papilla basilaris of some turtles and snakes

The papillae basilares of three species of turtles and four species of snakes were studied by SEM. The papillae of turtle are relatively large among reptiles and are characterized by a long, horizontal middle section resting on wide basilar membrane. Both terminal ends of the papilla extend onto the surrounding limbus in the form of a forked or "T" -shaped end or as a curved, "hook"- like processes. Details vary with the species. In the three species of turtles studied, there were between 1,100 and 1,400 hair cells on a papilla. The tectorial membrane covering the horizontal portion of the papilla is heavy in appearance and tightly attached to the kinocilial bulbs. The terminal ends of the papilla are covered by a thin gelatinous material. In addition, mat-like tectorial network covers the supporting cells and extends from the microvilli of the supporting cells to the overlying tectorial membrane. All hair cells are unidirectionally and abneurally oriented. The supporting cell surfaces form a large part of the papilla and, thus, hair cell density is low. The papillae of the two boid snake species studied are moderately long among snakes and contain a moderate number of hair cells (574 in Epicrates and 710-780 in Constrictor). Papillar form is elongate, avoid, or canoe-shaped. The tectorial membrane may be either highly fenestrated or moderately dense and covers all but a few of the terminal hair cells. A tectorial-like mat covers all but a few of the terminal hair cells. Most hair cells are unidirectionally and abneurally oriented. A few terminal cells in boids may show reverse orientation. Hair cell density is similar to that of turtles.     

Development of the supporting cells and structures derived from them in the inner ear of the grass frog,Rana temporaria (Amphibia,Anura)

Summary The inner ear of Rana t. temporaria comprises sensory structures with various special functions, i.e., the detection of spatial orientation (utricle, saccule, lagena), of rotation (ampullae), and of acoustic signals (amphibian and basilar papillae). In each of these structures, there is a sensory epithelium made up of hair (sensory) cells and supporting cells. As the supporting cells differentiate, they produce the organic matrix of the otoconia in the gravity-sensing organs, the ground substance of the cupulae in the ampullae, and the ground substance of the tectorial membranes in the auditory papillae. The supporting cells associated with these various derivative structures have correspondingly different cytoplasmic properties. The preotoconia are formed by extrusion; the otoconia develop from these filamentous precursors by growth and calcium deposition. The organic material that forms the cupulae and tectorial membranes is released from the supporting cells by exocytosis. The organization of this material into the ground substance is initiated mainly around the distal ends of the hair-cell kinocilia, eventually giving rise to the marked morphological differences that distinguish the cupulae from the tectorial membranes.Abbreviations bb basal body - c cilia - ca crista ampullaris - ch chromosome - cu cupula - d dictyosome - hc hair cell - kc kinocilia - ld lipid droplet - m mitochondrion - ma main axis - mb multilamellated body - mc macula communis - mi mitosis - mv microvillus - n nucleus - on organic net - pa amphibian papilla - pb basilar papilla - pg pigment granule - po preotoconia - rer rough endoplasmic reticulum - s saccule - sc supporting cell - sci stereocilia - sd spot desmosome - t tegmentum - tf tonofilaments - tj tight junction - tm tectorial membrane - yp yolk platelet     

Midbrain auditory sensitivity in toads of the genus Bufo (amphibia — bufonidae) with different vocal repertoires

Summary South American male toads Bufo chilensis emit a release call in contact with other individuals and a soft amplectic call, B. spinulosus males emit a release call while isolated in breeding areas, and B. arenarum produces a release call plus an intense mating call. Release calls of the 3 species measure 72–86 dB SPL RMS at 20 cm in front of the animal and the mating call of B. arenarum is 84–87 dB SPL at 4 m.Audiograms obtained with multiunit recordings in the torus semicircularis (TS) show a low frequency region (LFR), centered at 352, 356 and 491 Hz, and a high frequency region (HFR), centered at 1199, 1161 and 1423 Hz, in B. chilensis, B. spinulosus and B. arenarum, respectively. Center frequencies (CFs) in the HFR are in gross correspondence with average dominant frequencies (DFs) of the vocalizations of these species. Best thresholds (BTs) in the HFR are similar between B. chilensis and B. arenarum while in B. spinulosus average BTs are 10.8 and 13.5 dB higher, respectively. The similar auditory thresholds between B. chilensis and B. arenarum denote a conservative nature of auditory sensitivity among these anura.Abbreviations AP amphibian papilla - BP basilar papilla - BT best threshold - CF center frequency - DF dominant frequency - HFR high frequency region - LFR low frequency region - TS torus semi-circularis - SPL sound pressure level     

Acoustic,auditory, and morphological divergence in three species of neotropical frog

Advertisement calls, auditory tuning, and larynx and ear morphology were examined in 3 neotropical frogs, Hyla microcephala, H. phlebodes and H. ebraccata, H. microcephala has the highest call dominant frequency (6.068 kHz) and basilar papilla tuning (5.36 kHz). H. phlebodes and H. ebraccata calls have lower dominant frequencies (3.832 and 3.197 kHz respectively) and basilar papilla tuning (2.79 and 2.56 kHz). The primary call notes of H. ebraccata are longer (181.6 ms) than those of H. microcephala (95.5 ms) or H. phlebodes (87.3 ms). Morphometric analysis suggests that temporal call features differ as laryngeal musculature changes, in the process changing the overall size of the larynx. The spectral aspects of the call differ as head size, and hence the size of its resonating and radiating structures, changes, modifying the dominant frequency of calls by accentuating their higher harmonics when head size decreases. Decreasing head size decreases the size of the middle and inner ear chambers, changing the mechanical tuning of the ear in the same direction as the change in dominant frequency. These changes result in divergent spectral-temporal characteristics of both the sending and receiving portions of the acoustic communication system underlying social behavior in these frogs.Abbreviations AP amphibian papilla - BEF best excitatory frequency - BP basilar papilla - dB SPL decibels sound pressure level re:20 N/m²     

The separate and combined effects of harmonic structure, phase, and FM on female preferences in the barking treefrog (Hyla gratiosa)

In natural advertisement calls of the barking treefrog, Hyla gratiosa, a small amount of incoherent frequency modulation (FM) is present. Incoherency in the FM of a call creates inharmonicity and phase changes between its frequency components. In this study, the combined and separate effects of the harmonic structure, phase spectrum, and FM of an advertisement call on female choice were tested. The harmonic structure of a call can have a direct effect on female preference; females showed a significant preference for static-inharmonic calls over static-harmonic calls. Neither differences in phase or FM alone conferred a preference in two choice tests. However, when FM is present in both calls it does influence female preference for harmonic structure -namely harmonic calls become preferable to inharmonic calls. This reversal of female preference for inharmonicity in a call by the presence of FM suggests that call parameters may interact, and thereby effect mate choice.Abbreviations AP amphibian papilla - BP basilar papilla - FM frequency modulation - PM phase modulation - HS harmonic structure - GB Gaussian Band     

Mechanics of the inner ear of the bullfrog (Rana catesbeiana): the contact membranes and the periotic canal

The frog inner ear consists of a complex of fluid-filled membranous sacs and canals containing eight distinct clusters of sensory hair cells. In this study we attempt to delineate the potential pathways for acoustic energy flow toward two of these clusters located within the amphibian papilla and the basilar papilla. Detailed morphological measurements of the periotic canal based on internal casts of the inner ear in the bullfrog (Rana catesbeiana) revealed that it is divided into a wide, tapered section and a narrower section comprised of two branches – one short and blind projecting into the endolymphatic space and another longer, terminating in the round window. Additionally, we used laser Doppler velocimetry to record the velocity responses of the contact membranes of the amphibian papilla and basilar papilla. We found that the acoustic energy flow through these two structures is frequency dependent such that the amphibian papilla contact membrane displays a peak velocity amplitude at frequencies less than 500 Hz, whereas the basilar papilla contact membrane velocity response exhibits a maximum above 1100 Hz. Our data advocate a mechanical substrate underlying the frequency segregation in the auditory nerve fibers innervating the amphibian papilla and the basilar papilla. Accepted: 9 March 2000     

江西赣江源区域两栖动物的群落组成和物种多样性特征

赣江发源于武夷山脉南段西麓的高山岭间,该区域独特的地理环境和气候特征蕴育了丰富的生物多样性。然而关于该区域两栖动物群落组成和物种多样性调查非常匮乏,不利于赣江源头两栖动物物种多样性的保护。于2016年4-9月期间在江西赣江源区域采用样线法调查了两栖动物的资源状况、群落组成及物种多样性特征,比较了它们在山地森林区、丘陵森林与农田区和盆地农田区3类栖息地之间的差异性。结果表明：赣江源区域分布有8科23种两栖动物,新增记录3个物种,包括尖舌浮蛙、寒露林蛙和九龙棘蛙,泽陆蛙和饰纹姬蛙为优势种。赣江源区域的两栖动物群落组成和物种多样性存在显著的季节间差异和栖息地间差异;两栖动物季节性繁殖是造成前者差异的主要因素,而土地利用类型、栖息地特征、空间距离、生活习性的物种特性等因素成就了后者差异的出现。因此,春、夏季一般有比秋季见到更高的两栖动物物种丰富度和多样性;山地森林区的两栖动物物种丰富度和多样性最高,盆地农田区次之,丘陵森林与农田区的最低。山地森林区应成为赣江源区域两栖动物多样性保护的优先区域。国家Ⅱ级重点保护野生动物虎纹蛙,在3类栖息地中均有分布,且在盆地农田区和山地森林区能见到更多个体,但农田区分布的虎纹蛙遭受到更大的威胁,建议加强对农田区虎纹蛙及其栖息地的保护。     

Changes in the Frequency Structure of a Mating Call Decrease Its Attractiveness to Females in the Cricket Frog Acris crepitans blanchardi

In many species, females often prefer male signals that are more complex than in nature or beyond the range of calls naturally produced by conspecific males in spectral, temporal and amplitude features. In this study we examined both the ability of females to recognize signals outside the normal range of spectral frequency variation seen in male advertisement calls, and the influence of increasing call complexity by adding spectral components to enhance the attractiveness of a male advertisement call in the cricket frog Acris crepitans blanchardi, while keeping its amplitude constant. We used two different natural male call groups and created the following synthetic call groups: with a dominant frequency at 3500 Hz, i.e. at the normal dominant frequency with a frequency band within the sensitivity range of the inner ear basilar papilla; with a dominant frequency at 700 Hz, i.e. outside the normal range of variation and with a frequency band outside the sensitivity range of the basilar papilla but within the range of the amphibian papilla; with two dominant frequencies, one at 700 Hz and another at 3500 Hz, stimulating the basilar and amphibian papilla simultaneously. In double choice experiments we tested all combinations of the three call groups, and we tested the 3500 Hz call groups against the same natural call groups. Additionally, we tested the 700 Hz call groups against white noise to see whether these signals are meaningful in mate choice. Females preferred 3500 Hz call groups over all other call groups. The synthetic call group was as attractive to females as the same natural call group. The 700 Hz call group was not meaningful in mate choice. The combined (700 Hz + 3500 Hz) call group was significantly less attractive to females than the 3500 Hz call group. Thus, making a call more spectrally complex without increasing its overall amplitude decreases its attractiveness to cricket frog females.     

The tonotopic organization of the bullfrog amphibian papilla,an auditory organ lacking a basilar membrane

Summary Intracellular dye-injection studies have revealed tonotopic organization of the bullfrog (Rana catesbeiana) amphibian papilla, an auditory organ lacking a basilar membrane or its equivalent. The best excitatory frequency (BEF) for auditory stimuli was identified in each of twenty-nine VIIIth-nerve afferent axons that subsequently were traced to their peripheral terminations at the sensory surface. Among those axons, the five with BEFs greater than 550 Hz all terminated in the caudalmost region of the papilla, the ten with the BEFs greater than 300 Hz and less than or equal to 550 Hz all terminated in the central region of the papilla, and the fourteen with BEFs equal to or less than 300 Hz all terminated in the rostralmost region of the papilla (Fig. 4). The tectorium is very much larger and presumably more massive under the low-frequency region of the papilla than it is under the high-frequency region (Fig. 1). Higher-frequency axons tended to innervate few (one to four) receptor cells, and low-frequency axons tended to innervate many (six or more). Higher-frequency axons often terminated in large claw-like structures that engulfed the basal portions of individual hair cells and in this way were morphologically similar to type I terminals in the inner ears of higher vertebrates.Abbreviations BEF best excitatory frequency - HRP horseradish peroxidase     

The tectorial membrane of the lizard ear: types of structure

This study is concerned with the forms of the tectorial membrane in the lizard ear and its manner of attachment to the ciliary tufts of the hair cells. These structures and their variations were observed in 20 species representing eight families of lizards. Three forms of tectorial membrane were found, a continuous form that extends throughout the length of the auditory papilla, an abbreviated form that reaches the papilla only in one region, and a dendritic form that is particularly narrow at first and then branches extensively to supply all the hair cells. Occasionally the lower edge of the tectorial membrane makes direct connections with the hair tufts. More often there are special connecting structures between the membrane and the hair tufts. Seven types of these structures were identified, as follows: (1) simple fibers, (2) open network, (3) heavy network, (4) fiber plate, (5) finger processes, (6) sallets, and (7) remote connections. These types of tectorial connections are described and illustrated.     

A scanning electron microscope study of the papilla basilaris of Gekko gecko

Summary The sensory hair cells of the ventral 2/3 of the papilla basilaris of Gekko gecko are divided into anterior (pre-axial) and posterior (post-axial) portions by a mid-axial gap or hiatus where there are no hair cells. There is no separation of the hair cells in the dorsal third of the papilla. There are three tectorial membrane modifications: an attached thickened membrane covering the pre-axial hair cells, sallets covering the post-axial hair cells, and an attached filamentous membrane covering the dorsal hair cells. The number of hair cells is greatest ventrally and decreases dorsally. There are approximately 2000 to 2100 hair cells. The kinocilia of the hair cells of the anterior halves of both the pre- and the post-axial vertical hair-cell rows are oriented posteriorly, while the kinocilia of the posterior halves are oriented anteriorly. The kinocilia of the hair cells of the dorsal third of the papilla are mostly oriented posteriorly. Thus, kinocilial orientation of the ventral 2/3 of the papilla is doubly bidirectional, and the dorsal 1/3, largely unidirectional.I would like to thank Ms. Maria Maglio for her skill in handling the technical aspects of the scanning electron microscopy as well as her artistry in achieving photographic excellence on the scope, David Akers for expert photographic assistance, and Wayne Emery for the drawings. Research sponsored by United States Public Health Service Grant NS-09231.     

Morphology of the basilar papilla of the budgerigar,Melopsittacus undulatus

The budgerigar is a representative of the parrot-like birds that, like song birds, have developed complex communication signals. This species is interesting in a psychoacoustic sense, in that it shows unusually good frequency discriminative abilities above about 1 kHz. To begin to understand whether the peripheral hearing organ plays a role in such specializations, we have carried out a quantitative study of the fine anatomy of the basilar papilla and compared it to data from other avian species. The budgerigar basilar papilla is about 2.5 mm long in the living animal and contains about 5,400 hair cells. The hair cells of the papilla show regional specializations similar to those found in other birds and are described from scanning electron microscopic and light microscopic studies. Regiona changes in the basilar papilla, and in the basilar and tectorial membranes are described from light microscopic data. As noted for other avian species, the constellation of morphologic features found in the budgerigar is unique. In general, the hair cell patterns of the budgerigar papilla showed fewer specializations than found in, e.g., a songbird, the starling, but more than seen in a primitive land bird, e.g., the pigeon. There were no features that were obviously related to the unusal psychoacoustic performance of this species. © 1993 Wiley-Liss, Inc.     

From Puerto Rican to pan-ethnic in New York city

Abstract

The increasing diversity of the US population has stimulated interest in racial identification, which is complex for phenotypically heterogeneous groups such as Puerto Ricans. We overcome several limitations of the empirical literature on racial identification among Puerto Ricans with a study that is grounded in the experience of Puerto Rican women in New York City. Our analysis focuses on two questions: How do Puerto Rican women in New York identify themselves racially? What are the sources of racial identification? The results indicate that most Puerto Rican women in New York conflate race and ethnicity by designating their race as either ‘Puerto Rican’ or ‘Hispanic’. Moreover, the decision to ‘become’ pan-ethnic has complex roots. In particular, the effect of skin tone on pan-ethnic identification is conditioned by socioeconomic and neighbourhood characteristics.     

Global amphibian declines: a perspective from the Caribbean

Recent concern over the possibility of a global decline in amphibians prompted this assessment of the West Indian species. At the species level, the West Indian amphibian fauna (156 species, all frogs and toads) has not undergone a general decline, and no species is known to be extinct. However, one Puerto Rican species (Eleutherodactylus karlschmidti) has not been seen in over ten years despite considerable search effort. Seven other species, including the Puerto Rican livebearing frog (E. jasperi), have not been seen recently, although their present status cannot be determined until additional effort is made to locate them. Two stream-associated species on Hispaniola (E. semipalmatus and Hyla vasta) appear to have declined in recont years, probably due to the alteration of riparian habitats by deforestation. Other vertebrate groups in the West Indies, such as mammals, have been more affected by human-caused environmental degradation than have amphibians. Large-scale extinctions of frogs and other forest-dwelling species are not expected to occur until forest cover reaches very low levels. Haiti is on the brink of such extinctions with less than 1% of its forest cover remaining. Two recommendations are made to help curtail the expected loss of biodiversity: (i) import charcoal to replace that produced by burning native trees (used as cooking fuel), as an immediate measure, and (ii) control human population growth, as a long-term solution.     

Scanning electron microscope studies of some skink papillae basilares

Summary The papilla basilaris of scincid lizards is relatively long, slightly curved or bowed, and characteristically has an apical terminal expansion. A limbus-attached tectorial membrane is present but is apparently not continuous with the tectorial material covering the hair cells of the papilla. The hair cells of the apical expansion are covered by a thick spongy mass of tectorial material, while the hair cells above (dorsal to) the apical region are covered by thickened tectorial material that is in the form of uniquely sculptured, twisted or folded drape-like masses (sallets). The surface of the basal (dorsal) quarter of the papilla is unusual in that it is concave rather than convex. The expanded terminals of the hair cell kinocilia are also unusual in being arrowhead-shaped.Kinocilial orientation of the non-apical papillary hair cells is simply bidirectional; the hair cells on each side of the papillary axial midline are oriented toward the midline. Kinocilial orientation of the hair cells of the apical expansion is more complex with the peripheral neural and abneural rows both being abneurally directed, and the central rows being at first neural in orientation, but becoming abneurally oriented as the apical tip is approached. At the apical tip region, most all hair cells are abneurally oriented.I would like to thank Ms Maria Maglio for her skill in handling the technical aspects of the electron microscope, Mr. David Akers for expert photographic assistance, and Ms. Michiko Kasahara for aid in all aspects of the work. Research sponsored by United States Public Health Service Grant NS-09231.     

The inner ear of gymnophione amphibians and its nerve supply: A comparative study of regressive events in a complex sensory system (Amphibia,Gymnophiona)

Summary The inner ears of representatives of all six gymnophionan families, as well as an ontogenetic series of one species, were studied in order to understand the origin and changes of the amphibian and basilar papillae. The amphibian papilla is in close proximity to the papilla neglecta in some adult gymnophionans. During ontogeny, both epithelia are adherent before they are separated by the formation of the utriculosaccular foramen. The nerve fibers to both epithelia run together, and both epithelia show a comparable variation in size and position among amphibians (amphibian papilla) and among vertebrates (papilla neglecta). Based on these arguments we propose that the amphibian papilla is a translocation of a part of the papilla neglecta specific to amphibians. Present in all primitive gymnophionans, the basilar papilla is lost in all derived gymnophionans. In contrast to anurans, but similar to some urodeles, amniotes, and Latimeria, the basilar papilla rests partly on a basilar membrane. Because of similarities in structure, topology, and innervation, the basilar papilla is suggested to be homologous in Latimeria and tetrapods. The structural differences of most amphibian basilar papillae, compared to those of amniotes and Latimeria, may be due to the different course of the periotic system and the formation of a basilar papillar recess rather than to a separate evolution of this epithelium. In addition to loss of the basilar papilla, some derived gymnophionans have lost the lagena, presumably independently, and the amphibian papilla is extremely reduced in the only genus without a stapes (Scolecomorphus). The papilla neglecta is, for unknown functional reasons, relatively large in aquatic gymnophionans, whereas it is almost lost in some thoroughly terrestrial gymnophionans. The regressive changes in the inner ear are not reflected in obvious changes in the pattern of eighth nerve projection. However, there is a rearrangement of cell masses in the rhombencephalic alar plate of derived gymnophionans, which may be related to the partial or complete loss of lateral line afferents. We propose that the presence of a basilar papilla is a synapomorphy of tetrapods and Latimeria, that the translocation of the papilla neglecta is related to the unique course of the amphibian periotic canal, and that regressive changes in the inner ear are related to the primitive absence of a tympanic ear.     

Seed predation,disease and germination on landslides in Neotropical lower montane wet forest

Abstract. Seed mortality (caused by predators and pathogens) and germination were compared between Puerto Rico and Costa Rica on landslides in lower montane wet forest. Seeds of six common species on five Puerto Rican landslides and four common species on two Costa Rican landslides were used with a Cecropia species and a Gonzalagunia species included at both sites. In the Puerto Rican experiments Cecropia schreberiana was the only species to show significant seed predation (which was due to insects), pathogens grew from all species and fewer seeds were lost to predators than pathogens. Also in Puerto Rico mean germination across all species was 57 % before dispersal (filled seeds collected while still on the tree) and 71 % after, with Phytolacca rivinoides seeds germinating most abundantly, followed in descending order by Ocotea leucoxylon, Cecropia spec, Miconia racemosa, Palicourea riparia and Gonzalagunia spicata. In the Costa Rican experiments three species had significant predation: Cecropia polyphlebia and Urera caracasana (both due to insects) and Witheringia coccoloboides (due to mammals); pathogenic disease caused more seed loss than predation, and germination was high (61 % pre-dispersal, 69 % post-dispersal). Similarities between these island and mainland sites included (1) percentage of seeds lost to predation and percentage lost to pathogens (all in the 5–15 % range), (2) generalist pathogens which claimed more seeds than predators and (3) majority germination with a general increase after dispersal. Finally sites were dissimilar only in the number of species with significant predation loss and whether it was by insects or mammals, casting doubt on the traditional island/mainland dichotomy.     

Directionality of phase locking in auditory nerve fibers of the leopard frog Rana pipiens pipiens

Summary A dorsal approach to the eighth nerve and free-field stimulation were used to investigate the effect of sound direction and intensity on phase locking in auditory nerve fibers of the leopard frog Rana pipiens pipiens.Tuning curves of 75 auditory neurons were analyzed (Fig. 2). Amphibian papillar neurons, but not basilar papillar neurons, exhibit significant phase locking to short tone bursts at the characteristic frequency (CF), the degree of phase locking (vector strength) decreasing with the neuron's CF (Figs. 3, 4 and 10E). Vector strength increases with sound pressure level to saturate about 20 dB above threshold, while the preferred firing phase is only slightly affected (Figs. 5 and 6).In contrast, sound direction hardly affects vector strength (Figs. 7, 8, 9A and 10A and C), but has a strong influence on the preferred firing phase (Figs. 7, 8, 9B and C, 10B and D): With respect to anterior tone presentation there are phase lags for ipsilateral and phase leads for posterior and contralateral presentation. Phase differences between both ears show a sinusoidal or cardioid/ovoidal directional characteristic; maximum differences are found with antero-lateral tone presentation (Fig. 11). The directionality of phase locking decreases with the neuron's CF (Fig. 10F) and only slightly changes with sound pressure level (Fig. 12). Thus, phase locking of amphibian papilla neurons can potentially provide intensity-independent information for sound localization.Abbreviations SPL sound pressure level - FTC frequency threshold curve - CF characteristic frequency - TF test frequency - VS vector strength - AP amphibian papilla - BP basilar papilla