Signal recognition by frogs in the presence of temporally fluctuating chorus-shaped noise

The background noise generated in large social aggregations of calling individuals is a potent source of auditory masking for animals that communicate acoustically. Despite similarities with the so-called "cocktail-party problem" in humans, few studies have explicitly investigated how non-human animals solve the perceptual task of separating biologically relevant acoustic signals from ambient background noise. Under certain conditions, humans experience a release from auditory masking when speech is presented in speech-like masking noise that fluctuates in amplitude. We tested the hypothesis that females of Cope's gray treefrog (Hyla chrysoscelis) experience masking release in artificial chorus noise that fluctuates in level at modulations rates characteristic of those present in ambient chorus noise. We estimated thresholds for recognizing conspecific advertisement calls (pulse rate=40-50 pulses/s) in the presence of unmodulated and sinusoidally amplitude modulated (SAM) chorus-shaped masking noise. We tested two rates of modulation (5 Hz and 45 Hz) because the sounds of frog choruses are modulated at low rates (e.g., less than 5-10 Hz), and because those of species with pulsatile signals are additionally modulated at higher rates typical of the pulse rate of calls (e.g., between 15-50 Hz). Recognition thresholds were similar in the unmodulated and 5-Hz SAM conditions, and 12 dB higher in the 45-Hz SAM condition. These results did not support the hypothesis that female gray treefrogs experience masking release in temporally fluctuating chorus-shaped noise. We discuss our results in terms of modulation masking, and hypothesize that natural amplitude fluctuations in ambient chorus noise may impair mating call perception.     

Female mate selection in the natterjack toad: active choice or passive atraction?

Summary Variation in seasonal mating success among male natterjack toads (Bufo calamita) was influenced by the number of nights that males spent at the pond and by male body size. Large males produced louder and lower frequency calls than small males, and maintained larger acoustic territories. After arriving at the pond, one half of all observed females mated with the first male they encountered. The remainder visited several males before initiating amplexus, but no criteria could be identified that females might have used when deciding whether to accept or reject a male. Movements between several males seem to be best explained by low female responsiveness to male advertisement calls on cold nights which were nonoptimal for oviposition. Females attempted to reject non-calling males both before and after amplexus, but this may be a mechanism to avoid mismating with males of the common toad (Bufo bufo), an explosive breeder that utilised the same pond. In two-choice playback experiments using synthetic advertisement calls, females showed no preference for calls based on their frequency. Females preferred calls of intermediate pulse repetition rate equivalent to those produced by a male at the same body temperature. Pulse rate is thus potentially subject to stabilishing selection and may be an important character for species-recognition. Females preferred fast rather than slow call rates, but only when the alternative rates were extreme. They also preferred calls which they perceived at the highest sound pressure level, but did not discriminate between absolute sound pressure levels of alternative stimuli at different distances. Since females that delay mating and oviposition may suffer predation, it is suggested that female preference for loud, rapidly repeated calls may be adaptive in the sense of minimizing the costs of locating conspecific males, rather than maximizing the probability of obtaining a high quality mate. Competition between males to maintain large acoustic territories and produce calls that can be easily detected by females would seem to be a sufficient mechanism to explain the evolution of the striking calls produced by male natterjacks.     

Density dependence and habitat quality modulate the intensity of display territory defence in an exploded lekking species

We evaluated the effect of conspecific abundance and habitat quality of leks on the territorial behaviour of males in an exploded lekking species, the Little Bustard (Tetrax tetrax). The hypothesis that males more intensely defend territories with higher conspecific abundance and better habitat quality was evaluated experimentally analysing the agonistic response of experimental males to male decoys placed on their displaying areas. Decoy experiments showed that the intensity of display territory defence by little bustard males is density dependent. The time experimental males took to return to their display sites after decoy placement decreased with abundance of both males and females. The strength of their final response was positively associated to local male and female abundance in the vicinity of their display sites. Habitat quality also influenced males’ display territory defence since the intensity of male response increased with the degree of natural vegetation cover. Habitat quality was particularly relevant in explaining variation of experimental males’ snort call rate, which decreased with the degree in plough cover and increased with the number of fields in the lekking area. Snort call rate decreased with the level of male aggregation and was lowest in males exhibiting the strongest aggressive response to decoys. These results add new evidence for the density dependence of species’ breeding territorial behaviour, supporting density-dependent models of lek formation and reinforcing the role of resources defence in exploded lek mating systems.     

Evolution of male mating behavior: male spadefoot toads preferentially associate with conspecific males

The evolution of male breeding aggregations is difficult to explain because males may reduce their reproductive success by associating with their closest competitors. We examined aggregative behavior by male New Mexico spadefoot toads, Spea multiplicata, which form breeding choruses in rain-filled pools. We specifically asked whether males are attracted to conspecific calls and, if so, whether they preferentially associate with those male calls that are also attractive to females. Field observations revealed that males showed significant clustering with conspecifics within breeding ponds, whereas laboratory phonotaxis experiments revealed that males preferentially associated with conspecific male calls. Moreover, when males were presented with conspecific calls that differed in call rate, smaller males associated with the stimulus preferred by females (average call rate). Thus, males appear to evaluate the attractiveness of competitors using the same trait employed by females to assess potential mates, and males adjust their positions relative to competitors depending on their size. We discuss these results in the light of several current hypotheses on the adaptive significance of male breeding aggregations. Received: 20 December 1999 / Accepted: 18 March 2000     

Acoustically mediated neighbor recognition in the North American bullfrog,Rana catesbeiana

Summary Playback experiments were conducted to determine whether territorial male bullfrogs (Rana catesbeiana) were capable of discriminating between advertisement calls of neighbors and strangers. Territorial males adjacent to subject males were removed and replaced with a speaker which broadcast calls of a stranger or the removed male. Ten of 11 males responded more strongly to calls of strangers than to calls of neighbors. When advertisement calls of neighbors were broadcast to subject males from positions within the removed neighbor's territory and from positions opposite the subject male, all 9 males tested responded more strongly to calls of a neighbor broadcast from a new position than to playbacks of the same call broadcast within the removed neighbor's territory. Because male bullfrogs recognize familiar calls and associate these calls with a particular direction or location, these data provide the first evidence for acoustically mediated neighbor recognition in frogs.     

Female preferences for multiple attributes in the acoustic signals of the Italian treefrog, <Emphasis Type="Italic">Hyla intermedia</Emphasis>

The advertisement call of frogs and toads is an example of multiple message signal because different acoustic properties encode different kinds of biologically significant information. In the Italian treefrog, Hyla intermedia, pulse rate and frequency have been found to be under stabilizing female preferences and to encode information important for mate recognition, whereas the number of calls per call group have been found to be under directional preferences and, thus, to be important for mate quality assessment. In this study, we investigate preferences for calls that differ simultaneously in frequency, pulse rate, and number of calls per call group, and we ask how these properties interact with each other in influencing female mating decisions. Results of two-choice phonotaxis experiments provide no evidence to support the hypothesis that females process multi-attribute signals in a hierarchical way. In contrast, the pattern of preferences is consistent with the ‘preference function’ hypothesis, that is, with the hypothesis that females rank signals along an ordinal scale of values and choose accordingly. Pulse rate and frequency influence mating preferences more than does the number of calls per call group. The interaction between pulse rate and frequency is not additive but multiplicative: small differences in either pulse rate or frequency that, alone, have no effects on female choice, interact synergistically so that their combination has strong influence on female preferences. A preference repeatability test shows strong among-female differences in preference for multi-attribute signals. We suggest that this result reveals not only a variation in attribute values among females, but also a variation in the way females weight and combine attribute values into a single preference score.     

The relative value of call embellishment in túngara frogs

Facultative traits that have evolved under sexual selection, such as the acoustic ornaments present in the advertisement signals of male túngara frogs (Physalaemus pustulosus), offer a unique opportunity to examine selection for trait exaggeration with a focus on individual differences amongst signalers. By contrast, many studies of mate choice use experimental designs that obscure the inter-individual variation amongst signalers available for selection to act on—through the use of “typical” or average signals from the population. Here, we use dichotomous female phonotaxis choice tests to determine how the value of male call embellishment varies across 20 individual males frogs recorded from the wild—a sample which captures the acoustic diversity present in the population. We tested 20 females for each male call pair (i.e., 400 females). The results show widespread preference amongst females for ornamented calls (“whine–chucks”) over simple calls (“whines”), yet also demonstrate substantial variation in the relative benefits for individual male frogs—some males enjoy appreciable benefits by using ornaments while others (30% of males in this study) do not. We also show that the relative amplitude of the chuck to the whine correlates positively with the value of call elaborations across these 20 males. Finally, by manipulating the relative amplitude of whines and chucks using both natural and synthetic calls, we demonstrate directly that this single call parameter is key to determining the relative value of call elaborations across males.     

The function of call alternation in the African reed frog (Hyperolius marmoratus): precise call timing prevents auditory masking

The function of call alternation in the African painted reed frog, Hyperolius marmoratus was studied. Males actively avoided call overlap with neighboring males in their natural habitat. Advertisement calls produced by groups of two or three males showed less overlap than expected if they called at random. In addition, isolated males significantly reduced their calling rate to match the periodicity of a playback of periodic tone pulses, with vocalizations given during the silent intervals between tones. Gap-detection experiments showed that males suppressed vocalizations during playbacks of constant-frequency tone bursts and gave more calls during silent periods than expected by chance. Females discriminated against conspecific advertisement calls with many pulses in favor of calls with few or no pulses. This suggests that there would be little selection pressure on males to alternate calls so that pulses are not obscured. To test if call alternation functions to make calls more conspicuous, females were presented with identical conspecific advertisement calls from two speakers in four different temporal patterns: simultaneous, overlapping, abutting, and alternating. Females did not discriminate when calls were presented in a simultaneous, abutting, or alternating time pattern. When calls overlapped with the trailing call delayed from 0.5 to 70 ms females discriminated in favor of the leading call. When the intensity of the leading call was reduced by 6 dB the preference for the leading call was maintained when calls overlapped by 2 and 40 ms but was abolished or reversed at 0.5 and 70 ms, respectively. These results support the notion that the second of two partially overlapping calls was acoustically masked, rendering female painted reed frogs unwilling to approach or unable to locate such calls. It is suggested that either simultaneous masking or the precedence effect are responsible for the observed behavior. Acoustic masking of the second call by the first when calls overlapped was maintained even when the frequency of the first call was altered by 150 Hz above and below the more preferred frequency of the second call. Received: 13 April 1995/Accepted after revision: 5 November 1995     

Advertisement-call modification,male competition,and female preference in the bird-voiced treefrog <Emphasis Type="Italic">Hyla avivoca</Emphasis>

Senders and receivers influence dynamic characteristics of the signals used for mate attraction over different time scales. On a moment-to-moment basis, interactions among senders competing for a mate influence dynamic characteristics, whereas the preferences of receivers of the opposite gender exert an influence over evolutionary time. We observed and recorded the calling patterns of the bird-voiced treefrog Hyla avivoca to assess how the dynamic characters of calls vary during interactions among groups of males in a chorus. This question was also addressed using playback experiments with males. Playback experiments with females showed how changes in dynamic call properties are likely to affect male mating success. Frogs calling in pairs, groups, or in response to playbacks produced longer calls than did isolated males. During call overlap, males often increased the duration of the silent interval (gaps) between the pulses of their calls so that the pulses of the calls of two neighbors interdigitated. This change resulted in increased variability of pulse rate, a traditionally static acoustic property; however, males also produced high proportions of non-overlapped calls in which variability in pulse rate was low and had species-typical values. Females preferred long calls to short- and average-duration calls, and non-overlapped calls to overlapped calls. Given a choice between pairs of overlapped calls, females preferred pairs in which the proportion of overlap was low and pairs in which the pulses of such calls interdigitated completely. The observed patterns of vocal competition thus reflect the preferences of conspecific females, which have influenced the evolution of the calling behavior of H. avivoca. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The functional significance of the diphasic advertisement call of Geocrinia victoriana (Anura: Leptodactylidae)

Summary The advertisement call of Geocrinia victoriana is markedly diphasic and consists of one introcuctory note (rarely two or three), followed by a series of repeated notes of similar carrier frequency, but much shorter duration and higher pulse rate. In two-choice field discrimination experiments with the two phases of the advertisement call presented as alternative stimuli, reproductively ripe females were attracted only to the repeated notes and contacted the source of these signals (a loudspeaker). Field playback experiments were carried out on residential males, with a complete call, an introductory note, or a series of repeated notes being used as the stimulus, and intensity varied upwards in 10 dB increments. With the complete call or the introductory note as the stimulus, calling behaviour of subjects altered significantly from the pre-stimulatory pattern, with a great reduction in output of repeated notes, and an increase in duration and decrease in pulse rate of introductory notes. The threshold intensity (lowest level for a significant change in calling behaviour) with the introductory note as the stimulus, 90–99.9 dB peak sound pressure level (PSPL), was at least 10 dB lower than that with the complete call as the stimulus (110–125 dB, PSPL). Playback of repeated notes had little effect on calling behaviour until the intensity exceeded 120 dB, PSPL. Playback of all three classes of stimulus at constant intensities below and above the threshold for the complete call (i.e. 99–99.9, and 110–125 dB, PSPL) indicated that changes in calling behaviour were due to the intensity of stimulus rather than to a cumulative effect based on the number of stimuli. Measurements of intensities of advertisement calls of nearest neighbours in natural breeding assemblages (modal class=104–106 dB, PSPL) were consistent with the experimental results. It was thus demonstrated that in G. victoriana the two functions of the advertisement call are partitioned: the repeated notes attract breeding females (hence are equivalent to the mating call), and the introductory notes are directed at other males in a territorial context. The increase in duration of the introductory note is graded rather than discrete, so that this phase of the advertisement call changes progressively from the equivalent of a long-range (first-order) to a short-range (second-order) territorial call, then to an encounter call.     

Intrasexual competition,territoriality and acoustic communication in male strawberry poison frogs (<Emphasis Type="Italic">Oophaga pumilio</Emphasis>)

In many species male reproductive success is limited by access to females. Territoriality is one behavioural strategy which helps to acquire females. In the present study, we investigated the correlation between territory size and (1) female availability and (2) rate of intrusion by conspecific males in strawberry poison frogs, Oophaga pumilio. Males defended smaller territories in areas with a high female density and high rate of intrusion by conspecific males. Only males with high body condition values were able to establish territories in areas of high female density probably due to better fighting abilities. Moreover, dominant calling frequency was lower during agonistic interactions. Because only males with high body condition values were able to produce very low dominant frequencies, the acoustic properties appear to be an honest signal containing information about fighting abilities. Thus, the negative correlation between dominant frequency and mating success of males found in previous studies seems to be in part the result of intrasexual competition between males.     

No evidence for female mate choice based on genetic similarity in the túngara frog Physalaemus pustulosus

In most sexually reproducing animals, the behavior of one or both sexes during courtship critically influences the success at mating of the opposite sex. This behavior is often interpreted as “mate choice,” and there is great interest in why such choices are exercised. The explanation for the evolution of mate choice that has received the most attention and generated the most controversy is based on assumed genetic effects. In this study, we investigated whether female túngara frogs, which choose mates based on acoustic cues, have a preference for genetically less related males. Specifically, we determine if there is disassortive mating based on microsatellite markers, if there is information in the advertisement call that could be used to assess genetic similarity, and if females exhibit acoustic-based mating preferences that would promote choice for genetic diversity. Using seven microsatellite markers, we found no correlation of male call similarity and male genetic relatedness. Female choice experiments showed no female preference for calls of less related males, and there was no evidence for inbreeding avoidance in the field. Our results do not support the hypothesis of mate choice based on information about genetic relatedness conveyed by acoustic signals in túngara frogs.     

Habituation in the green frog, Rana clamitans

Habituation and its role in the dear enemy effect was investigated in a population of green frogs, Rana clamitans. Green frogs have a prolonged breeding season, and males defend territories centered around suitable oviposition sites. We tested the prediction that male green frogs will habituate to broadcasts of synthetic conspecific stimuli. Our results indicate that male green frogs can discriminate familiar from unfamiliar stimuli. We suggest that habituation helps to mediate the territorial interactions between male green frogs. Strangers present a greater threat than familiar neighbors. By habituating to the advertisement vocalizations of their near neighbors, males avoid costly interactions with individuals that are not a major threat to their territories. Received: 20 July 1998 / Accepted after revision: 6 September 1998     

Female preferences for male calling bout duration in a field cricket

Summary The calls of male field crickets attract sexually receptive females. In Gryllus integer, males differ from one another in their durations of uninterrupted calling (calling bout lengths). Tape recordings of the calls of 50 wild-caught males revealed that 14 males spent most of their calling time in short bouts (Fig. 1A), 18 in both short and long bouts (Fig. 1B), and 18 in long bouts (Fig. 1C). Re-recordings of 32 males after 3 weeks showed that calling bout lengths of individual males are stable with time (age) (Fig. 2). Three phonotaxis experiments investigated whether calling bout lengths of males affect female preferences. They demonstrated that (1) females can discriminate among conspecific males on the basis of calls alone; (2) females are preferentially attracted to males with long calling bout lengths; and (3) calling bout length is the specific factor responsible for preferential attraction. These results precisely identify a criterion that females use to discriminate among potential mates of their own species.     

Interspecific acoustic interactions of the neotropical treefrog Hyla ebraccata

Summary Hyla ebraccata, H. microcephala and H. phlebodes commonly occur together in Panama. The three species have calls exhibiting broad frequency overlap and call during the same season and time of day from similar microhabitats, frequently in close proximity. The vocal repertoires of the three species are structurally and functionally similar. All employ multi-part advertisement and aggressive calls which consist of a primary note followed by a variable number of clicks. H. ebraccata males often responded to heterospecific calls with multi-note synchronized responses, and calls with primary notes greater than 150–200 ms were most effective in eliciting synchrony. Playback experiments with synthetic 1-note advertisement calls of different durations and both synthetic 1-note advertisement calls and 200 ms tones of different frequencies demonstrated that H. ebraccata males will synchronize with stimuli which are similar in frequency and duration to conspecific calls. Data from a two-choice experiment with female H. ebraccata demonstrate that calls of individual H. microcephala can reduce the attractiveness of a H. ebraccata male's calls if primary notes overlap. By synchronizing response calls to those of H. microcephala, a H. ebraccata may reduce the chances that his calls are rendered less attractive to potential mates.Aggressive calls of these species are graded and are characterized by higher pulse repetition rates and often longer durations than advertisement calls. H. ebraccata males respond to aggressive calls of H. microcephala and H. phlebodes as they do to their own calls. Heterospecific aggressive interactions probably occur because the species interfere acoustically. Our results demonstrate that H. ebraccata males behave in ways which enhance their ability to communicate in a noisy assemblage of conspecific and heterospecific males.     

Interspecific aggression in Leucorrhinia dragonflies: a frequency-dependent discrimination threshold hypothesis

Summary Male Leucorrhinia dragonflies defend territories from conspecific and heterospecific intruders. Defense against heterospecifics is surprising, as mating and oviposition are the only activities that occur on the territories, and heterospecific males are not expected to pose a reproductive threat. L. frigida and L. intacta males respond aggressively with equal frequency and intensity against intrusions by conspecifics and heterospecifics. In contrast, L. proxima males respond more aggressively against conspecifics. The apparent lack of species discrimination shown by L. frigida and L. intacta males may result because territorial males that assess intruders (as do L. proxima) suffer a tactical disadvantage from hesitating when an intruder flies in. This assessment process may lead to reduced fighting success by the territorial male. Thus there is a tradeoff between assessment cost incurred when the intruder is a conspecific and benefit gained from avoiding conflict when the intruder is a heterospecific. Given this assessment cost, males of species that only rarely encounter conspecific intruders are more likely to evolve species discrimination than males of species that commonly encounter conspecific intruders.     

An experimental examination of female preference patterns for components of the male advertisement call in the quacking frog,<Emphasis Type="Italic"> Crinia georgiana</Emphasis>

Even though females prefer particular components of a male display, their preferences may not be expressed during mate choice. Here, we quantified female preference patterns in the frog Crinia georgiana for call rate, pulse number and dominant frequency using two-speaker trials. Females typically chose signals emitted at a higher rate, with more pulses (when variation was extreme) and with an average dominant frequency. The results for pulse number and call rate agree with a previous field study which found that these two call components explained significant variation in male mating success. In contrast, the strong preferences for average dominant frequencies detected here disagree with the previous field study which failed to find any relationship between dominant frequency and male mating success. To explain the discrepancy we investigated whether the patterns of female preference for dominant frequency changed when another property, call rate, was varied simultaneously. Most females chose the call with an average dominant frequency when offered a choice between a call with an average dominant frequency and call rate or a non-average dominant frequency (±2 SD) and high call rate. When the differences in dominant frequency were reduced (±1 SD), females showed no clear preference for either signal. Accordingly, female preference patterns for one call component can vary with the expression of another. These results do not explain why dominant frequency did not account for any variation in male mating success under field conditions.Communicated by T. Beschlitz     

Fighting,assessment, and frequency alteration in Blanchard's cricket frog

Summary This study examines the use of dominant frequency for assessment of fighting ability in Blanchard's cricket frog Acris crepitans blanchardi. Like most anurans, the dominant frequency of the call is negatively correlated with size. However, unlike many anurans, dominant frequency varies within individual males, providing a less reliable signal of size. Wrestling contests between male cricket frogs were differentially won by larger males. I thus tested the hypothesis that males use dominant frequency for assessment of an opponent's fighting ability. Males retreated from, or became satellites of, broadcasts of synthetic low frequency calls, simulating the calls of a large male. In contrast, males attacked broadcasts of synthetic high frequency calls, simulating the calls of a small male. The dominant frequency of the call therefore appears to contain information about size which males use to assess the fighting ability of opponents, despite the lower degree of reliability resulting from individual variation in the signal. Individual variation in dominant frequency arises partially as a consequence of active alteration of the signal in response to social competition. Males differentially lowered their dominant frequencies in response to lower frequency broadcasts, thus in response to larger opponents. Furthermore, the higher a male's dominant frequency relative to that of an opponent, the greater was the decrease in dominant frequency. These results suggest that smaller males may conditionally lower their dominant frequencies in order to sound larger to larger opponents, thereby inflating their apparent fighting ability. Two alternative hypotheses are discussed.     

A mechanism for female choice of large males in the treefrog Hyla chrysoscelis

Summary In this study, we combine both field and laboratory experiments to address the effects of female preference for certain call characteristics on a large-male mating advantage in the treefrog H. chrysoscelis. In laboratory-choice experiments, females always chose the call with the lower fundamental frequency when call rate and call intensity were held constant and the difference in frequency between the two calls was 15%. The lower frequency call was preferred by 8 out of 12 females when the difference in fundamental frequency was 7.4%. These results are consistent with field comparisons of the size of unmated males calling within 2 m of a mated male: Male body size was negatively correlated with fundamental frequency and the greater the size difference, the more likely that the larger male mated. In field choice experiments, females preferred males with higher call rates. Since size differences between males used in this experiment averaged only 2.3 mm, we would not expect the fundamental frequency of a male's call to be the best predictor of mating success. Laboratory results demonstrated that call rate could override female preference for the low frequency call over the high frequency call, while intensity could at least dilute this preference. However, individual males in the field varied both call rate and the call intensity as perceived by the female. We suggest that the interaction between call rate, male size and mating success should be studied further through the use of field-choice experiments.     

Provisioning of nestlings by dunnocks,Prunella modularis,in pairs and trios compensation reactions by males and females

Summary The mating systems in a population of dunnocks included monogamy, polygyny, polyandry and polygynandry. Broods were provisioned by lone females, by females with the part-time help of one male, by females with the full-time help of one male (pairs) or by females with the part-time or full-time help of two males (trios). We compared provisioning of nestlings in these different systems and used the results of natural and experimental removals to examine how individuals reacted to the provisioning by others. In pairs, males and females provisioned at similar rates (Fig. 2a). In trios, females and alpha males fed chicks at the same rate, and at a higher rate than beta males (Fig. 2b). Females attained maximum male help when two males shared provisioning equally (Fig. 6). Females were more likely to achieve this when they were able to escape alpha male guarding during the mating period and exercise some control over mating access by the two males (Fig. 7). Female provisioning did not increase when their help was reduced from two males to one (Fig. 4 a), but it did increase when male help was further reduced to either one male's part-time help (Fig. 5 a) or no male help (Fig. 3 a). Beta males increased their provisioning rate when alpha males were removed from a trio (Fig. 4b). Alpha males may have increased their rate when beta males were removed but any reaction was small. When one male was removed from a trio, the remaining male's provisioning rate was as expected for a male in a monogamous pair. When reactions occurred, they were not sufficient to compensate for the loss of the removed adult and nestling weight was reduced. We discuss the relevance of these results to the maintenance of parental care by pairs and trios.