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Although mate searching behavior in female túngara frogs (Physalaemus pustulosus) is nocturnal and largely mediated by acoustic cues, male signaling includes visual cues produced by the vocal sac. To compensate for these low light conditions, visual sensitivity in females is modulated when they are in a reproductive state, as retinal thresholds are decreased. This study tested whether estradiol (E2) plays a role in this modulation. Female túngara frogs were injected with either human chorionic gonadotropin (hCG) or a combination of hCG and fadrozole. hCG induces a reproductive state and increases retinal sensitivity, while fadrozole is an aromatase inhibitor that blocks hCG-induced E2 synthesis. In an analysis of scotopic electroretinograms (ERGs), hCG treatment lowered the threshold for eliciting a b-wave response, whereas the addition of fadrozole abolished this effect, matching thresholds in non-reproductive saline-injected controls. This suggests that blocking E2 synthesis blocked the hCG-mediated reproductive modulation of retinal sensitivity. By implicating E2 in control of retinal sensitivity, our data add to growing evidence that the targets of gonadal steroid feedback loops include sensory receptor organs, where stimulus sensitivity may be modulated, rather than more central brain nuclei, where modulation may affect mechanisms involved in motivation. [ABSTRACT FROM AUTHOR]

In the search for understanding female sexual decision-making, progress has been made in uncovering a variety of perceptual biases and most of these concern the animal's sensory biology and cognitive processes. We are now poised to dig deeper into the female's decision-making and ask if incentive salience, which plays a role in all types of appetitive behaviors, also influences a female's "taste for the beautiful." The incentive salience hypothesis suggests that dopamine assigns value or salience to objects or actions. After value is assigned to all potential actions, an action selection system then chooses among potential options to select the most valuable action. In this view, dopamine stimulates reward-seeking behavior by assigning incentive salience to specific behavioral actions, which in turn, increases pursuit and focus on objects or stimuli that represent the valuable action. Here, we apply this framework to understand why females are compelled to respond maximally to some male courtship signals over others and how this process may reveal a female's hidden mate preferences. We examine studies of dopamine and the mesolimbic reward system because these may play a role in expanding the female's perceptual landscape for novelty in male courtship signals and establishing novel hidden preferences. We review three avenues of research that may identify signatures of incentive salience in females during sexual decision-making. This review includes studies of dopamine agonist or antagonist administration in females during mate choice or partner preference tests, measures of neural activity in dopaminergic neural circuits during mate choice or partner preference tests, and social regulation of dopamine in females when entering reproductive contexts and/or exposure to mate signals. By applying the incentive salience hypothesis to female reproductive decision-making, it redefines how we see the female's role in sexual encounters. Females cannot be considered passive during reproductive encounters; rather they are seeking sexual encounters, particularly with males that tap into their perceptual biases and initiate a reward-seeking response. Incentive salience applied to reproductive behavior requires considering females as viewing sexual stimuli as rewarding and initiating action to seek out this reward, all of which indicates females are driving sexual encounters. [ABSTRACT FROM AUTHOR]

Visual cues are often a vital part of animal communication and courtship. While a plethora of studies have focused on the role that hormones play in acoustic communication of anurans, relatively few have explored hormonal modulation of vision in these animals. Much of what we do know comes from behavioral studies, which show that a frog's hormonal state can significantly affect both its visual behavior and mating decisions. However, to fully understand how frogs use visual cues to make these mating decisions, we must first understand how their visual system processes these cues, and how hormones affect these processes. To do this, we performed electroretinograms (ERGs) to measure retinal sensitivity of túngara frogs (Physalaemus pustulosus), a neotropical species whose mating behavior includes previously described visual cues. To determine the effect of hormonal state on visual sensitivity, ERGs were recorded under scotopic and photopic conditions in frogs that were either non-reproductive or hormone-treated with human chorionic gonadotropin (hCG) prior to testing. Additionally, measurements of optical anatomy determined how túngara frog eye and retina morphology related to physiological sensitivity. As expected, we found that both sexes display higher visual sensitivity under scotopic conditions compared to photopic conditions. However, hormone injections significantly increased retinal sensitivity of females under scotopic conditions. These results support the hypothesis that hormonal modulation of neural mechanisms, such as those mediating visually guided reproductive behavior in this species, include modulation of the receptor organ: the retina. Thus, our data serve as a starting point for elucidating the mechanism of hormonal modulation of visual sensitivity. [ABSTRACT FROM AUTHOR]

Multimodal signaling is common in communication systems. Depending on the species, individual signal components may be produced synchronously as a result of physiological constraint (fixed) or each component may be produced independently (fluid) in time. For animals that rely on fixed signals, a basic prediction is that asynchrony between the components should degrade the perception of signal salience, reducing receiver response. Male túngara frogs, Physalaemus pustulosus, produce a fixed multisensory courtship signal by vocalizing with two call components (whines and chucks) and inflating a vocal sac (visual component). Using a robotic frog, we tested female responses to variation in the temporal arrangement between acoustic and visual components. When the visual component lagged a complex call (whineþchuck), females largely rejected this asynchronous multisensory signal in favor of the complex call absent the visual cue. When the chuck component was removed from one call, but the robofrog inflation lagged the complex call, females responded strongly to the asynchronous multimodal signal. When the chuck component was removed from both calls, females reversed preference and responded positively to the asynchronous multisensory signal. When the visual component preceded the call, females responded as often to the multimodal signal as to the call alone. These data show that asynchrony of a normally fixed signal does reduce receiver responsiveness. The magnitude and overall response, however, depend on specific temporal interactions between the acoustic and visual components. The sensitivity of túngara frogs to lagging visual cues, but not leading ones, and the influence of acoustic signal content on the perception of visual asynchrony is similar to those reported in human psychophysics literature. Virtually all acoustically communicating animals must conduct auditory scene analyses and identify the source of signals. Our data suggest that some basic audiovisual neural integration processes may be at work in the vertebrate brain. [ABSTRACT FROM AUTHOR]

Sexual communication can evolve in response to sexual selection, and it can also cause behavioral reproductive isolation between populations and thus drive speciation. Anurans are an excellent system to investigate these links between behavior and evolution because we have detailed knowledge of how neural mechanisms generate behavioral preferences for calls and how these preferences then generate selection on call variation. But we know far less about the physical mechanisms of call production, especially how different laryngeal morphologies generate call variation. Here we review studies of a group of species that differ in the presence of a secondary call component that evolved under sexual selection. We discuss how the larynx produces this call component, and how laryngeal morphology generates sexual selection and can contribute to speciation. [ABSTRACT FROM AUTHOR]

Many sexual displays contain multiple components that are received through a variety of sensory modalities. Primary and secondary signal components can interact to induce novel receiver responses and become targets of sexual selection as complex signals. However, predators can also use these complex signals for prey assessment, which may limit the evolution of elaborate sexual signals. We tested whether a multimodal sexual display of the male túngara frog (Physalaemus pustulosus) increases predation risk from the fringelipped bat (Trachops cirrhosus) when compared with a unimodal display. We gave bats a choice to attack one of two frog models: a model with a vocal sac moving in synchrony with a mating call (multisensory cue), or a control model with the call but no vocal sac movement (unimodal cue). Bats preferred to attack the model associated with the multimodal display. Furthermore, we determined that bats perceive the vocal sac using echolocation rather than visual cues. Our data illustrate the costs associated with multimodal signaling and that sexual and natural selection pressures on the same trait are not always mediated through the same sensory modalities. These data are important when considering the role of environmental fluctuations on signal evolution as different sensory modalities will be differentially affected. [ABSTRACT FROM AUTHOR]

Mate choice can vary in response to internal or external conditions that alter the costs and benefits of being choosy. The relationship between mate choice and hybridization, however, is not well understood. An important influence on mate choice is the rate at which potential mates are encountered: low rates increase sampling costs, favoring reduced choosiness. We investigated the influence of conspecific encounter rate on female choice in a naturally hybridizing species of swordtail, Xiphophorus birchmanni. We exposed females to conspecific males, followed by either no delay or a long (24 h) delay before their next male encounter. In this second encounter, females were offered the choice of a heterospecific (X. malinche) male only or a choice between a conspecific and heterospecific male. When not given a choice between 2 males, females spent more time with the heterospecific following a long delay between male encounters than after no delay, suggesting a decrease in choosiness. When offered a choice between males, however, females preferentially associated with the conspecific, regardless of the time between male encounters. These results suggest that females are sensitive to conspecific encounter rate but may employ a sample-based (vs. standard-based) comparison tactic, which could make hybridization less likely. We also found that, contrary to our expectations, females with only the heterospecific male to choose from visited him more frequently following a long delay between male encounters than following no delay, possibly indicating an increase in sampling effort. Our study highlights the potential importance of context-dependent mate choice in animal hybridization. [ABSTRACT FROM PUBLISHER]

Sexual selection is responsible for the evolution of costly elaborate male traits. When male displays are dynamic, display strategy is sensitive to contextual cues that alter the relative costs and benefits of producing each signal in a male’s repertoire. Because females often prefer more elaborate signals, males often respond to female presence by elaborating their display. When added elaboration increases assessment information or reproductive stimulation, females might benefit by extracting the maximum amount of signal elaboration from males. Thus, we expect that females could exaggerate their presence and cause males to produce even costlier and more attractive signals by exhibiting “elicitation” behaviors. We asked whether female túngara frogs elicit increased call complexity from prospective mates. In túngara frogs, adding complexity increases both attractiveness and predation risk. We found that females exhibit a repertoire of movements that function not in mate acquisition, per se, but in display manipulation, by eliciting increased complexity from calling males. The probability that males add complexity to their display increases when females produce these movements. Thus, females actively influence males to produce riskier signals. [ABSTRACT FROM PUBLISHER]

Disentangling the influence of multiple signal components on receivers and elucidating general processes influencing complex signal evolution are difficult tasks. In this study we test mate preferences of female squirrel treefrogs Hyla squirella and female túngara frogs Physalaemus pustulosus for similar combinations of acoustic and visual components of their multimodal courtship signals. In a two-choice playback experiment with squirrel treefrogs, the visual stimulus of a male model significantly increased the attractivness of a relatively unattractive slow call rate. A previous study demonstrated that faster call rates are more attractive to female squirrel treefrogs, and all else being equal, models of male frogs with large body stripes are more attractive. In a similar experiment with female túngara frogs, the visual stimulus of a robotic frog failed to increase the attractiveness of a relatively unattractive call. Females also showed no preference for the distinct stripe on the robot that males commonly bear on their throat. Thus, features of conspicuous signal components such as body stripes are not universally important and signal function is likely to differ even among species with similar ecologies and communication systems. Finally, we discuss the putative information content of anuran signals and suggest that the categorization of redundant versus multiple messages may not be sufficient as a general explanation for the evolution of multimodal signaling. Instead of relying on untested assumptions concerning the information content of signals, we discuss the value of initially collecting comparative empirical data sets related to receiver responses. [ABSTRACT FROM AUTHOR]

Multimodal signals (acoustic+visual) are known to be used by many anuran amphibians during courtship displays. The relative degree to which each signal component influences female mate choice, however, remains poorly understood. In this study we used a robotic frog with an inflating vocal sac and acoustic playbacks to document responses of female túngara frogs to unimodal signal components (acoustic and visual). We then tested female responses to a synchronous multimodal signal. Finally, we tested the influence of spatial and temporal variation between signal components for female attraction. Females failed to approach the isolated visual cue of the robotic frog and they showed a significant preference for the call over the spatially separate robotic frog. When presented with a call that was temporally synchronous with the vocal sac inflation of the robotic frog, females did not show a significant preference for this over the call alone; when presented with a call that was temporally asynchronous with vocal sac inflation of the robotic frog, females discriminated strongly against the asynchronous multimodal signal in favor of the call alone. Our data suggest that although the visual cue is neither necessary nor sufficient for attraction, it can strongly modulate mate choice if females perceive a temporal disjunction relative to the primary acoustic signal. [ABSTRACT FROM AUTHOR]

The plasticity of animal behavior allows individuals to maximize fitness in a wide range of contexts. Both production of and preference for mating signals are context-dependent according to internal factors such as hormonal state, and external factors such as predation risk. In many species, male-to-female proximity also defines an important context for mating communication. Males often possess short-distance courtship signals, and females often exhibit distance-related variation in signal response. Such variation in response may occur when a signal's relevance changes with male-to-female distance, but it may also result from perceptual constraints that are unrelated to fitness. Túngara frogs produce variably complex advertisement calls, and sexual selection theory predicts that females should prefer calls of greater complexity. Preference tests, however, have not demonstrated consistent trends for preference between calls of variable complexity. We tested whether proximity to males influences female response to variable signal complexity and found that both preference and memory for signal complexity are proximity-dependent. [ABSTRACT FROM AUTHOR]

Males and females can differ both in the social behaviors they perform and in the contexts in which they engage in these behaviors. One possible mechanism of sex differences in behavior is a sexual dimorphism in the relay of sensory information to motor areas, but no studies have examined the role of such a relay in vertebrate sexually dimorphic behaviors. We used egr-1 expression as a marker of neural activation in frogs exposed to conspecific and heterospecific acoustic signals to compare activation patterns throughout the brains of males and females. We determined how the sexes differ in the transformation of social signals into motor responses in the context of social communication. We examined the relationships between egr-1 mRNA levels in the auditory midbrain and forebrain areas, as well as how forebrain expression related to the behavioral responses of the animals. Forebrain network activation patterns and forebrain-behavior relationships were similar in males and females. By contrast, we found a sex difference in the relationship between midbrain and forebrain activation; midbrain auditory responses predicted forebrain responses in females but not in males. This sex difference suggests that sensory inputs differentially regulate motor systems underlying social behaviors in males and females. This sensorimotor transformation may be a common locus for generating sex differences in behavior. [ABSTRACT FROM AUTHOR]

The potential for ornament evolution in response to sexual selection rests on the interaction between the permissiveness or selectivity of female preferences and the constraints on male development of signaling related traits. We investigate the former by determining how latent female preferences either exaggerate the magnitude of current traits (i.e. elaborations) or favor novel traits (i.e. innovations). In túngara frogs, females prefer complex mating calls (whine-chucks) to simple calls (whine only). The whine is critical for mate recognition while the chuck further enhances the attractiveness of the call. Here we use a combination of synthetic and natural stimuli to examine latent female preferences. Our results show that a diversity of stimuli, including conspecific and heterospecific calls as well as predator-produced and human-made sounds, increase the attractiveness of a call when added to a whine. These stimuli do not make simple calls more attractive than a whine-chuck, however. In rare cases we found stimuli that added to the whine decrease the attractiveness of the call. Overall, females show strong preferences for both elaborations and innovations of the chuck. We argue that the emancipation of these acoustic adornments from mate recognition allows such female permissiveness, and that male constraints on signal evolution are probably more important in explaining why males evolved their specific adornment. Experimentally probing latent female preferences for stimuli out of the species' range is a useful means to gain insights about the potential of female choice to influence signal evolution and thus the astounding diversity in male sexually-selected traits. [ABSTRACT FROM AUTHOR]

We examined the emergence of a critical component of sex, response to sexual signalsphonotaxis-in male and female túngara frogs (Physalaemus pustulosus). We determined the ontogenetic trajectories of phonotactic responses as animals developed from metamorphic froglets to reproductive adults. The results demonstrated that species-typical phonotaxis emerges quite early during postmetamorphic development, well before sexual maturity, suggesting that a developmentally early bias in the auditory system for species-typical signals might be a more general phenomenon than previously thought, and that the neural circuits responsible for processing and responding to conspecific advertisement signals in a species-typical manner might develop long before the coordinated behavior is demanded of the organism. [ABSTRACT FROM AUTHOR]

Mate choice studies most often examine female preferences based on population responses, thus potentially overlooking individual differences in behavior. Moreover, such studies typically use invariant stimulus conditions to infer preferences. By using population responses and static stimulus presentations, it is difficult to thoroughly understand the complexity of the mate choice process, including variation present between individuals. Here, we investigated phonotactic mate choice behavior in female túngara frogs (Physalaemus pustulosus) in response to temporally dynamic presentations of male advertisement calls. We tested females on repeated trials to examine individual differences and found considerable variation in the extent to which females update their mate choice decisions. Females in our study were bimodally distributed and thus broadly classified as either committed or uncommitted to an initial mate approach. We compared body condition measures of females differing behaviorally and determined that females with larger residual body masses were more committed to initial mate choices than less massive individuals, despite the fact that all females were in reproductive condition and field collected in amplexus. Our results suggest that anuran phonotaxis, once considered to be a highly stereotyped behavior, is more complex and variable than previously thought. [ABSTRACT FROM PUBLISHER]

In order for a signal to be transmitted from a sender to a receiver, the receiver must be within the active space of the signal. If patterns of sound radiation are not omnidirectional, the position as well as the distance of the receiver relative to the sender is critical. In previous measurements of the horizontal directivity of mating calls of frogs, the signals were analyzed using peak or root-mean-square analysis and resulted in broadband directivities that ranged from negligible to a maximum of approximately 5 dB. Idealized laboratory measurements of the patterns of acoustic radiation of the mating calls of male túngara frogs (Physalaemus pustulosus), along axes relevant to three receivers in this communication network, female frogs in the horizontal plane, and frog-eating bats and blood-sucking flies above the ground, are reported. The highest sound pressure level was radiated directly above the frog, with a 6 dB reduction radiated along the horizontal direction. Band-limited directivities were significantly greater than broadband directivities, with a maximum directivity of 20 dB in the vertical plane for harmonics near 6 kHz. The implications with regard to mating and predator-prey interactions are discussed. [ABSTRACT FROM AUTHOR]

Anurans have long been a model system for studies of animal communication, but little is known about how individuals acquire acoustically linked mating behaviors. The manner in which behaviors are acquired may be a source of variation in these behaviors. In this study, we reared Physalaemus pustulosus in four acoustic treatment groups: hearing a conspecific chorus of P. pustulosus frogs, acoustically isolated from all frog calls, hearing a chorus of the congener P. enesefae, and hearing noise. We then measured the spectral and temporal characteristics of the calls produced by males and tested them for differences between treatment groups. Males reared in isolation produced calls that were shorter in duration. Females showed discrimination against these shorter calls. Early experience can alter the advertisement call of male P. pustulosus, and acoustic isolation leads to the acquisition of calls that are less attractive to females. Males reared in other groups produced species-typical calls. The calls of male P. pustulosus may be the product of a gene by environment interaction. [ABSTRACT FROM AUTHOR]

The Amazon molly, Poecilia formosa, is a gynogenetic, all-female fish. Its mating system relies on heterospecific matings with males of closely related sexual species. In mixed populations, males mate with conspecific sexual females and heterospecific asexual females. Such matings are not isolated dyadic interactions but rather elements of a communication network, because multiple females can observe these interactions. This is the only known case of heterospecific mate-copying and, thus, a system in which the potential for mate-copying could be influenced by the presence of another species. Here we show that mate-copying is exhibited by the sexual species P. mexicana and P. latipinna, and the asexual P. formosa. Both sexual and asexual females copy each other's mate choice decisions in sympatry, but females from allopatric populations do not show heterospecific mate-copying. Males benefit from heterospecific matings with Amazon mollies because these increase their attractiveness to the conspecific sexual females. In mixed shoals, mate-copying potentially imposes costs as it increases a male's attractiveness to heterospecific females. We argue that the net-effect of mate-copying is beneficial to males because the relative strength of mate-copying is lower in Amazon mollies. We hypothesize that an added benefit to males lies in the signal value of copulations. [ABSTRACT FROM AUTHOR]

The vocal sac is a visually conspicuous attribute of most male frogs, but its role in visual communication has only been demonstrated recently in diurnally displaying frogs. Here we characterized the spectral properties of the inflated vocal sac of male túngara frogs (Physalaemus pustulosus), a nocturnal species, and túngara visual sensitivity to this cue across reproductive state and sex. We measured the spectral and total reflectance of different male body regions, including inflated and non-inflated vocal sacs, along with samples of the visual background against which males are perceived. Inflated vocal sacs were the most reflective of all body parts, being one log unit more reflective than background materials. We utilized an optomotor drum with black stripes and stripes that mimicked the spectral reflectance of the inflated vocal sacs with various nocturnal light intensities to measure the visual sensitivity thresholds of males, non-reproductive females and reproductive females. All three groups exhibited visual sensitivities corresponding to intensities below moonless conditions in open habitats or at the edge of secondary tropical forests. Reproductive females exhibited the greatest visual sensitivity of all groups, and were significantly more sensitive than non- reproductive females. Though the mechanism for this physiological difference between reproductive and non-reproductive females is unknown, it is consistent with previously observed patterns of light-dependent phonotaxic behavior in túngaras. We suggest that the visual ecology of the vocal sac; especially in nocturnal frogs, offers a rich source for investigations of visual ecology and physiological regulation of vision. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Mating decisions contribute to both the fitness of individuals and the emergence of evolutionary diversity, yet little is known about their cognitive architecture. We propose a simple model that describes how preferences are translated into decisions and how seemingly disparate patterns of preference can emerge from a single perceptual process. The model proposes that females use error-prone estimates of attractiveness to select mates based on a simple decision rule: choose the most attractive available male that exceeds some minimal criterion. We test the model in the túngara frog, a well-characterized species with an apparent dissociation between mechanisms of mate choice and species recognition. As suggested by our model results, we find that a mate attraction feature alters assessments of species status. Next, we compare female preferences in one-choice and two-choice tests, contexts thought to emphasize species recognition and mate choice, respectively. To do so, we use the model to generate maximum-likelihood estimators of preference strengths from empirical data. We find that a single representation of preferences is sufficient to explain response probabilities in both contexts across a wide range of stimuli. In this species, mate choice and species recognition are accurately and simply summarized by our model. While the findings resolve long-standing anomalies, they also illustrate how models of choice can bridge theoretical and empirical treatments of animal decisions. The data demonstrate a remarkable congruity of perceptual processes across contexts, tasks, and taxa. [ABSTRACT FROM AUTHOR]

Female preferences for male mating signals are often evaluated on single parameters in isolation or small suites of characters. Most signals, however, are composites of many individual parameters. In this study we quantified multivariate traits in the advertisement call of the túngara frog, Physalaemus pustulosus. We represented the calls in multidimensional scaling space and chose nine test calls to represent the range of population variation. We then tested females for phonotactic preference between calls in each pair of the nine test calls. We used statistics developed for paired comparisons in such "round robin" competitions to evaluate the null hypothesis of equal attractiveness, and to examine the degree to which females responded to calls as being different from or similar to one another in attractiveness. We then examined the attractiveness of each test call relative to all other test calls as a function of their location in multivariate acoustic space (the acoustic landscape) to visualize sexual selection on calls. Finally, we used methods from cognitive psychology to illustrate the females' perception of call attractiveness in multivariate space, and compared this perceptual landscape to the acoustic landscape of quantitative call variation. We show that correlations between individual call characters are not strong and thus there are few biomechanical constraints on their independent evolution. Most call variables differed among males, and there was high repeatability of call characters within males. Females often discriminated between pairs of calls from the population, and there were significant differences among calls in their attractiveness. Female preferences for calls were not stabilizing. The region of the acoustic landscape that was most attractive to females included the mean call but was not centered around it. The females' perceptual or preference landscape did not correlate with the call's acoustic landscape, and female... [ABSTRACT FROM AUTHOR]

The evolution of sexual signaling systems is influenced by natural and sexual selection acting on complex interactions among traits. Natural hybrid zones are excellent systems for assessing fitness effects on sexual phenotypes. Most documented hybrid zones, however, show little variation in sexual signals. A hybrid zone between the swordtails Xiphophorus birchmanni and Xiphophorus malinche is characterized by numerous recombinants for male sexual traits. Analyses of geographic variation in morphological and isozyme traits in the Río Calnali, Hidalgo, Mexico, reveal an upstream-to-downstream gradient from X. malinche- to X. birchmanni-type traits. A second hybrid zone, likely isolated from the R. Calnali, occurs in the nearby Arroyo Pochutla. Although the presumed female preference for swords predicts the introgression of swords from X. malinche-like populations into hybrid populations, the opposite pattern was observed. Swords are reduced in populations otherwise characterized by X. malinche traits. Sexually dimorphic traits were poorly correlated within individuals, indicating that sexual selection does not act against recombinant phenotypes. Hybrid males also exhibit trait values outside the range of parental variation. These patterns are consistent with predictions that females are permissive, preferring generally conspicuous males without attending to specific features. [ABSTRACT FROM AUTHOR]

Investigates male and female mate choice copying in a wild population of the sailfin molly. Preference of males to associate with a female adjacent to a male; Evaluation the influence of shoaling behavior on male and female preference; Assumption of models of sexual selection on the basis of female choice of mates.

The article presents information on a study which demonstrated that within individual female pygmy swordtails, Xiphophorus (X.) pygmaeus, directional preferences for conspicuous ornamentation are inversely related to discrimination against a sympatric heterospecific, X. cortezi. Information on X. pygmaeus and X. cortezi is given. Findings suggest that different arenas of mate choice can constrain one another, even when females assess multiple cues.

Investigates the degree of preference of female tungara frogs (Physalaemus pustulosus) for both extant and ancestral advertisement calls. Females' inability to discriminate between calls of males from their own species and calls at their most recent ancestral node; Ancestral history shared; Call convergence.

Animals frequently experience changes in their environment, including diel and seasonal shifts in abiotic and biotic factors. In addition to physiological and morphological changes, animals alter their behavior in response to environmental variation. This study examined the impacts of heterogeneous environments on mating behaviors. We examined both male and female túngara frog phonotactic responses to multimodal (audiovisual) and unimodal (acoustic) stimuli. We altered aspects of the physical environment by changing substrate (terrestrial and aquatic) and ambient light levels. Females demonstrated a similar preference for the audiovisual stimulus regardless of substrate but decreased latency to choose in an aquatic environment. When ambient light levels were increased (relative to darker control), females reversed their preference, avoiding the multimodal stimulus, but the latency to choose was unchanged. Males demonstrated no preference for the multimodal signal on either substrate, but like females, male latency was reduced in an aquatic environment. Different environments carry their own associated costs, including varying levels of predation risk. Increased light levels and an aquatic environment likely carry higher predation risk and therefore should lead to changes in female and male responses. Interestingly, these two environments do not cause uniform changes in female responses. The addition of an aquatic environment led to a reduction in latency, whereas an increase in ambient light levels induced a change in female mate preference. These findings demonstrate the importance of the environment on mating responses to multimodal signals. Significance statement: Responses to conspecific mating signals (e.g., mate preferences) have often been assumed to be static. In this study, we tested responses of both male and female túngara frogs to a multimodal (visual + vocal) advertisement signal under varying environmental conditions. Elevated light levels changed female responses to mating signals. When both sexes were required to swim, rather than walk to a signal, their choices did not change. They did respond faster, however. These results indicate that measuring the strength of sexual selection should be considered as a function of both innate preferences and the environmental conditions experienced by the animals. [ABSTRACT FROM AUTHOR]

Focuses on behavioral ecology. Sexual selection favoring conspicuous signals; Risks of conspicuous signals; Natural selection generated by predation as a constraining force in signal evolution; Reference to a study by Philip Stoddard in the July 15, 1999 issue of 'Nature' on gymnotiform electric fish; Implications of the study.

The evolution of elaborate signals can emerge from changes in anatomical signaling structures. In the male túngara frog, a simple advertisement call (‘whine’) can be ornamented facultatively with a suffix (‘chuck’) to produce a more attractive complex call, or ‘whine-chuck’. A fibrous mass (FM1) supported by the vocal cords plays a role in chuck production. Here, we examine the effects of FM1 ablation on a large set of spectral and temporal features of both the whine and chuck and we test the hypothesis that FM1 ablation reduces call attractiveness to females. Both call components were impacted by FM1 ablation, but especially the suffix. The proportion of energy in the suffix’s odd compared to even harmonics diminished markedly as did the relative amplitude, effectively eliminating the chuck percept. FM1 ablation also reduced the whine’s frequency and its rate of frequency modulation. Moreover, post-surgery chucks no longer enhanced the attractiveness of the simple call and whines also appeared to diminish in attractiveness. Together, our results demonstrate that FM1 plays a role in the production of both call components in a way that stimulates the female auditory system and that the growth of FM1 had potentially positive sexual selection implications for the pre-existing simple call. [ABSTRACT FROM AUTHOR]

Multimodal (multisensory) signalling is common in many species and often facilitates communication. How receivers integrate individual signal components of multisensory displays, especially with regard to variance in signal complexity, has received relatively little attention. In nature, male túngara frogs, Physalaemus pustulosus , produce multisensory courtship signals by vocalizing and presenting their inflating and deflating vocal sac as a visual cue. Males can produce a simple call (whine only) or a complex call (whine + one or more chucks). In a series of two-choice experiments, we tested female preferences for variation in acoustic call complexity and amplitude (unimodal signals). We then tested preferences for the same calls when a dynamic robotic frog was added to one call, generating a multimodal stimulus. Females preferred a complex call to a simple call; when both calls contained at least one chuck, additional numbers of chucks did not further increase attractiveness. When calls contained zero or one chuck, the visual stimulus of the robofrog increased call attractiveness. When calls contained multiple chucks, however, the visual component failed to enhance call attractiveness. Females also preferred higher amplitude calls and the addition of the visual component to a lower amplitude call did not alter this preference. At relatively small amplitude differences, however, the visual signal increased overall discrimination between the calls. These results indicate that the visual signal component does not provide simple enhancement of call attractiveness. Instead, females integrate multisensory components in a nonlinear fashion. The resulting perception and behavioural response to complex signals probably evolved in response to animals that communicate in noisy environments. [ABSTRACT FROM AUTHOR]

Summary: A new study shows that biparental care in frogs is more likely to evolve when tadpoles are reared under environmentally harsh conditions. Biparental care facilitates both social monogamy and genetic monogamy; frogs that work together to raise their offspring have higher mating fidelity to one another. [Copyright &y& Elsevier]

Summary: Polymorphisms in reproductive strategies are among the most extreme and complex in nature. A prominent example is male body size and the correlated reproductive strategies in some species of platyfish and swordtails of the genus Xiphophorus. This polymorphism is controlled by a single Mendelian locus (P) that determines the onset of sexual maturity of males. Because males cease growth after reaching puberty, this results in a marked size polymorphism. The different male size classes show pronounced behavioral differences (e.g., courtship versus sneak mating), and females prefer large over small males. We show that sequence polymorphisms of the melanocortin receptor 4 gene (mc4r) comprise both functional and non-signal-transducing versions and that variation in copy number of mc4r genes on the Y chromosome underlies the P locus polymorphism. Nonfunctional Y-linked mc4r copies in larger males act as dominant-negative mutations and delay the onset of puberty. Copy number variation, as a regulating mechanism, endows this system with extreme genetic flexibility that generates extreme variation in phenotype. Because Mc4r is critically involved in regulation of body weight and appetite, a novel link between the physiological system controlling energy balance and the regulation of reproduction becomes apparent. [ABSTRACT FROM AUTHOR]

Unlike in terrestrial animals, the boundary between internal (e.g., hormones) and external (e.g., social) stimulation can be blurred for aquatic and amphibious species. When chemicals such as hormones and glandular secretions leach into the water, they can further interact with other signaling systems, creating multimodal stimuli. It is unclear, however, whether water-borne chemical secretions from courting male frogs affect the physiology and behavior of their rivals. In order to address this question we first established non-invasive, continuous sampling methods for simultaneously measuring both hormones and behavior in amphibious species. Then, we examined whether interactions between water-borne chemical secretions and conspecific calls affect reproductive behavior and physiology (testosterone and corticosterone) of courting male túngara frogs. Our results demonstrate that conspecific acoustic stimulation alone increases locomotor activity, decreases latency to call, and increases calling behavior but does not alter the amount of hormones excreted. In response to water containing chemical secretions from rivals, but in the absence of calls from other males, males excrete more testosterone. Interestingly, the combined acoustic and chemical stimulus causes a multiplicative increase in both calling behavior and hormonal excretion. Taken together, our results suggest that a multimodal chemical-acoustic stimulus physiologically primes males for aggressive behavior. • Male frogs perceive and respond to water-borne chemical secretions from rivals. • Acoustic stimulation enhances locomotor activity, motivation to call, and calling. • Chemical stimulation enhances androgen excretion. • Multimodal stimulation multiplicatively increases behavioral and hormonal responses. [ABSTRACT FROM AUTHOR]