Multisensory modalities increase working memory for mating signals in a treefrog

Noise affects mate choice based on visual information via cross-sensory interference

Animal communication is often hampered by noise interference. Noise masking has primarily been studied in terms of its unimodal effect on sound information provision and use, while little is known about its cross-modal effect and how animals weigh unimodal and multimodal courtship cues in noisy environments. Here, we examined the cross-modal effects of background noise on female visual perception of mate choice and female preference for multimodal displays (sound + vocal sac) in a species of treefrog. We tested female mate choices using audio/video playbacks in the presence and absence of noise (white noise band-filtered to match or mismatch female sensitive hearing range, heterospecific chorus). Surprisingly, multimodal displays do not improve receiver performance in noise. The heterospecific chorus and white noise band-filtered to match female sensitive hearing ranges, significantly reduced female responses to the attractive visual stimuli in addition to directly impairing auditory information use. Meanwhile, the cross-modal impacts of background noise are influenced to some extent by whether the noise band matches female sensitive hearing range and the difficulty of distinguishing tasks. Our results add to the evidence for cross-modal effects of noise and are the first to demonstrate that background noise can disrupt female responses to visual information related to mate choice, which may reduce the communication efficiency of audiovisual signals in noisy environments and impose fitness consequences. This study has key ecological and evolutionary implications because it illustrates how noise influences mate choice in wildlife via cross-sensory interference, which is crucial in revealing the function and evolution of multimodal signals in noisy environments as well as informing evidence-based conservation strategies for forecasting and mitigating the multimodal impacts of noise interference on wildlife.

Can you hear/see me? Multisensory integration of signals does not always facilitate mate choice

Females of many species choose mates using multiple sensory modalities. Multimodal noise may arise, however, in dense aggregations of animals communicating via multiple sensory modalities. Some evidence suggests multimodal signals may not always improve receiver decision-making performance. When sensory systems process input from multimodal signal sources, multimodal noise may arise and potentially complicate decision-making due to the demands on cognitive integration tasks. We tested female túngara frog, Physalaemus (=Engystomops) pustulosus, responses to male mating signals in noise from multiple sensory modalities (acoustic and visual). Noise treatments were partitioned into three categories: acoustic, visual, and multimodal. We used natural calls from conspecifics and heterospecifics for acoustic noise. Robotic frogs were employed as either visual signal components (synchronous vocal sac inflation with call) or visual noise (asynchronous vocal sac inflation with call). Females expressed a preference for the typically more attractive call in the presence of unimodal noise. However, during multimodal signal and noise treatments (robofrogs employed with background noise), females failed to express a preference for the typically attractive call in the presence of conspecific chorus noise. We found that social context and temporal synchrony of multimodal signaling components are important for multimodal communication. Our results demonstrate that multimodal signals have the potential to increase the complexity of the sensory scene and reduce the efficacy of female decision making.

Frog embryos use multiple levels of temporal pattern in risk assessment for vibration-cued escape hatching

Stereotyped signals can be a fast, effective means of communicating danger, but animals assessing predation risk must often use more variable incidental cues. Red eyed-treefrog, Agalychnis callidryas, embryos hatch prematurely to escape from egg predators, cued by vibrations in attacks, but benign rain generates vibrations with overlapping properties. Facing high false-alarm costs, embryos use multiple vibration properties to inform hatching, including temporal pattern elements such as pulse durations and inter-pulse intervals. However, measures of snake and rain vibration as simple pulse-interval patterns are a poor match to embryo behavior. We used vibration playbacks to assess if embryos use a second level of temporal pattern, long gaps within a rhythmic pattern, as indicators of risks. Long vibration-free periods are common during snake attacks but absent from hard rain. Long gaps after a few initial vibrations increase the hatching response to a subsequent vibration series. Moreover, vibration patterns as short as three pulses, separated by long periods of silence, can induce as much hatching as rhythmic pulse series with five times more vibration. Embryos can retain information that increases hatching over at least 45 s of silence. This work highlights that embryo behavior is contextually modulated in complex ways. Identical vibration pulses, pulse groups, and periods of silence can be treated as risk cues in some contexts and not in others. Embryos employ a multi-faceted decision-making process to effectively distinguish between risk cues and benign stimuli.

Sexual selection and the ascent of women: Mate choice research since Darwin

Darwin's theory of sexual selection fundamentally changed how we think about sex and evolution. The struggle over mating and fertilization is a powerful driver of diversification within and among species. Contemporaries dismissed Darwin's conjecture of a "taste for the beautiful" as favoring particular mates over others, but there is now overwhelming evidence for a primary role of both male and female mate choice in sexual selection. Darwin's misogyny precluded much analysis of the "taste"; an increasing focus on mate choice mechanisms before, during, and after mating reveals that these often evolve in response to selection pressures that have little to do with sexual selection on chosen traits. Where traits and preferences do coevolve, they can do so whether fitness effects on choosers are positive, neutral, or negative. The spectrum of selection on traits and preferences, and how traits and preferences respond to social effects, determine how sexual selection and mate choice influence broader-scale processes like reproductive isolation and population responses to environmental change.

Females and males respond differently to calls impaired by noise in a tree frog

Both human and nonhuman animals communicating acoustically face the problem of noise interference, especially anurans during mating activities. Previous studies concentrated on the effect of continuous noise on signal recognition, but it is still unknown whether different notes in advertisement calls impaired by noise affect female choice and male-male competition or not. In this study, we tested female preferences and male-evoked vocal responses in serrate-legged small tree frog (Kurixalus odontotarsus), by broadcasting the five-note advertisement call and the advertisement call with the second, third, or fourth note replaced by noise, respectively. In phonotaxis experiments, females significantly discriminated against the advertisement call with the fourth note impaired by noise, although they did not discriminate against other two calls impaired by noise, which indicates that the negative effect of noise on female preference is related to the order of impaired notes in the advertisement call. In playback experiments, males increased the total number of notes in response to noise-impaired calls compared with spontaneous calls. More interestingly, the vocal responses evoked by noise-impaired calls were generally similar to those evoked by complete advertisement calls, suggesting that males may recognize the noise-impaired calls as complete advertisement calls. Taken together, our study shows that different notes in advertisement calls replaced by noise have distinct effects on female choice and male-male competition.