Effects of domestication on neophobia: A comparison between the domesticated Bengalese finch (Lonchura striata var. domestica) and its wild ancestor, the white-rumped munia (Lonchura striata).

Bengalese finches (Lonchura striata var. domestica) have more complex song traits than their wild ancestors, white-rumped munias (Lonchura striata). Domesticated finches are likely able to allocate more resources to reproduction (e.g. singing) rather than to mechanisms intended for coping with predation, which are no longer needed under domesticated conditions. Here, we aimed to examine the effects of changes in selection pressure due to domestication on the behaviour of Bengalese finches and to contemplate the possible evolutionary mechanisms underlying these changes. To do so, we compared neophobic responses to novel-object conditions as an assessment of reactions to potential predators. We studied groups of Bengalese finches and white-rumped munias and found that Bengalese finches were more likely to eat the food provided to them under novel-object conditions. Bengalese finches had a shorter latency time to eat, and this latency time was less affected by the novel object in the case of Bengalese finches compared to white-rumped munias. Therefore, Bengalese finches have reduced neophobic responses due to domestication. The behavioural strategies of white-rumped munias appear to be more suitable for natural environments, which include unpredictable risks, whereas Bengalese finches have likely adapted their behaviour to the conditions of artificial selection.

Presence of Microplastics in Four Types of Shellfish Purchased at Fish Markets in Okayama City, Japan.

The worldwide microplastic pollution in our environment is a matter of great concern. Harmful effects of plastics have been reported in various types of organisms including murine animals. We examined the presence of microplastics in four types of shellfish purchased from fish markets in Okayama, Japan and served to the public: short-neck clam (Ruditapes philippinarum, asari in Japanese), hard-shell clam (Meretrix lusoria, hamaguri), brackishwater clam (Cyrenidae, shijimi), and oyster (Crassostrea gigas, kaki). Our analyses demonstrated that approx. 3 pieces of microplastics were present per single shellfish, based on the division of the total number of pieces of microplastic obtained from all 4 types of shellfish by the total number of shellfish examined. Since health problems in humans due to microplastics have not yet been confirmed, further examinations of the effects of ingested microplastics are needed.

Cytotoxic Effects of Alcohol Extracts from a Plastic Wrap (Polyvinylidene Chloride) on Human Cultured Liver Cells and Mouse Primary Cultured Liver Cells.

An increasing accumulation of microplastics and further degraded nanoplastics in our environment is suspected to have harmful effects on humans and animals. To clarify this problem, we tested the cytotoxicity of two types of plastic wrap on human cultured liver cells and mouse primary cultured liver cells. Alcohol extracts from plastic wrap, i.e., polyvinylidene chloride (PVDC), showed cytotoxic effects on the cells. Alcohol extracts of polyethylene (PE) wrap were not toxic. The commercially available PVDC wrap consists of vinylidene chloride, epoxidized soybean oil, epoxidized linseed oil as a stiffener and stabilizer; we sought to identify which component(s) are toxic. The epoxidized soybean oil and epoxidized linseed oil exerted strong cytotoxicity, but the plastic raw material itself, vinylidene chloride, did not. Our findings indicate that plastic wraps should be used with caution in order to prevent health risks.

Variation in auditory neural activation in response to strain-specific songs in wild and domesticated female Bengalese finches.

Female songbirds identify and prefer conspecific male songs. Songs are an important cue for species discrimination. Bengalese finches are domesticated species and their male songs seem to have evolved as they comprise more complex sequences and tonal sounds than the songs of their wild ancestors, white-rumped munias. Previous research suggested that the degeneration of song functionality for species identification may have been one of the factors that promoted the evolution of song complexity in domestic strains. We hypothesized that female responses to conspecific songs have changed between the two strains: white-rumped munias could distinguish songs of their own species more readily than Bengalese finches. Because the song discrimination is affected by developmental experiences, we used adult female Bengalese finches and white-rumped munias reared with or without exposure to songs of their own strains (i.e., socially-reared or untutored). To evaluate their song discrimination, we quantified zenk-labeled cells in the auditory areas after exposure to song stimuli, either with songs of own strains or those of other strains. Socially-reared white-rumped munias exposed to songs of Bengalese finches showed lesser zenk expression than munias exposed to songs of their own strain. However, there were no significant differences among the groups in Bengalese finches. The result suggests that white-rumped munias could distinguish songs of their own species more strictly than Bengalese finches.

Affective valence of neurons in the vicinity of the rat amygdala: Single unit activity in response to a conditioned behavior and vocal sound playback.

We recorded single unit activity within and around the rat amygdala while rats were engaged in an operant task (which included both reward and aversive trials) and during playback of ultrasonic vocalizations (USVs) to determine if there existed neurons which responded to two different types of either positive contexts (i.e., water reward and positively associated 50kHz vocalizations) or negative contexts (i.e., white noise and negatively associated 22kHz vocalizations). Ultimately, we wanted to determine if these two contexts (operant condition task and vocal sounds) could be represented as either positive or negative in a single neuron. Neural activity in 90% of cells was modulated in response to one or more of those events. A small number of those cells showed neural responses to both the aversive operant trials and 22kHz USVs, but did not show responses to reward operant trials or 50kHz USVs, suggesting the activity of these neurons encodes for similar negative emotion in response to these two contexts. Some cells showed responses to either the reward trials or 50kHz USVs, but no cells showed responses to both, suggesting that these cells do not show a common response to events associated with positive emotion. This might mean that 50kHz vocal sounds and the operant rewards were segregated into two different categories within the neural representation at the level of the amygdala, even though it appeared that both events were associated with positive emotions in rats.

Cognitive bias in rats evoked by ultrasonic vocalizations suggests emotional contagion.

Emotional contagion occurs when an individual acquires the emotional state of another via social cues, and is an important component of empathy. Empathic responses seen in rodents are often explained by emotional contagion. Rats emit 50kHz ultrasonic vocalizations (USVs) in positive contexts, and emit 22kHz USVs in negative contexts. We tested whether rats show positive or negative emotional contagion after hearing conspecific USVs via a cognitive bias task. We hypothesized that animals in positive emotional states would perceive an ambiguous cue as being good (optimistic bias) whereas animals in negative states would perceive the same cue as being bad (pessimistic bias). Rats were trained to respond differently to two sounds with distinct pitches, each of which signaled either a positive or a negative outcome. An ambiguous cue with a frequency falling between the two stimuli tested whether rats interpreted it as positive or negative. Results showed that rats responded to ambiguous cues as positive when they heard the 50kHz USV (positive vocalizations) and negative when they heard the 22kHz USV (negative vocalizations). This suggests that conspecific USVs can evoke emotional contagion, both for positive and negative emotions, to change the affective states in receivers.

Limitations of a habituation task to demonstrate discrimination of natural signals in songbirds.

The habituation-dishabituation (HDH) paradigm is a common method used to examine animal cognition. Recent studies reported that spontaneous vocalizations could be used as an index of song familiarity and novelty in songbirds. However, these studies assigned only a few stimulus sets for all subjects, which might cause pseudoreplication. Therefore, we examined universality and general applicability of this method in Bengalese finches using a variety of stimulus sets. Seven unfamiliar conspecific songs were collected as a stimulus pool and a habituation song was randomly chosen for each subject. The subject was exposed to the habituation song repeatedly over 2h. During the test phase, the habituation song and a novel song randomly chosen from the stimulus pool were presented. We compared the degree of increase in call production during playback of those two songs. Although the degree was greater for the novel song compared with the habituation song in some birds, the trend was not consistent across all stimulus sets tested in these birds. Our results show that the HDH paradigm is not suitable to test song discrimination in songbirds unless precautions are taken to increase external validity by utilizing a variety of stimulus sets for each subject.

Domestication changes innate constraints for birdsong learning.

Birdsongs are acquired by imitating the sounds produced by conspecifics. Within a species, songs diverge by cultural transmission, but the range of species-specific features is restricted by innate constraints. Bengalese finches (Lonchura striata var. domestica) are a domesticated strain of the wild White-rumped munia (Lonchura striata). The songs of the domesticated strain have more tonal sounds and more variable sequences than those of the wild strain. We compared the features of songs that were produced by normal birds, isolation-reared birds, and cross-fostered birds in both White-rumped munias and Bengalese finches to identify differences in the genetic and environmental factors of their songs. Factor analyses were conducted based on 17 song measurements. We found that isolated songs differed from normal and cross-fostered songs, especially in unstable prosodic features. In addition, there were significant differences in sound property of mean frequency between the two strains regardless of the rearing conditions. Thus, innate constraints that partially determine birdsong phenotypes may be altered through domestication.

A simple explanation for the evolution of complex song syntax in Bengalese finches.

The songs of Bengalese finches (Lonchura striata var. domestica) have complex syntax and provide an opportunity to investigate how complex sequential behaviour emerges via the evolutionary process. In this study, we suggest that a simple mechanism, i.e. many-to-one mapping from internal states onto syllables, may underlie the emergence of apparent complex syllable sequences that have higher order history dependencies. We analysed the songs of Bengalese finches and of their wild ancestor, the white-rumped munia (L. striata), whose songs are more stereotypical and simpler compared with those of Bengalese finches. The many-to-one mapping mechanism sufficiently accounted for the differences in the complexity of song syllable sequences of these two strains.

Song performance and elaboration as potential indicators of male quality in Java sparrows.

Bird songs have evolved under sexual selection pressure. Songs include multiple features that are subject to female preference, but recent comparative research has indicated evolutionary tradeoffs between song performance and complexity in some species. Trill, a repetition of the same sound, is a performance-related song trait; higher trill performance can be achieved at the cost of song complexity at the among-species or population level. The aim of this study was to examine whether such tradeoffs also account for within-species variation in Java sparrow songs, which include both multiple trill types and non-trill parts. We found a great individual variation in trill proportion, trill performance, and song complexity. A positive association between trill performance and body size suggested that trills can serve as an indicator of male quality. However, contrary to the tradeoffs predicted by previous studies based on other passerine species, trill performance and song complexity, i.e., note repertoire, were positively correlated: males in better condition can sing songs with larger note repertoires and higher trill performance, which may explain how trills and non-trill notes are both maintained and have co-evolved by sexual selection in Java sparrow songs.

Song complexity and auditory feedback in birds: a comparison between two strains of Bengalese finches with different degrees of song complexity.

In adult songbirds, the degree of dependency on audition for maintenance of stable song structure varies from species to species. To date, studies suggest that song deterioration after deafening may be related to the song complexity of the species. Bengalese finches sing songs that are composed of complex note-to-note transitions, and their songs are critically dependent on auditory feedback. Song deterioration occurs within five days of auditory deprivation surgery, much faster than in other species. In contrast, white-rumped munias, a wild strain of Bengalese finches, sing simple songs. To test the hypothesis that the degree of dependency on auditory feedback for the maintenance of song structure is related to song complexity, we deafened two adult white-rumped munias by cochlear removal. Songs of white-rumped munias changed in syntax within five days of surgery, a similar trend observed in Bengalese finches. We suggest that real-time auditory feedback is important in white-rumped munias, despite the simplicity of their song structure. The time course of song alteration by deafened adult birds not determined solely by song complexity.