Timing of developmental stress and phenotypic plasticity: Effects of nutritional stress at different developmental periods on physiological and cognitive-behavioral traits in the zebra finch (Taeniopygia guttata)

Developmentally plastic organisms can respond to stressful environmental conditions by altering multiple aspects of their phenotype, often in a permanent fashion. The timing of developmental stress influences these phenotypic alterations because the prioritization of resources to traits necessary to overcome the stressor may be costly for the development of other traits. Despite the importance of this timing, few studies in birds have accounted for it, and those that have usually examined the effect on a single or few variables. This dissertation addresses the outstanding issues regarding i) the effects of timing of developmental stress on developmental plasticity, and ii) the extent to which poor nutritional conditions, as opposed to changes in nutritional conditions, drive phenotypic plasticity. Using zebra finches (Taeniopygia guttata) as my study species, I manipulated food accessibility during early and or juvenile development (i.e. before and after nutritional independence) and measured various physiological and cognitive-behavioral traits. Results indicated that timing of stress significantly affected many (but not all) aspects of phenotype measured, including growth rates, body composition, immune function, associative learning, spatial memory, and endocrine function. In particular, nutritional stress during the juvenile period appeared to have strong programming effects on phenotype. Nevertheless, individual differences and sex differences in developmental plasticity greatly moderated the influence that timing of stress had on phenotypic development

MELATONIN, AGGRESSION, AND SOCIAL DOMINANCE IN BLACK-CAPPED CHICKADEES (POECILE ATRICAPILLUS)

Non-breeding black-capped chickadees form linear dominance hierarchies in the winter. Dominants establish and maintain status by repeatedly directing aggression towards subordinates despite having regressed testes and likely also basal levels of testosterone. Melatonin has been shown to facilitate aggression in some animals under non-breeding conditions. The first aim of this study was to investigate whether melatonin was associated with aggressive black-capped chickadee dominant-subordinate interactions during the establishment of dominance status. The second aim of this study was to determine whether exogenous melatonin affected aggressive vocalizations more than non-aggressive vocalizations. Plasma melatonin was not significantly correlated to aggression. Moreover, exogenous melatonin treatment had no effect on aggressive or non-aggressive vocalizations. Results from this study therefore indicate that there is no relationship between melatonin and aggression and also no relationship between melatonin and dominance status in black-capped chickadees

Revisiting vocal perception in non-human animals: a review of vowel discrimination, speaker voice recognition, and speaker normalization

The extent to which human speech perception evolved by taking advantage of predispositions and pre-existing features of vertebrate auditory and cognitive systems remains a central question in the evolution of speech. This paper reviews asymmetries in vowel perception, speaker voice recognition, and speaker normalization in non-human animals – topics that have not been thoroughly discussed in relation to the abilities of non-human animals, but are nonetheless important aspects of vocal perception. Throughout this paper we demonstrate that addressing these issues in non-human animals is relevant and worthwhile because many non-human animals must deal with similar issues in their natural environment. That is, they must also discriminate between similar-sounding vocalizations, determine signaler identity from vocalizations, and resolve signaler-dependent variation in vocalizations from conspecifics. Overall, we find that, although plausible, the current evidence is insufficiently strong to conclude that directional asymmetries in vowel perception are specific to humans, or that non-human animals can use voice characteristics to recognize human individuals. However, we do find some indication that non-human animals can normalize speaker differences. Accordingly, we identify avenues for future research that would greatly improve and advance our understanding of these topics

Revisiting vocal perception in non-human animals : a review of vowel discrimination, speaker voice recognition, and speaker normalization

The extent to which human speech perception evolved by taking advantage of predispositions and pre-existing features of vertebrate auditory and cognitive systems remains a central question in the evolution of speech. This paper reviews asymmetries in vowel perception, speaker voice recognition, and speaker normalization in non-human animals topics that have not been thoroughly discussed in relation to the abilities of non-human animals, but are nonetheless important aspects of vocal perception. Throughout this paper we demonstrate that addressing these issues in non-human animals is relevant and worthwhile because many non-human animals must deal with similar issues in their natural environment. That is, they must also discriminate between similar-sounding vocalizations, determine signaler identity from vocalizations, and resolve signaler-dependent variation in vocalizations from conspecifics. Overall, we find that, although plausible, the current evidence is insufficiently strong to conclude that directional asymmetries in vowel perception are specific to humans, or that non-human animals can use voice characteristics to recognize human individuals. However, we do find some indication that non-human animals can normalize speaker differences. Accordingly, we identify avenues for future research that would greatly improve and advance our understanding of these topics.Publisher PDFPeer reviewe

Vocal tract constancy in birds and humans

Humans perceive speech as relatively stable despite acoustic variation caused by vocal tract (VT) differences between speakers. Humans use perceptual ‘vocal tract normalisation’ (VTN) and other processes to achieve this stability. Similarity in vocal apparatus/acoustics between birds and humans means that birds might also experience VT variation. This has the potential to impede bird communication. No known studies have explicitly examined this, but a number of studies show perceptual stability or ‘perceptual constancy’ in birds similar to that seen in humans when dealing with VT variation. This review explores similarities between birds and humans and concludes that birds show sufficient evidence of perceptual constancy to warrant further research in this area. Future work should 1) quantify the multiple sources of variation in bird vocalisations, including, but not limited to VT variations, 2) determine whether vocalisations are perniciously disrupted by any of these and 3) investigate how birds reduce variation to maintain perceptual constancy and perceptual efficiency.PostprintPeer reviewe

Speaker and accent variation are handled differently : evidence in native and non-native listeners

Listeners are able to cope with between-speaker variability in speech that stems from anatomical sources (i.e. individual and sex differences in vocal tract size) and sociolinguistic sources (i.e. accents). We hypothesized that listeners adapt to these two types of variation differently because prior work indicates that adapting to speaker/sex variability may occur pre-lexically while adapting to accent variability may require learning from attention to explicit cues (i.e. feedback). In Experiment 1, we tested our hypothesis by training native Dutch listeners and Australian-English (AusE) listeners without any experience with Dutch or Flemish to discriminate between the Dutch vowels /I/ and /ε/ from a single speaker. We then tested their ability to classify /I/ and /ε/ vowels of a novel Dutch speaker (i.e. speaker or sex change only), or vowels of a novel Flemish speaker (i.e. speaker or sex change plus accent change). We found that both Dutch and AusE listeners could successfully categorize vowels if the change involved a speaker/sex change, but not if the change involved an accent change. When AusE listeners were given feedback on their categorization responses to the novel speaker in Experiment 2, they were able to successfully categorize vowels involving an accent change. These results suggest that adapting to accents may be a two-step process, whereby the first step involves adapting to speaker differences at a pre-lexical level, and the second step involves adapting to accent differences at a contextual level, where listeners have access to word meaning or are given feedback that allows them to appropriately adjust their perceptual category boundaries.Publisher PDFPeer reviewe

A general auditory bias for handling speaker variability in speech? Evidence in humans and songbirds

Different speakers produce the same speech sound differently, yet listeners are still able to reliably identify the speech sound. How listeners can adjust their perception to compensate for speaker differences in speech, and whether these compensatory processes are unique only to humans, is still not fully understood. In this study we compare the ability of humans and zebra finches to categorize vowels despite speaker variation in speech in order to test the hypothesis that accommodating speaker and gender differences in isolated vowels can be achieved without prior experience with speaker-related variability. Using a behavioral Go/No-go task and identical stimuli, we compared Australian English adults’ (naïve to Dutch) and zebra finches’ (naïve to human speech) ability to categorize / I/ and /ε/ vowels of an novel Dutch speaker after learning to discriminate those vowels from only one other speaker. Experiments 1 and 2 presented vowels of two speakers interspersed or blocked, respectively. Results demonstrate that categorization of vowels is possible without prior exposure to speaker-related variability in speech for zebra finches, and in non-native vowel categories for humans. Therefore, this study is the first to provide evidence for what might be a species-shared auditory bias that may supersede speaker-related information during vowel categorization. It additionally provides behavioral evidence contradicting a prior hypothesis that accommodation of speaker differences is achieved via the use of formant ratios. Therefore, investigations of alternative accounts of vowel normalization that incorporate the possibility of an auditory bias for disregarding inter-speaker variability are warranted.Publisher PDFPeer reviewe

Music for animal welfare: a critical review & conceptual framework

Music can have powerful effects on human health and wellbeing. These findings have inspired an emerging field of research that focuses on the potential of music for animal welfare, with most studies investigating whether music can enhance overall wellbeing. However, this sole focus on discovering what effects music have on animals is insufficient for advancing scientific and practical understanding of how music can be used as an enrichment tool and can also lead to problems in experimental design and interpretation. This paper argues for a different approach to the study of music for welfare, where music is used to address specific welfare goals, taking account what animals hear in music and selecting or creating ‘musical’ compositions that test current hypotheses about how music is able to influence animal behaviour and physiology. Within this conceptual framework, we outline the process through which perceptual abilities influence welfare outcomes and suggest reframing music for welfare research as Auditory Enrichment Research which adopts a targeted approach that does not purpose music as an all-round welfare enhancer but rather investigates whether auditory enrichment can ameliorate specific welfare problems based on species-specific perceptual abilities, needs, and welfare goals. Ultimately, we hope that these discussions will help to bring greater unification, vision, and directionality in the field

Early life conditions reduce similarity between reproductive partners in HPA axis response to stress

Social environments modulate endocrine function, yet it is unclear whether individuals can become like their social partners in how they physiologically respond to stressors. This social transmission of hypothalamic-pituitary-adrenal (HPA) axis reactivity could have long-term consequences for health and lifespan of individuals if their social partners react to stressors with an exaggerated HPA axis response. We tested whether glucocorticoid levels in response to stress of breeding partners changes after breeding depending on whether partners had similar or dissimilar postnatal conditions. We manipulated postnatal conditions by mimicking early life stress in zebra finch chicks (Taeniopygia guttata) via postnatal corticosterone exposure. When they reached adulthood, we created breeding pairs where the female and male had experienced either the same or different early life hormonal treatment (corticosterone or control). Before and after breeding, we obtained blood samples within 3 min and after 10 min or 30 min of restraint stress (baseline, cort10, cort30). We found that corticosterone levels of individuals in response to restraint were affected by their own and their partner's early life conditions, but did not change after breeding. However, across all pairs, partners became more similar in cort30 levels after breeding, although differences between partners in cort10 remained greater in pairs with a corticosterone-treated female. Thus, we show that HPA axis response to stressors in adulthood can be modulated by reproductive partners and that similarity between partners is reduced when females are postnatally exposed to elevated glucocorticoids

Transient and permanent effects of suboptimal incubation temperatures on growth, metabolic rate, immune function and adrenocortical responses in zebra finches

n birds, incubation temperature can vary by several degrees Celsius among nests of a given species. Parents may alter incubation temperature to cope with environmental conditions and/or to manipulate embryonic development, and such changes in incubation behavior could have long-lasting effects on offspring phenotype. To investigate short- and long-term effects of suboptimal incubation temperatures on survival and physiological functions in zebra finches, eggs were incubated at 36.2, 37.4 or 38.4°C for the entire incubation period. The post-hatch environment was identical among the treatment groups. We found that hatching success was lowest in the 38.4°C group, while post-hatch survival was lowest in the 36.2°C group. Incubation temperature had sex-specific effects on offspring phenotype: incubation temperatures affected body mass (Mb) but not physiological parameters of males and conversely, the physiological parameters but not Mb of females. Specifically, males from the 38.4°C group weighed significantly less than males from the 36.2°C group from the nestling period to adulthood, whereas females from different incubation temperature groups did not differ in Mb. In contrast, females incubated at 36.2°C had transient but significantly elevated basal metabolic rate and adrenocortical responses during the nestling and fledgling periods, whereas no treatment effect was observed in males. Innate immunity was not affected by incubation temperature in either sex. These results suggest that a 1°C deviation from what is considered an optimal incubation temperature can lower offspring performance and offspring survival.Publisher PDFPeer reviewe