Showing papers by "Carel ten Cate published in 2010"

A noisy spring: the impact of globally rising underwater sound levels on fish

Abstract: The underwater environment is filled with biotic and abiotic sounds, many of which can be important for the survival and reproduction of fish. Over the last century, human activities in and near the water have increasingly added artificial sounds to this environment. Very loud sounds of relatively short exposure, such as those produced during pile driving, can harm nearby fish. However, more moderate underwater noises of longer duration, such as those produced by vessels, could potentially impact much larger areas, and involve much larger numbers of fish. Here we call attention to the urgent need to study the role of sound in the lives of fish and to develop a better understanding of the ecological impact of anthropogenic noise.

Sounds of male Lake Victoria cichlids vary within and between species and affect female mate preferences

Abstract: Sound production in fish is widespread and occurs in several contexts, such as species recognition, mate choice, and aggression. However, there is little experimental evidence for the importance of acoustic signals in social contexts and the influence of sound on mating decisions of females. Cichlid fish are known for their bright nuptial coloration, which plays an important role in mate choice and reproductive isolation between the many species of cichlid fish in East Africa. They also produce sounds in both aggressive and courtship interactions. In this study, we show that the sounds produced by males of Lake Victoria cichlids are species specific. There is also a correlation between fish size and peak frequency of sounds across species. We did not find context-dependent differences within a species (Pundamilia nyererei) between male sounds produced during aggressive displays toward males or sexual displays toward females. We also show with playback experiments that courtship sounds influence the mate preferences of female cichlids. In combination with many studies in the literature on visual signaling, our results suggest that multimodal communication plays an important role in sexual selection in cichlids. Key words: cichlid, fish, mate choice, playback, sound, species specific. [Behav Ecol]

Zebra finches exhibit speaker-independent phonetic perception of human speech

Abstract: Humans readily distinguish spoken words that closely resemble each other in acoustic structure, irrespective of audible differences between individual voices or sex of the speakers. There is an ongoing debate about whether the ability to form phonetic categories that underlie such distinctions indicates the presence of uniquely evolved, speech-linked perceptual abilities, or is based on more general ones shared with other species. We demonstrate that zebra finches (Taeniopygia guttata) can discriminate and categorize monosyllabic words that differ in their vowel and transfer this categorization to the same words spoken by novel speakers independent of the sex of the voices. Our analysis indicates that the birds, like humans, use intrinsic and extrinsic speaker normalization to make the categorization. This finding shows that there is no need to invoke special mechanisms, evolved together with language, to explain this feature of speech perception.

Vocal tract articulation in zebra finches.

Abstract: Background Birdsong and human vocal communication are both complex behaviours which show striking similarities mainly thought to be present in the area of development and learning. Recent studies, however, suggest that there are also parallels in vocal production mechanisms. While it has been long thought that vocal tract filtering, as it occurs in human speech, only plays a minor role in birdsong there is an increasing number of studies indicating the presence of sound filtering mechanisms in bird vocalizations as well. Methodology/Principal Findings Correlating high-speed X-ray cinematographic imaging of singing zebra finches (Taeniopygia guttata) to song structures we identified beak gape and the expansion of the oropharyngeal-esophageal cavity (OEC) as potential articulators. We subsequently manipulated both structures in an experiment in which we played sound through the vocal tract of dead birds. Comparing acoustic input with acoustic output showed that OEC expansion causes an energy shift towards lower frequencies and an amplitude increase whereas a wide beak gape emphasizes frequencies around 5 kilohertz and above. Conclusion These findings confirm that birds can modulate their song by using vocal tract filtering and demonstrate how OEC and beak gape contribute to this modulation.

Threat signaling in female song—evidence from playbacks in a sex-role reversed bird species

Abstract: Prominent research areas such as animal communication and sexual selection use birdsong as a model system. Most studies on these subjects are conducted on species with typical sex roles with male-biased song production. Accordingly, the functions of birdsong, mate attraction, and territorial defense have hardly been studied in females. We investigated the territorial function of female song in the sex-role reversed African black coucal (Centropus grillii) to test whether females in such species demonstrate the same principles as male birds in species with typical sex roles. When territorially challenged, female black coucals changed their vocalizations in comparison to when they were singing spontaneously: They altered the composition of songs, lowered the pitch, and increased the duration of song elements. When challenged, larger females vocalized at lower pitch than smaller ones suggesting that pitch might be a reliable indicator of competitive abilities. To study whether females pay attention to such variation, we exposed them to playback experiments in which songs varied 1) in the composition and 2) in pitch and duration of song elements. Females did not respond differently to stimuli that varied in the composition. However, they reacted more cautiously to low-pitched and long stimuli compared with unchanged stimuli. This suggests that females were intimidated by the songs with low-pitched and long elements and that those songs signaled a higher level of threat. Thus, female black coucals paid attention to song parameters that reliably indicated competitive abilities. This confirms the general role of intrasexual selection in vocal communication of birds. Key words: aggressive signals, female birdsong, sex-role reversal, signal evolution, signal reliability, vocal communication. [Behav Ecol]

A cultural evolutionary model of patterns in semantic change

Abstract: Language change has been described as an unintended eect of language in use (Keller 1994). In this view, change results from the way individuals use their language; the challenge is thus to explain change and its properties in terms of factors operating on the individual level, and population dynamics. An intriguing example of such a phenomenon is the finding that language change shows some highly regular tendencies. This has recently received considerable attention in the literature (Bybee et al. 1994; Heine and Ku- teva 2002; Traugott and Dasher 2002; Hopper and Traugott 2003). In un- related languages, similar words often change in similar ways, along similar ''trajectories'' of development. This phenomenon is called ''unidirectional- ity'', and it is an important part of processes of grammaticalization, items changing from a lexical meaning to a grammatical function. It has been claimed that around 90-99% of all processes of grammaticalization are uni- directional (Haspelmath 1999). This article explores several mechanisms that may lead to language change, and examines whether they may be responsible for unidirectional- ity. We use a cultural evolutionary computational model with which the ef- fects of individual behavior on the group level can be measured. By using this approach, regularities in semantic change can be explained in terms of very basic mechanisms and aspects of language use such as the frequency with which particular linguistic items are used. One example is that fre- quency dierences by themselves are a strong enough force for causing uni- directionality. We argue that adopting a cultural evolutionary approach may be useful in the study of language change.

Unidirectional Hybridization and Introgression in an Avian Contact Zone: Evidence from Genetic Markers, Morphology, and Comparisons with Laboratory-Raised F1 Hybrids

Abstract: . Examination of contact zones between closely related species is important for understanding speciation, because the interactions in such zones may change the evolutionary direction of one or both taxa. To expose the composition and dynamics of a contact zone between two dove species, Streptopelia vinacea and S. capicola, we used mitochondrial DNA, amplified fragment-length polymorphism (AFLP) markers, and morphological and color measurements. We combined a field study on contact-zone and parental-species individuals with an examination of F1 hybrids reared in captivity. We found that the contact zone is a narrow hybrid zone characterized by a high frequency of hybrids, a lack of clear parental species forms, a high incidence of S. capicola mtDNA, and an AFLP marker distribution more similar to that of S. vinacea. In morphology and color, field hybrids were more similar to S. vinacea and significantly different from S. capicola. F1 hybrids were more similar to S. capicola in color. The laboratory...

Reply to Gentner et al.: As simple as possible, but not simpler

Abstract: In our recent paper (1) we showed that zebra finches, like starlings (2), can learn to discriminate between stimuli generated by two simple formal grammars, but argued that neither study provided a “convincing demonstration” of recursive language learning. Gentner et al. (3) criticize this conclusion and the design of our experiment. Their comments underscore our point that it is critical to exclude that seemingly complex syntactic tasks are solved by applying relatively simple rules.