Wednesday 29 March 2017, 15:00–16:00
G15, 7 Bristo Square
Domestication and evolution of signal complexity in Bengalese finches
Kazuo Okanoya (University of Tokyo)
Among vocalizations birds make, a class of sounds that are consisted of more than two types of sound patterns arranged in a certain temporal sequence is called as a ‘birdsong’, not only because of the organization of sound patterns, but also because our musical aesthetics intuitively allow such an analogy. Scientific investigations of birdsong to date suggest that certain properties of birdsong extend beyond the musical to the developmental analogies Bengalese finches (BFs) are domesticated strains of wild white-rumped munias (WRMs) imported from China to Japan 250 years ago. BF songs are composed of multiple chunks and each chunk is a combination of 2-4 song notes. Furthermore, chunks are arranged in a finite-state probabilistic automaton. We studied how and why BFs sing such complex songs. We found the following facts. 1) The ancestral strain sing simpler songs. 2) There is high learning specificity in WRMs but not in BFs. 3) BFs have larger song control nuclei and higher level of glutamate receptor gene expressions than WRMs. 4) Both BF and WRM females prefer complex songs as measured by the nest string assay and males with complex songs are physically fitted than the males with simpler songs. These results promoted sexual selection scenario of song complexity in BFs. We further examined factors related with domestication. We examined songs of WRMs in subpopulations of Taiwan. Where there is a sympatric species to WRMs, songs were simpler. This leads to a hypothesis that in the wild songs needed to be simple to secure species identification, but under domestication this constrains was set free. We also examined socio-emotional indexes including neophobic tendency, tameness, behavioral stress reactions, and corticosterone levels. All indexes suggested that WRMs have higher level of stress and social shyness, which should be adaptive under natural environment, but could be limiting opportunities for learning complex songs. Thus, evolution of song complexity involves not only factors related with strengthen of sexual selection and relaxation of species identification, but also socio- emotional factors due to domestication. Furthermore, recent suggestion of ‘neural crest’ hypothesis that might account for the domestication syndrome fits well with the properties of Bengalese finches. These results on Bengalese finches must be useful in discussing possible biological origin of human speech in terms of proximate and ultimate factors.
The plasticity of song learning and tutor choice by cross-fostering and multiple tutor experiments in Bengalese finches.
Miki Takahasi (University of Tokyo)
The Bengalese finch (Lonchura striata var. domestica) is a domesticated strain of wild white-rumped munias (Lonchura striata). Through the domestication, the courtship songs of Bengalese finches have been differentiated from those of wild munias. The songs have tonal phonology and complex syntax in Bengalese finches, although munia songs have noisy sound with stereotyped syntax. The cross-fostering experiment revealed that there was significantly different in the accuracy of song learning between Bengalese finches and white-rumped munias. The proportion of shared elements with tutors was about 90 % regardless of tutor strain in Bengalese finches. In munias, they shared 75% song elements from the foster tutor (Bengalese finches) although they could copied almost 100% from own strain. Bengalese finches lost the accurate song learning, it will lead to increase the plasticity of song learning instead. We set a colony with eleven males and ten females of Bengalese finches and let them bred freely. Under the multiple tutor condition, most out of 32 juveniles learned parts of songs from two tutors. They segmented the songs by transition probability and combined some parts into own song. We also conducted a multiple tutor experiment in munias. 11 munia juveniles learned their father songs and only one juvenile learned from two tutors. While munias learned songs from several tutors, munias tended to learn from their familiar songs (their father). These results suggest that the accuracy of song learning is related to how many tutors juveniles select.