Ben Creisler
Some additional recent avian-related papers:
Free pdf:
Tobias Riede , Scott L. Thomson, Ingo R. Titze & Franz Goller (2019)
The evolution of the syrinx: An acoustic theory.Â
PLoS Biology 17(2): e2006507.
Free pdf:
Abstract
The unique avian vocal organ, the syrinx, is located at the caudal end of the trachea. Although a larynx is also present at the opposite end, birds phonate only with the syrinx. Why only birds evolved a novel sound source at this location remains unknown, and hypotheses about its origin are largely untested. Here, we test the hypothesis that the syrinx constitutes a biomechanical advantage for sound production over the larynx with combined theoretical and experimental approaches. We investigated whether the position of a sound source within the respiratory tract affects acoustic features of the vocal output, including fundamental frequency and efficiency of conversion from aerodynamic energy to sound. Theoretical data and measurements in three bird species suggest that sound frequency is influenced by the interaction between sound source and vocal tract. A physical model and a computational simulation also indicate that a sound source in a syringeal position produces sound with greater efficiency. Interestingly, the interactions between sound source and vocal tract differed between species, suggesting that the syringeal sound source is optimized for its position in the respiratory tract. These results provide compelling evidence that strong selective pressures for high vocal efficiency may have been a major driving force in the evolution of the syrinx. The longer trachea of birds compared to other tetrapods made them likely predisposed for the evolution of a syrinx. A long vocal tract downstream from the sound source improves efficiency by facilitating the tuning between fundamental frequency and the first vocal tract resonance.
Author summary
The larynx is an important valve in the respiratory system of all air-breathing vertebrates that is located at the upper end of the trachea. In some amphibians, in nonavian reptiles, and in mammals, it has also assumed the function of a vocal organ. In contrast, birds have evolved a new and unique vocal organ, the syrinx, which is located at the lower end of the trachea. The selective forces that underlie the evolution of the syrinx as a novel organ have remained unclear. Among all air-breathing vertebrates, birds have the longest necks, and long necks require a long trachea. With a vocal organ at the base of the trachea, this long tube can act as vocal tract resonator and, therefore, can improve the conversion of aerodynamic energy into acoustic energy if fundamental frequency and a resonance frequency are matched. Here, we conducted experiments with simplified physical models, with real birds and a computational simulation in order to investigate the effect of the two different positions of a sound source within the respiratory tract. We find that sound is produced with greater efficiency by a sound source in syrinx position and that favorable interactions between sound source and vocal tract occur with syringeal position. The data provide support for the hypothesis that a selective pressure for high vocal efficiency may have contributed to the evolution of the syrinx in its unique location within the air tract.
=====
Eric Buffetaut, CÃdric Audibert, JÃrÃme Tabouelle and Delphine Angst (2019)
Useful old casts: a comment on Hansford & Turvey (2018), 'Unexpected diversity within the extinct elephant birds (Aves: Aepyornithidae)'.
Royal Society Open Science 6: 181826
Free pdf:
==
Eudyptes warhami sp. nov.ÂÂ
Theresa L. Cole, Daniel T. Ksepka, Kieren J. Mitchell, Alan J. D. Tennyson, Daniel B. Thomas, Hailin Pan, Guojie Zhang, Nicolas J. Rawlence, Jamie R. Wood, Pere Bover, Juan L. Bouzat, Alan Cooper, Steven Fiddaman, Tom Hart, Gary Miller, Peter G. Ryan, Lara D. Shepherd, Janet M. Wilmshurst & Jonathan M. Waters (2019)
Mitogenomes uncover extinct penguin taxa and reveal island formation as a key driver of speciation.
Molecular Biology and Evolution, msz017 (advance online publication)Â
The emergence of islands has been linked to spectacular radiations of diverse organisms. Although penguins spend much of their lives at sea, they rely on land for nesting, and a high proportion of extant species are endemic to geologically-young islands. Islands may thus have been crucial to the evolutionary diversification of penguins. We test this hypothesis using a fossil-calibrated phylogeny of mitochondrial genomes (mitogenomes) from all extant and recently extinct penguin taxa. Our temporal analysis demonstrates that numerous recent island-endemic penguin taxa diverged following the formation of their islands during the Plio-Pleistocene, including the GalÃpagos (GalÃpagos Islands), northern rockhopper (Gough Island), erect-crested (Antipodes Islands), Snares crested (Snares) and royal (Macquarie Island) penguins. Our analysis also reveals two new recently extinct island-endemic penguin taxa from New Zealandâs Chatham Islands: Eudyptes warhami sp. nov. and a dwarf subspecies of the yellow-eyed penguin, Megadyptes antipodes richdalei ssp. nov. Eudyptes warhami diverged from the Antipodes Islands erect-crested penguin between 1.1 million years ago (Ma) and 2.5âMa, shortly after the emergence of the Chatham Islands (â3âMa). This new finding of recently-evolved taxa on this young archipelago provides further evidence that the radiation of penguins over the last 5âMa has been linked to island emergence. Mitogenomic analyses of all penguin species, and the discovery of two new extinct penguin taxa, highlight the importance of island formation in the diversification of penguins, as well as the extent to which anthropogenic extinctions have affected island-endemic taxa across the Southern Hemisphereâs isolated archipelagos.
====
Free pdf:
Romana Gruber, Martina Schiestl, Markus Boeckle, Anna Frohnwieser, Rachael Miller, Russell D. Gray, Nicola S. Clayton & Alex H. Taylor (2019)
New Caledonian Crows Use Mental Representations to Solve Metatool Problems.
Current Biology (advance online publication)
Free pdf:
Highlights
Crows solved metatool problems where each stage was out of sight of the others
Crows avoided distractor apparatuses during problem-solving
This shows crows mentally represent the goals and sub-goals of metatool problems
Crows can preplan three behaviors into the future while using tools
Summary
One of the mysteries of animal problem-solving is the extent to which animals mentally represent problems in their minds. Humans can imagine both the solution to a problem and the stages along the way, such as when we plan one or two moves ahead in chess. The extent to which other animals can do the same is far less clear. Here, we presented New Caledonian crows with a series of metatool problems where each stage was out of sight of the others and the crows had to avoid either a distractor apparatus containing a non-functional tool or a non-functional apparatus containing a functional tool. Crows were able to mentally represent the sub-goals and goals of metatool problems: crows kept in mind the location and identities of out-of-sight tools and apparatuses while planning and performing a sequence of tool behaviors. This provides the first conclusive evidence that birds can plan several moves ahead while using tools.
======
Free pdf:
Barbara C. Klump , Mathieu Cantat and Christian Rutz (2019)
Raw-material selectivity in hook-tool-crafting New Caledonian crows
Biology Letters 15: 20180836
Free pdf:
Animals that manufacture foraging tools face the challenge of identifying suitable raw materials among a multitude of options. New Caledonian crows exhibit strong population-specific material preferences for the manufacture of hooked stick tools, but it is unknown how they identify their favourite plants. We investigated experimentally whether crows pay attention to the stems of plants (from which the tools are made) and/or their leaves (which are usually discarded during manufacture but may enable rapid and reliable species identification at a distance). Subjects were highly selective in choice trials with multiple plant species. Two additional treatments with experimental leafâstem combinations revealed that birds can identify their preferred plant species by its stems alone, and possibly also its leaves. These findings encourage future experiments that investigate whether New Caledonian crows attend to features of the stem that are required for the production of efficient hooked stick tools. Our study provides one of the most detailed assessments to date of how non-human animals identify raw materials for tool manufacture.
 Â
===========
===
Free pdf:
Yu-Ting Lai, Carol K. L. Yeung, Kevin E. Omland, Er-Li Pang, Yu Hao, Ben-Yang Liao, Hui-Fen Cao, Bo-Wen Zhang, Chia-Fen Yeh, Chih-Ming Hung, Hsin-Yi Hung, Ming-Yu Yang, Wei Liang, Yu-Cheng Hsu, Cheng-Te Yao, Lu Dong, Kui Lin, and Shou-Hsien Li (2019)
Standing genetic variation as the predominant source for adaptation of a songbird.
Proceedings of the National Academy of Sciences 116 (6) 2152-2157
Free pdf:
Significance
It is a tenet of modern biology that species adapt through natural selection to cope with the ever-changing environment. By comparing genetic variants between the island and mainland populations of a passerine, we inferred the related age of genetic variants across its entire genome and suggest that preexisting standing variants played the predominant role in local adaptation. Our findings not only resolve a long-standing fundamental problem in biology regarding the genetic sources of adaptation, but imply that the evolutionary potential of a population is highly associated with its preexisting genetic variation.
Abstract
What kind of genetic variation contributes the most to adaptation is a fundamental question in evolutionary biology. By resequencing genomes of 80 individuals, we inferred the origin of genomic variants associated with a complex adaptive syndrome involving multiple quantitative traits, namely, adaptation between high and low altitudes, in the vinous-throated parrotbill (Sinosuthora webbiana) in Taiwan. By comparing these variants with those in the Asian mainland population, we revealed standing variation in 24 noncoding genomic regions to be the predominant genetic source of adaptation. Parrotbills at both high and low altitudes exhibited signatures of recent selection, suggesting that not only the front but also the trailing edges of postglacial expanding populations could be subjected to environmental stresses. This study verifies and quantifies the importance of standing variation in adaptation in a cohort of genes, illustrating that the evolutionary potential of a population depends significantly on its preexisting genetic diversity. These findings provide important context for understanding adaptation and conservation of species in the Anthropocene.