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Ontogenetic Shape Change in Chicken Brain + Alula Function + Avian Color Vision



Ben Creisler
bcreisler@gmail.com

A number of recent papers that may be of interest:

Soichiro Kawabe, Seiji Matsuda, Naoki Tsunekawa & Hideki Endo (2015)
Ontogenetic Shape Change in the Chicken Brain: Implications for Paleontology.
PLoS ONE 10(6): e0129939.
doi:10.1371/journal.pone.0129939
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0129939

Paleontologists have investigated brain morphology of extinct birds
with little information on post-hatching changes in avian brain
morphology. Without the knowledge of ontogenesis, assessing brain
morphology in fossil taxa could lead to misinterpretation of the
phylogeny or neurosensory development of extinct species. Hence, it is
imperative to determine how avian brain morphology changes during
post-hatching growth. In this study, chicken brain shape was compared
at various developmental stages using three-dimensional (3D) geometric
morphometric analysis and the growth rate of brain regions was
evaluated to explore post-hatching morphological changes. Microscopic
MRI (μMRI) was used to acquire in vivo data from living and
post-mortem chicken brains. The telencephalon rotates caudoventrally
during growth. This change in shape leads to a relative caudodorsal
rotation of the cerebellum and myelencephalon. In addition, all brain
regions elongate rostrocaudally and this leads to a more slender brain
shape. The growth rates of each brain region were constant and the
slopes from the growth formula were parallel. The dominant pattern of
ontogenetic shape change corresponded with interspecific shape changes
due to increasing brain size. That is, the interspecific and
ontogenetic changes in brain shape due to increased size have similar
patterns. Although the shape of the brain and each brain region
changed considerably, the volume ratio of each brain region did not
change. This suggests that the brain can change its shape after
completing functional differentiation of the brain regions. Moreover,
these results show that consideration of ontogenetic changes in brain
shape is necessary for an accurate assessment of brain morphology in
paleontological studies.


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Sang-im Lee, Jooha Kim, Hyungmin Park, Piotr G. Jabłoński & Haecheon Choi (2015)
The Function of the Alula in Avian Flight.
Scientific Reports 5, Article number: 9914  (open access)
doi:10.1038/srep09914
http://www.nature.com/srep/2015/150507/srep09914/full/srep09914.html


The alula is a small structure located at the joint between the
hand-wing and arm-wing of birds and is known to be used in slow flight
with high angles of attack such as landing. It is assumed to function
similarly to a leading-edge slat that increases lift and delays stall.
However, in spite of its universal presence in flying birds and the
wide acceptance of stall delay as its main function, how the alula
delays the stall and aids the flight of birds remains unclear. Here,
we investigated the function of alula on the aerodynamic performance
of avian wings based on data from flight tasks and wind-tunnel
experiments. With the alula, the birds performed steeper descending
flights with greater changes in body orientation. Force measurements
revealed that the alula increases the lift and often delays the stall.
Digital particle image velocimetry showed that these effects are
caused by the streamwise vortex, formed at the tip of the alula, that
induces strong downwash and suppresses the flow separation over the
wing surface. This is the first experimental evidence that the alula
functions as a vortex generator that increases the lift force and
enhances manoeuvrability in flights at high angles of attack.


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Keita D. Tanaka (2015)
Journal of Ornithology (advance online publication)
A colour to birds and to humans: why is it so different?
DOI: 10.1007/s10336-015-1234-1
http://link.springer.com/article/10.1007/s10336-015-1234-1


The avian visual model has become nowadays a standard for quantifying
colours of birds. Here, I review the biological bases of the
importance of visual modelling to most ornithologists, focusing on the
causes of the difference in colours to birds and to humans, both
proximately and ultimately. Not only the sensitivity of retinal
photoreceptors and performances of ocular media, but also the number
of photoreceptor types are all attributed to the bird–human difference
proximately. As the ultimate cause, the evolutionary history of birds
and humans should divide the colours perceived by them: birds would
retain their colour vision from the ancient ancestry, while primates
such as humans would have reacquired the colour vision relatively
recently. Finally, I review how to process and to analyze data
produced by the visual model.
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