Thursday, July 20, 2006
Our increased knowledge of epigenetic reprogramming supports the idea that epigenetic marks are not always completely cleared between generations. Incomplete erasure at genes associated with a measurable phenotype can result in unusual patterns of inheritance from one generation to the next. It is also becoming clear that the establishment of epigenetic marks during development can be influenced by environmental factors. In combination, these two processes could provide a mechanism for a rapid form of adaptive evolution.
Current Opinion in Genetics and Development
Chong S, Whitelaw E
School of Molecular and Microbial Biosciences, Biochemistry Building-G08, University of Sydney, New South Wales 2006, Australia.
Wednesday, July 19, 2006
Color blindness and contrast perception in cuttlefish (Sepia officinalis) determined by a visual sensorimotor assay
Full paper at above link
We tested color perception based upon a robust behavioral response in which cuttlefish (Sepia officinalis) respond to visual stimuli (a black and white checkerboard) with a quantifiable, neurally controlled motor response (a body pattern).
In the first experiment, we created 16 checkerboard substrates in which 16 grey shades (from white to black) were paired with one green shade (matched to the maximum absorption wavelength of S. officinalis' sole visual pigment, 492 nm), assuming that one of the grey shades would give a similar achromatic signal to the tested green.
In the second experiment, we created a checkerboard using one blue and one yellow shade whose intensities were matched to the cuttlefish's visual system.
In both assays it was tested whether cuttlefish would show disruptive coloration on these checkerboards, indicating their ability to distinguish checkers based solely on wavelength (i.e., color).
Here, we show clearly that cuttlefish must be color blind, as they showed non-disruptive coloration on the checkerboards whose color intensities were matched to the Sepia visual system, suggesting that the substrates appeared to their eyes as uniform backgrounds.
Furthermore, we show that cuttlefish are able to perceive objects in their background that differ in contrast by approximately 15%. This study adds support to previous reports that S. officinalis is color blind, yet the question of how cuttlefish achieve "color-blind camouflage" in chromatically rich environments still remains. [colour]