For whales and seals the ocean i...( be. When light travels through clear w...)

be. When light travels through clear water, e. g. in the open ocean, the longer waves are preferentially scattered and the remaining light becomes more and more blue-shifted with depth - an effect well known to divers. In these conditions the loss of blue cones appears as a particularly bad adaptation. Even if colour vision (on the basis of two spectral cone types) is of little importance in a monochrome blue underwater world, there should be some advantage in keeping the cone type best suited to the spectral environment for contrast and brightness detection. In fact, many fish living in similar lighting conditions possess blue cones.

Fig. 2: Cone photoreceptors in the retina of the ringed seal, immunocytochemically labeled by an antiserum against the visual pigment of green-sensitive cones. Seals and whales only possess this green-sensitive cone type. The spaces between the cones are occupied by the more numerous rod photoreceptors which operate at low light levels.

Photograph: Max Planck Institut for Brain Research / L. Peichl

The authors hypothesize that the blue cone loss occured at an early stage of evolution, when the ancestors of modern whales and seals at their return to the sea initially inhabited coastal waters. Coastal waters contain a larger amount of inorganic and organic debris (due to land-drainage and a richer flora), which preferentially scatters the shorter wavelengths. Hence the underwater light field is shifted to longer wavelengths and contains little blue. In these conditions, the loss of 'idle' blue cones may have been advantageous or at least a neutral event. A loss of colour vision could have simplified visual information processing and hence freed cortical capacity for other sensory abilities. Indeed, many whales have evolved echolocation, and seals are able to track prey by detecting turbulences with their whiskers. At least for the species that have remained in coastal waters, the blue cone loss continues to be
'"/>

Contact: Dr. Leo Peichl
peichl@mpih-frankfurt.mpg.de
49-69-96769-348
Max-Planck-Gesellschaft
19-Apr-2001

Page: 1 2 3 4
Related biology news :

1. Ocean scientists assess impact of seismic pulses in effort to protect whales
2. Research into cetacean reproduction leads to birth of killer whales by artificial insemination
3. Climate linked to reproduction of right whales
4. Collapse of seals, sea lions & sea otters in North Pacific triggered by overfishing of great whales
5. Endangered northern right whales exposed to paralytic shellfish poisoning
6. Humanitys din could be blocking whales courtship songs
7. URI oceanography models migration and foraging strategies of North Atlantic right whales
8. Hopkins scientist evaluates latest findings on the ancestry of whales
9. New fossils suggest whales and hippos are close kin
10. Scientists record extraordinary sounds made by minke whales
11. Speaking of sperm whales