Biological complexity: horseshoe crab eye lens (Introduction)

by David Turell , Monday, November 21, 2022, 17:47 (733 days ago) @ David Turell

Carefully analyzed:

https://phys.org/news/2022-11-scales-scientists-horseshoe-crab-cuticle.html

"The primitive compound eyes of a horseshoe crab are one the largest to be found in nature. In contrast to many insects and spiders that build their eyes from glassy proteins, the horseshoe crab uses cuticle, the same material that builds its skin and legs.

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"The compound eyes of the horseshoe crab are primitive in comparison to other arthropods, like dragonflies or shrimp. Instead of using the typical glassy proteins to build the lens, the horseshoe crab repurposes the material that builds its exoskeleton—the cuticle. "The arthropod cuticle is a composite material consisting of proteins and a crystalline polymer known as chitin. It is the characteristic component of insects, spiders, and other arthropods who use it to build their skin and legs, the so-called exoskeleton," says Prof. Politi.

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"The researchers looked both at the global organization of the cuticle layers, as well as the ratio of the individual components, the water content, and the elemental composition of the material. As a result, they found a variety of adaptations that together allow the cuticle to become an excellent optical element.

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"Taken together, the team found not one but a host of adaptations at all levels that allow the horseshoe crab to use cuticle for optical elements. "Everything from the local composition of the cuticle, in particular the addition of Bromine, to multiple changes in the architecture of the composite, i.e., the ratio between its components, organization of the proteins, the varying water content, and the overall shape of the lens… It all contributes to making cuticle into a material with excellent optical properties," says Prof. Politi. (my bold)

"'What surprised us, in the end, the most was that the cuticle lenses seem to work so well that the animal needed to introduce pigments to actually reduce the amount of light that is collected by the lens," adds Prof. Politi."

Comment: the bolded statement demonstrates this is an irreducibly complex development that requires design.