In my presentation, I talked about the roles of melanin in human, mostly focusing on the compound’s protective properties from UVA and UVB rays. I mentioned slightly that melanin is found in all types of animal and even insects. Since I did not go into further details within my presentation, I want to bring this article on the blog to open up this topic for discussion.

This article, written by Manickam Sugumaran, compares the properties for melanin production in animals verses melanin production in insects. The article details the processes and the distinct types of protein factors for melanogenesis. Through the presentation I discussed Eumelanin.in human, which is responsible of hair, eye, and skin color.  Eumelanin is produced from the hydroxylation of tyrosine by tyrosine. Insects contain produce their melanin through an different process, which employs phenoloxidase and dopachrome( decarboxylating) isomerase for melanin production. Since the pathways for creating melanin is significant different between animals and insects, Sugumaran says that the advantages of are also an mirror to these differences.

In insects, phenoloxidase and melanin has many functions, Sugumaran talks about the major three physiologically important biochemical processes. The first is sclerotization of the insect cuticle. Sclerotization is the transformation of the soft and pale cuticle (outer shell of the insect) into a hard exoskeleton. If the exoskeleton does not harden and dry quickly the insect will die of dehydration. The second hypothesis is insect immunity. Insects lack immunoglobulin, and melanin forms a second line of defense (first being the exoskeleton) that traps pathogens by depositing melanin on the forging object. The melanin goes through the phenoloxidases cascade, which prevents the multiplication and the growth of the parasite. The last hypothesis is healing injury. Melanin and phenoloxidase is uses a clotting factor in insects to prevent the lost of haemolymph. Here we see major differences between melanin in animals and insect, but yet understand why has evolution left such differences.

This is a good article to start off with the continuation of the advantages of melanin from the oral presentation. It also offers new material for discussion on why melanin productions was conserved by yet has different advantages in various organisms.

http://onlinelibrary.wiley.com/doi/10.1034/j.1600-0749.2002.00056.x/pdf