Re: What physiological effects does the sun have on different animals/humans?

There are many phsiological effects of the sun, and it gets a little muddled and 
complicated because several hormones are involved.  The involved hormones have 
multiple effects on the body.  The Vitamin D effect, which you mentioned, is one 
of the best studied effects of sun exposure. 

Sunlight can also cause the release of POMC (pro-opiomelanocortin).  This is a 
peptide hormone that is split up into about 5 active short peptide hormones which 
have a variety of effects on the body. The proopiomelanocortin (POMC) gene 
encodes the common precursor for MSH-related and beta-endorphin-related end 
products. One of the hormones, MSH, melanocyte stimulating hormone, causes some 
skin cells to start making melanin.  Melanin makes you brown.  This stimulation 
is why you tan when you go into the sun.  

If you would like to learn more about POMC, and its varied and interesting 
effects on the body, see:
http://www.ultranet.com/~jkimball/BiologyPages/M/MSH.html

Another well studied effect is that of UV radiation on skin cells.  As you 
probably know, exposure to UV rays from the sun can damage DNA by causing thymine 
(the T in ACGT) to dimerize.  When two of these thymine dimers are excised from 
DNA by the DNA damage surveillance machinery, a double strand break can be 
caused, leading to loss of part of a chromosome.  Enough of this sort of damage 
can lead to cancer.

Here is some more information about skin cancer:
http://www.maui.net/~southsky/introto.html

Erin