Your spouse is never considered your dependent.

you can claim one exemption for your spouse on a joint return.

the 183 days rule only applies to the definition of resident/nonresident. Dont get confused with the dependent exemption...

1. Not a qualifying child test,

2. Member of household or relationship test,

3. Gross income test, and

4. Support test. 

5. For all the details about dependent exemption, you can refer to publication 501 on the IRS website