What should I expect when joining a collegiate a capella group?

I’m considering auditioning for an a capella group in college next year. I know you can’t tell me what my specific college’s groups will be like, but I’m wondering if anyone knows much about collegiate a capella groups in general. How “formal” are they? Do you generally need to have professional vocal training to be accepted? What skills do I need (other than the obvious decent singing) and what can I do now to prepare? What can I expect the audition to be like? Aside from these specific questions, general information on what it’s like is welcome too.

I don’t know how much these things vary from college to college, so I apologize if these aren’t questions that anyone can answer.