Rescue dogs with behavioral issues

I’m curious what issues are typical with dogs who were dumped as puppies. I have an 18-week rescue puppy who came to me as a 6lb, 8 week old foster. All six were emaciated and full of roundworms and giardia. What I notice in my now physically healthy puppy is hyper vigilance, fear, and in trying to work through handling found he startles even with a hand placed for a second on his rear. (Very cuddly tho, interestingly). His brother who I also had in foster for three weeks was reactive and a major chomper at 8 weeks. Are there common outcomes? No training advice needed, just looking for profiles.