C++11 types for variables defined with auto

I am reading Bjarne Stroustrup's book The C++ Programming Language, and in section 3.2.4, he demonstrates a class hierarchy, starting with an abstract class. His code looks something like this:

class Shape
{
public:
    virtual Point center()const = 0; //Point is a class defined elsewhere and is unimportant for this question
    virtual void move(Point to) = 0;

    virtual void draw()const = 0;
    virtual void rotate(int angle) = 0;
}

class Circle: public Shape
{
    //overrides functions
}

void rotate_all(vector<Shape*>& v, int angle)
{
    for(auto p:v)
        p->rotate(angle);
}

My question is this: what type is the p variable when the function rotate_all is called with a vector of Circle objects? If it was a Shape, then wouldn't the objects be sliced into generic Shape objects? If it was a Circle, then wouldn't the function work only for vectors of Circle objects, and not other subclasses of the Shape class?