Voles possessing the long version allele of avpr1a are:

Answer; 
Voles possessing the long version allele of avpr1a are more likely to exhibit pro-social behavior. 

Explanation; 
The vasopressin receptor 1A, has a role in social recognition which is important in the lateral septum, as using viral vectors to replace inactivated Avpr1a expression rescues social recognition, and also increases behaviors that are related to anxiety.