Hi, 

I have a conceptual doubt regarding reproductive parasites. They are considered as selfish genetic elements, because of that I guess they must show vertical transmission. Wolbachia is the best example at this respect. 

However, some parasite could manipulate host sex-determination and no present vertical transmission. Just because they are more prone to infect one sex in hosts adult life. For example, parasite A can defeat female immune system, manipulate their host reproduction to produce more females because they can parasite females and not males, but do not show vertical transmission. In this case, is such parasite considered as a selfish element or vertical transmission is a must to be considered like that?

Thanks!