The underlined portion of the text discusses the hypothesis proposed by scientist Atma Ivancevic and her team regarding how invertebrate parasites can facilitate horizontal gene transfer between vertebrate species through their feeding behavior. This explanation focuses on a specific mechanism by which genetic material can be exchanged between different species via parasites.
Therefore, the choice that best describes the function of the underlined portion is:
(Choice D) It describes a means by which horizontal gene transfer might occur among vertebrates.