Francesca L. Ware

Haemostasis is the prevention of blood fluidity in vertebrates and is the first stage of wound healing. Haematophagous animals use the blood of vertebrates as their sole source of nutrition and have evolved many salivary constituents to counteract the haemostatic response of their prey. These animals and their saliva have been studied for many years, with some applications in medicine. The purpose of this study is to compare the salivary constituents of leeches (Hirudinae), ticks (Argasidae and Ixodidae) and vampire bats (Desmodontinae) and to consider their evolutionary origin. Salivary constituents include plasminogen activators (PAs), anticoagulants (activated factor X, FXa; inhibitors), vasodilators, platelet aggregation inhibitors (PAgI) and thrombin inhibitors. The animals studied all tend to possess an anticoagulant and a form of apyrase (PAgI) to assist with blood feeding. Ticks and vampire bats have a form of PA but the leech does not. The vampire bat has a PAgI but no vasodilator. The animals studied are from taxonomically unrelated groups but exploit similar mechanisms of action to facilitate their haematophagy. Given that the haematophagous lifestyle of these animals developed much later than their common ancestors, we conclude that their mechanisms for haematophagy have arisen by convergent evolution. Some molecules, e.g. serine proteases found in invertebrate saliva, are probably derived from a common ancestral gene. The possible paths that have led to evolution of vampire bat salivary components are considered. Further research into the homology of these salivary constituents is required to give insight into how these animals adapted to haematophagy and their further therapeutic potential.