Blood-feeding is a dangerous trade, involved with many challenges that have certainly been overcome through the course of evolution. Interestingly different arthropods lineages evolved similar protective adaptations to establish themselves in a blood-feeding environment (Bruno, 2005). These adaptations are essentially morphological, behavioral and physiological.
Development of morphological adaptation has been of primary importance in acquiring the blood meal. It is clear that developing mouthparts have been fundamental in the establishment of hematophagy.
Before blood meal, hematophagous arthropods must locate their host. To do this, several factors drive their host-seeking behavior. Several hematophagous have developed chemosensory organs such sensilla on their antennae and palps to sense the air and detect the presence of a potential host. Substances such as carbon dioxide exhaled by the host and lactic acid have been widely shown to attract arthropods blood-feeders.
Other insects have developed visual cues to detect their host. Behavioral adaptation to blood-feeding is also driven by some internal cues that allow the hematophagous insect to find its host very precisely. Among these internal cues, circadian rhythms dictate the time of the day or night within a specific insect will feed. For instance the malaria mosquito,Anopheles gambiae feeds during night time, while the dengue fever vector, Aedes aegypti feeds mostly during the day. Behavioral adaptation also involves the tendency of a species to host selectivity. For instance, some species are anthropophilic, while others are zoophilic.
Many physiological adaptions have been of primary importance to the establishment of hematophagy. At the molecular level, adaptations to hematophagy are reflected by the presence of a variety of pharmacologically active molecules in blood-feeders saliva that prevent pain and itching, which are triggered by tissue destruction and immune reactions to insect products (Ribeiro, 1995) and enable successful feeding. These molecules are essentially anti-aggregating factors, anticoagulants, and vasodilators.
Anti-aggregation factors include nitric oxide, prostaglandins, apyrase, molecules that sequester ADP and a range of peptides and proteins that interact specifically with integrin receptors. Anticoagulants include a variety of inhibitors that target thrombin and factor Xa, as well and tissue factor FVIIa complexes.
Vasodilators molecules found in different hematophagous saliva are essentially amines, prostaglandins, peptides and proteins (Ribeiro, 1995). In addition, a potent mechanism for storing large amounts of nitric oxide and delivering it into the skin (Nitrophorins) has identified (Valenzuela et al, 1998).
Moreover, these biomolecules have the capability of eliciting the host immune system. Such roles of saliva allow the hematophagous arthropod to feed efficiently by preventing the blood from clotting and avoiding the host defensive behavior. For instance, the Ixodid ticks remain attached to their hosts and acquire a blood meal over a period ranging from days to weeks (Ben et al, 2003).