Sialomic perspectives on the evolution of blood-feeding behavior in arthropods: Future therapeutics by natural design

Blood-feeding behavior evolved more than 20 times independently in Arthropods. This happened at least 6 times in the Arachnida (Acari) and 15 times in the Hexapoda (Neoptera). This is recapitulated when transcriptomes from the secretory component of salivary glands (Sialomes) are compared. As such, unique protein families are found for the different lineages that adapted to a blood-feeding lifestyle with only a limited number of protein families conserved across all lineages. Closely related lineages might share similar sets of protein families in their sialomes, even if no apparent orthologous or conserved functional relationships exist. This suggests that sialomes of such lineages where already defined before adaptation to a blood-feeding lifestyle, with subsequent innovation. In this regard, the same sets of shared protein families tend to be abundant and prone to lineage specific expansion (gene duplication) with specialized functions associated with various gene duplicates. Perhaps not surprisingly, all sialomes show evidence of convergent evolution in regard modulatory strategies that targets host defenses, even if the molecular mechanisms differ. As such, a checklist of expected functions can be composed for any blood-feeding arthropod not yet characterized. The diversity of mechanisms that counteract vertebrate host immune and hemostatic systems is a veritable pharmacopoeia, optimized by natural evolution, that can be exploited for therapeutic use.