Abstract
While snake venoms have been the subject of intense study, comparatively little work has been done on lizard venoms. In this study, we have examined the structural and functional diversification of anguimorph lizard venoms and associated toxins, and related these results to dentition and predatory ecology. Venom composition was shown to be highly variable across the 20 species of Heloderma, Lanthanotus, and Varanus included in our study. While kallikrein enzymes were ubiquitous, they were also a particularly multifunctional toxin type, with differential activities on enzyme substrates and also ability to degrade alpha or beta chains of fibrinogen that reflects structural variability. Examination of other toxin types also revealed similar variability in their presence and activity levels. The high level of venom chemistry variation in varanid lizards compared to that of helodermatid lizards suggests that venom may be subject to different selection pressures in these two families. These results not only contribute to our understanding of venom evolution but also reveal anguimorph lizard venoms to be rich sources of novel bioactive molecules with potential as drug design and development lead compounds.
Highlights
Reptile venom evolution in general is an area of controversy and lizard venom is contentious
Differential evolution was evident in the stronger serrations of the V. varius clade, while the clade of V. acanthurus, V. baritji, V. gilleni, V. mitchelli, V. scalaris, and V. tristis were typified by a secondary loss of serrations, which the exception of V. scalaris which re-evolved within this clade
The venoms of varanoid lizards remain understudied in evolutionary toxinology; multiple sources of evidence point to the adaptive evolution of venom in varanoid lizards
Summary
Reptile venom evolution in general is an area of controversy and lizard venom is contentious. Anecdotal data on complications following V. komodoensis bites triggered scientific interest and were at first explained by the potential existence of pathogenic bacteria unique to the lizards’. The origin of this idea dates back to folk myths; Auffenberg is often quoted as the originator of it. In his monumental 1981 study [1], he reports the presence of Staphylococcus sp., Providencia sp., Proteus morgani and Proteus mirabilis in mucoid samples from the external gum surface of the upper jaw of two freshly captured “oras” (the local name for V. komodoensis).
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