An investigation of the evolution of the anguimorph lizard venom system

Abstract

Over the course of the last two decades significant advances were made in our understanding of the evolution of venom in squamate reptiles. Several studies looked at nuclear genes from various lizards and snakes and confirmed the hypothesis put forth in E. Kochva's article "Phylogeny of the oral glands in reptiles as related to the origin and evolution of snakes" -that anguimorph lizards form part of a monophyletic clade with all the snakes. This confirmation confounded decades of morphology based taxonomy, as did evidence of the inclusion of the Iguania lizard lineage into that group. The new group received the name Toxicofera, emphasizing the role of oral toxins in the evolution of the lineage. Despite being supported by genetic, anatomical and proteomic data, the Toxicofera hypothesis remains controversial. This strengthens the necessity for thorough investigation of toxicoferan reptile venom evolution. The oral secretions of anguimorph lizards demand particular attention not only because they are understudied, but also for the reason that Anguimorpha contains species with the considerable morphological diversity of venom glands -from incipient to advanced and almost snake-like.Therefore the primary goal of this thesis is to address the lack of knowledge on anguimorph lizard oral secretions, in particular that of varanoid lizards which include various monitor species (genus Varanus) as well as Heloderma (gila monster) and Lanthanotus (Borneo earless monitor). This has been achieved through the implementation of several proteomic techniques (in particular, gel electrophoresis) as well as transcriptomic analysis and bioactivity testings.Chapter One reviews all previously published information on anguimorph venom evolution, highlighting the data in support of the Toxicofera hypothesis. Chapter Two presents new data on Heloderma lizard venoms and the striking similarities between the venom profiles of specimens from different localities as well as between species. The data presented and discussed in Chapter Three represents the core finding of this study: the surprising complexity and diversity of varanid lizard oral secretions.Taken together, this study present a compelling argument in favour of functional diversity and differential complexity of the venom of anguimorph lizards and discusses the evolutionary forces that helped generate this diversity.

Chemical properties of commonly available hydrocarbons

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