A central role for venom in predation by Varanus komodoensis (Komodo Dragon) and the extinct giant Varanus ( Megalania ) priscus

Abstract

The predatory ecology of Varanus komodoensis (Komodo Dragon) has been a subject of long-standing interest and considerable conjecture. Here, we investigate the roles and potential interplay between cranial mechanics, toxic bacteria, and venom. Our analyses point to the presence of a sophisticated combined-arsenal killing apparatus. We find that the lightweight skull is relatively poorly adapted to generate high bite forces but better adapted to resist high pulling loads. We reject the popular notion regarding toxic bacteria utilization. Instead, we demonstrate that the effects of deep wounds inflicted are potentiated through venom with toxic activities including anticoagulation and shock induction. Anatomical comparisons of V. komodoensis with V. (Megalania) priscus fossils suggest that the closely related extinct giant was the largest venomous animal to have ever lived. evolution ͉ phylogeny ͉ squamate ͉ protein ͉ toxin P redation by Varanus komodoensis, the world's largest extant lizard, has been an area of great controversy (cf. ref. 1). Three-dimensional finite element (FE) modeling has suggested that the skull and bite force of V. komodoensis are weak (2). However, the relevance of bite force and cranial mechanics to interpretations of feeding behavior cannot be fully evaluated in the absence of comparative data. Moreover, this previous analysis did not account for gape angle, which can significantly influence results (3). Irrespective of evidence for or against a powerful bite, V. komodoensis is clearly capable of opening wounds that can lead to death through blood loss (4). Controversially, the proposition that utilization of pathogenic bacteria facilitates the prey capture (4, 5) has been widely accepted despite a conspicuous lack of supporting evidence for a role in predation. In contrast, recent evidence has revealed that venom is a basal characteristic of the Toxicofera reptile clade (6), which includes the varanid lizards (7), suggesting a potential role of venom in prey capture by V. komodoensis that has remained unexplored. This is consistent with prey animals reported as being unusually quiet after being bitten and rapidly going into shock (4) and the anecdotal reports of persistent bleeding in human victims after bites (including B.G.F.'s personal observations). Shock-inducing and prolonged bleeding pathophysiological effects are also characteristic of helodermatid lizard envenomations (cf. ref . 8), consistent with the similarity between helodermatid and varanid venoms (6).Here, we examine the feeding ecology of V. komodoensis in detail. We compare the skull architecture and dentition with the related extinct giant V. priscus (Megalania). In this 3D finite element modeling of reptilian cranial mechanics that applies a comparative approach, we also compare the bite force and skull stress performance with that of Crocodylus porosus (Australian Saltwater Crocodile), including the identification of optimal gape angle (an aspect not considered in previous nonreptilian comparative FE analyses). We als...

Dynamic evolution of venom proteins in squamate reptiles

“…snakegenomics.org/) and formatted into a BLAST-able database. Both databases were interrogated using representative venom sequences utilised by Fry et al [10][11][12]29 . Sequence searches were undertaken for 12 toxin families identified as basal to the Toxicofera (AVIT, cystatin, cysteine-rich secretory protein, CVF, crotamine, hyaluronidase, kallikrein, lectin, natriuretic peptides, NGF, veficolin and vespryn) [10][11][12] .…”

“…Contig hits were incorporated into DNA data sets of toxin (derived from members of the Toxicofera) and non-toxin (sampled from outside groups -that is, non-reptilian species) sequences used in the analyses of Fry et al [10][11][12]29 . All sequences were obtained from GenBank -GI accession numbers are displayed in the resulting gene trees (Figs 2-5; Supplementary Figs S2-S6).…”

The birdlike raptor Sinornithosaurus was venomous

“…The presence of a venom delivery system in a wide variety of squamates (12,22) suggests that this adaptation can be expected in other diapsids, including the dromaeosaurs. Venom glands in lizards tend to be mandibular whereas those in snakes are maxillary; the basal condition is to have both (6).…”

Proteome of Hydra Nematocyst

“…Venoms are produced in probably all animal phyla (2,3) and represent a mixture of effector proteins often aimed at tissue integrity by targeting extracellular matrix (ECM) 3 and receptor molecules. Intriguingly, many toxins share close structural and functional properties with ECM proteins, indicating a common evolutionary origin or co-evolution (4).…”