Varanus

Lizards that prey on snakes hut are also eaten hy larger snakes discriminate skin chemicals of snakes very well. Monitor lizards, Varanus albigularis, fall in this group. Hatchling monitors attacked harmless snakes but avoided venomous species. However, they accepted meat of all snakes if carefully skinned. The hatchlings tongue flicked to invertebrate prey covered with skin from venomous snakes and rejected these samples (Phillips and Alberts, 1992). 

Young Komodo monitors, Varanus komodoensis, roll themselves in the feces of prey animals. This may protect them from predation by larger conspecifics, as these avoid gut contents of their prey by shaking them out before eating the prey (Auffenberg, 1981 Ciofi, 1999). 

Monitor lizards include 24 living species of large lizards in the genus Varanus, family Varanidae. Monitors inhabit tropical and sub-tropical regions of Africa, Asia, and Australia. Monitors are among the most advanced of the lizards, in terms of achieving an active, predaceous lifestyle. 

Haslewood and Wootton isolated varanic acid, 3a,7a,12a,24-tetrahydroxy-5)S-cholestan-26-oic acid, from bile of the monitor lizard, Varanus niloticus [53]. Varanic acid was later found in bile of the frog, Bombina orientalis, where it occurs in the unconjugated form [18]. Une et al. synthesized 4 diastereoisomers at C-24 and C-25 of 3a,7a,12a,24-tetrahydroxy-5y3-cholestan-26-oic acid. Comparisons with these synthetic bile acids of known absolute configuration showed that the varanic acid in frog bile is (24i ,25S )-3a,7a,12a,24-tetrahydroxy-5jS-cholestan-26-oic acid [54]. 

The 12-deoxy derivative of varanic acid, 3a,7a,24-trihydroxy-5)8-cholestan-26-oic acid was detected in the bile of Varanus monitor, as a minor companion of varanic acid, the major bile acid of this lizard [69]. 

A trihydroxycholestenoic acid was isolated as a major bile acid from bile of the toad, Bufo vulgaris formosus [70] and was characterized as (25/ )-3a,7a,12o(-trihy-droxy-5/8-cholest-23-en-26-oic acid by oxidation to 23-norcholic acid and hydrogenation to (25/ )-3a,7a,12a-trihydroxy-5j8-cholestan-26-oic acid [71]. The 5a isomer, 3a,7a,12a-trihydroxy-5a-cholest-23-en-26-oic acid, was recently detected as a minor bile acid in toad bile [46]. The bile of Varanus monitor contains as minor constituents 3a,7a,12a-trihydroxy-5j8-cholest-23- and 24-enoic acids [69]. The acid has been synthesized prior to its detection in nature [72]. 

Luebke, J. I., Weider, J. M., McCarley, R W., and Greene, R. W. (1992) Distnbu-tion of NADPH-diaphorase positive somata in the brainstem of the monitor lizard Varanus exanthematicus. Neurosci Lett 148, 129—132... 

Figure 5 Relationship between the percent change in ventilation (Ali) tidal volume (AFt), and breathing frequency (A/) and the partial pressure of O2 in inspired air (PI02) in various species of reptile. (B.p.= Bufo paracnemis, X.. =Xenopus laevis, C.p. = Chrysemys picta, C.n. = Crocodilus niloticus, L.. = Lacerta viridis, Y.e.= Varanus exanthematicus, A.y=Acrochordus javanicus, N.r. = Natrix rhombifera. (From Ref. 64.)...

---