Reproductive biology

Male monitor lizards engage in ritualized combat, fighting over females. Larger species wrestle in an upright posture, using their tails for support, grabbing each other with their forelegs and attempting to throw their opponent to the ground. Smaller species grapple each other while lying horizontally, with legs wrapped around each other, rolling over and over on the ground. The victor then courts the female, first flicking his tongue all over her, and if she concurs, climbing on top of her and mating by curling the base of his tail beneath hers and inserting one of his two hemipenes into her cloaca. Male varanids have a cartilaginous or bony support structure in each hemipenis called a hemibaculum.

All monitor lizards lay eggs. Clutch sizes vary widely among species from two to three in the smallest monitors such as V. brevicauda to 35-60 in large African species like V. al-bigularis and V. niloticus. Some monitors (V. rosenbergi, V. niloticus, V. prasinus, and V. varius) excavate termitaria for nesting burrows. Termites close off the entrance, sealing the eggs inside in an almost ideal, protected, humid environment of nearly constant temperature. Sometimes, females return to the same termitarium nine months later to open it and free their hatchlings. In some species of monitor lizards, hatch-lings are much more vividly marked and colorful than adults (V. dumerilii, V. griseus, V. rosenbergi, V. tristis).

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