Genital maturation of male nile monitors (Varanus niloticus) in three sahel populations

Genital maturation of male monitor lizards, a subject poorly documented up to now in spite of the heavy exploitation of these animals, was studied on a sample of 211 Nile monitors (Varanus niloticus) from Chad (Lake Chad), Ma ll (central delta of the Niger), and Nigeria (Hadejia-N'Guru wetlands). Sno ut-vent lengths (LC) in the sample ranged from 15.6 to 85.5 cm. After a mor phometric study of the monitors, their testes were sampled, weighed at +/-0 .01 g and fixed for histology. The age of each specimen was estimated by sk eletochronology. The testes of monitors less than 36 cm LC (Malian specimen s) or 40 cm LC (Chadian and Nigerian individuals) do not contain mature spe rmatozoa, whereas the testes of larger specimens do. Most Malian monitors a ged 18 months (1.5 years) have mature spermatozoa. Conversely, in Chadian a nd Nigerian individuals, mature gametes appear only in specimens aged 30 mo nths (2.5 years). These data indicate that genital maturity in the Nile mon itor is reached at 36-40 cm LC and 1.5-2.5 years according to the populatio ns. The growth in mass of the testes, compared with LC, is an accurate indi cator of body size at sexual maturity, and confirms the precocity of Malian specimens. Conversely, testis growth is poorly related to age. These resul ts are discussed with reference to the possible accommodation of Nile monit or populations to heavy exploitation by means of precocious recruitment of the male breeding stock.