Maturation génitale des varans du nil mâles (Varanus niloticus) dans trois populations du Sahel

Abstract

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), Mali (central delta of the Niger), and Nigeria (Hadejia-N'Guru wetlands). Snout-vent lengths (LC) in the sample ranged from 15.6 to 85.5 cm. After a morphometric 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 skeletochronology. The testes of monitors less than 36 cm LC (Malian specimens) or 40 cm LC (Chadian and Nigerian individuals) do not contain mature spermatozoa, whereas the testes of larger specimens do. Most Malian monitors aged 18 months (1.5 years) have mature spermatozoa. Conversely, in Chadian and Nigerian individuals, mature gametes appear only in specimens aged 30 months (2.5 years). These data indicate that genital maturity in the Nile monitor is reached at 36-40 cm LC and 1.5-2.5 years according to the populations. The growth in mass of the testes, compared with LC, is an accurate indicator of body size at sexual maturity, and confirms the precocity of Malian specimens. Conversely, testis growth is poorly related to age. These results are discussed with reference to the possible accommodation of Nile monitor populations to heavy exploitation by means of precocious recruitment of the male breeding stock.