The reproductive cycle of the Nile crocodile (Crocodylus nilotkus)

Abstract

The reproductive cycle of the Nile crocodile (Crocodylus niloticus) was studied in Zimbabwe. Females attained sexual maturity after they had reached a total length of about 262 to 287 cm and males, 270 to 295 cm. Some adult females did not reproduce every year. Follicle growth and vitellogenesis occurred from April to mid August during the dry winter. During this time reproductive females had elevated levels of plasma oestradiol‐17β, testosterone, calcium and magnesium, but lowered levels of iron. The measuring of plasma calcium was an ‘early pregnancy’ test, reliable up to four months before nesting. Elevated levels of plasma testosterone in reproductive females corresponded to the time of courtship and mating. Ovulation occurred during the latter half of August. Males had viable sperm from mid May to mid September, during the winter. Courtship and mating occurred from late June to mid August, when crocodiles were confined to pools. Females nested on the higher sand ridges in the dry river bed from early September to early October, and eggs hatched during December.

The reproductive hormone cycle of adult female American alligators from a barrier island population

“…Regardless, it is interesting that distinct seasonal patterns in plasma P 4 concentrations were not observed in this study given that robust seasonal patterns have been shown not only in American alligators (Lance 1989, Guillette et al 1997, Lance et al 2009) but also in other reptiles as well as birds, which are closely related to archosaurs (Donham 1979, Amey & Whittier 2000. Nile crocodiles (Crocodylus niloticus) do not show distinct seasonal patterns in plasma P 4 concentrations, however, and show highly variable concentrations throughout the year in both reproductive and non-reproductive individuals (Kofron 1990).…”

Unique bone histology in partial large bone shafts from Aust Cliff (England, Upper Triassic): an early independent experiment in gigantism

“…The latter are indeed extensive in the LAG-forming specimen BRSMG Cb3870, implying a possible female sex. Linking LAGs with reproduction would imply annual reproduction cycles, which does occur in wild crocodiles but their reproduction frequency is usually rather variable from annually to every 2-5 years (Joanen and McNease 1971;Lance 1989;Kofron 1990). …”

Multiple paternity and mating patterns in the American alligator, Alligator mississippiensis

“…Females in captivity move freely between the territories of rival males, and while the dominant male is often the preferred partner, a female may engage in courtship and mating with subordinates as well (Garrick & Lang 1977). The peak of mating in American alligators occurs one month prior to nesting and, similar to Nile crocodiles, probably either coincides with ovulation or ends just prior to ovulation (Joanen & McNease 1976; Kofron 1990). Interestingly, one major difference among crocodilian species with regard to their mating system can be attributed to differences in climate.…”

“…1999). Multiple paternity is suspected as a reproductive strategy in crocodilians (Kofron 1990), but until now has not been demonstrated.…”