Alligator mississippiensis
American alligator

Life cycle

Taxonomy

cellular organisms - Eukaryota - Fungi/Metazoa group - Metazoa - Eumetazoa - Bilateria - Coelomata - Deuterostomia - Chordata - Craniata - Vertebrata - Gnathostomata - Teleostomi - Euteleostomi - Sarcopterygii - Tetrapoda - Amniota - Sauropsida - Sauria - Archosauria - Crocodylidae - Alligatorinae - Alligator - Alligator mississippiensis

Developmental stages

• Oocyte The ovary of the alligator is similar in appearance to that of chicken, but unlike the chicken, is paired. The right ovary contains more follicles and is generally larger than the left. No actively dividing germ cells, such as are seen in the ovaries of lizards and snakes, have been seen in crocodilian ovaries which suggests that crocodilians hatch with complete complement of germ cells as do birds. Mature ova are present for a short period of time in late May-early June.
• Fertilization In Louisiana, when the temperature rises above 16 °C in late March or early Apri,l females emerge from their winter dens, estradiol level increases, vitellogenesis (yolk deposition in the oocyte) starts and active courtship begins. Vitellogenetic period lasts for about 5-6 weeks in March-May and ovulation occurs in late May-June.
• Embryo
  • Before oviposition The nesting begins shortly after copulation. Nest is usually built near den (a small pond made by the alligator for refuge during nesting, post-nesting, and often, for overwintering. Nests are constructed from plant material on patches of flattened and matted vegetation usually at night. Alligators nests are ~70 cm high. The average clutch is located centrally within the nest mound 20-25 cm from the top. The eggs form layers 18-20 cm thick. Nest construction may take 2.5-3.5 weeks. During this period, albumin layer and the hard calcified shell are deposited.
  • After oviposition Egg deposition occur from end of May until early July; most eggs are laid in second half of June. Females lay about 40 eggs in one night. Each egg weighs about 70 g. Once the eggs are laid, the female remains in the vicinity guarding the nest throughout incubation period that lasts for about 65-75 days. Temporary submergence of eggs during floods is tolerated. The outer, densely calcified layer of the alligator eggshell shows progressive crystal dissolution that is caused by the acidic metabolic by-products of nest bacteria. Extrinsic degradation increases the porosity and decreases the strength of the eggshell facilitating hatching. Many (not all) females guard and defend their nests from intruders. The nest guarding include ritualized elements such as opened-mouth hissing and lunging.
• Hatchling At hatching alligators weigh 35-40 g (~56% of egg's weight). Approximately 74% of the egg lipid content remains in hatchlings (most of it in the yolk sac), and 26% of the egg lipids are metabolized during development of the embryo. When the alligators hatch and start vocalizing, the female comes promptly, excavates the nest and carries the hatchlings to the water one by one. First 2-3 days hatchling obtains nutrients from its yolk sac. Hatchling alligators are dark brown/black with series of white stripes down their dorsal side from head nape to tail tip. Individual hatchlings exhibit variation in both the intensity of the dark regions of the body and in the number of stripes along the body and tail. Females are generally paler and have fewer white stripes than males. Hatchlings remain in vicinity of the nest from 3-4 days to several weeks. They usually stay in a wallow or widened alligator trail used by female. Females that defended their nests usually also defend their young coming swiftly to calls of distress.
• Juvenile Immature alligators under 6 years of age and less than 1.8 m in length in the wild. Growth in male and female alligators is not significantly different for the first 6 years of life. On reaching about 1.8 m in length, both sexes exhibit a pronounced slowing of the growth rate, but males continue to grow at a greater rate and grow bigger than females. In Louisiana wild alligators grow at about 30 cm per year for first 6 years of life. In captivity alligators can grow as much as 150 cm per year.
• Adult Alligators reach sexual maturity at about 1.85-2 m total length. As a result of differences in temperature and nutrition sexual maturity is reached at about 18 years in North Carolina and at about 10 years in Louisiana. In much warmer southern Florida, however, sexual maturity is estimated at 12-14 years because of scarcity of food in the Florida Everglades. In captivity alligators mature as early as at 6 years of age. The number of females reproducing each year in the wild is rarely more than 50%. Captive crocodiles and alligators have been reported to live well into their ninth decade. Information on longevity of wild crocodilians is lacking. Growth in crocodilians is indeterminate - they continue growing their whole life. Accurate records of very large crocodiles in excess of 6 m and weighing more than 1000 kg have been published.

American alligators mating
(St. Augustine, Florida, 05/30/2011)

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More about crocodilians at GeoChemBio.com