Temperature of egg incubation determines sex in Alligator mississippiensis

  title={Temperature of egg incubation determines sex in Alligator mississippiensis},
  author={Mark W. J. Ferguson and Ted Joanen},
The factors controlling sexual differentiation in crocodilians are unknown, but heteromorphic sex chromosomes are absent from all species1. Nichols and Chabreck2 speculated that the sex of Alligator mississippiensis was not rigidly determined at the time of hatching but could be influenced by the post-hatching environment. They presented little evidence to support their hypothesis3 (no histological sections of hatchling gonads, no indication of the sex ratio at hatching), and their study failed… 
Temperature‐dependent sex determination in Alligator mississippiensis
The structure of the reproductive systems of hatchling and 1 -year-old alligators was investigated macroscopically and histologically and revealed that heavy females become sexually mature ahead of either light females or light males, which constitutes a selective biological advantage for the evolution of temperature-dependent sex determination in Alligator mississippiensis.
The mechanism of temperature dependent sex determination in crocodilians: a hypothesis
The hypothesis is used to explain the late temperature sensitive periods defined by high to low temperature shift experiments, why cooler temperatures are more effective at determining sex, how intermediate temperatures can produce both sexes, and geographical similarities in the pattern of TSD within crocodilians despite differing climates.
Environmental regulation of sex determination in reptiles.
  • D. Deeming, M. Ferguson
  • Biology
    Philosophical transactions of the Royal Society of London. Series B, Biological sciences
  • 1988
The phylogenetic implications of TSD for crocodilians, and reptiles in particular, are related to the life history of the animal from conception to sexual maturity, and those animals that develop under optimal conditions grow fastest and largest and become male.
Effects of Incubation Temperature on Crocodiles and the Evolution of Reptilian Oviparity
Crocodylus porosus is a mound-nesting crocodilian in which incubation temperature influences the rate of embryonic development, the probability that embryos will survive to hatching, post-hatching
Temperature-Dependent Sex Determination and Artificial Incubation of Tuatara, Sphenodon Punctatus
The evaluation of artificial incubation as a conservation management tool demonstrated that it is a procedure that benefits conservation as it can be used reliably to produce founders; hatching success was 94% during this study.
Temperature‐Dependent Sex Determination in Gekko japonicus (Gekkonidae, Reptilia)
The effects of temperature on sexual differentiation in early development of the gekkonid lizard, Gekko japonicus were studied and the sex ratios do not seem to be related to a predetermination of sex with a differential mortality.
Incubation temperatures, sex ratios and sex determination in a population of Nile crocodiles (Crocodylus niloticus)
A demographic study of the Nile crocodile Crocodylus niloticus at Lake Ngezi, Zimbabwe, revealed that females predominated in all size classes and among embryos. The sex of C. niloticus was shown to
Influence of temperature variation on incubation period, hatching success, sex ratio, and phenotypes in Caiman latirostris.
A masculinizing effect is found when incubation was at 31 ± 2°C compared with a constant 31°C; and temperature fluctuations at 32°C had a negative effect on hatchlings size and mass, and hatching success compared with constant incubation temperatures of32°C and 33°C.
Alternative life-history styles in reptiles
Analysis of the effects of size and phylogeny on patterns of co-variation in certain squamate life-history traits reveals that although many variables scale allometrically with body size, significant variation in clutch size and age at maturity remains at order, family and generic level.
Gonadal sex differentiation in Alligator mississippiensis, a species with temperature-dependent sex determination
Ovarian formation in alligators may depend upon presumptive Sertoli cells differentiating prior to a critical event in embryogenesis, such as germ cell proliferation and meiosis, as at lower incubation temperatures.


Sex Determination in Reptiles
  • J. Bull
  • Biology
    The Quarterly Review of Biology
  • 1980
Temperature-dependent sex determination (TSD) is common in turtles and has been reported in two lizards and alligators; however, data on TSD are available for few non-turtle species and an attempt is made to deduce their ancestries.
Temperature levels and periods of sex determination during incubation of eggs of Chelydra serpentina
Eggs of Chelydra serpentina were shifted during incubation between the female producing temperatures of 20°C or 30°C and the male producing temperature of 26°C, and the stages during which incubation temperature determined sex were stage 14 through stage 16.
On the Variability of Alligator Sex Ratios
It is hypothesized that environmentally associated variation in age at sexual maturity of females produces sufficient variation in relative fitness of females to result in selection for low sex ratios during periods of resource abundance.
When is sex environmentally determined?
It is proposed that labile sex determination (not fixed at conception) is favoured by natural selection when an individual's fitness (as a male or female) is strongly influenced by environmental conditions and where the individual has little control over which environment it will experience.
Temperature-dependent sex determination in turtles.
The sex of hatchling map turtles is determined by incubation temperature of eggs in the laboratory as well as in nature. Temperature controls sex differentiation rather than causing a differential
Thermal Biology of Sea Turtles
The role of temperature in determining sexual differentiation of the embryos, incubation duration, emergence from the nest, activity, growth, survival, hibernation, internesting interval and distribution of sea turtles is discussed.
Sex ratio evolution when fitness varies
The sex ratio may coevolve with the offspring's choice of patch type and the environmental cue it uses in determining sex; when possible, embryos are selected to avoid patches detrimental to both sexes, and areselected to determine sex in response to the cue which indicates the greatest differential benefit to maleness versus femaleness.
A series of stages in the embryonic development of Chelydra serpentina
Eggs of the common snapping turtle, Chelydra serpentina serpentina, were incubated at 30°C and at 20°C to determine the incubation period and a series of 26 stages of development is described.
Possible adaptive value of water exchanges in flexible-shelled eggs of turtles.
Use of energy reserves by embryos of common snapping turtles (Chelydra serpentina) is related to the hydric conditions to which eggs are exposed during incubation and to the net exchanges of water
The Genetical Theory of Natural Selection
Although it is true that most text-books of genetics open with a chapter on biometry, closer inspection will reveal that this has little connexion with the body of the work, and that more often than not it is merely belated homage to a once fashionable study.