IACUC Learning Module - Xenopus laevis

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Breeding and Reproduction

Amphibians have an almost universal dependence on water for reproduction. Breeding activity may be preceded by hibernation and is usually triggered by environmental factors like increased rainfall, increased day length (photoperiod), increased temperature or humidity and increased abundance of food.

In captivity, frogs can be bred by manipulating their environment to simulate breeding conditions. The environmental temperatures can be decreased and then gradually raised again. Humidity can be lowered to simulate a dry period, and then increased by misting, to simulate a wet period. Feeding can be increased to mimic increased food abundance. Photoperiods can be altered to increase day length to match seasonal changes.

 

Side View: Xenopus in amplexus and the false bottom of a breeding tank. The frogs will sit on the false bottom during ovulation and eggs will fall through the screen, away from the frogs.

In Xenopus, breeding can be artificially induced by hormone manipulation with gonadotropic hormone injections. This is the method of choice and can be done at any time of the year, all year long, to maximize breeding. Pregnant Mare Serum Gonadotropin (PMSG) or Human Chorionic Gonadotropin (HCG) or Gonadotropic Releasing Hormone (GnRH) is injected into females to induce ovulation. For mating or release of sperm to occur, males are also injected with HCG or GnRH. See Appendix I for Nasco's Xenopus breeding recommendations. (It should be noted that inappropriate hormone administration has been noted to provoke infectious disease and even death.) Xenopus generally receive an initial dose of hormone and then a larger second dose 8-36 hours later to initiate amplexus (mating embrace) and egg laying. Frogs should be paired after the second dose and left undisturbed in a darkened breeding tank until mating is over.

Amphibian ova require a prolonged maturation process which depends heavily on favorable nutritional status of the females. Stress is a powerful inhibitor of amphibian reproduction!

Females should be bred no more than once per month. Females that have not been bred for a period of 4-6 months tend to deposit an increased percentage of necrotic eggs and will produce poorer quality embryos. The expected breeding life of female Xenopus is usually 1-2 years. (Males can be bred 2-3 times per month if necessary. Males have a breeding life expectancy of 3 or more years if they remain in good health.)

Pond Water Formula

Mix 20 ml of solution A and 20 ml of solution B to 5 liters of distilled water to make artificial pond water.

Dead or diseased animals should be discarded daily from larval stage cages. Tadpoles should be handled carefully to avoid injury to gills and skin. Tadpoles should NOT be netted! Scooping with containers is recommended.

Hibernation

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