Snake and Lizard Reproduction - Anatomy & Physiology

Lizards (Squamata)

Male

Anatomy of the Male Lizard

^{© L.Wilkie 2008}

Lateral View of the Male Chameleon

^{© L.Wilkie 2008}

Testes

• Located cranial to the kidneys.
• Attached to the dorsal wall by a mesochorium.
• In some species, the kidney has a posterior sexual segment that becomes swollen during the breeding season and contributes to seminal fluid.
• Right testis lies cranial to the left.
  • Intimately connected to the vena cava by short blood vessels.
• Left testis lies close to the adrenal gland.
  • Has its own testicular blood vessels.

Phallus

• Paired hemipenes
• Stored in the base of the tail.
  • Visualised externally by bulges at the ventral proximal tail.
• Only one hemipene is used during copulation.
  • Erected by vascular engorgement and muscular action.
  • Everted to protrude through the cloaca.
• Sperm passes from the ductus deferens into the male urodeum.
• Sperm is then carried in a groove down the hemipene to be deposited in the female cloaca.

Female

Anatomy of the Female Lizard

^{© L.Wilkie 2008}

Ventral View of the Female Lizard

^{© L.Wilkie 2008}

Ovary

• Paired
• Consists of a cluster of oocytes lined by a thin mesovarium.
• Right ovary is close to the vena cava.
  • Attached to vena cava by tiny blood vessels.
• Left ovary lies close to the left adrenal gland.
  • Has its own ovarian blood supply.

Oviduct

• Paired
• Pleated
• Wide infundibulum

Oviparity

This is the usual state for lizards, including all Geckos and Iguanas.

• Eggs are retained within the mother until birth.
• Normal clutch size is 3-5.
• Eggs covered by a leathery shell
• Can appear shrunken when laid.

Viviparity

About 1/5 of lizards are viviparous including the common European Lizard.

• Foetus retained within the oviduct.
• Primative placental type of circulation.

Breeding Season

Temperate Species

• Gonads reach maximum size on emergence from hibernation.
• Gonads are smallest during the summer months.

Tropical Species

• Breeding season coincides with the start of the wet season.
  • Moisture for egg incubation.
  • Abundant food supply for hatchlings.

Snakes (Squamata Serpentes/Ophidia)

Sexual Maturity

• Smaller species can reach sexual maturity in 1 year.
• Larger, more long-lived species may not be sexually mature until 5 years of age.

Male

Anatomy of the Male Snake: (1. Oesophagus 2. Trachea 3. Tracheal lungs 4. Rudimentary left lung 5. Right lung 6. Heart 7. Liver 8. Stomach 9. Air sac 10. Gallbladder 11. Pancreas 12. Spleen 13. Intestine 14. Testes 15. Kidneys )

^{©RVC 2008}

Testes

• Intra-abdominal
• Situated between the pancreas and the kidneys.

Phallus

• Two hemipenes
  • Paired, sac-like extensions of the cloaca.
• Lie within the ventral tail base.
• Each hemipene has a retractor muscle that extends from the tail vertebrae to the tip and sides of the hemipene.
• Large glands lie above the hemipenes.
• Hemipene retractor muscle and anal glands are all surrounded by a larger propulsor muscle.
• When the hemipene is engorged with blood, the propulsor muscle contracts.
  • Everts the hemipene.
• After engorgement has subsided, the retractor muscle contracts.
  • Inverts the hemipene.

Female

Female snakes can be oviparous, or viviparous.

Ovary

• Paired
• Located asymmetrically near the pancreas.
• Right oovary usually larger and more cranial.
• Left ovary may be reduced or undeveloped.

Sperm Storage

• Some female snakes can store sperm in a cavity lined by mucosa glands near the top of the oviduct.
  • Stored here until conditions are right.
• Can be stored for months or even years.
  • Thus snakes may suddenly appear fertile in abscence of a male.

Maternal Behaviour

The Indian Python is the only reptile to exibit maternal behaviour. This can be achieved owing to her large body size.

• Generate a 7ºC increase in heat by spasmodic contractions of muscles as they coil around the eggs.
• Coil tightly around the egg mass to prevent heat loss from the eggs.
• Unlike mammalian shivering, the muscle contractions are coordinated.
• Metabolic rate of the mother increases 20-fold.

Breeding Season

Temperate and Subtropical Species

• Breeding season is in Spring.

Tropical Species

• Breed at the start of the wet season.
  • Ideal climate for egg incubation.

Copulation

• Male initates courtship by moving his body over the female and rubbing his tail against her.
• If female is receptive, she dilates her cloaca and raises her tail.
• Copulation lasts 2-20 hours.
• During copulation one hemipene is evaginated and inserted into the female cloaca.
• Hemipene has spines and ridges that enable it to remain in the cloaca for a long period of time.
• Hemipene is withdrawn at the end of copulation by contraction of the retractor muscle.
• During multiple mating, the male can use the left and right hemipene alternately.