Reptile Reproductive Physiology

Reproductive Physiology of Reptiles, Birds, and Small Mammals

General Reminders

• It is crucial to understand the exact species when working with non-domestic, exotic, zoologic, companion animal, or wildlife species due to the significant differences among them.
• Focus on broad concepts and major points (in bold type) when studying.
• Clinically relevant anatomic and physiologic features, as well as wildlife-specific considerations, will be discussed.

Reptiles

• There are approximately 300 species of turtles, 4,000 species of lizards, and 2,700 species of snakes.
• Significant differences exist among the three reptile groups and among species within each group.
• Research on the specific species presented is always recommended.
• Reproductive-related problems are common in captivity in all reptile groups.

Turtles: Male or Female?

• Gender can be determined by the length of the tail and vent position
• Gender differences vary by species.
• Sex determination based on anatomy may not be reliable in young hatchling turtles
• Eastern box turtle males have a curved plastron to fit the carapace during mating, while females have a straighter plastron.
• Some male eastern box turtles have bright red irises, while females have brown irises, however even within the species it is not consistent
• Male aquatic turtles use long front nails in courtship dances.

Turtles: General Anatomy

• Gonads are located at the cranial pole of the kidney.
• Testes are intracoelomic.
• The intracoelomic characteristic applies to all reptiles.
• The reproductive tract, urinary tract, and GI tract all open into the cloaca.
• Sharing the cloaca characteristic applies to all reptiles.
• Male turtles have a phallus that is not visible unless prolapsed.
• The phallus has no urinary function and may be extruded when stressed.
• The prolapsed phallus can be mistaken for a prolapsed GI tract.
• Traumatization of the phallus is common in captive turtles and might need amputation.
• The body cavity in a repitle is referred to as the coelom

Lizards: Male or Female?

• Sexual dimorphism is evident in some species.
• Male chameleons may have horn-like structures.
• Male green iguanas have pronounced femoral pores.

Lizards: General Anatomy

• Gonads are located at the cranial pole of the kidney.
• The right testis and right ovary are attached to the vena cava.
• Males have hemipenes located in the tail base.
• Hemipenes are not visible unless prolapsed and have no urinary function.

Snakes: Male or Female?

• Males have a wider tail base due to the presence of hemipenes.
• Females are usually larger than males.
• Probing can be used to locate the pocket in which the hemipenes reside, but requires care.

Snakes: General Anatomy

• Gonads are cranial to the kidneys.
• Ovarian tissue is diffuse and not defined as organs.
• Males have hemipenes located in tail base, with no urinary function, and is not visible unless prolapsed.
• Ovarian tissue is spread out across the length of the snake

Female Anatomy

• There are bilateral or unilateral oviducts.
• There are no uterine horns or uterine body.
• Oviducts open into the cloaca.
• The size and appearance of ovaries and oviducts change dramatically between inactive and active states.
• Turtles have multiple eggs in the oviducts at the same time.
• Birds produce one egg at a time, and only one egg will be present in the oviduct.
• Reptiles have a single tube (oviduct) that can be bilateral or unilateral, with the ovary loosely attached.
• The top of the oviduct is called the ostium, which receives the follicle.
• The female reproductive anatomy structure and function are the same in oviparous and viviparous reptiles.

Vitellogenesis: Yolk Production

• Vitellogenin is a complex lipoprotein taken up by developing follicles.
• Vitellogenin is a major component of yolk.
• Vitellogenin is produced in the liver, transported in the blood, and deposited in oocytes.
• Vitellogenesis occurs prior to ovulation.
• Estrogen stimulates the formation of vitellogenin by the liver.
• Vitellogenesis is a very energy-expensive process that requires adequate body condition and fat stores in the female.

Modes of Reproduction

• Oviparous: Fetal development occurs after egg laying.
• All turtles and crocodilians, and most lizards and snakes are oviparous.
• All pythons are oviparous
• Viviparous: Retain eggs in oviduct until embryos are fully developed and "give birth" to live young.
• Some snakes and lizards are viviparous.
• All rattlesnakes and gartersnakes are viviparous
• Placentation occurs to some extent in viviparous animals, primarily for gas exchange.
• Placentas are most highly developed in some skinks where nutrient exchange occurs.

Reproductive Maturity

• Determined primarily by size; will occur at a younger age in captive reptiles because of their faster growth rate.
• Turtles reach maturity in 5-7 years in captivity.
• Small lizards reach maturity in 1-2 years in captivity.
• Large lizards reach maturity in 3-4 years in captivity.
• Snakes reach maturity in 2-3 years in captivity.

Hormonal Control of Folliculogenesis

• Hormonal control is not thoroughly understood in reptiles.
• Estrogen is at its highest level during folliculogenesis.
• Surges in testosterone and progesterone occur during the peri-ovulatory period.
• Levels of all three hormones decrease after nesting.
• A corpus luteum exists, but its exact function is not understood.

Hormonal Control of Egg Laying

• Arginine vasotocin (not oxytocin) is the primary hormone determining oviposition.
• Arginine vasotocin is clinically important for egg retention/egg binding.
• Oxytocin, which is structurally similar to arginine vasotocin, is used clinically to induce egg laying, though it doesn't always work.
• Turtles respond most reliably to oxytocin, followed by snakes, and then lizards.

Reproductive Cycles

• Dependent on climate.
• Temperate species: Ovulation and fertilization in spring, egg laying late spring-summer, hatching occurs late summer-early fall.
• Folliculogenesis for the next season's eggs begins late summer-fall and may be interrupted by hibernation and continue the following spring.
• Tropical species: Activity tied to changes in rainfall.
• Some species nest in dry season, others during the rainy season.
• The dormant phase in reptiles is called brumation

Mating

• A phallus (turtles) or one hemipene (snakes, lizards) of male inserted into the cloaca of the female.
• Insertion of phallus or hemipene guides sperm into cloaca.
• There is no "tube" in the phallus or hemipene.

Maternal Care

• Turtles lay their eggs and leave the nest.
• Crocodilians may protect young for up to a year.
• Some snakes guard nests or "incubate" eggs.
• Large and/or venomous snakes and pythons exhibit nest guarding or incubation.
• Females coil around eggs and muscular contractions generate heat (muscular thermogenesis).

Birds

• There are greater than 10,000 species of birds and greater than 300 species of psittacine birds.
• There is species variation in anatomy and reproductive strategy among birds.
• Research on the species is always recommended.

Birds: General Anatomy

• Male and female external anatomy is identical.
• Gonads are located at the cranial pole of the kidney.
• Avian kidneys have 3 lobes: cranial, middle, and caudal.

Birds: Anatomy of the Male

• Intra-coelomic testes.
• Birds have high body temperatures.
• Sperm production in some species happens in the morning when it's cooler.
• The size of testes changes dramatically between breeding and non-breeding states.
• Testes' size adaptation for remaining lightweight for flight.
• Phallus is present in some species. Chickens, turkeys, waterfowl and ratites
• The phallus, if present, is not visible unless prolapsed.
• The phallus has no urinary function.

Birds: Anatomy of the Female

• Ovary and oviduct on the LEFT side ONLY for most bird species.
• Exceptions include the kiwi that has 2 ovaries but still only has LEFT oviduct.
• The size and appearance dramatically change between breeding and non-breeding states.

Follicular Development

• Follicles develop in a hierarchical manner.
• There are 4-6 large follicles and numerous smaller follicles.
• Post-ovulatory follicle is metabolically active and likely influences oviposition and nesting behavior.
• Follicles that are not ovulated undergo atresia.

Continuous vs Non-Continuous Breeders

• Continuous breeders breed year-round. Chickens
• Non-continuous breeders have yearly cycle and include Temperate species.
• Tropical species breed less than yearly and are opportunistic.

Determinate vs Indeterminate Layers

• Determinite layers will not continue to lay if eggs are removed from the nest or destroyed.
• Most avian species, including budgies, are Determinite layers
• Indeterminite layers will continue to lay if eggs are removed from the nest or destroyed.
• Most psittacine species, chickens, ducks and some passerines
• Chronic egg laying is a common problem in some pet birds.

Hormones

• GnRH in birds is more accurately thought of as “LHRH.”
• GnRH does not directly cause FSH release.
• FSH function is not fully understood in birds
• In females, FSH facilitates folliculogenesis and follicle maturation, steroid synthesis by the ovary, and follicular atresia.
• LH facilitates spermatogenesis in males
• In females, LH peaks 4-6 hours prior to ovulation.
• LH facilitates testosterone production in males.

Behavior

• Species-dependent, possible factors include:
• Photoperiod: Long day length stimulates GnRH release in many seasonal breeders; emperor penguin: short day length.
• Rainfall, temperature, food supply are important factors for tropical species.
• Presence of the male and male vocalization stimulates reproductive behavior in the female in some species.
• In the male: environmental conditions affect testosterone production which in turn affects song.

Mating

• Cloacal contact occurs between male and female.
• In species with a phallus, male inserts phallus into cloaca of female.
• The phallus guides sperm into the cloaca of the female.

Egg Formation and Laying

• Preceded by vitelllogenesis.
• Oviduct divided into the Infundibulum where fertilization occurs, then the Magnum where albumen is added
• Isthmus is subsequently then shell membranes are added and finally into the Uterus where Uterus (shell gland): shell is formed
• Oviposition is controlled by arginine vasotocin (not oxytocin) and prostaglandins.
• The egg spends most of its time developing in the shell gland region of the oviduct, acquiring the calcified shell.

Incubation

• Influenced by prolactin where continued prolactin secretion is stimulated by physical contact with the egg.
• Species variations in who incubates where both male and female; female only; male only
• Temperature requirements vary across species.
• Most species require 99-100 °F for incubation.
• Brood patch develops a few days before the female lays eggs.
• Feathers on abdomen and chest fall out/are plucked out and the skin becomes very vascular
• The brood patch allows for transfer of heat to the egg because otherwise the feathers are such amazing insulating structures

Incubation/Hatching

• Incubation time varies with species
• Finches incubate for 11 days
• Albatrosses incubate for 80 days
• Chicks can be precocial or altricial depending on the species.
• Waterfowl are precocial
• Red-tailed hawk hatchlings need parental care to stay warm and be fed
• Altricial chicks are highly dependent on care from their parents
• Precocial chicks are less dependent on parental care

Small Mammals

• Rabbits
• Rodents: Guinea pigs, Rats
• Ferrets

Rabbits: Male or Female?

• Males are called bucks.
• Females are called does.
• Young rabbits are called kits
• Male rabbits have open inguinal rings that can retract testicles into abdomen and lack of nipples
• Males do not have an os penis
• Accurate differentiation between male and female rabbits requires familiarity with the appearance of the urogenital area and the shape of the urogenital orifice

Rabbits: Female Anatomy

• Female Rabbits have along, coiled oviducts and a duplex uterus with two cervices.
• There is no true uterine body and a long flaccid vaginal body
• Uterine adenocarcinoma is very common in rabbits.
• Pet rabbits should be spayed to prevent uterine cancer

Rabbits: The Facts

• Sexual maturity: Small breeds: 4-5 months and Large breeds: 5-8 months
• Induced ovulators.
• Periods of receptivity last for 14 to 16 days, followed by nonreceptivity for 1-2 days.
• Seasonal and Ovarian activity increases with long day length.
• Gestation: 31-32 days.
• An average litter size of 5-8.
• Rabbits can have approximately 60 young/year

Guinea Pigs: Male or Female

• Females are called sows
• Young guinea pigs are called pigs
• Males have open inguinal rings.
• Guinea pigs have an os penis
• Guinea pigs have large seminal vesicles located dorsal to bladder.
• Seminal vesicles can be confused with uterine horns
• Secretions form copulatory plug after breeding.

Guinea Pigs: Female Anatomy

• Guinea pig females have Bicornate uterus and single cervix
• There is a single pair of mammary glands.

Guinea Pigs: The Facts

-Guinea pigs exhibit Sexual maturity.

• Females: 6 weeks
• Males: 10 weeks
• They exhibit Polyestrous, nonseasonal.
• Estrus cycle: 15-17 days
• Estrus: 6-8 hrs
• Spontaneous ovulators
• Gestation: 68 days which is a long gestation compared to other rodents.
• Approximately 3-4 young per litter that will be precocial.

Guinea Pigs: Important Facts

• If intended to be bred, females should have first litter before 6 months of age.
• After 6 months of age, pubic symphysis mineralizes and female may experience dystocia.

Rats: Male or Female?

• Males have open inguinal rings and an OS penis present.
• Male rats lack nipples and have Accessory glands that are highly developed and produce copulatory plug.
• Anatomy is similar in mice

Rats: Female Anatomy*

• Ovaries encased in fat p
• Oviducts encircle the ovaries
• There is a very short uterine body
• Anatomy is similar in all small rode species animals

Rats: The Facts

• Exhibit sexual maturity at 65 - 1
• They are Spontaneous ovulators and are Polyestrous
• 4-5-day estrous cycle and Estrus is 12 hours long
• Continuous/nonseasonal breeders
• Gestation period: 21-23 days
• Average Litter size: 3-18

Rats: Important Fact

• Have 6 mammary glands where Mammary tissue is extensive.
• Mammary tumors occur commonly in female rats and is similar in mice.

Ferrets

• Family Mustelidae
• Related to weasels, otters, mink
• Males are called hobs, Females = jills and Young ferrets are called kits
• Ferrets kept as pets in US are sterilized at 6 weeks of age which lead to Adrenal disease is common in these ferrets
• Ferret adrenal disease results in production of sex hormones
• Most ferrets kept as pets in the US come from facilities that breed them for biomedical research and, as such, are prone to the same diseases

Ferrets: Male Anatomy

• Prostate gland completely surrounds urethra.
• Prostatomegaly secondary to adrenal disease can lead to urethral obstruction and death.
• Os penis present and has a curled tip making urinary catheterization difficult.

Ferrets: Female Anatomy

• Bicornuate uterus, with long uterine horns that combine immediately in front of the cervix.
• Very short uterine body.

Ferrets: The Facts

• Exhibit Sexual maturity in males and females between 6-12 months of age
• Induced ovulators where If fertilization does not occur, a 40 day pseudopregnancy occurs, followed by return to estrus
• Seasonally polyestrous where Ovarian activity increases with long day length.
• Jills are very sensitive to photoperiod.
• Gestation lasts 40-44 days and the litter size ranges from 1-12 with an average of 8.

Ferrets: Important Fact

• If the jill does not mate, the ovaries continue to produce estrogen, which will result in hyperestrogenism and severe anemia and thrombocytopenia.
• A jill in estrus must be bred with a male which can be vasectomized to prevent pregnancy.

Wildlife repro problems Considerations

• Caused by people thinking they are abandoned due to lack of understanding of their normal behavior
• Advise people to leave them alone and keep pets away from animal
• Black bear cubs may need care if found without their mothers in March or April.

Wildlife repro problems Considerations for Fledgling birds

• Caused by people thinking they are injured because they are hopping around on the ground as part of a normal process of learning to fly.
• Advise people to leave them alone and keep pets away and keep an eye out for a parent coming to feed.
• Lack of understanding of normal fledgling bird behavior results in picking up healthy animals that should have been left alone

Turtles

• Female turtles are susceptible to getting hit on the road while crossing it to get to a nesting sight
• Inducing egg laying is done prior to release where the eggs will be later incubated
• Post-mortem egg retrieval and
• Female turtles are particularly susceptible to getting hit by cars when they are crossing the road during nesting season
• It is ideal to fix injured and gravid turtles, but if it is not possible to save an injured specimen, their eggs can still be retrieved and incubated.

Egg Binding In Wild Birds

• Egg binding does not generally occur in wide bird
• If a red-tailed hawk has a normal sized egg it is an incidental finding!
• Wild birds coming into rehab centers with eggs will generally lay them on their own soon after admission
• Knowing How long is the egg in the shell gland is important and more information can be found on slide 44

Imprinting In Wildlife

• Imprinting should be avoided
• Red-tailed hawk hatchlings should not be handled by people and birds of prey will imprint on humans if given the opportunity.

Wildlife Fact

• Porcupines are rodents with a gestation of 210 days