Female Mating Behavior

Puberty signifies a critical phase in animal breeding.
- It marks the longest phase of infertility in animals.
- Represents the first indication of an animal's breeding capability.

Prepubertal Stage:
- Characterized by immature ovaries and uterus.
- Neuroendocrine function is underdeveloped.
Pubertal Stage:
- The reproductive system becomes functional.
- Body size becomes capable of gestation.
- Animals continue to grow: full range of sexual behaviors is expressed.

Age at which different species reach puberty varies. Examples include:
- Rat: 3 months
- Chicken: 5 months
- Sheep/Goats/Swine: 6-7 months
- Dog: 6-24 months
- Cat: 6-10 months
- Cattle: 12 months
- Horses: 16 months
- Rhesus Monkey: 2-3 years
- Gorilla: 6-8 years
- Chimp: 7-11 years
- Women (North America): 12.5 years (menarche - first menstruation)
Observations indicate a decline in the average age of puberty in girls by approximately 5 years since 1920.

Prepubertal Phase:
- Limited levels of Gonadotropin-releasing hormone (GnRH) and Luteinizing hormone (LH).
- Ovaries contain small follicles with low estrogen production.
- The positive feedback system is not yet developed.
Pubertal Phase:
- Maturation of the neuroendocrine system.
- Hypothalamus develops the ability to respond to positive feedback from estrogen.
- GnRH releases influence leading to the production of Follicle-stimulating hormone (FSH) and LH, enabling the growth of large follicles and ovulation.

Seasonal reproduction is common in many wild species, especially those in regions with distinct seasons.
- Species react to photoperiod changes and temperature fluctuations.
- Infertility periods (anestrus) may alternate with fertile periods (estrus).

Most animals respond to variations in light and dark environments.
- Changes in day length are minimal near the equator, which means photoperiod effects are limited.
Animals primarily sense light through their eyes, which affects the pineal gland's release of melatonin.

Melatonin is released during the nighttime (darkness).
The release of melatonin is linked to the activity of the pineal gland located in the brain.
Changes in melatonin levels can affect reproductive hormone actions such as GnRH, LH, and FSH production during breeding seasons.

In certain species, increased melatonin leads to higher GnRH, LH, and FSH release during the breeding season.
For mammals such as horses, sheep, and cats, changes in reproductive hormone levels are common in response to seasonal variations.

In the Northern Hemisphere, manipulating light exposure for mares can influence their reproductive cycles.
- Increasing light duration by 30 minutes per week after late December can advance the timing of estrus and ovulation in the spring.

Early development influences female estrous cycles and estrus behavior.
- Estrogen from the placenta and other sources binds to Alpha-fetoprotein (AFP) in females, preventing it from crossing the blood-brain barrier. This allows for the development of the hypothalamic-pituitary axis (HPX) in females.
- In males, fetal testes produce testosterone that does not bind AFP, enabling it to cross the blood-brain barrier where it is aromatized to estrogen, resulting in the 'de-feminization' of HPX (elimination of estrous cycles).

Female sexual behaviors are largely influenced by hormonal changes, notably driven by estrogen and inhibited by progesterone.
- Levels of estrogen increase before the onset of estrus across species.
Types of Sexual Behaviors:
- Proceptive behaviors: Active seeking of sexual partners driven by visual, auditory, olfactory, and tactile cues.
- Receptive behaviors: Involves standing to be mounted (lordosis).
- Refractory behaviors: Period of refusal to mate during the estrus stage.

Pheromones can impact reproductive behavior, with evidence observed in species such as rodents, pigs, ruminants, and horses.
- These are small, volatile steroid compounds or fatty acids influencing the sexual behavior of members of the same species.
- Sources may include vaginal secretions, urine, saliva, or skin.
- The vomeronasal organ (VNO) in the nasal cavity detects these substances and signals the olfactory bulb to modify hormonal responses or behavior.
Types of Pheromones:
- Primer Pheromones: Induce endocrine changes over extended periods, affecting puberty.
- Releaser Pheromones: Immediate responses that attract partners or initiate mating behavior.
- Modulator Pheromones: Affect mood or behavior in species, including humans.

Rodent Examples:
- Bruce Effect: Exposure to a new male in early pregnancy may result in abortion (observed in mice).
- Whitten Effect: Males can synchronize cycles in female populations (observed in mice).
Human Studies:
- Interest in pheromone effects exist, but empirical evidence is limited.
- Reports suggest women living in close quarters may experience menstrual cycle synchronization over several months.
- Tests on responses to 16-androstenes (found in armpit secretions) have revealed varied cyclic, mood, and attraction responses among women.
- Notably, humans do not possess a functional VNO.