3. Sex: Evolutionary, Hormonal, and Neural Basis Flashcards
Reproductive behavior can be divided into 4 stages
Sexual attraction, appetitive behavior, copulation, postcopulatory behavior
Sexual attraction
Brings males and females together, which may be synchronized with:
- Physiological readiness to reproduce
Females of many species won’t engage in sexual activity unless ovulating
- Learned associations, such as appearances or displays
In some species, mates males and females will form pair bonds
Appetitive behavior
Establishes, maintains, or promotes sexual interaction
- If a female is willing to copulate, she is said to be sexually receptive and exhibits lordosis (also referred to as estrus or heat)
- A proceptive female rat may approach males, engage in hopping and darting, perform ear-wiggling, or produce ultrasonic vocalizations
- Male appetitive behaviors include staying near the female, sniffing, nest-building, etc.
Appetitive phase lasts longer than the copulatory phase
Copulation
Involves one or more intromissions in which the male penis is inserted in the female vagina
Following stimulation, the male ejaculates sperm-bearing semen into the female
After copulation, a refractory phase follows
Length varies across species
The Coolidge Effect
The Coolidge Effect
Refers to the faster resumption of mating behavior with a different partner
Postcopulatory behavior
Varies across species
In a copulatory lock, occurring in dogs and some mice, the penis swells temporarily and cannot be withdrawn from the female
What are the 2 purposes of gonads?
To produce steroid hormones and gametes
Gonadal steroids activate sexual behavior
Circulating gonadal steroid hormones are required for males and females of many species to engage in sexual activity
Gonadectomy (removing gonads) eliminates sexual behavior
Estrous cycle
In rats, females ovulate, or release eggs, every 4 or 5 days
This is called the estrous cycle
What is the estrous cycle controlled by?
Hormones, via the hypothalamic-pituitary-gonadal axis (HPG axis)
Anterior pituitary
What determines the estrous cycle’s length?
The rate-limiting step is the time it takes to develop the egg
Testes
Produce and secrete testosterone, which is an androgen
Male HPG axis
GnRH from hypothalamus causes an increase in LH (from anterior pituitary), which regulates testosterone production in the Leydig cells of the testes
Not pulses, but steady and constant
Production of testosterone and sperm remain fairly constant once they begin at puberty, unlike the cyclical nature of the female cycle
Male castration
A castrated male loses interest in mating because testosterone is no longer produced, behavior is restored with testosterone treatment
Level of T does not seem to matter, in that having higher levels does not further increase sexual behavior except in seasonal breeders
Female HPG axis
The hypothalamus kicks everything off by releasing gonadotropin releasing-hormone in a pulsatile fashion
GnRH stimulates anterior pituitary to release follicle-stimulating hormone and luteinizing hormone
FSH acts on the ovary to cause development of the follicle; LH increases release of estradiol from the ovary
Estradiol acts to increase further LH secretion (positive feedback), resulting in a surge of LH that causes ovulation
Progesterone production then increases, inhibiting the hypothalamus from releasing more GnRH (negative feedback)
If the egg isn’t fertilized, progesterone levels drop, and the cycle starts over again
Female hormonal contraceptive
Oral contraceptives contain synthetic progesterone that inhibits release of GnRH
The lack of GnRH prevents release of FSH and LH, so no egg is released by the ovary
A female rat who is in estrus
will exhibit lordosis (arched back) when a male mounts her, allowing for copulation to occur (vaginal canal accessible)
