Lecture 7 Flashcards
Is there more research and public health policy on female reproduction or male reproduction?
Female reproduction
Basics of Mammalian Reproduction - Men
- there are ~15,000,000-200,000,000 spermatozoids per ejaculate
- spermatozoids are produced continuously
- spermatozoids can survive up to 48hrs in the vaginal tract
- reproductive life span ~ 45 years (based on a 1st birth at 25 & ~70 year life span)
Basics of mammalian reproduction - women
- at birth women have about 2 million follicles reduced to ~300,000-400,000 when women reach puberty
- one follicle matures each month - 400 follicles will mature, in the current “contraceptive environment” (<100 in non contraceptive environments)
- each egg survives between 6 and 24 hs after ovulation
- reproductive life span < 30 years
Mammalian Reproduction: What is the “limiting reactant?”
Women
- ~100 eggs in lifetime
- egg survival 6-24 hs
- reproductive life span
Men
- ~15,000,000-200,000,000 spermatozoids per ejaculate + continuous production
- spermatozoids can survive up to 48hs
- reproductive life span > 55 years
Problem with women reproduction research
- A lot of what we know or believe we know about women reproduction has been actually derived from animal research and women with pathologies
- women with pathologies are not representative of the general population
- comparisons are not only odious but they are often wrong and inappropriate
Women: A special kind of mammalian female
- in most mammalian species females ovulate a few times a year, in some cases only once
What ecological factors may have played a role in the evolution of such unusual ovulatory frequency?
- in some species estrus takes place at specific times of the year (e.g. ungulates, phocids)
- in others it is induced by males presence (some rodents) and in others by copulation (some felids)
In most cases there are obvious signs for the male to know a female is in her fertile window (pheromones, redness, swelling, etc)
No obvious signs of ovulation in humans
- researchers are still debating whether there are any behavioural or physical cues that precede ovulation in humans
- in any case if the cues exist, they are quite subtle
Explain “in some species estrus takes place at specific times of the year (e.g. ungulates, phocids)”
Estrus: This is a phase in the reproductive cycle of female mammals when they are fertile and can conceive. During estrus, females exhibit behaviors that attract males and are physiologically prepared for mating.
Specific Times of the Year: In some species, estrus is synchronized with environmental factors such as seasonal changes, food availability, or climate conditions. This synchronization can enhance the chances of successful reproduction and survival of offspring.
Ungulates: This group includes hoofed mammals like deer, cattle, and horses. Many ungulates have a breeding season in the fall or spring, aligning their estrus cycles with optimal conditions for raising young.
Phocids: This family includes seals. Many seal species also have specific breeding seasons, often timed to coincide with environmental conditions that favor the survival of pups.
Overall, this reproductive strategy helps ensure that offspring are born during times when resources are abundant, increasing their chances of survival.
Explain “in others it is induced by males presence (some rodents) and in others by copulation (some felids)”
Induced by Male’s Presence (Some Rodents):
In certain rodent species, the presence of a male can stimulate the female’s reproductive system to enter estrus. This means that the female may not show signs of being in heat until a male is nearby. The male’s pheromones (chemical signals) or behaviors can trigger hormonal changes in the female, leading to ovulation and receptivity to mating. This strategy can ensure that mating occurs when a male is available, increasing the likelihood of successful reproduction.
Induced by Copulation (Some Felids):
In some species of felids (cats), the act of copulation itself is necessary to induce ovulation. Female cats, for example, are known to be induced ovulators, meaning that they only release eggs in response to mating. The physical stimulation from the male’s mating behavior triggers hormonal changes that lead to ovulation. This mechanism ensures that the female’s eggs are released at a time when they are likely to be fertilized, maximizing reproductive success.
Overall, these different reproductive strategies reflect the diverse adaptations animals have developed to optimize their chances of successful reproduction in varying environmental and social contexts.
The origin of “concealed ovulation” and “continuous” fertility? Great unknown
Hypotheses:
1. “Daddy-at-home” hypothesis: mating guarding - increased bonding - increased male derived benefits (defence, energetic resources, social support, etc.) - increased paternity certainty - increased paternal investment
2. “Many father” hypothesis: multiple partners, unclear paternity, multiple “male benefits”, lower paternal investment yet multiple fathers
3. Both?: genes are resources may not come from the same male
4. The female rivalry hypothesis: computational model suggest that females who concealed ovulation avoided female-female aggression and succeeded in forming parenting relationships with males and had more children
The costs of continuous ovulation
Nowadays humans spend large amounts of time and energy to time pregnancies in accordance with:
- religious beliefs
- family and social mandates
Or the facilitate the achievements of life goals (e.g.: academic and economic)
But there are also more ancestral costs
- maternal depletion
- increased offspring mortality
The costs of continuous ovulation: What happens in biology when there are costs and there are geno/phenotypic alternatives?
Alleles associate with less costly phenotypes spread in the population.. and, therefore, new traits evolve
Women’s Sexual Health TODAY: Orgasm
- only 25-35% of women consistently reach orgasm during vaginal intercourse, no matter how long it lasts, no matter what size the man’s penis, and no matter how the women feels about the man or the relationship
Based on that sort of data, SJG argued that women’s clitoris is inappropriately located - does not get directly stimulated during sex
Thus, he argued, that the clitoris was a “spandrel” … “the clitoral site would represent the different expression of a male adaptation”
Exaptation
- develop the describe a trait that evolves due to the benefits that it confers with regard to a certain function and is then co-opted for a different use
Now, isn’t that the way all traits evolved?
The clitoris
- located in front of the pubic symphysis, in the anterior perineal region
- its roots are located in contact with the ischipubic ramus, covered by the ischiocavernosus muscles: they cannot come into contact with the anterior vaginal wall and there is no evidence for the existence of an “inner clitoris”
Nerve endings clitoris vs penis
- the G-spot is located in the pelvic wall of the urethra, 2-3cm into he vaginal
- some argue that the male penis cannot come into contact with the (situated at the angle of the clitoris) or with the roots of the clitoris (but these do not have sensory receptors or erogenous sensitivity) during vaginal intercourse
