ANTH Final: PART 6 - Reproductive Ecology

What are “costs of reproduction” for female mammals? In what part of reproductive cycles are these highest?

“Costs of reproduction” are the energetic, physiological, and survival demands associated with pregnancy, childbirth, and lactation. These costs are highest during late pregnancy and lactation, when energy demands are at their peak.

“Ovarian functioning” refers to the complicated sequence of hormonal effects involved in leading to estrus in some mammals and to menstrual cycles in humans and some other primates. Have some idea of how increases in energy expenditure and decreases in energy intake can influence ovarian functioning and, in particular, can influence the probability that (a) women who are not lactating have menstrual cycles; (b) that they ovulate during these cycles; (c) that they conceive if they ovulate; and (d) that conception leads to successful pregnancies. Why does it make sense that ovarian functioning is highly sensitive to energetics, given our long ancestry as hunter-gatherers?

• (a) Low energy availability can stop menstrual cycles (amenorrhea).

• (b) Even if menstruation occurs, ovulation might not if energy is too low.

• (c) If ovulation occurs under poor energetic conditions, conception rates can drop.

• (d) Conception is more likely to fail or end in miscarriage if energy levels can't support pregnancy.
  This sensitivity makes evolutionary sense because in a hunter-gatherer context, reproduction during times of low energy could risk maternal and offspring survival.

What does ovulation rely on? How does the corpus luteum relate to this?

Yes, ovulation relies on a mid-cycle surge in LH (luteinizing hormone). If this surge is blunted—due to stress, poor nutrition, or excessive exercise—ovulation may not happen. If ovulation does occur, low hormone output from the corpus luteum can reduce chances of implantation and pregnancy success.

You don’t need to memorize the details of ovarian hormone cycles, but know that ovulation depends on a mid-cycle surge in luteinizing hormone (LH) and that anything that reduces the increase in LH, that decreases the amount of hormone secretion by the corpus luteum if ovulation occurs, etc. can reduce probabilities of ovulation, conception, and successful pregnancy.

Related to the above questions: what is energetic status? Energy balance? Energy flux? How important are the effects of each of these variables on ovarian functioning? Again, does this make sense in terms of our evolutionary history?

• Energetic status = total energy available in the body (e.g., stored fat).

• Energy balance = energy intake minus energy expenditure.

• Energy flux = the overall rate of energy turnover (how quickly energy is used and replaced).
  All three influence ovarian function. Poor energetic status or negative energy balance can shut down reproductive function. This makes evolutionary sense: conserving energy in hard times protects maternal health and future reproductive success.

What are some of functions of testosterone? What are possible costs of maintaining high testosterone levels?

Testosterone supports muscle growth, aggression, libido, and male reproductive functions. But high levels can suppress the immune system, increase metabolic costs, and elevate the risk of injury or disease.

Related to this question, what is the “challenge hypothesis”?

The challenge hypothesis states that testosterone levels increase temporarily in response to social or reproductive competition (like male-male rivalry) and decline during parenting, reflecting a tradeoff between mating effort and parental care.

What are “winner/loser effects”, and do we see them in humans?

• Winner effect: Winning a competition raises testosterone, increasing the chance of winning again.

• Loser effect: Losing lowers testosterone, reducing future competitive motivation.
  Yes, these effects have been observed in humans, especially in sports and social hierarchies.