Reproduction and sexual selection

Question 1

What are the advantages and disadvantages of sexual reproduction?

Answer 1

Advantages:

1. Sexual selection evolved to promote genetic variation in offspring
2. Recombination can bring favorable alleles together and purge deleterious alleles

Disadvantages:

1. Recombination can break up favorable allele combinations
2. Logistically challenging
3. Males

Question 2

How did mammary glands evolve?

Answer 2

Mammary glands evolved from apocrine-like glands (skin glands) to provide:

1. Nourishment
2. Immunological competence
3. Endocrine maturation

Breast milk composition is highly variable due to adaptation to ecological niche and physiology

Question 3

How did the placenta evolve?

Answer 3

The placenta is the fusion of the fetal membranes to the uterine mucosa for physiological exchange.

Its evolution was very rapid, and it is one of the most morphologically diverse organ in mammals, due to adaptation to ecology and physiology and the maternal-fetal conflict:

• Fetus: optimize own growth and survival
• Mother: optimize lifetime reproduction; only 50% related to the fetus

Question 4

How is human placenta?

Answer 4

Internal morphology human placenta

• Especially deep extravillous invasion
• Large contact surface
• Derived characteristic

Combination of traits makes human placenta most invasive
- Support brain growth

Question 5

What is the role of genomic imprinting in evolutionary conflict?

Answer 5

Genomic imprinting is the process of de-activation of X-chromosomes:

• Maternal imprinting suppresses fetal or juvenile growth
• Paternal imprinting stimulates growth

Regulated by
- igf2 and igf2R

Affect:

• nutrient signaling and growth
• circadian rhythm and sleep
• sexual dismorphism and brain development

Question 6

What are the types of sexual selection?

Answer 6

Sexual selection by competition:

1. Scramble competition
   
   • Speed is essential to reach limited resources
2. Endurance rivalry
   
   • Persistence to display or await mates
3. Direct contest
   
   • Fights or display
   • Evolution of “weapons”
   • Sexual size dimorphism

Sexual selection by mate choice:
- Immediate benefits, e.g. territory, protection, food
- Good genes: preference for indicators of genetic health and fitness
that predicts offspring fitness

Question 7

What are some examples of sexual selection in humans and primates?

Answer 7

Primates:
1. sexual dimorphism linked to living in harem groups

Humans:

1. good genes (waist-to-hip ratio; body hair; facial symmetry)
2. Odour cues
3. Voice

Question 8

Why are odour cues important?

Answer 8

Chemical (odour) signalling plays a pivotal role in reproduction and partner choice in many animal species

• Information about reproductive status and health
• Pheromones: secreted chemicals that trigger a response in conspecifics

Question 9

Why are vocal characteristics important?

Answer 9

Levels of gonadal sex hormones (testosterone & estrogen)

• Immune system activation suppresses testosterone
• Male voice indicates health
• But: testosterone is also linked to male infidelity and violence