Social mating systems

Question 1

What factors shape mating systems

Answer 1

1. Differential investment between species (females have fewer larger eggs, male have many small sperm- more investment in females)
2. Dependence of young and impact of care (precocial, more polygynous as less need for paternal investment, whereas more monogamy with altricial offspring as need paternal investment
3. Certainty of paternity- increased monogamy if male is certain, even safeguarding by male when female is fertile. less certainty results in polygyny
4. Ecological factors: the environmental potential for polygyny depends on the level to which having multiple mates (or resources necessary to attract multiple mates) are defensible- uniform, spread out female, leads to increased incidence of monogamy whereas clumped together–> polygyny potential

Question 2

What are the three hypotheses to explain evolution of monogamy?

Answer 2

1. Mate guarding hypothesis: monogamy is adaptive (i.e. produces more offspring) when female left by one male readily mates with another male. -clown shrimp
2. Mate assistance hypothesis: monogamy is adaptive when parental care can greatly increase offspring survival – often in altricial species i.e. male leaves–> decrease in offspring
3. Female-enforced monogamy hypothesis: males are not monogamous because it is in their best interest, but rather because females impose this on them. -burying beetles, fighting

Question 3

Forms of polygamy are classified as:

Answer 3

1. Female defense polygyny
2. Resource defense polygyny
3. Scramble competition polygyny
4. Lek polygyny

Question 4

Why form leks?

Answer 4

for females: Females get their pick of males and can easily compare them – they can secure ‘good genes’ from high quality males
for males: 3 hypotheses:
1.Hotspot hypothesis: males cluster around routes or places frequented by females. Four species of birds in Costa Rica used the same location to lek. This suggests that topology determines where females go and respond accordingly.
2.Hotshot hypothesis: subordinate males gather around attractive dominant males. Removing dominant male lead to subordinate dispersal
3.Female preference hypothesis: males cluster because females prefer sites with larger groups of males.