W3: Parental Care & Mate Choice

Question 1

Sexual Dimorphism

Answer 1

• any differences in males and females of the same species
• males typically have
  1) brighter colors
  2) more elaborate weaponry
  3) specialized and more elaborate signals

Question 2

What is the most basic difference between sexes?

Answer 2

anisogamy

sexual reproduction with two dissimilar gametes

Question 3

6 Important points about anisogamy

Answer 3

1) males produce more gametes than females
2) female fitness is limited by egg production
3) male fitness is limited by mating success
4) males are expected to compete for females
5) females are expected to be choosy about their mates
6) male mating success should be more variable than female mating success

Question 4

Parental Investment

Answer 4

anything that a parent does for existing offspring that reduces it’s ability to invest in future offspring.
Usually the sex that invests more is a limiting factor to the sex that invests less.

Question 5

Sex-role reversal

Answer 5

when male provides more parental role than female (exception: fish/seahorses)
Does not require complex parental care.

Question 6

Sex-role reversal examples:

Answer 6

1) Seahorses
Males care for eggs in a specialized pouch into which females lay eggs.
2) Sandpipers
Females more actively court males and defend territories because the males care for young. Females may help with the last clutch of the season but will desert if there are other options.
3) Waterbugs
Females cement eggs on the back of males and leave. Males care for eggs and eventually stop eating to avoid accidentally eating offspring when they hatch.

Question 7

What 3 evolutionary conflicts over division of parental care lead to an observed division of parental care?

Answer 7

1) Reproductive biology
2) Ecological constraints
3) Phylogenetic constraints

Question 8

Reproductive biology

Answer 8

• internal.external fertilization
• location of development
• presence of specialized care structures

Question 9

Ecological constraints

Answer 9

• resource distribution

- predators & parasites

Question 10

Phylogenetic constraints

Answer 10

-type of care seen in ancestors

Question 11

Primary sexual characters

Answer 11

the necessary differences between the sexes (i.e.reproductive organs)

Question 12

Secondary sexual characters

Answer 12

everything else (behavioral and morphological) that differs between the sexes. These often have costs in terms of energy or survival.

Question 13

Sexual selection

Answer 13

-favors traits that give the bearer an advantage in competing for mates.
-a subset of natural selection
-acts in variation in mating success
-usually is costly in terms of survival
(increasing number of offspring, even at the cost of longevity)
when we see variation in mating success, sexual selection may explain this

Question 14

Intra-sexual selection

Answer 14

(usually) MALE-MALE
- Fight for dominance
- Fighting to exclude
- sneaking
- sperm competition

Question 15

Inter-sexual selection

Answer 15

(usually) FEMALE choose mates
- non-genetic, direct benefits
- Fisher’s runaway process
- Good genes
- pre-existing biases

Question 16

Are females conscious of their mate choice?

Answer 16

No.

Females are not conscious of their mate choice. Their behavior influences who they choose.

Question 17

What is the relationship between total copulations and male dominance (heirarchy) in male elephant seals?

Answer 17

high-ranking elephant seals copulate more

Question 18

Sperm conpetition

Answer 18

• competition amoung the sperm of different males to fertilize the same females invovles morphological and behavioral traits which may include adaptations to remove sperm
  (i. e. bristled penises, cloacal pecking)

Question 19

How do variations in mating systems affect fly genitalia?

Answer 19

polygamous males have more genitalia variation than monogamous flies.

Question 20

What is the relationship between the fitness and successful fathered offspring in blue milkweed beetles?

Answer 20

Mate guarding has a significant impact on the success of males fathering offspring. Mate-guarding increases fitness.

Question 21

EPC

Answer 21

extra pair copluations

Question 22

What are some non-genetic, direct genefits for female choice?

Answer 22

• nuptial gifts (i.e. food)
• high quality territories, nesting sites
• paternal care
• parasite avoidence
• male courtship behavior and the SS characters themselces could be indicators of non-genetic benefits.

Question 23

Describe the long-tailed widowbirds experiment:

Answer 23

Focus: studied effect of tail length on female choice
Cut piece of tail off of some males and glued it onto others.
1) short tailed males: tail removed
2) control males: held & not cut, cut and re-pasted
3) long tailed males: tail added
Counted how many new nests were added
Result: females prefer males with long tails

Question 24

Fisher’s runaway process

Answer 24

aka: the ‘sexy son’ hypothesis
Starting conditions:
1) genetic variation in male trait
2) genetic variation in an initial female preference for the male trait
= offspring of both sexes inherit genes for the preference and male trait (so sons get trait, females get preference)

Leads to:
1) sexual selection by female preference causes male evolution
2) genetic correlation with male trait causes female preference evolution
3) male traits become elaborate/costly until natural selection puts a check on further elaboration
=positive feedback loop

Question 25

Good genes hypothesis

Answer 25

Traits are handicaps and female preferences evolove because they are ‘reliable’ indicators of male quality.
Apply Fisher’s runaway process here.

Question 26

Pre-existing sensory bias

Answer 26

• Genes that afect mate preferences have pleiotropic effects on other sensory system functions (females have evolved mechanisms to detect prey and these same movement and size detection mechanisms can function in other ways)
• Male traits evolve to exploit these pre-existing female preferences.

Question 27

Sensory exploitation

Answer 27

male traits evolve to exploit pre-existing sensory biases or ‘hidden’ preferences.
i.e. water mites: male leg trembling courtship may have evolved to exploit a pre-existing female bias for prey detection.