Reproductive Behaviour & Mating Systems

Question 1

sexual selection

Answer 1

• process that depends on the advantage certain individuals have over others of the same sex and species in relation to reproduction
• involves intra- and inter-sexual selection
• plays a role in majority of mating systems
• related to natural selection

Question 2

intra-sexual selection

Answer 2

• members of one sex compete with each other for access to the other sex (competition for motes)
• In most species, males compete for females -> females tend to be more choosy due to the high amounts of energy they invest in having offspring (energy is critical for reproduction!)
• Related to type and number of gametes produced by each sex (female gametes/eggs are larger and more scarce, limited number -> more of a valuable resource than sperm)

Question 3

Bateman Principal

Answer 3

• falls under category of intra-sexual selection
• States that females are the choosier sex because:
• • Their gametes are eggs -> energetically expensive
• • Female reproductive success is limited, compared to the male
• • As a result of females being the “choosier” in mate selection, this is expected to translate into increased variance in reproductive success in males

Question 4

factors influencing intrasexual selection

Answer 4

• Environment
• Cognitive ability
• Species differences
• Could be other factors too?

Question 5

competition for mates

Answer 5

• Dangerous bouts between males to gain access to females
• “Battles to the death” are less common
• Result: winner gains mating opportunities

Question 6

intersexual selection

Answer 6

• individuals of one sex choose which individuals of the other sex to take as mates (mate choice)
• Less research on this: easier to study intrasexual; in the past evolutionary biologists didn’t acknowledge importance of mate selection by females (nowadays, research examining female mate selection predominates)
• Includes female selection of a male and male selection of a female

Question 7

epigametic sexual characteristics

Answer 7

• Secondary sexual traits that are favoured by sexual selection as a result of their effect of mate choice
• Strategies employed by males to attract females:
• • Ornamental plumage
• • Bright colouration
• • Courtship displays/dances
• • Courtship songs (ie. Male drosophila/fruit flies sing to females via wing vibration – pulse song)

Question 8

types of pairing/mating systems

Answer 8

• Monogamous pairing (1 male + 1 female)
• Polygamous paring (1 male + multiple females)
• Polyandrous pairing (1 female + multiple males)

Question 9

what type(s) of parings/mating systems is sexual selection strongest in? Why?

Answer 9

• polygamous and polyandrous pairings
• higher because if sexual selection deems 1 animal to be a good mate, there are much more mating opportunities for them in those mating systems

Question 10

how is sexual selection related to natural selection?

Answer 10

• fitness consequences
• If trait x confers a mating and fertilization advantage, trait x will increase in the population and males with trait x will produce more offspring

Question 11

models of sexual selection (female mate selection)

Answer 11

• direct benefits model
• good genes model
• runaway selection model
• sensory exploitation model

Question 12

direct benefits model

Answer 12

• Sexual selection favours females who have a genetic predisposition to select mates that provide them with tangible resources
• • Resources: increase fecundity
• – Food, safe habitat, parental care of offspring, etc.
• – Females that select males who provide them with resources will benefit – over time, numbers of choosier females will increase
• ex. Scorpionflies

Question 13

Scorpionfly example (direct benefits model)

Answer 13

• Thornhill et al hypothesized that female mate selection is influenced by male presentation of “nuptial gift”
• Results: females do select males based on presentation of large prey; larger prey = longer copulation; males without gifts rejected
• Why:
• • Nutritional benefit -> larger gift = less time spent hunting
• • Females selecting males with large gifts produce more eggs and have longer lifespans
• • Longer copulation -> more sperm transfer -> more offspring
• Risks for the male in gift presentation: More dangerous to hunt for large prey
• Strong selection have resulted in additional male-specific behaviours:
• • Male will catch small prey and discard it if it’s not likely to win over the female
• • Prey theft by males -> male mimics behaviour of a female and then steals the prey delivered to them

Question 14

good genes model

Answer 14

• Sexual selection involving females choosing mates with good genes
• Cheaters exist -> males making it appear that they have good genes
• • Sexual selection does favour male cheating behaviours, but honest indicators are more favoured over evolutionary time since they’re a true indication of male genetic quality
• • Females can distinguish because honest traits cost more energetically, so hard to fake/cheat
• ex. Pronghorn antelopes

Question 15

what are “good genes”? How are they determined?

Answer 15

• Good genes:
• • Code for favourable traits
• • Passed on to the offspring
• • Fitness advantage
• Exact nature of good genes is environment-dependent:
• • High predation: genes resulting in strong anti-predator behaviour
• • Scarce food sources: genes resulting in successful foraging abilities

Question 16

pronghorn antelopes (good genes model)

Answer 16

• Byers et al: observational study in Montana -> tracked females and recorded mating pairings; tracked offspring and measured their survival
• Hypothesis: females base their mate selection on “good genes” that improve survival of offspring
• Results: females travel long distances to visit reproductively active males with harems (group of female animals sharing a single mate), observe male’s ability to protect harem -> males w/large harems = better protectors -> offspring have better survival rates

Question 17

runaway selection model

Answer 17

• Involves relationship between alleles on 2 different loci (positions on a chromosome)
• • Ex. Subset of females prefer bright-coloured males, remaining females have no preference; males will therefore have colour variation (more vs. Less colourful)
• – Assumption: Loci for both the female preference and the male colouration are found in both male and female with preference for colourful mates -> over time, these genes become linked -> the frequency of both change together

Question 18

sensory exploitation model

Answer 18

• Model hypothesis: when a male trait first emerges, it will be preferred by females due to initiation of a neurobiological response already in place in females (not related to mate selection)
• Hypothetical example:
• • Bird species prefers red berries (energy-rich food)
• • Females better able to locate red berries = higher survival and reproduction
• • Natural selection: favours ability of males to hone in on berries
• • Mutation arises in males: results in red feathers
• • Female expected to prefer males with red feathers: neurocircuitry in place to prefer red colouration
• • Note: preference for red must come first

Question 19

primate example (sensory exploitation model)

Answer 19

• Females prefer males with red fur/facial skin
• Experimental question: is there a sensory base for preference?
  – Most mammals have 2 types of photoreceptor cones in the eye -> dichromatic vision
  — Subset of primates has 3 types of photoreceptor cones in the eye -> trichromatic vision -> red/orange detected
  Trichromatic vision improves abilities in detecting red-orange food-> primates withtrichromatic vision show preference for red-orange foods
  – Did female mating preference for red colouration in males arise due to trichromatic vision and the effects on foraging?
• Experiment by Fernandez et al.: used primate data examining colour vision and red fur/face colour -> Phylogenetic data supports this hypothesis