Parental Investment Flashcards
Who discovered the principles of parental investment and what do they explain?
Trivers (1972)
Parental investment explains sex differences in behaviour and morphology.
The relative parental investment of the sexes in their young is a key variable in controlling sexual selection
What is the definition of parental investment?
Any investment by the parent in an individual offspring that increases the offspring’s chance of survival and hence reproductive success at the cost of the parents ability to invest in other offspring.
What are some of the conflicts that can arise through parental investment?
- Conflict between parents and offspring when weaning.
- Conflict between successive offspring due to sibling rivalry for care and attention.
- Conflict between parents (battle of the sexes)
What are the limiting factors for maximising reproductive success in terms of parental investment?
Females - Number of offspring they can successfully produce and rear.
Males - Number of females/ fertilisations they can access.
Thus for the majority of species; males invest more in mating typically competing for access to fertile females and females invest more in parenting.
What is the definition of anisogamy?
sexual reproduction by the fusion of dissimilar gametes.
Describe female and male anisogamy
Females invests in a few large gametes such as an ovum or egg and males invest in the production of a large number of small mobile gametes called sperm.
What do you find if you compare female and male anisogamy in terms of energy?
A female invests more energy in the production of a single gamete than a male
Give a brief comparison of mammal investments between males and females
Females
- large nutrient rich egg
- ~400 eggs produced in a lifetime
- typically 1 egg produced per month
- high gestations costs
- high lactation costs
Males
- Small sperm
- Billions produced per month
- no gestation
- no lactation
What is the inter and intraspecific variation between primate species?
There is a similar level of parental investments between the sexes.
- Similar behaviour and/or morphology between the sexes.
E.g Pair bonding and monomorphism in owl monkeys, gibbons
-Polygyny and dimorphism in Hamadrayas baboons
What are the behavioural consequences due to parental investment?
- Females should be choosey as they have much more to lose by mating with the wrong males.
Female reproductive potential is lower than a male’s which has led to female choice.
- Males have less to lose with each fertilisation so they are selected to seek out as many fertilisation’s as possible which has led to male-male competition.
Triver’s predicted “where on sex invests considerably more than the other, members of the latter will compete among themselves to mate with members of the former.”
Give an overview of paternal investment
-Generally associated with lower offspring mortality because of protection from predators and con-specifics. Males provide resource provisioning like food.
This results in healthier adults being able to compete for mates and produce larger, healthier offspring themselves.
Paternal investment is uncommon in mammals (5%) but found in species of birds, fish and insects.
Paternal investment varies with benefits to offspring, paternity certainty, availability of other mates.
Should we expect infidelity from human males? Are males programmed to cheat?
“infidelity… whether in humans or animals, is a topic of great interest to those wanting to understand whether animals show us our own biologically based behaviours” Zuk, 2009: 12
- Males may want to seek out additional mates
- As may females
- Remember, every behaviour has both a biological and environmental component.
1) Be wary of the naturalistic fallacy (just because warblers, robins and other “models of monogamy” have extra-pair matings, doesn’t mean it is natural and we should do it)
2) Multiple matings by both sexes are quite common in many species - (even supposedly monogamous ones) If such behaviour solves a specific biological/ ecological ‘problem’
What are the types of female competition?
Direct aggression to pregnant females (seen in yellow baboons) and to cycling females to prevent mating.
Pheremones can suppress reproductive ability of subordinates (seen in cotton-top tamarins)
Indirect by being more attractive to males. This is due to the evolution of conspicuous signals like sexual swelling.
What are the 3 main reasons male and female reproductive strategies and behaviour are typically so different?
- Different levels of parental investment
- Different variance in reproductive success - lower potential reproductive output for females.
- Different limiting factors
What are the variations in reproductive success among female primates?
- Females have similar number of babies.
- They typically have X number of offspring where X = reproductive lifespan divided by inter-birth interval.
- Not much difference between least and most successful females compared to males.
