Family Life Flashcards
Parental care in different taxa
- Broad range from no parental involvement to heavy involvement
- Depends largely on physiology and environmental factors
- E.g. in mammals, prolonged internal gestation and lactation require female care
- In fish, parental care often involves just guarding or fanning eggs, tasks that can usually be done by one parent. The predominance of male-only care is related to the fact hat male fish externally fertilize
How much care should a parent devote?
- What is the optimal investment per offspring?
- Trade-offs between:
1) Offspring quantity and quality within a brood
2) Investment in current vs. future broods - There is a theoretical optimal investment per offspring from the parent’s point of view
Trade-offs in parental care: side-blotched lizards
- Females have extra mass of eggs to carry and giant abdomens that make it hard to walk
- Miles et al. surgically removed 1/2 of the eggs from some females
- They could then walk more easily and were more likely to survive to produce another clutch
- Increased investment in offspring reduces female survival
- Trade-off in this case is between increased reproductive effort and greater exposure to predators
- Increased reproductive effort reduces breeder’s survival
Trade-offs in parental care: burying beetles
- When given larger broods to care for as their first brood, beetles subsequently produced fewer larvae in future broods
- Opposite for smaller broods as first brood
- Increased investment in offspring reduces an adult’s future fecundity
Do parents vary their care in relation to costs and benefits?
- Some species can adjust their parental care in a current brood relative to prospects of future reproduction
-In nectar-feeding bird from New Zealand:
- Chicks have bright red mouths when they beg for food, and the red mouth signal inspires parents to feed
-Researchers provided sugar feeders with extra carotenoids:
- Chick mouths redder –> enhanced begging display –> parents brought more food to offspring
- Respond to increased begging by providing more
- Chick mouths redder –> enhanced begging display –> kept provisioning constant and produced a second brood
- Respond to increased begging by doing nothing –> leaves resources for a second brood
Flexible care in St. Peter’s Fish
-Parental care by either sex alone or both parents
-Mouth brooding
- Monogamous pairs dig holes together and lay eggs. After fertilization, one parent puts the eggs in their mouth to incubate/hatch
- Which parent does the care? Why do they both care sometimes?
-Evidence:
- Different numbers of females and males together in tanks, observed which sex ultimately did the parental care
- When the population is biased towards females, males desert more
- When biased towards males, females desert more
- Both sexes desert more frequently when the cost (of missing out on future mating opportunities) is higher
Filial cannibalism
- Rowher: suggested filial cannibalism might be adaptive for a parent
- Males alternate between a 2-3 day mating phase (gold in color, display), and 4-5 day parental phase (lose color, stop displaying, guard eggs)
Conflict over who should care
- A key issue parents face: stay or care, or desert
- Some factors (like lactation in mammals) dictate costs and benefits of these two options
- BUT, one factor we haven’t discussed yet is the behavior of the other parent
- If the females care, it may pay the male to desert, but if the female deserts, it may pay the male to care
John Maynard Smith: model based on game theory
- Assume: each parent decides independently whether to stay or desert
- A pair of strategies exist (one for male and one for female)
- It pays a male to diverge from some strategy depending on what the female does, but not otherwise, same for the female
- P0, P1, and P2 are the probabilities of egg survival when eggs are (0) not cared for, (1) cared for by one parent, and (2) cared for by two parents
- A male who deserts has a chance p of mating again
- A female who deserts lays W eggs, and who cares lays w eggs (W>w)
What’s missing from parental care prediction model?
ssumption is that parents act independently, but they don’t. They know what the other one is doing
Conflict over how much care
- When only one parent provides care, they need to provide 100% of care
- But, when two parents provide care: conflict. Why?
- Many experiments in species where both parents provide care have removed one parent, and shown the other increases its rate of provisioning to compensate
- Thus, each parent has the potential to work harder than it is working in a pair
- Parents must come to an agreement over how hard each should work. What’s the problem here?
- Cheating: a parent may be tempted to do less than its fair share of work, because its partner can compensate by working harder
Another ‘game’: how much care
- Each partner independently ‘plays’ some fixed effort - the optimal effort for each parent is resolved over evolutionary time
- An ESS exists where each parent invests a fixed level of effort that maximizes its own fitness, given the effort its mate is putting in
- Consider a pair. For the male, there is a best response (in terms of parental effort to vie), for a given effort by the female. Likewise for the female.
Incomplete compensation is key:
- The key theoretical prediction: when biparental care exists, parents should compensate for their partner, but not fully
- In some experiments, these predictions are supported
- In starlings, the effort of one partner has been experimentally reduced by various means (including clipping feathers, adding weights)
- The means response of the other partner is to increase its effort, but only to partially compensate… and males and females respond differently
Triver’s theory of parent-offspring conflict
Sibling rivalry drives parent-offspring conflict
- Siblings compete for parental resources, often because of unpredictable food resources
- It pays mothers to produce an optimistic brood size in the hopes that conditions will be good
- But, if conditions are bad, sibling competition will ultimately reduce the brood size
Facultative siblicide
- Galapagos fur seals: females have one pup at a time
- In good years, a mother can wean her pup at 18 months
- In poor conditions, put grow slowly and nurse up to 3 years
- Thus, 23% of pups per year are born while the older sibling is still being nursed –> pups have to compete
- Usually, the younger pup dies within a month
Obligate siblicide
- In some birds of prey, pelicans, and boobies, the mother lays two eggs but the older sibling (the one that hatches first) ALWAYS kills the younger sibling
Why lay two eggs at all?
- The second egg is an ‘insurance egg’ in case the first egg fails to hatch
- The second egg often produces a surviving offspring if the first egg fails
Sibling relatedness influences rivalry
- Offspring demand should depend not only on benefits, but also on costs incurred (genetically) from depriving siblings of resources
- More distantly related siblings, lower cost of depriving them
- In theory, when siblings are less genetically related, each offspring’s demand for resources should increase
