IB Exam 3

Parental Care - Costs

• time

• energy

• vunerable to predation

Bigger gametes

increases zygote size and survival

more gametes

increases potential number of offspring

variance in reproductive success

usually greater for males than females (especially in polygynous species)

• time spent caring for offspring = less mating opportunities

• potential reproductive rate is greater for males than females

how much investment should parents make on current offpsring

Increased investment:

• increased probability of young surviving

• increased fitness for parents

time, energy, risks spent by parent on current offspring influences possibility of having future offspring

Life history traits:

characteristics of an individual that influences survival and reproduction

• age at maturity

• number of offspring

• interoparous (reproduce multiple times) or semelparous (reproduce once)

mouse: mature at 2 months and have 5-8 babies every month

african elephant: matures at 11-20 years, has 1 baby every 3-8 years.

Atlantic salmon: matures at 3-6 years and has 1,500 to 8,00 eggs at once

potential tradeoff

more energy invested now, less energy available for future reproductive efforts

• increased parental investment can affect survival of adults (potentially decreasing fitness)

• each increment of parental care is subject to selection

operational sex ratio

ratio of sexually receptive males to receptive females

• females limited by number of eggs, gestation, so ratio often male biased

male biased parental care

bi parental care is common (particularly in birds)

• in some species, males provide more care than females

  • greater rhea (ostrich), seahorse, african cichlids

• giant water bugs: the eggs need to exchange gases which is easier out of water,

  • males carry the eggs on their backs

  • males moisten eggs laid out of water

caring for the right offspring

cliff swallows can recognize their own young, rough winged swallows cannot

• it is not worth making a mistake and NOT caring for your own young - causing recognition systems to not be perfect

• communal care of offsprings common in some species that live in groups

  • dwarf mongoose

sibling conflict

sibling aggression and siblicide

• occurs when resources are variable or in short supply

• offspring compete for resources - only share 50% of genes

  • masked booby: have 2 eggs, first hatched chick always kills the second chick

parent - offspring conflict

Trivers 1974

selection may act on offspring and parents differently

• some actions that increases of fitness of offspring may reduce fitness of parents

  • conflict higher w younger parents = still have high potential reproduction

  • conflict increases as offspring age = benefit/cost ratio of taking care of young decreases

parental favoritism

likely occurs when resources are variable and adults have more young than they can raise (bet hedging)

• females can invest in eggs differently - some species can even choose the sex

• young can be fed preferentially

asynchrony in hatching

can promote or reduce sibling conflict and parental favoritism

haploid/diploid organisms - controlling offspring sex

ants, bees, wasps

• fertilized egg = female; un fertilized egg = male

temperature dependent sex determination

many reptiles can do this like turts n crocs

genetic basis for mating system / parental care - THE VOLES

prairie voles: monogamous, male parental care

• the males, vasopressin and dopamine in the forebrain regulate affiliation between mates (bond formation)

• vasopressin receptor is expressed at higher levels in prairie voles (monogamous species) than in meadow voles (polygons species)

meadow voles: polygynous, no male parental care

Lim, Colleagues, and the VOLES

used a viral vector to transfer the vasopressin receptor gene from the prairie vole into the meadow voles

• with this genes change, the polygynous species became monogamous and there was more male parental care

parental care is costly and this cost ___ as parents get older and have fewer opportunities to reproduce

DEcreases

nest helpers

in some animals, juveniles help to stay for the second nestling effort

• more common among female juveniles

• both direct and indirect

  • direct: learning about maternal care, inherit resources

  • indirect: inclusive fitness by helping related offspring

inclusive fitness

direct fitness (own reproduction) + indirect fitness (relatives reproduction)

• we share more genes with our relatives than we do with population at large

• by helping relatives, we pass on those genes that we share

hamiltons rule

cooperation is favored when rB - C > 0