parental care:

Question 1

kin selection/inclusive fitness - Hamilton’s rule…

Answer 1

Relatedness x Benefit > Cost

altruism (benefits others at cost to itself) will evolve if the benefit of the behavior received by the recipient multiplied by the relatedness of the recipient to the donor is greater than the cost of the behavior to the donor

Question 2

parental care =

Answer 2

Any form of parental behavior that appears likely to increase the fitness of a parent’s offspring

= an altruistic behavior

Question 3

Parental Expenditure =

Answer 3

expenditure of parental resources on parental care of one or more offspring

Question 4

Parental Investment =

Answer 4

Any form of parental behavior that increases an individual offspring’s fitness at the cost of the parent’s ability to invest in future offspring

Question 5

Like all behaviour, parental care requires energy and time, which can then not be invested in…

Answer 5

a) other behaviours
b) other offspring now or in the future.

As a consequence, parental care has costs, and there are trade-offs between the amount of parental care provided and the number of offspring produced, and between current investment and future reproductive success

Question 6

Types of parental care before birth:

Answer 6

A. Investment in gamete production
(e.g. female katydid crickets consume spermatophores to have larger eggs with improved survival (male invests in females gametes)

B. Preparation of the natal environment
e.g. building nests, digging burrows, or defending territories = wards off predators and allows parents to leave offspring to forage

C. Care and nutrition of embryos
- e.g. placenta (mammals), incubation (birds), guarding (fish), carrying ( male seahorses)

Question 7

Types of parental care after birth:

Answer 7

A. Provisioning or protecting young
e.g. provisioning (birds), lactation (mammals)

B. Care following nutritional independence
e.g. support in conflicts (social primates), feeding (frigate birds)

Question 8

Taxonomic variation in parental care - terrestrial arthropods:

Answer 8

• parental care is relatively uncommon
• Care by females much more common than care by males (all social insect workers are female)
• Exceptions, e.g. carry young on back (scorpions, spiders) or providing food for larvae
• Social insects (e.g. ants) all show care - parental or other family members

Question 9

Taxonomic variation in parental care - fish:

Answer 9

• At least 25 % of fish demonstrate parental care
• Male care more common than female care
• e.g. of care: egg guarding, fanning with oxygenated water to aid development, oral brooding, cleaning eggs

Question 10

Taxonomic variation in parental care - Amphibians

Answer 10

• 18% salamanders and 6% frogs and toads exhibit some sort of parental care
• Care by males or females
• e.g. egg attendance and transport, tadpole attendance and transport, tadpole feeding, midwife toad

Question 11

Taxonomic variation in parental care - Reptiles

Answer 11

• parental care is uncommon - most lay eggs and leave them to hatch e.g. turtles
• Maternal more common than paternal
• Exceptions, e.g. Crocodilian parents respond to calls of hatchlings and dig them up to bring them to water

Question 12

Taxonomic variation in parental care - Birds

Answer 12

• Most species show biparental care
• e.g. of care includes provisioning of female by male prior to and during egg laying and incubation, nest building, incubation of eggs, feeding nestlings

Question 13

Taxonomic variation in parental care - Mammals

Answer 13

• All mammals provide parental care by females, with the primary behaviours being a prolonged gestation period, followed by lactation, feeding post-lactation, transport of young and protection from predation.
• Less than 5% show direct male care – male care mostly in monogamous breeders (e.g. tamarins, wolves, naked mole rats)

Question 14

Why is care by females more common than care by males?

Answer 14

Four non-exclusive hypotheses have been proposed to understand why females should be more likely to provide care than males - all play a role…

• The investment hypothesis
• The paternity uncertainty hypothesis
• The ‘order of gamete release’ hypothesis
• The association hypothesis

Question 15

The investment hypothesis:

Answer 15

• Females invest heavily in few potential offspring (big gametes); abandoning offspring without providing care is risky

Question 16

The paternity uncertainty hypothesis:

Answer 16

• Female can be 100% sure of their paternity, but males cannot be so certain
• Male does not gain from parental care if offspring not his (parental care evolves via kin selection)
• Better strategy for male to seek additional matings elsewhere

Question 17

The ‘order of gamete release’ hypothesis:

Answer 17

• Patterns of parental care result from differences in the opportunities for males and females to desert offspring.
• Internal fertilization
  Situation enables males to desert (females more likely to “hold” the fertilized eggs = forced to provide care)
• External fertilization -
  females can turn roles around and desert.
• Exceptions - males provide the care in most fish species +
  males care is common in frogs who release sperm in nest before females deposit eggs

Question 18

The association hypothesis:

Answer 18

• females more likely to be the parent present during egg laying or birth - males may not be around during this phase.

Exceptions - doesn’t make sense with external fertilization with simultaneous release of gametes - majority of care from males

Question 19

Proximate constraints on parental care - birds:

Answer 19

• Internal fertilisation; egg incubation
• Primary parental care is chick provisioning
• Food delivery rates are important in determining reproductive success
• Provisioning is a non-divisible resource (one parental unit of investment goes to one chick))
• Two parents can feed twice as many offspring
• Desertion would (at least) halve the reproductive output of either parent

Question 20

Proximate constraints on parental care - mammals:

Answer 20

• Internal fertilization, gestation and lactation means females cannot desert
• Males cannot contribute directly to offspring care (but can protect female)
• Males generally desert; further reproductive opportunities probably outweigh benefits of remaining

Question 21

Why are female fish not the primary care givers -

Answer 21

• External fertilization emancipates female from further care
• Female care will often reduce the female’s fecundity more than it would the males = In females, fitness increases exponentially with increasing body size. Not so with males (linear).
• Energy costs of parental care affect growth and egg production in females - Female has to be big enough to produce a large brood = The more energy she spends in parental care, the less time she may have to feed, reducing growth and the ability to make more eggs

Question 22

why are male fish the primary caregivers -

Answer 22

• Male parental care may lead to higher male RS - Guarding eggs often attracts even more eggs from other females
• Small size of fish eggs -> male look after a lot in a small territory
• One parent often sufficient to care for offspring - do not provision offspring, so less care needed

Question 23

evidence for the benefits of care:

Answer 23

Experimental removal of guarding males reduces egg survival in frogs and bluegill sunfish

Female vervet monkeys with care-giving mothers still present in the group - Receive less aggression from others, get defence from mother and better at manipulating others - Possibly leading to higher rates of pregnancy, and more surviving infants

Question 24

Costs of parental care:

Answer 24

• parental Investment in current offspring is costly as it reduces parent’s ability to invest in future offspring.
• Opportunity costs (lost opportunity to mate) or direct costs (direct physical costs)
• Limits to offspring / per brood (Chickens – selection for larger egg size reduces output)

Direct costs…

• Mouthbrooding by cichlids meansparent cannot eat
• Egg guarding parents often do not feed, reducing breeding success the next season and retarding growth (long-term effects)
• Incubation costs in birds may be up to 30% of Basal Metabolic Rate, feeding young may raise Basal Metabolic Rate by 4x
• Lactation in mammals can raise Basal Metabolic Rate to 5x normal levels

Question 25

Parent-Offspring Conflict:

Answer 25

• conflict over termination of care:

Parent - increase reproductive success by producing more offspring = at a certain age it is more profitable to send offspring on their way and devote efforts exclusively to another one.

Infant – maximise parental care

• Initially cost to parent is small compared to large benefit received by offspring
• Intermediate time period in which cost to mother exceeds benefit to offspring
• Eventually, cost is greater to parent and offspring benefits less (as they are more self-sufficient)