11. parental care

reproductive behavior and the mating systems that result only matter if…

offspring survive to reproduce

how does variation in parental care across species arise?

arises from costs and benefits of care, which can differ by sex of the parent

what can cause parent-offspring conflict?

the limited amount of energy a parent can allocate to an indiv offspring

3 costs of providing energy in the form of parental care

1. less energy to produce or care for additional young

2. missed opportunity to attract additional mates

3. care directed at non-genetic young

2 hypothesis to explain how offspring signal to parents or other caregivers

1. the signal of need hypothesis

2. the signal of quality hypothesis

signal of need hypothesis + env

signals that advertise an offspring’s level of need in order to maximize their chance of being fed by their parents

species in envs where resources are not limiting

signal of quality hypothesis + env

signals that advertise an offspring’s quality or merit in order to maximize their chance of being fed by their parents

species in envs that are resource limited

reproductive value

a measure of the potential for an indiv to leave surviving descendants in the future

nestling birds w brightly colored red mouths and how they support the signal for quality hypothesis

• red coloration is produced by carotenoid pigments in blood

• carotenoids can’t be synthesized and must come from the diet

• they contribute to immune function and may be an honest signal of quality

what does this graph show?

• color of the mouth gape affects the amt of food that nestling barn swallows (Hirunda rustica) are given by their parents

• chicks w redder mouths weighed more at 6 days of age and had longer feathers at age 12 yrs

• after experimenters colored the gapes of some nestlings w 2 drops of red food coloring, they received more food

• in contrast, nestlings that received 2 drops of yellow food coloring or water were not fed more

siblicide + example animal

when siblings kill each other, resulting in brood reduction

the great egret (Ardea alba) expresses this

parent-offspring conflict in siblicide

siblings see killing each other as a fitness enhancing activity, but parents do not

siblicide in brown boobies

• asynchronous egg laying leads to 2 different sized offspring in brown boobies

• older ejects younger; younger dies; no parental intervention

• species probably lays 2 eggs as insurance against hatch failure

• other species of booby intervene to reduce sbiling conflict

what does this graph show?

• the rate of early siblicide by Nazca booby (NB) chicks declines when they’re placed in nests w intervention-prone blue-footed booby (BFB) foster parents

• the rate of early siblicide by BFB chicks rises when they’re given NBs as foster parents

• NBs - obligate siblicide (permit siblicide)

• BFBs - facultative siblicide (intervene to prevent siblicide)

are first laid eggs of seabirds provisioned w extra androgens?

ye

facultative siblicide hypothesis

parents permit siblicidal behavior only when resource availability is low

what does this graph show?

• arrow indicates control

• 3 treatments for cattle egrets

• eggs of 3 different ages (same day, 1.5 days apart, 3 days apart)

• taken from different nests

• placed in focal nest

• members of synchronous broods fought more and had lower survivorship

• they also required more food per day

uniparental maternal care

only mothers provide care to offspring

3 reasons why parental care may fall to females in many species

• they’ve invested much more in offspring

• they may have greater incentive to make sure that their large gametic investment isn’t wasted

• they have greater (usually absolute) assurance of genetic maternity

in egg guarding invertebrates, females incur a cost for care demonstrated by removing females from egg clutches (ex: a maternal female earwig takes one week longer to produce a new clutch of eggs since they are busy guarding their initial clutch from predators). how is the cost offset?

cost is offset by increased survival of eggs to hatching

why is uniparental paternal care uncommon?

bc the costs of lost additional matings are high for males

paternal mouthbrooding has evolved in … families of fish

7

how does a male Randall’s jawfish (Opistognathus randalli) care for offspring?

holds his mate’s eggs in his mouth, limiting him to one clutch at a time

how does a male three-spined stickleback (Gasterosteus aculeatus) care for offspring?

cares for a NEST w a clutch of eggs by aerating them w water

what do these figures show?

• shows differences in cost of care btwn male and female St. Peter’s fish

• males and females can both mouth brood, and both sexes lose out if they do it (bc of missed foraging opportunities)

• but males lose less — 7 day vs. 11 day inter-spawn interval

• therefore male parental care should be favored

how are amphibians (like male hellbenders) certain of paternity?

they fertilize eggs externally, circumventing sperm storage by females

exclusive paternal care is relatively common in … and it may be an outgrowth of… + what trait of theirs may contribute to paternal care?

dart-poison frogs

territorial defense by males

they are terrestrial and breed on land. they have external fertilization — assured paternity

what does this figure show?

• test of the importance of paternity assurance in paternal care

• rxns of nest-defending bluegill males to potential egg and fry predators under 2 conditions

• experimental male had been exposed to clear containers holding smaller male bluegills, mimicking the presence of rivals that might fertilize some of the eggs in the defender’s nests

• thus, altering the perceived paternity of nest defender

• control males weren’t subjected to this treatment

why is the ability to recognize one’s own offspring important in species w communal nesting (bats, colonial birds, birds that deal w brood parasites)?

bc misdirected parental care is costly

what does offspring recognition do?

functions to minimize misdirected parental care

barn swallows vs. cliff swallows in offspring recognition

• cliff swallows are colonial and barn swallows are solitary

• barn swallow parents readily accept transplants, cliff swallows rarely mistakenly feed non-relatives

what does this figure show?

• chicks of cliff swallows, a colonial species, produce highly structured and distinctive calls, helping their parents recognize them as individuals

• the calls of barn swallow chicks, a less colonial species, are much less structured and more similar

brood parasitism

female birds laying eggs in other birds’ nests

what does this graph show?

• the size of an experimental “brood parasite” nestling relative to its host species determines its survival chances

• larger great tit nestlings survived well when transferred to the nests of smaller blue tits, whereas blue tits did poorly in great tit nests

• red bar shows smaller “parasite” loses

• green bar shows larger “parasite” survives as well as conspecifics

what do these figures show?

• the common cuckoo chick’s begging call matches that of a brood of four baby reed warblers

• B - a single reed warbler chick

• C - a brood of four reed warblers

• D - a single cuckoo chick

origin of brood parasitism was in … it was … first in … bird species and followed by parasitizing closely related species. tactics evolved to parasitize … non-related species

cowbirds

intraspecific

200 (exact number is 216)

smaller

how many times has brood parasitism evolved?

3 times

what do blue and red branches indicate?

• blue branches indicate those lineages whose modern descendants are specialist parasites

• red branches are for 2 species that are occasional parasites