Download Predicting family dynamics in social vertebrates

Predicting family dynamics in
social vertebrates
鄭先祐
靜宜大學 生態學系
Family dynamics in social vertebrates
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10.1 The changing scope of cooperative breeding
research
10.2 Ecological constraints and the formation of
family groups
10.3 Kinship and the tendency to cooperate
10.4 Conflicts with changing family composition
10.5 Conflict over who reproduces
10.6 The myth of the stable family?
10.7 Toward a unified evolutionary social theory
Appendix Evolutionary predictions of living within
family kin groups
Family dynamics
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Family definition (家庭的定義)
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The definition of families is where offspring
continue to interact, into adulthood, with their
parents.
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Simple family, only a single and female group members
breed, while
Extended families, two or more group members of one
ore both sexes reproduce.
The presence of a breeding male is not essential to the
definition of a family. (biparental, matrilineal母系的)
Intact families, the original breeders are still the
reproductives, and
Replacement (or step-) families, a breeder has been
replaced.
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10.1 The changing scope of cooperative
breeding research
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合作養育的行為 occur in roughly 3% of bird and
mammal species. 倘若野外研究愈多，這個比率可以
再加倍。
於1978年的問題，
1.
2.
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Did ‘helpers’ really contribute significant assistance to
the breeders that they attended?
If they did, 這樣的行為是如何演化出來的？
於1984年的問題，
1.
2.
The most common form of group found was that of
grown offspring helping their parents to rear younger
siblings.
Why did offspring remain with their parents?
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第一個問題，可用 ecological constraints 解釋。
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Offspring stayed home when opportunities for
successful dispersal and independent breeding
were ‘constrained’.
第二個問題，it turned out that helpers
themselves benefited in several additive
ways by their helping actions.
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They increased their own probability of becoming
breeders in the future.
They increased their inclusive fitness by helping
to rear close genetic relatives.
Family dynamics
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The early 1980s,
reproductive skew theory
In the cooperative societies genetic
conflicts of interest are inevitable.
 Competition will exist between group
members over who breeds and who does
not.
 A general theory of such conflict and its
resolution, now termed reproductive skew
theory.
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Family dynamics
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By 1991
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The original paradox of cooperative
breeding largely disappeared with the
widespread confirmation that
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Helpers frequently do improve their chances of
becoming breeders by staying at home and
helping temporarily
They frequently do obtain large indirect
genetic benefits by helping to rear collateral
kin (Emlen, 1991)
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目前的研究
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The vast majority of birds and mammals that
exhibit cooperative breeding do live in
multigenerational family groups.
Families provide an excellent arena for developing
and testing evolutionary social theory.
By focusing on families one seeks similarities,
rather than differences, among cooperative species.
Focusing on the family structure of many animal
societies highlights parallels with the early social
organization of our own species.
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10.2 Ecological constraints and the
formation of family groups
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In most organisms, young disperse from
their area of birth well before or at least
by the age of sexual maturity.
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If offspring and parent come into contact later
in life, they show no signs of recognition or
preferential interaction with one another.
於multigenerational families, offspring
remain in association with their parent(s)
beyond the age of sexual maturity and,
commonly, throughout their lifetimes.
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The key to understanding the evolution of
families is understanding delayed dispersal.
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Why should a growing offspring
postpone its dispersal?
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Most mature birds or mammals that
remain in their natal group do not
reproduce; their breeding is suppressed
by their more dominant parents.
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This is an automatic cost to saying home
Some researchers have emphasized the
importance of the constraints on leaving;
others the benefits of staying home.
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There are very few ‘vacancies’ for dispersing
individuals, or that the vacancies are of poor
quality.
Family dynamics
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Economic model of family formation
1. Delayed breeding occurs when the production of
mature offspring exceeds the availability of
acceptable opportunities for their independent
reproduction
2. Under such circumstances, some offspring must
postpone personal reproduction until acceptable
breeding opportunities arise and they are able
to successfully compete to obtain them
3. Families will form when such waiting is best
done at home.
Family dynamics
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Acorn woodpeckers, Melanerpes formicivorus
Live in groups of two to 12 individuals and
typically occupy permanent, year-round
territories in the American Southwest.
 High-quality territories are in short supply,
and most offspring become reproductives
by weiting for an established breeder on
an existing territory to die, and then
successfully competing to fill the breeding
vacancy. (Fig. 10.1)
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Family dynamics
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Fig. 10.1 (a) Ecological constraints and family formation in acorn
woodpeckers (a) the proportion of yearlings that remain at home,
plotted as a function of the severity of territorial shortages.
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Fig. 10.1 (b) the likelihood that yearlings stay at home,
plotted as a function of the quality of their natal
territories.
Family dynamics
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Superb fairy wren(鷦鷯), Malurus cyaneus
Live in southeastern Australia in families
consisting predominantly of parents and
grown sons.
 Shortages of both territories and mats
(females) have been suggested as
possible constraints to independent
breeding.
 By removing breeding males from nearby
territories they created breeding vacancies,
Thirty-one of 33 mature sons left home to
fill the newly created breeding vacancies.
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Family dynamics
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The Seychelles warbler, Acrocephalus sechellensis
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Is a formerly endangered species whose range is
restricted to a few small islands north of
Madagascar.
In 1960, when the population consisted of just 26
individuals, habitat restoration programmes were
implemented.
Over the following 30 years, the population grew
impressively.
No family groups were reported until 1973,
roughly the time at which all suitable breeding
habitat became occupied (Fig. 10.2a)
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Fig. 10.2 Ecological constraints and family formation in Seychelles
warblers (a) the number of individuals and occupied territories on
Cousin island between 1959 and 1990.
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Fig. 10.2 (b) the likelihood that yearlings stay at home, plotted as as
function of the quality of their natal territories.
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10.3 Kinship and the tendency to cooperate
Families are fundamentally different form
other forms of social groupings because
they form by the retention of grown young
with their parents.
 Families are comprised primarily of close
genetic relatives.
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Inclusive fitness theory
Kin selection has long been hypothesized
to be a selective factor favouring the
evolution of cooperative breeding.
Family dynamics
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合作養育 和
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multigenerational family group
There 112 species of birds and 63 species
of mammals (excluding primates) reported
to live in multigenerational family groups.
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Of these, fully 96% of the birds and 90% of the
mammals exhibit cooperative breeding.
Fully 88% of the birds and 95% of the
mammals that breed cooperatively live in
multigenerational family groups (Emlen, 1995)
絕大多數，都是有明顯的kin favouritism
已知只有一種例外，Maxican jay, Aphelocoma
ultramarina, (Brown and Brown, 1990)
Family dynamics
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White-fronted bee-eaters (birds)
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Live in extended family groups in which up to four
pairs may breed simultaneously.
Helpers are non-breeding individuals that join one
of the active nests and aid in incubation as well as
nestling and fledgling care.
Only 50% of the non-breeders become helpers;
the rest sit out the season as non-participants.
Kinship proved to be a strong predictor (Fig. 10.3)
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They preferentially help the breeding pair to whom they
are most closely related (94% of 115 cases)
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Fig. 10.3 Data are
presented as
dyadic
comparisons of
nest choices
plotted according
to the helper’s
relatedness to the
recipient
nestlings.
親緣相關係數
Family dynamics
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Incest avoidance
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Incestuous matings between close kin have
deleterious genetic consequences in most
normally outbreed species.
因此於Family group, 應該有 inbreeding avoidance
mechanisms.
Family dwelling species provide an excellent
testing ground for incest avoidance predictions
because mature offspring remain in close social
contact with their parents and siblings throughout
subsequent reproductive episodes.
Incestuous matings within families are statistically
rare.
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但是 incest avoidance is not universal among vertebrates.
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10.4 conflicts with changing family
composition
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The death, divorce or departure of a
breeding parent, and its replacement from
outside the group, will alter the basic
genetic and dominance structure of the
family unit.
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As a result, 家庭組成改變 (replacement families)，
情況將會不同。
A replacement mate will typically be
unrelated to extant family member. 如此就
沒有 incest restrictions.
 Son could mate with its stepmother,
daughter could mate with its stepfather.
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Family dynamics
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Stripe-backed wrens, Camphylorhynchus nuchalis
Live in nuclear families of two to seven
individuals in the savannas of Venezuela.
 Piper and Slater (1993) contrasted the
behaviour of sons in intact versus
replacement families.
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Sons displayed no sexual interest in their
mothers, but they frequently engaged in
courtship activities with their stepmothers.
When sons attempted to consort sexually with
their stepmothers, fathers upped their mateguarding behaviours and became increasingly
aggressive toward their sons. (Fig. 10.4)
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Fig. 10.4 Differences in sexually related behaviours within intact
(open bars) and replacement (shaded bars) families of stripe-backed
wrens.
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White-fronted bee-eaters
extended family
 Male offspring pair with unrelated females
but bring their mates home to breed
within their natal family groups.
 Sons show no sexual interest in their
mothers but brothers do attempt sexual
activity with their sisters-in-law and
fathers occasionally copulate with their
daughters-in-law.
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Infanticide
Replacement mates are not expected to
invest substantially in dependent young
remaining from previous breedings
because they are genetically unrelated to
such offspring.
 倘若照顧這些小孩的代價過高，infanticide 的
情況就有可能發生。
 This point has been repeatedly confirmed
in studies of family-dwelling rodents,
carnivores and primates, as well as in
many species of birds.
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Replacement families
Offspring in replacement families also
suffer a reduction in the indirect fitness
benefit.
 The offspring will share only 25% of their
genes with future half-siblings, in contrast
to the 50% shared with full-siblings.
 因此，percentage of helper 應該會下降。
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Florida scrub jay and Seychelles warbler (Fig.
10.5)
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Fig. 10.5 The likelihood that non-breeding family members will
serve as helpers, plotted as a function of family type. (a) Florida
scrub jay
Family dynamics
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Fig. 10.5 The likelihood that non0breeding family members will
serve as helpers, plotted as a function of family type. (b) Seychelles
warbler
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Replacement families
Red-cockaded woodpeckers and stripebacked wrens, in contrast, did not alter
their feeding rates when provisioning fullversus half-siblings.
 Replacement families are predicted to be
less stable than intact biological families.
 Instability, in terms of increased dispersal
tendencies of mature offspring or in terms
of increased separation rates of re-paired
breeders.
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Fig. 10.6 Generalized genealogical diagrams of two forms of
replacement family (a) A stepfamily formed from a formerly intact
nuclear family when, following the death of the original breeding
female the male parent takes a new mate and reproduce again.
(b) A ‘blended’ family in which two formerly nuclear families, each
with offspring, join when the widowed male parent from one pairs
with the widowed female of the other.
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10.5 Conflict over who reproduces
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The dominant pair monopolizes breeding
Subordinates would often increase their
fitness if they could become reproductive
themselves.
They are two ways a subordinate may
become a breeder within its natal group.
1. It can simply replace the dominant breeder
2. It can share reproduction alongside the
dominant
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10.5 Conflict over who reproduces
10.5.1 The benefit of group-living
 10.5.2 The probable success of attempted
independent reproduction
 10.5.3 kinship
 10.5.4 social dominance and fighting
ability
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Family dynamics
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10.5.1 the benefit of group-living
This provides the adaptive explanation for
why dominant individuals share breeding
at all.
 The greater the magnitude of the groupliving benefit realized by the dominant,
the greater the potential leverage wielded
by the subordinate.
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10.5.2 The probable success of
attempted independent reproduction
Consider the case where the chance of
successful independent reproduction is
near zero
 In such instances, parents have extreme
leverage because an offspring has little
option but to remain at home.
 The situation changes when opportunities
for independent reproduction improve.
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Family dynamics
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10.5.3 kinship
Genetic relatedness between group
members is the third critical parameter.
 A dominant breeder 會與其近親分享
breeding?
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No.
通常是基因型差異較大的，才需要分享。
This prediction has been confirmed in
numerous species.
Family dynamics
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Kinship consideration also predict that
reproduction will be shared more equitably
in sibling-sibling associations than in
parent-offspring groupings.
 Reproductive sharing generally will not be
favoured between mothers and daughters
(or fathers and sons).
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Family dynamics
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10.5.4 social dominance and fighting
ability
Dominance hierarchies exist in most
vertebrate families.
 Dominant individuals are always at risk of
losing their top position.
 The costs of challenges can be high for
both participants.
 When the risk is sufficiently great, it will
become advantageous for the dominant to
share reproduction as a ‘peace incentive’
with its potential challenger.
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Family dynamics
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10.6 the myth of the stable family?
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Family structure is dynamic.
Predictable changes should occur:
1.
2.
3.
4.
As the benefits of large group size wane;
As ecological opportunities for independent
breeding increase or decrease;
As breeder deaths and replacements, as well as
immigrations alter family composition;
As the social dominance of individual changes
with age and experience.
Family dynamics
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10.7 toward a unified evolutionary social
theory
The building blocks of a unified science, as
described in this chapter, consist of
ecological constraints theory, kin-selection
theory, social dominance theory and
reproductive skew theory.
 Cooperatively breeding species have
played, and will continue to play, a pivotal
(樞軸的) role in the development of
evolutionary social theory.
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Family dynamics
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Appendix Evolutionary predictions of
living within family kin groups
1. Family groupings will be inherently unstable.
2. Families that control high-quality resources will
be more stable than those with lower quality
resources.
3. Assistance in rearing offspring will be more
prevalent in family groups than in otherwise
comparable groups comprised of non-relatives.
4. Assistance in rearing offspring will be expressed
to the greatest extent between those family
members that are the closest genetic relatives.
5. Sexually-related aggression will be less prevalent
in family groups than in otherwise comparable
groups comprised of non-relatives.
Family dynamics
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6. Breeding males will invest less in offspring as
their certainty of paternity decreases.
7. The loss of a breeder will result in family conflict
over the filling of the resulting reproductive
vacancy.
8. Sexually-related aggression will increase after
the re-pairing of a parent.
9. Replacement breeders (step-parents) will invest
less in existing offspring then will biological
parents.
10.Non-reproductive family members will reduce
their investment in future offspring following the
replacement of a closely related breeder by a
more distantly or unrelated individual.
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11.Replacement families will be inherently less
stable than biologically intact families.
12.Reproduction within a family will become
increasingly shared as the severity of ecological
constraints decreases.
13.Reproduction within a family will become
increasingly shared as asymmetry in social
dominance between potential cobreeders
decreases.
14.Reproduction within a family will be shared more
equitably when the potential cobreeders consist
of siblings than when they consist of parent and
grown offspring.
15.Reproduction will be shared most with those
family members to whom the dominant breeders
are least closely related.
Family dynamics
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Family dynamics
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