Transcript Chap.32 Evolution of Life histories

Chap.32
Evolution of Life histories
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Introduction
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Organisms have limited time, energy, and
nutrients at their disposal.
Adaptive modifications of form and function
serve two purposes in this regard.
One is to increase the resources available
to individuals.
The other is to use those resources to their
best advantage, this is in a manner that
maximizes the survival and reproduction.
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Every modification involves a trade-off.
Therefore, each individual is faced with
the problem of allocation of time and
resources.
In this chapter, we shall consider some
general rules governing the allocation of
time and resources in life strategies.
Each life history has many components,
maturity, parity, fecundity, and
termination of life.
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Evolution of life histories
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32.1 Interest in life history adaptations has
been stimulated by their variation among
species.
32.2 Life history theory developed rapidly
during the 1960s.
32.3 Natural selection adjusts the allocation of
limited time and resources among competing
demands.
32.4 Age at first reproduction generally
increases in direct relation to adult life span.
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32.5 Perennial life histories are favored
by high and relatively constant adult
survival.
32.6 Optimal reproductive effort varies
inversely with adult survival.
32.7 When survival and fecundity vary
with age, models of life history evolution
must be based on the life table.
32.8 Bet hedging minimizes reproductive
failure in an unpredictable environment.
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32.9 Extensive preparation for breeding
and uncertain or ephemeral
environmental conditions may favor a
single, all-consuming reproductive
episode.
32.10 Senescence evolves because of the
reduced strength of selection in old age.
32.11 Life history patterns vary according
to the growth rate of the population.
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32.1 Interest in life history adaptations
has been stimulated by their variation
among species.
 Fig. 32-1
Relationship
between annual
fecundity and
adult mortality
in several
populations of
birds.
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Table 32-1 Life history traits of several
populations of the fence lizard
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Clutch size (平均值)： 6.2 - 11.8
Clutches per year： 1 - 4
Eggs weight (g) ： 0.22 - 0.42
Relative clutch mass：0.21 - 0.28
Age at maturity (月)：12, 21, 23
Survival to breeding ： 0.03 - 0.11
Annual adult survival ： 0.11 - 0.49
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Varied life histories may be found even among
different populations of the same species, as
illustrated by fence lizards (Table 32-1).
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Table 32-2 Typical life histories of plants
in environments with different selective
factors.
 Competitors (競爭型)
 Ruderals (荒地型)
 Stress tolerators (耐壓型)
 於不同的環境狀況下，各有不同適應的
策略。
 兩類影響因素：disturbance 和 stress
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Life history variation
in plants
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32.2 Life history theory developed
rapidly during the 1960s.
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Fisher (1930) The genetical theory of
Natural selection
Lack (1940s)suggested that because of
the longer day length at higher latitudes
in the season when offspring are reared,
birds living at temperate and arctic
latitudes could gather more food, and
therefore rear more offspring, than birds
breeding in the Tropics, where day length
remains close to 12 hours year-round.
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Lack 的觀點
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Lack made three important points.
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(1) he related life history traits to
reproductive success and thus to
evolutionary fitness.
(2) he demonstrated that life histories vary
consistently with respect to factors in the
environment.
(3) he proposed a hypothesis that could be
subjected to experimentation.
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during the 1960s.
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The early 1960s marked a turning point
in population studies and saw the birth
of modern evolutionary ecology.
Life history study burst in 1966 with the
publication of papers by Martin Cody
and George C. Williams.
K-selected and r-selected traits
Hamilton (1966) , Gadgil and Rossert
(1970), Schaffer (1974)….
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32.3 Natural selection adjusts the allocation
of limited time and resources among
competing demands.  Fig. 32-2 Proportional
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distribution of dry
weight among
different plant parts
of the groundsel
during its life cycle.
The development of
reproductive parts ar
the expense of leaves
and roots toward the
end of the growing
season.
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Allocation of limited time and resources
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Fig.32-2 Proportional distribution of dry
weight among different plant parts of the
goundsel, Senecio vulgaris, during its life
cycle.
於開花結果過程，是 at the expense of
leaves and roots. (葉子和根的部份縮小)。
這就是 trade-offs
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歐洲鵲，每窩
產7個蛋。
運用人為的方
法，添加蛋數
或減少蛋數。
再看其蘊育成
功子代的數量。
最成功的是原
來的每窩7個
蛋。
Fig. 32-3 Number of chicks fledged from nests of
European magpies in which seven eggs were laid, but
manipulated clutches of between
five and nine eggs.
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Fig. 32-4 clutch size and young surviving
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大山雀，英國，1960-1982年間。
統計4,489鳥窩的蛋數。
灰色的是clutch size的frequencies
淡紅色是 每窩存活的young之數目，至
少存活至下一個季節。
存活數最高的，並不是 the most
common clutch size.
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Fig. 32-4 The frequencies of clutch sizes (gray bars) of
the great tit between 1960 and 1982, and the number of
young per clutch surviving at least to the next season
(green bars) as a function of clutch size.
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Fig. 32-5 Decrease in the rate of larval survival
to emergence with increasing numbers of larvae
deposited per bean in the bruchid beetle.
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Fig. 32-6 female guppies(孔雀魚)
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於3種不同食物供應量下，生殖、脂肪和
身體的能量分配情況。
分成兩組，一組是有與雄的接觸(R)，另
一組是沒有與雄的接觸(N)。
與雄的接觸，增加生殖的投入，但並沒
有因而減少脂肪和身體的能量投入。
這裡並沒有發現是trade-offs的現象。
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Fig. 32-6 Content of
energy in somatic
tissues, fat deposits,
and reproductive
tissues (including
eggs) in female
guppies raised at
three food levels and
which were either
permitted to be (R),
or prevented from
being(N), courted
and inseminated by
males.
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Evolution of life histories
Three questions:
 (1) When should an individual begin to
produce offspring? (成熟年齡)
 (2) How often should it breed? (多少次數)
 (3) How many offspring should it attempt to
produce in each breeding episode?
(每次生多少個)
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32.4 Age at first reproduction generally
increases in direct relation to adult life span.
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Fig. 32-7
Relationship
between age
at maturity
and annual
adult survival
rate, which is
directly
proportional to
life span, in a
variety of
birds.
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Age at first reproduction
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Figure 32-3 age at maturity and adult
survival rate 的關係。
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壽命較長的生物，成熟的年齡通常是較晚。
Why should this be so?
Table 11.3 假設每年可生10個蛋，但若
延後一年才生，則可生20個蛋，延後到
第三年才生，則一年可生30個蛋。
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如此可看出其壽命長短，對何時開始生殖的
影響。
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若壽命只有5歲，那第3年開始生殖，所得的子代
數最高。但壽命若有8歲，那第4或第5年才開始，
才可有最多的子代數。
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32.5 Perennial life histories are
favored by high and relatively
constant adult survival.
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Plants and animals either reproduce
during a single season and die (annual
reproduction), or have the potential to
reproduce over a span of many seasons
(perennial reproduction).
A theoretical comparison of annual and
perennial reproduction
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A theoretical comparison of annual
and perennial reproduction
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Annual plant 的種子產量(Ba) x their
survival to reproductive age (S0)
a = BaS0
perennial plant 還要多加一項，個體存活下
去的機率(S)
p = BpS0 + S
Ba - Bp > S / S0
，如此就會保持在
annual reproduction
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32.6 Optimal reproductive effort
varies inversely with adult survival.
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the balance between fecundity and
survival
 = BS0 + S SR
SR 是與生殖相關的survival
d = S0 dB + S dSR
B的增加，牽動使SR 減少
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Table 32-4 slow growth/high fecundity
and rapid growth/low fecundity的比較
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假設兩種魚，都是在體重10克時性成熟。
但是其中一種是運用較多能量在持續的成
長，另一種則用較多用於生殖上。
Fish A allocates 20% to growth, 80% to
eggs. Fish B allocates half to growth and
half to eggs.
發現於壽命4年的，high fecundity較有利。
多於4 年的，low fecundity 較有利。
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Each weighing 10 grams at sexual maturity, but
which allocate resources to growth and
reproduction differently.
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32.7 When survival and fecundity vary with
age, models of life history evolution must be
based on the life table.
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32.8 Bet hedging minimizes reproductive
failure in an unpredictable environment.
 As a general rule, selection shifts
allocation away from stages of the life
cycle with the greatest uncertainty.
 This strategy is sometimes referred to
as bet hedging. (賭預防)
 Fig. 32-8 mosquitofish ( 大肚魚)
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於變動大的水域，或是在穩定的水域
生殖投資量不同。
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Fig. 32-8 Life history characteristics of populations of
mosquitofish introduced into reservoirs in Hawaii
indicate greater total reproductive investment.
Reproductive allocation is the proportion of the dry mass
constituting embryos.
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32.9 Extensive preparation for breeding and uncertain
or ephemeral environmental conditions may favor a
single, all-consuming reproductive episode.
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Semelparity，如鮭魚，big-bang reproduction，
一生只生一次。一生可生多次，則稱 iteroparity
the occurrence of semelparity or iteroparity
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(1) variable environments might favor iteroparity.
但事實上，semelparity 通常發生在更variable
(usually drier) 的環境。
(2) variable environments might favor semelparity.
(3) 集體開花更可以吸引pollinators，有利於
semelparity.
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Fig. 32-9 Kaibab agave in the Grand
cayon.
An plant grows as a rosette of thick,
fleshy leaves (a) for up to 15 years.
Then it rapidly sends up its flowering
stalk (b) and sets fruit, after which the
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Table 32-6 兩種植物的 life histories
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Semelparity is associated with dry habitats
that are highly variable in both space and
time.
In summary, semelparity appears to arise
either when preparation for reproduction is
extremely as in the undertaking of long
migration to breeding grounds, or when the
payoff for reproduction is highly variable
and predictable.
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It suggests that semelparity is associated with
dry habitats that are highly variable in both
space and time.
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32.10 Senescence evolves because of the
reduced strength of selection in old age.
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The rates of most physiological functions
in humans decrease in a roughly linear
fashion between the age 30 and 85 years,
by 15-20% for nerve conduction and
basal metabolism, 55-60% for volume of
blood circulated through the kidneys, and
63% for maximum breathing capacity.
Birth defect發生的機率，隨婦女的年齡而
增加(Fig. 32-10)
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Fig. 32-10 In humans,
the risk of abnormal
numbers of
chromosomes in
offspring increase
with the mother's
age.
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How can senescence evolve?
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Senescence may reflect the accumulation of
molecular defects that fail to be repaired.
(mutation-accumulation theory of senescence)
selection 的作用：倘若基本死亡率高，那
selection 將應會使其老化慢。但事實上，卻剛
好相反(Fig. 32-11)
antagonistic pleiotropy. 有些基因於年幼時是可
增加fitness，但於年老時反而是減少其fitness。
(Table 32-7)
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Fig. 32-11 species of birds and mammals with a
high baseline mortality rate appear to have a
high rate of aging as well.
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Selection for later egg laying also increased
longevity
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disposable-soma theory of
senescence
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Kirwood and Rose (1991) suggested that
the most important trade-off involved in
senescence is between allocating energy
to the repair and maintenance of germ cell
DNA and somatic DNA).
This idea, known as the disposable-soma
theory of senescence.
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32.11 Life history patterns vary according
to the growth rate of the population.
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Eric Pianka (1970) listed a variety of traits that
could be considered either r-selected or Kselected (Table 32-8).
The concept of r- and K-selection has been
useful in helping to formalize the definition of
fitness in density-regulated populations, but
attempts to transfer the concept to actual
populations without regard to the realities of
the complexities in life history have probably
been detrimental rather than helpful.
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Suggested readings
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Bazzaz, F. A., N. R. Chiarello, P. D. Coley, and L. F.
Pitelka (1987) Allocating resources to reproduction
and defense. BioScience 37:58-67.
Fleming, I. A. and M. R. Gross (1989) Evolution of
adult female life history and morphology in a
Pacific salmon (Coho: Oncorhynchus kisutch).
Evolution 43:141-157.
Gross, M. R. (1996) Alternative reproductive
strategies and tactics: Diversity within sexes.
Trends in Ecology and Evolution 11:92-98.
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Janzen, D. H. (1976) Why bamboos wait so long to
flower. Annual Review of Ecology and Systematics
7:347-391.
Reznick, D.N. (1985) Costs of reproduction: An
evaluation of the empirical evidence. Oikos 44:257267.
Reznick, D.N., H. Bryga, and J. A. Endler (1990)
Experimentally induced life-history evolution in a
natural population. Nature 346:357-359.
Schlichting, D. C. (1989) Phenotypic integration and
environmental change. BioScience 39:460-464.
Strathmann, R. R. (1990) Why life histories evolve
differetly in the sea. American zoologist 30:197-207.
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