Transcript 第12章 生活史Life Histories

Life history evolution
1 Some Important Concepts
1.1 Life History
Life history – the adaptations of an organism that influence
aspects of its biology such as the number of offspring it produces,
its survival, and its size and age at reproductive maturity.
Adaptation _ A process of genetic change in a population whereby,
as a result of natural selection, the average state of a character
becomes improved with reference to a specific function, or
whereby a population is thought to have become better suited to
some features of its environment . OR a feature that has become
prevalent in a population because of selective advantage in the
improvement in some function.
The life history of a hypothetical female Virginia opossum (负鼠)
1.2 Fitness: 适应度（适合度）
Fitness— ① The relative competitive ability of a given
genotype conferred by adaptive morphological,
physiological or behavioral characters, expressed and
usually quantified as the average number of surviving
progeny of competing genotypes;
② a measure of the contribution of a given genotype
to the subsequent generation relative to that of other
genotypes.
1.3 Reproduction Value (生殖价值)
(i) Reproductive value (RV) at a given age or stage is the sum
of the current reproductive output and the residual (i.e.
future) reproductive value (RRV);
(ii) RRV combines expected future survival and expected future
fecundity （生殖力）;
(iii) RV takes account of the contribution of an individual to
future generations, relative to the contribution of others;
(iv) the life history favored by natural selection from amongst
those available in the population will be the one for which
contemporary output and RRV is highest.
Measuring Reproductive Value:
the reproductive value of an individual of age x is:
 ly
x y

RVx  m x     my  R
y  x 1  l x
y  y max

future
reproductive
output
mx – the birth rate of individual in age-class x, as
contemporary reproductive output
lx – the probability that the individual will survive to age x
R – the net reproductive rate of the whole population per unit
time (age interval).
1.4 Methodology for Life History Study
Every life history, and every habitat, is unique.
We must find ways in which life histories might be grouped,
classified and compared, so as to search for association between
one life history trait and another or between life history traits
and features of the habitats in which the life histories are found.
The idea of optimization (最优思想）: observed combinations
of life history traits are those with the highest fitness.
The idea of ‘bet-hedging’(‘两面下注’思想): when fitness
fluctuates, it may be most important to minimize the setbacks
from periods of low fitness rather than evolving to a single
optimum.
2. Three types of questions
(1) Individual life history traits: Why some birds produce
clutches of three eggs, while others produce larger clutches?
(2) Links between life history traits: Why is it that the
ratio between age at maturity and average lifespan is often
roughly constant within a group of organism but markedly
different between groups?.
(3) Links between life histories and
habitats: Why is it different in fecundity
between populations from subtropical and
temperate regions?
2.1 Life History Traits
① Individual size — Being large or small?
Increasing
competition
Decreasing survival
of a shortage of
food, or of defense
Increasing
survival
Increasing
offspring
production
Increasing success
in predation or in
defense
Large body size
???
So, an intermediate size might be optimal ?
The relationship between seed size, seedling mass, and seedling
recruitment (增员) among herbs and grasses living in seminatural grasslands in southeastern Sweden.
Seedling dry mass
Larger seeds produce large seedlings.
Seed mass（mg)
Seed mass and seedling mass among grassland plants in Sweden
On average, larger seeds were associated with a higher rate of
recruitment (增员).
Seed mass and recruitment rates in grassland plants
There is also a positive
relationship between
seed size and seedling
height among trees.
Relationship between seed mass and
seedling height among trees.
Predicted optimum size
Sampled
optimum size
Adult male damseflies (豆娘)
② Development — Being rapid or slow?
Early reproduction
Rapid
Development
Slow
Development
Early emerging from host
More storage of energy, longer
lifespan and reproduction period;
Large body size
3 Trade-offs (得失，权衡)
A ‘trade-off’ is a negative relationship between two life
history traits in which increase in one are associated
with decrease in the other as a result of a compromise.
A trade-off
Life history trait 2
Life history trait 1
3.1 How to detect trade-offs?
(1) Correlation between the means of two or more traits in
different populations or species can strongly suggest a trade-off,
although such correlations might result from other, unknown
different among the populations.
(i) Egg size and number in fish
鲈鱼科物种丰富，1个属有100多种，生活在溪流底，体色鲜
艳（尤其在繁殖季节），是理想的研究生活史特征的材料
15 darter species
Turner & Trexler(1998) sampled 64 locations on streams and rivers in US.
(ii) Seed size and number in plants
Plants vary widely in the number of offspring they
produce，ranging from those that produce many small
seeds to those that produce a few large seeds.
A small sample of the great diversity of seed sizes and shapes
在4个大科（菊科、禾本科、十字花科和豆科）植物中，
correlation between
seed mass and
number of seeds.
Number of seed per plant
The negative
Average seed mass
(2) Phenotypic (表型) or, better, genetic correlations
between traits within populations can be useful
indicator of the extent to which enhancement of one
component of fitness would be immediately
accompanied by reduction of another.
(ii) Development time and body size in parasitic wasps
The alternative
approach is to
use experimental
manipulation to
reveal a trade-off
directly from a
negative
phenotypic
correlation.
发育时间
体型
寄主龄期
死亡率
Developmental characteristics of M. pulchricornis on
different instars of S. exigua larvae.
Graphical representations
(A–C) of the three most
frequently reported
empirical relationships
(trade-offs?) between host
size (age) and egg-to-adult
development time (left
column) and adult body size
(right column) in koinobiont
parasitoids (寄生蜂) .
(3) Correlated responses to artificial or natural selection provide
some of the most consistent evidence of trade-offs.
‘young’ population has a
higher mortality rate, but
… has a higher egg production
(4) Experimental manipulation of one trait and observation of
the effect on other traits often reveals trade-offs.
The costs of reproduction increase mortality
The difference in mortality rate between ‘old’ and ‘young’
populations disappeared when a gene that prevent females
reproduction was crossed into the populations.
3.2 Adult survival and reproductive allocation
（成体生存与生殖分配）
①Where adult survival is lower, organisms begin reproductive
at an earlier age and invest a greater proportion of their energy
budget into reproduction;
②where adult survival is higher, organisms defer reproduction
to a later age and allocate a smaller proportion of their resources
to reproduction.
①成体存活率低的生物在年轻时就生殖，而且投入较大能量
到生殖中；
② 相反，成体存活率高的生物则推迟生殖，而且投入较小能
量到生殖中。
Age at maturity (year)
Lizards and snakes that have
higher survival mature at a
later age or …
Adult survival
…fish with higher mortality
rates reach reproductive
maturity at an early age
Adult fish mortality
Species with higher mortality 生殖-身体质量指数
would show higher relative
reproductive effort (fig.)
(reproductive efforts were
measured as GSI
(Gonadsomatic Index), which
was taken as the ovary
weight of each species
divided by the species body
weight and adjusted for the
number of batches of
offspring produced by each
species per year.)
Relationship between adult fish mortality and reproductive efforts
4. Life History Classification
可以根据几个重要的种群参数来划分生活史类型，如生殖
力或后代数量(mx)、存活率(lx)、性成熟年龄(a)等
4.1 r and K selection (MacArthur and Wilson, 1967)
Characteristics favored by r and K selection
Population attribute
rm （内禀增长率）
Competition ability
r selection
High
Not strongly favored
K selection
Low
Highly favored
Development
Rapid
Reproduction
Early, single
Late, Repeated
Body size
Small
Large
Offspring
Many, small
Slow
Few, large
r selection
蚜虫
K selection
天牛
4.2 Plant Life Histories
竞争型物种
Grime(1979) select
two variables as
important selective
pressure on plants:
intensity of
disturbance (扰动
程度) and intensity
of stress (胁迫程
度).
桦
1年生草
胁迫忍耐型物种
山毛榉
杂草型物种
4.3 Opportunistic，Equilibrium and Periodic life histories
（机会型、平衡型 和周期型生活史） High juvenile survival,
Guppy,
finch, Anole
fecundity
Low juvenile survival,
low fecundity, early
maturity
Opportunistic
Life history
Juvenile survivorship
high fecundity, late
maturity
Periodic life
history
Ocean sunfish
Age of
reproductive
maturity
Equilibrium
life history
High juvenile survival， low
fecundity, late maturity
Shark,
human
(4) Reproductive effort, Offspring size, and Benefit-cost
ratios
Charnov (2002) developed a classification free of the influences of
size and time by using relative variables (dimensionless):
I/m: is the mass of offspring at independence from the
parent ,(I), divided by the average adult mass (m).
E/α: is the average length (e.g. years) of a species’s
reproductive life ,(E), divided by the average length of time
required to reach reproductive age ,(α).
C· E: is the proportion of adult body mass allocated to
reproduction per unit time (C), multiplied by the adult lifespan
(E). It is a benefit-cost ratio without dimensions, as high
reproductive effort, benefit, is associated with high rates of
mortality, a cost.
Life history
cub
classification of fish, mammals, and altricial (晚成雏的）birds
思考题
1、举例说明研究生活史特征的理论或实践意义。
要求：
1）何种生物？描述基本生物学特征。
2）有哪些生活史特征？为什么是这些而不是其他特征？
3）阐述这些生活史特征的理论意义或可能的实践价值