Life history evolution 1.1 Life HistoryLife 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. 1 Some Important Concepts 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 ()

1.2 Fitness: Fitness 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; a measure of the contribution of a given genotype to the subsequent generation relative to that of other genotypes.

1.3 Reproduction Value ()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 ; (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: mx the birth rate of individual in age-class x, as contemporary reproductive output lx the probability that the individual will survive to age xR the net reproductive rate of the whole population per unit time (age interval).future reproductive output

1.4 Methodology for Life History Study Every life history, and every habitat, is unique. The idea of optimization (: observed combinations of life history traits are those with the highest fitness. The idea of bet-hedging(): when fitness fluctuates, it may be most important to minimize the setbacks from periods of low fitness rather than evolving to a single optimum. 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.

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 Individual size Being large or small? Increasing competitionIncreasing success in predation or in defenseIncreasing survival Increasing offspring productionDecreasing survival of a shortage of food, or of defense???So, an intermediate size might be optimal ?Large body size

The relationship between seed size, seedling mass, and seedling recruitment () among herbs and grasses living in semi-natural grasslands in southeastern Sweden.Seed mass and seedling mass among grassland plants in SwedenLarger seeds produce large seedlings. Seedling dry massSeed massmg)

Seed mass and recruitment rates in grassland plantsOn average, larger seeds were associated with a higher rate of recruitment ().

Relationship between seed mass and seedling height among trees. There is also a positive relationship between seed size and seedling height among trees.

Adult male damseflies ()Predicted optimum sizeSampled optimum size

Development Being rapid or slow?Rapid DevelopmentSlow DevelopmentEarly reproductionEarly emerging from hostMore storage of energy, longer lifespan and reproduction period; Large body size

3 Trade-offs () 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. Life history trait 1Life history trait 2A trade-off

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 fish1100

Turner & Trexler(1998) sampled 64 locations on streams and rivers in US. 15 darter species

(ii) Seed size and number in plants A small sample of the great diversity of seed sizes and shapesPlants vary widely in the number of offspring they produceranging from those that produce many small seeds to those that produce a few large seeds.

Average seed massNumber of seed per plant4The negative correlation between seed mass and number of seeds.

(2) Phenotypic () 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.

Developmental characteristics of M. pulchricornis on different instars of S. exigua larvae. The alternative approach is to use experimental manipulation to reveal a trade-off directly from a negative phenotypic correlation. (ii) Development time and body size in parasitic wasps

Graphical representations (AC) 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 () .

(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 difference in mortality rate between old and young populations disappeared when a gene that prevent females reproduction was crossed into the populations. The costs of reproduction increase mortality

3.2 Adult survival and reproductive allocationWhere adult survival is lower, organisms begin reproductive at an earlier age and invest a greater proportion of their energy budget into reproduction; where adult survival is higher, organisms defer reproduction to a later age and allocate a smaller proportion of their resources to reproduction.

Age at maturity (year)Adult survivalfish with higher mortality rates reach reproductive maturity at an early ageLizards and snakes that have higher survival mature at a later age or Adult fish mortality

Relationship between adult fish mortality and reproductive effortsSpecies with higher mortality 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.)-

4. Life History Classification4.1 r and K selection (MacArthur and Wilson, 1967)(mx)(lx)(a)Characteristics favored by r and K selectionPopulation attribute r selection K selection rm High LowCompetition ability Not strongly favored Highly favoredDevelopment Rapid SlowReproduction Early, single Late, RepeatedBody size Small LargeOffspring Many, small Few, large

K selectionr selection

4.2 Plant Life HistoriesGrime(1979) select two variables as important selective pressure on plants: intensity of disturbance () and intensity of stress ().1

4.3 OpportunisticEquilibrium and Periodic life histories High juvenile survival low fecundity, late maturityEquilibrium life historyAge of reproductive maturityPeriodic life historyOpportunisticLife historyLow juvenile survival, low fecundity, early maturityHigh juvenile survival, high fecundity, late maturityfecundityJuvenile survivorshipShark, humanGuppy, finch, AnoleOcean sunfish

(4) Reproductive effort, Offspring size, and Benefit-cost ratiosCharnov (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/: is the average length (e.g. years) of a speciess reproductive life ,(E), divided by the average length of time required to reach reproductive age ,(). 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.

classification of fish, mammals, and altricial (birdsLife history cub

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