life history strategies

sets of physiological and behavioral features that incorporate not only reproductive traits but also survivorship, length-of-life characteristics, preferred habitat type, and competitive ability

life history strategies have important implications for

how populations grow and for the reproductive success of populations and species

types of life history strategies

-iteroparity versus semelparity

-continuous versus seasonal iteroparity

-R and K selection

-grime's triangle

semelparity (common in insects and invertebrates)

a pattern when offspring are produced in a single reproductive event

other organisms reproduced in

successive years or breeding seasons

iteroparity (common in vertebrates and perennial plants such as tree)

a pattern of repeated reproduction at intervals throughout the life cycle

seasonal iteroparity

species such as birds, mammals, or temperate forest trees have distinct breeding seasons that lead to distinct groups of individuals all born at the same time

continuous iteroparity

for a few species, individuals reproduced repeatedly and at any time of the year (as well as some parasites, and some primates exhibit this strategy

semelparous mode will favor if

the environments is stable, a single act of organism, will devote all energy in making offspring and not maintaining its own body

iteroparos mode wil favor is

survival of juveniles is very poor and unpredictable, repeated/long reproductions will increase survival

K-selected species

stable populations adapted to exist at or near the carrying capacity, K, of the environment

r-selected species

high rate of per capita population growth, r, but poor competitive ability

according to McArthur and Wilson such strategies can be considered a

continuum

type I

most individuals die late inlife

type II

individuals die at a uniform rate

type III

most individuals die at a young age

ruderals

are adapted to take advantage of habitat disturbance (annual plants adapted to colonizing disturbed areas)

competitors

are adapted to live in highly competitive but benign [not harmful] environments (many tree species)

stress tolerators

are adapted to cope with extreme environmental conditions such as high soil salt or temperatures that exist in salt marshes and deserts (mangroves and cacti)

grime's triangle

plant life histories based on a model in which stress, disturbance, and competition are the important selective factors (based on data in grime 1979)

life history strategies are subject to

evolution

virginia opossums (Dipelphis virginiana) life only

20 months on average

Austad (1993) found that possums living on Sapelo Island (GA) where no predators are found, lived

25% longer than average

life history traits vary

widely among different species

life histoy traits involve trade-offs

limited amount of energy to invest in survival, maintainance, and reproduction

natural selection optimizes life history in light of trade-offs

-maximizes number of offspring surviving to maturity

-depends on likelihood of survival to different age classes

kirkwood (1979,2000) noted that

cells require repair and argued that narutal selection should favor levels of seld-repair that are good enough to keep an organism in sonund condition only for as long as it has a reasonable chance of reproducing

data from opossums support predictions from

life history theory (island possums appeared to age slowly than the mainland possums)

predation risk drives life history evolution in

guppies

reznick et al. (2006)

compared guppies in streams with numerous predators to those in streams with few predators. fouund effect on number of offspring, offspring weight, and mean size at sexual maturity

trnasplant experiments deomstrate

rapid evolution of life history traits

transplanted fish exhibited rapid life history evolution in the

expected directions

trade-offs arise when

allocation of resources to one life history trait reduces investment in another trait

investment in reproduction often comes at the

expense of growth or body maintenance

brown anolis (anolis sagrei) with their ovaries removed,

grew faster, bigger, and lived longer

females are more likely than males to provide parental care

-males have less investment

-males have uncertain paternity

-these roles reversed in some species

fishers principle

states that a 1:1 sex ration is an evolutionarily stable strategy, but not all individuals are able to mate at all times

operational sex ratio (OSR)

is the ratio of male to female individuals who are available for reproducing at any given time (sexual selection becomes an important agent when members of one sex compete with each other to mate)

degree of polyandry

mean number of mates per females

male gulf pipefish cafry fertilized eggs in pouches. because males make bigger investment in rearing offspring,

males choose to mate with only a few high-quality females, eggs from larger females are more likely to develop into viable offspring

organisms may regulate the number of offpring to maximize

-miscarriage

-cannibalism

organisms may also regulate the sex ration of offspring to

maximize fitness

blank and nolan (1983)

found youn female red-winged blackbirds produced more females, while order females produced more male

sand gobies cannibalize eggs

these adjustments increase the proportion of offspring surviving

frequency-dependent selection

-production of each sex favored when rare

-rare sex has more mating opportunities

fewer feamles

sex ratio stabilizes (natural selection will favor mutant females that produce more males)

any population that deviates from the 50:50 sex ratio will be

shifted back to it by natural selection

females may alter sex ratios of

offspring

hymenopterans

often exhibit haplodiploidy (haploid males, diploid females) so females can alter sex ratio of offspring by choosing whether or not to fertilize eggs with sperm (fig wasps produce fewer mles with larger clutches)

trivers-willard hypothesis

states that parents in good condition tend to bias their offspring sex ration toward the sex with a higher variation in reproductive values, whereas parents in bad condition favor the opposite sex

mothers alter sex ratio depending on conditions

-produce females when in poor condition; daughters will likely have some offspring even if in poor condition

-produce males when in good condition; males likely to benefit more from being large and will more readily attract mates

some species switch sex in

trivers-willard-predicted manner (start as females and breed as such when young and small, but switch to male when they are large)

sex ratio adjustment in seychelles warblers

-with high resources females favored

-up to three helping daughters beneficial

-with low resources males favored

-disperse away from poor habitat

strategies to maximize offspring produced over a lifetime can

differ for the sexes

among penduline tits (remiz pendulinus), mothers and fathers has interest conflict over who should provide care the longest

consequently, male-only care, female-only care and biparental desertion all occur

parental-offspring conflict

occurs when parents benefit from withholding parental care from some offspring and invest in other offspring

skylark chicks within a nest compete for

attention with loud begging calls and bright red mouths

triming the feather of this chicks makes them

appear black, influencing parental feeding rates (sibling competition in American coots)

offspring-offspring conflict (sibling rivalry)

occurs when sibling compete for parental care for parental care or limited resources (in some cases it can lead to siblicide/the killing of another sibling)

parent-of-origin effect

effect on the phenotype of an offspring caused by an allele inherited from a particular parent (ex. hinny: result of horse stallion + female donkey)

genomic imprinting

occurs when genes inherited from one or the other parent are silenced due to methylation (offspring express either maternal or paternal copy of gene, but not both)

methylation

the process by which methyl groups are added to certain nucleotides (associated with altered gene expression)

wilkins and haig (2003) suggest that

imprinting genes evolved through conlfict between parents which is resolved in their offspring

intralocus seuxal conlfict

is a conflict between the fitness effects of alleles of a given locus on mals and females

senescence

deterioration in the biological functions of an organisms as it ages (cells accumulate malformed protein, immune less effective, etc)

calorie restriction can

slow the aging process (genes involved in repair switched on under stress

may involve trade-offs (increase fitness of an allele while decrease fitness of another allele)

worm mutants that age more slowly have lower fitness

transcription factor DAF-16 controls the expression of a battery of genes, many of which have small effects on

lifespan (promoting either aging ot longetivity) in Caenorhabditis elegans

genes that promote ageing include

some that encode yolk proteins and insulin-like INS-7

actuarial and reproductive senescence

age-related declines in survival and reproduction respectively (the rule in free-ranging populations of vertebrates

hamilton (1966) proposed that

the decrease in the force of natural selection inevitably leads to actuarial senescence in any age-structured population, but does not adress reproductive senescence

the force or strength of natural selection, a measure of how strongly selection acts on survival and/or reproduction,

declines as a function of age

aging exists because

selection is weak and ineffective at maintaining survival, reproduction, and somatic repair at old age

mutation accumulation (MA)

aging evolves because selection cannot efficiently eliminate deleterious mutations that manifest themselves only late in life

antagonistic pleiotropy (AP)

aging evolves as a maladaptive byproduct of selection for increased fitness early inlife, with beneficial early-life effects being genetically coupled to deleterious late-life effects that cause aging

aging clearly shortens lifdespan, but lifespan is also shaped by

selection fo an increased number of lifetime reproductive events (balance with pros and cons)

mother hypothesis

risk of reproduction at older age selects for reduced fertility (investment in current offspring)

grnadmother hypothesis

loss of fertility associated with shift in investment to grandchildren

human females live

long-reproductive lives