Life History & Phenotypic Plasticity Flashcards
life history traits:
fitness is built upon key events and decisions across individuals life
-growth
-reproduction
-survival/maintenace
life histories can be broken down into component life history traits
-the phenotypic traits closest to fitness
-integration of physiological process and behavioural traits
examples of life history traits:
Growth and development:
-size at birth
-growth pattern
-age at maturity
-size at maturity
examples of life history traits:
Reproduction:
-sexual or asexual
-no. of breeding attempts
-no. of offspring
-size of offspring
-parental care
maintenance/survival
-homeostatic function
-repair functions
-immune defence
life history trait control
resulting life history traits:
under complex endocrine control
underpinned by sequence of physiological changes and behavioural responses
closely tied to environmental stimuli
life history divesity: drosophila:
small at maturity
mature fast
short lived
ITEROPAROUS and HIGHLY FECUND (breed multiple times in life and have a lot of offspring)
FAST life history
life history divesity: salmon:
takes a bit longer to develop (1-3 yrs as freshwater smoults)(adults at sea 1-5 yrs)
semelparous: mate once and die soon after
highly fecund - have 1000s of eggs
no parental care (deadge)
life history diversity: albatross:
can take over decade to mature
produce 1 or a few eggs
chicks take ~1yr to fledge
parents (pair for life) care for chick
many species breed only every 2-3yrs (iteroparous tho)
slow life history
life history trade offs?
darwinian demon:
-unconstrained fitness
-matures just after birth
-produces huge numbers of offspring constantly
-lives indefinitely
no animals like this exist
something must be constraining allocation of resources to different components of fitness
energy bidgets
unconstrained fitness optimum can’t be reached
energy budgets?
input
food
drink
stores
uses
waste excretion
metabolism:
-basal
-active
-digestive
production:
-germline/gametes
-soma (non reproductive tissue production)
limited amount of energy
constrains how much an organism can allocate to each trait
zero sum - allocation to one trait takes away from another
why can’t reach unconstrained fitness optima?
plot survival investment against reproduction investment
unconstrained fitness optimum (no energy bidgets/zero sum allocation) would be at top right
however the constrained optimum is along a black line going Top-left -> bottom right
have to reduce fitness in one trait to increase in anothrt
LIFE HISTORY TRADE OFF
Y-model - giving resources to one trait reduces the amount of resources you have to allocate to the rest (zero sum allocation)
developmental life history trade offs:
-age at maturity vs size at maturity
(need to invest in germline to sexually mature sooner, but that takes away from soma investment - reduced size)
growing at a faster rate shown to affect developmental integrity too
life history trade offs - reproduction:
offspring size vs number (if have more, invest less in each for size)
altricial vs precocial young
-more offspring - less parental care for each
-more offspring earlier - less later on in life
many ungulates have fewer offspring (1 or a few) - but the offspring are larger and more well developed
-need to trade off number for size and developed because prey animals - need to be developed early (precocious) - cant stay helpless
maintenance life history trade offs
reproduction vs future survivial
having many offspring at once impacts future survivial
(e.g. immunity impacted as reproduction draws resources away from it, worse immune system = worse future survival)
(e.g. higher clutch size = increassed reproductive workload - drop in immune response)
Evidence for trade offs? (comparative studies)
Comparative studies:
-Eutherian orders with high fecundity have shorter periods of maternal investment
-also show offspring size-offspring number tradeoffs
evidence for trade offs - experimental manipulation:
experimental manipulations:
increased clutch size of birds
subsequent negative effects on offspring (fledgeling weight, survival in nest, survivial to next season, future reproduction) and parental traits (weight, survival to next season, future reproduction)
why is it hard for correlational/observational studies of wild populations to detect trade offs?
of trade offs present, expect to see negative correlations between traits
however most correlations positive (in deer example).
because:
different individuals have different access to resource
more access to resources = higher overall energy budget = higher optima that can be reached for each trait in the trade off - even with the trade of present as the increased energy budget means more can be allocated to both trait
e.g. trade off exists between survival and reproduction
BUT
higher overall budget means more to spend on both
so increase in both
different individuals in same population will invest more in either reproduction or survival
so correlations within specie will depend on variation in life history strategy AND access to resources
between species:
much variation in life history strat - so see negative correlation between traits - see trade off
in populations:
little variation in life history strat (as same species)
BUT there is much variation in resource access
so often see positive correlation which is the effect of the differing resource access masking the negative correlation between the traits due to the trade off
phenotypic plasticity
ability of a genotype to produce different phenotypes in response to different environmental conditions
e.g. egg laying dates in many birds responds to spring temps (to match peak food needs of chicks with peak caterpillar emergence)
P=G+E??
NO
P=GxE
P is not just the result of additive contributions of G and E
genotype by environment interactions
the phenotype produced by a given genotype DEPENDS on the environment
quantifying phenotypic plasticity?
Reaction norms:
plastic
or
non-plastic
sketch graphs in notes
-is there variation in different environments for a genotype? y/n
-is there a reaction in phenotype to the environment?
-what is the slope (how plastic is the trait)
-is there variation in how plastic traits are
GxE interactions?
genotype by environment interaction
MEANS THERE IS VARIATION IN PLASTICITY
-changing environments causing changing expression in genes
what could be causing plastic response?
-change in phenotype could just be result of simple physiological constraint/physiological acclimation
-could be a coordinated response to information (environmental cues) predicting change that allows organisms to “match” phenotype to environment
is plasticity direct vs indirect response?
-is the environmental effect on phenotype direct (eg changing temperatures affecting enzyme activity) or indirect (morphology/phenology altered in response to perceived cue)?
-DOES PLASTICITY RESULT IN INCREASED FITNESS
why might plasticity evolve?
environment is variable
so fitness optima change with environment
a large plastic response that is optimal in one condition may not be in another
so having a plastic response in phenotype to “match” to the changing environment allows organism to stay near to the fitness optimum as possible in variable environment (even if it doesnt perfectly trach the fitness optima changing - it still infers some benefit in changing environment)
non plastic response = good in static environment (dont have to invest in ways to detect cues e.g.)
but a lot less fit in variable environment
costs of platicity?
maintenance:
-energy costs of sensory and regulatory mechanisms (to mount and maintain mechanisms to detect and adapt to cues)
production:
-cost of producing phenotypic change
information aquision:
takes time and energy costs to sample environment
developmental:
possible costs to developmental precision/integrity of plasticity
limits of plasticity?
information reliability:
-cues can be unreliable
-fast environmental change can be hard to detect/keep up with
developmental constraints:
-some phenotypes that would be optimal may be out of developmental range
genetic constraints:
if there is no GxE interaction, plasticity can ot evolve in response to selection
example of amphibian plasticity: egg laying
spadefoot toads
lay eggs in ephemeral desert pools (<2 weeks)
if tadpoles hatch too late then there is not enough time to metamorphose - pond dries up and tadpole dies
if tadpoles metamorphose too early - smaller size as adult - reduced fitness
experiments shown that toads increase developmental rates if pond dries (and vice versa)
amphibian plasticity 2: hokkaido frog tadpoles
3 different phenotypic responses to environmental cues:
no predator cues:
no changes
dragonfly larva cues:
fast bite predator
High tail phenotype
fast swimming phenotype to escape them
salamander larvae cues:
swallowing predator
Bulgy phenotype (predator is gape limited)
larger so avoid being swallowed
exposed morph to other morph’s predator - no advantage inferred from phenotype
matches hypothesis for why they change like this
trade offs of amphibian plasticity
wood frog tadpoles
exposed to high competition
developed longer guts to improve digestive efficiency -> improved growth rate -> improved fitness in high competition
however when exposed to dragonfly larva predator
developed shorter guts
a cost of the larger tails developed for escape
(in turn worse in competition?? cost of big tails is smaller guts
