Phenotypic plasticity

Question 1

what is phenotypic plasticity?

Answer 1

the ability of a genetically determined phenotype to be modified by the environment

Question 2

is plasticity genetically determined?

Answer 2

yes according to Bradshaw; submitted to natural selection as any other trait

Question 3

what are reaction norms?

Answer 3

an array of phenotypic traits seeing in a range of environmental conditions

Question 4

how did Bradshaw see the environment for genetic studies?

Answer 4

a fundamental peace of the puzzle generating phenotypic diversity (others considered it as an error, disturbance, to be removed from experiments)

Question 5

In Bradshaw’s view, the “response” to environmental variation can be understood as an _____

Answer 5

adaptation

Question 6

what’s the difference between “physiological plasticity” and “morphological plasticity”? (Bradshaw)

Answer 6

“physiological plasticity” (which corresponds to all different forms of plasticity) from “morphological plasticity” (which corresponds to a particular manifestation of physiological plasticity, that refers to developmental changes); both are genetically determined (the capacity to display a diversity of traits under changing environments is genetically determined)

Question 7

why isn’t the observed diversity of leaves a product of developmental differences in a given species?

Answer 7

because if this was true, all plants would show the same leaf shape plasticity, which does not occur. Phenotypic plasticity is what explains leaf diversity (Bradshaw showed studies comparing different species with same development but different plasticity)

Question 8

what are the 3 main points (phenotypic plasticity) defended by Bradshaw?

Answer 8

1- plasticity is a property specific to individual characters in relation to specific environmental influences
2- plasticity of a trait is independent property of trait (under its own specific genetic control)
3- degree of modification is controlled by developmental pathways and epigenetics

Question 9

differentiate plasticity and flexibility (Bradshaw)

Answer 9

in Bradshaw’s view, he difference between “plasticity” and “flexibility” is that “plasticity” depicts the variability of the norm of reaction while “flexibility” may also include stable responses to environmental variation. For Bradshaw, “flexibility” had nothing to do with “norm of reaction,” since there was no actual phenotypic change. Therefore, he did not consider heat resistance as a plasticity phenomenon but only as phenotypic flexibility

Question 10

what are 2 contrasting, but nonexclusive, mechanisms that can
explain population responses to climate change? (phenotypic plasticity paper)

Answer 10

(i) a microevolutionary response to natural selection and (ii) phenotypic plasticity

Question 11

what is main conclusion of phenotypic plasticity paper on great tit birds studied for 50 years?

Answer 11

very close tracking of rapid environmental changes by populations which integrated this study, which resulted from phenotypic plasticity alone; advancement in breeding date starting in the 70s as correlated with temperature; food resource for this bird (moth) also showed an advancement of peak larval biomass period
population is growing and thriving, plasticity is adaptive

Question 12

the directionality of natural selection in the bird population depends on synchrony between egg laying date and food availability. What happens in a short and in a long interval?

Answer 12

when the interval is short, natural selection has a strong directionality towards individuals which lay eggs early; the opposite occurs when there is a long interval between egg laying and food availability (natural selection will favor individuals with a mean breeding date)

Question 13

when can climate change affect populations of birds in a more negative manner?

Answer 13

when the phenology of its food source is considerably changed in different ways or different rates as compared to bird vital rate timings

Question 14

why the responses of birds consist of phenotypic plasticity and not microevolution?

Answer 14

because the variability in breeding date is closely matching environmental variability, whereas there would be mismatches if this was the case of microevolution (phenotype in a given year is a result of selection in the previous year) in a changing environment

Question 15

compare dutch and UK bird populations in terms of phenotypic plasticity; discuss natural selection effects on dutch population

Answer 15

reaction norm of UK: all individuals track the environment the same way (laying date as a function of spring temperature) -> thriving pop
reaction norm of dutch: slopes of reaction norms differ amongst each other -> decreasing pop as a result of climate change -> this reaction norm is under strong selection for increased responsiveness, so fitness has declined as a result

Question 16

what does the invariance of UK birds responses to temperature tell us?

Answer 16

result of past natural selection to optimize this reaction norm

Question 17

what tells us that the UK bird responses are adaptive?

Answer 17

synchrony between egg laying and larvae emergency continued for many decades even if environment changed a lot

Question 18

differentiate transgenerational plasticity and within-generation plasticity

Answer 18

transgenerational plasticity = plasticity which occurs across generations
within-generation plasticity = plasticity among individuals within the same generation

Question 19

how can organisms respond to changing climates?

Answer 19

shifting their distributions,
adapting to new environments or
acclimating through phenotypic plasticity

Question 20

why is plasticity important to organisms facing rapid climate change in comparison with adaptation?

Answer 20

potential for rapid genetic adaptation may be constrained under predicted climate change

Question 21

define transgenerational plasticity

Answer 21

non-genetic effects that are observed in the current generation which is associated with the exposure of a previous generation to a new environmental condition. this should not include parental effects and developmental plasticity. in other words, TGP describes differences in offspring phenotype that occur due to the interaction between the current generation and previous generation’s environmental conditions

Question 22

define mechanisms behind transgenerational plasticity

Answer 22

non-genetic and epigenetic transmission (e.g. RNA-mediated modifications, epigenetic marks and DNA methylation) from both parental and maternal sides, which can be influenced by the environment

Question 23

differentiate developmental, reversible (or acute) and transgenerational plasticity

Answer 23

developmental, reversible (or acute): occur within a single generation transgenerational: environment experienced by earlier generations interacts with the environment of the current generation to determine the phenotype

Question 24

when environmental conditions vary between generations and parents can effectively predict their offspring’s environment, what kind of plasticity is favored?

Answer 24

transgenerational plasticity (offspring can accurately utilise parental cues)

Question 25

where the environment varies greatly and in an unpredictable manner between generations (e.g. marine organisms where juveniles disperse over large distances), what kind of plasticity is favored?

Answer 25

within generation plasticity: parents could be expected to hedge their bets by producing offspring with a range of phenotypes, although empirical evidence for bet hedging is scarce

Question 26

can diversified bet hedging occur around the norm of reaction?

Answer 26

yes, when transgenerational plasticity and bet hedging occur in combination, as environmental variance is often composed of both predictable and unpredictable components, with the concurrent evolution of both plasticity and bet hedging expected

Question 27

Given that increasing climate variability is predicted to pose an even greater risk to species than directional climate change (Vasseur et al., 2014), it is important to shift the focus away from a strictly mean phenotype perspective and also consider the role of …

Answer 27

phenotypic variance in future transgenerational plasticity studies, since selection may not favour the average offspring phenotype and instead may favour the extreme phenotypes of offspring produced. Consequently, a continued mean phenotype focused approach within TGP research could reduce our capacity to accurately forecast population responses.

Question 28

what is the risk that exists within climate change experiments completed to date, where the focus has overwhelmingly been to apply average projected future changes with no consideration of the natural variation that should be simulated around it?

Answer 28

the risk is detecting higher levels of transgenerational plasticity than might actually occur in nature since plasticity would be expected to occur more readily when conditions are predictable.

Question 29

why would future research benefit from a greater focus on environmental predictability and variability?

Answer 29

because determining plastic responses of species to future climate change requires experiments designed with an understanding of the environmental variation that naturally occurs in the study system and its predictability across generations

Question 30

which 2 life stages have been identified as critical periods when environmental conditions experienced by parents can influence the next generation?

Answer 30

early development (fertilisation-juvenile; as epigenetic changes affect more cells) and prior to and during reproduction (increasing cue length during reproductive phases results in a stronger transgenerational response; timing matters here, eg., exposure right before producing an egg works better than early periods of female gamete production)

Question 31

why does the timing of cue exposure matters for transgenerational plasticity?

Answer 31

because it can affect the transfer of environmental information across generations

Question 32

Some differences in when environmental change induces transgenerational plasticity, and when it does not, may be explained by differences in life histories. Give an example of that.

Answer 32

species in which juveniles migrate to a different environment: parents may be using cues from their own early developmental stages instead of relying in current environment conditions

Question 33

how can climate change studies investigate transgenerational plasticity?

Answer 33

a multigeneration study where generation 1 is submitted to warming and generation 2 is submitted by an additional warming is more realistic than just creating a study where the entire population is exposed to the total warming which will only happen in 100 years from now

Question 34

what kind of experiments can we do to recognize and differentiate transgenerational and within-generation plasticity?

Answer 34

experiments that cross individuals from parental environments with a range of within-generation conditions

Question 35

why is it hard to distinguish selection from plasticity in experimental designs including sexually-reproducing organisms? what is a solution for this?

Answer 35

because the changes seen can be due to each genotype being assigned to a different treatment instead of plasticity.
solution is:
experimental crosses from parents from different environments
get half of individuals and change environmental conditions to check if there is reversibility in their behavior (indicates plasticity instead of selection)

Question 36

what may happen if environments change from parents to offspring in term of phenotypic variability?

Answer 36

the combination of parental effects following exposure to environmental variation and offspring effects following exposure to other types of environmental variation can lead to novel phenotypic variability patterns

Question 37

what are the main limitations of transgenerational plasticity studies?

Answer 37

experimental designs: we need a better understanding of how environmental conditions vary over space and time; we need to add relevant magnitudes of environmental change per generation and varying the timing of environmental cues (e.g., early juvenile; reproductive stage)