Wayne Flashcards
(25 cards)
What do introductions involve
- Non-random selection of genotypes introduced (artificial selection
- Environmental conditions that differ from native range (biotic and abiotic)??
- Novel mixtures of genotypes (genetic admixture and hybridisation)
Non-random selection of genotypes
Depending on use we artificially select genotypes with preferred phenotypes for introduction: introduction bias
- cultivated alien plants in Switzerland germinate faster and in greater numbers than non-cultivated native plants
- artificial selection both pre and post introduction- eg better at germinating, selected plants allowed to survive
- for horticulture often spp have to be carefully bred/selection to be able to survive in new range
- Chrobock et al (2011) alien cultivars germinated quicker than non-cultivated plants/spp. Also more cultivated alien spp than native, non-cultivated plants. Process of evolution is already happening through artificial selection
Differences in biotic environment
Some species may be released from natural enemies. So new areas may not have eg herbivores or pathogens. Growth advantage bc natives will have their enemies
EICA- evolution of increased competitive ability. enemy release can result in reallocation of resources from defence to growth/other traits that improve competitive ability. there are finite resources
Can be:
- constitutive defense- always there eg tannins
- induced defence= eg when munched by herbivore that causes defence compound creation
EICA through incr allelopathy
Allelopathy is mutual suffering
Some plants compete with neighbours by producing compounds that are toxic to other spp (interference competition)
Release from herbivory might favour introduced genotypes with greater production of allelochemicals
which act against native neighbours (novel weapons)
eg goldenrod
used clones of this plant from artificial selection. clones either had herbivores present or not. they were grown alone or under competition with Poa grass or another goldenrod spp
allelopathy concentration with higher for no herbivore clones, decline in ramet production when herbivores (vegetative unit of growth) where present and under competiion with poa
selection may select more competitive clones though allelopathy. Allelo compounds highest when no herbivores and when in competition with other goldenrod species
How might post introduction evolution promote invasions?
Ecological niches of species can be constrained by biotic interactions, selecting against traits that would other be beneficial to eg competition and herbivory
Ecological release can result in relaxation of evolutionary constraints; allows selection that favour niche expansion/higher absolute fitness
Relaxation of evolutionary constraints
- Antagonistic selection
- Stabilising selection
- Trait variance suppression
Antagonistic selection
there may be a trait that interactions select against, but is selected for by other selection pressures. Release allows a response to the selection eg EICA. The trait may be selected against by herbivores in the natural range, get rid of enemies and advantageous traits may be selected for.
pics on phone
Stablisiling selection
Selection pressure from interactions (eg competition) constrains a range of resources (ie niche space) that can be used, suppressing resource-switching and overall fitness. Release increases both fitness and niche breadth. So something had been preventing switching resources or exploring more niche space that otherwise might be available
pics on phone
Trait variance suppression
Biotic interactions constraint the range of trait values expressed. Release allows expression of wider range of phenotypes, opening up genotypes to selection. Other trait values can be advantageous in different environments but selected against in native range.
pics on phone
The role of the abiotic enviromnet
Local adaptation of a species to novel environmental conditions may be required before it can invade eg expansion of climatic range at northern range edge may be limited by reproduction in plants that flower at a certain size. Selection should favour genotypes that have different phenology (eg flower earlier, when smaller)
local adaptation
Selection of genotypes that optimise fitness under environmental conditions at a particular location is known as local adaptation
Test of local adaption
Pic on phone
Best test for local adaptation is the reciprocal transplant experiment.
Grow A and B at home and in opposite environment. If genotype is locally adapted, should see higher fitness when they are in their own environments. Can collect data on reproductive biomass, number of seeds etc. –> measure of fitness
Test of local adaption Purple Loosestrife
Reciprocal transplants of purple loosestrife from northern and mid and southern latitudes in canada.
North plants had highest fitness in north - LA
Mid have highest in mid - LA
Selection of north result in smaller, earlier flowering genotypes
Southern later flowering genotype may suffer decrease in fitness in north
(interspecific) genetic admixture
Occurs when multiple divergent genetic lineages come into gene flow contact and interbreed. Recombining of genotypes across source populations. Likely a common occurrence for spp introductions with multiple origins and introduction events
Counterintuitive to the idea of local adaptation, admixture may benefit newly formed populations. Breaking down gene flow and getting rid of things that may have been adaptive in home range.
Genetic admixture benefits
‘Hybrid vigour’ (heterosis)- crossed offspring have higher fitness than either parent pop (pic on phone)
Novel crosses may have high fitness in novel environments. At lest initially may counteract effects of genetic bottleneck (inbreeding) by increasing heterozygosity (masking deleterious mutations)
Genetic admixture costs
Outbreeding depression may sometimes occur and is a cost to intermediate genotypes, especially if introduced. Can happen when offspring in an enviroment outside of where 2 parent pops adapted to. But novel crosses may have high fitness in novel environments
Is admixture the driver of success or a passenger? if more than one pop introduced to a location then higher propagule pressure which may increase success rather than the mixing of genotypes which is happening.
Example of genetic admixture
Invasive anolis lizards in california, body size is positively correlated to number of source populations. More populations that you mix together to get new admixture, bigger body size
Invasive harlequin lady bird. Invasive in Eu. Fitness of admixed native and biocontrol populations higher than non-adm pops in Eu and N america
Evolution of dispersal ability- Cane toad
An important dimension of invasion success is how fast a app can spread
the cane toad (intro in aus 1935) has spread rapidly across the north. Are they evolving a greater dispersal ability?
Rate of increase of range size is growing exponentially
An important morphological adaptation that increased dispersal is leg length. Longer legged toads do travel further.
At first arrival sites longer legged toads are more common. At new invasion front sites longer legs than range centre
Mechanisms of post introduction evolution
Artificial selection through introduction bias- eg introduction of ‘easy to grow’ traits in ornamental plants
Natural selection on (standing) genetic variation eg selection in favour of more competitive genotypes with lower herbivore defence (EICA)
Spatial selection eg greater dispersal ability of age toads
Epigenetic variation
What is epigenetic variation
Heritable variation in gene expression, not involving changes in underlying genes themselves- phenotype can change without genotype changes
At least 3 systems involved in gene expression can result in epigenetic changes:
- methylation- dna methylation is the most broadly studied (including within ecology)
- Histones
- Gene silencing by non-coding rna
DNA methylation
Addition of a CH3 methyl group to cytosine. Typically occurs at CpG sites in mammals (p stands for phosphate so where it is cytosine and guanine). In plants and other orders at CG, CHG, CHH sites (H is A T or C)
How is epigenetic variation generation and is it heritable
Genetic control (thus a product of genetic variation). Environmental induction: stress, differences in environmental conditions –> ‘transgenerational plasticity’ / paternal effects
Stochastic epimutations: rates and stability may vary. Rates are thought to be greater than for genetic mutation.
Epigenetic variation is reversible: demethylation.
‘resetting of environmentally induced changes occurs during meiosis (sexual reproduction( but not mitosis (asexual reproduction)
How might epigenetic variation play a role in mutations?
Faster
Invasion causes stress which induced epigenetic cane
Reduction in stress for invaders if released from a natural enemy
Asexual reproduction can’t get rid of methylation so phenotypic changes are permanent. If invasive then feasible no sexual reproduction
Should be important if change in phenotype has fitness advantage
Could be more important in asexual bc cant remove it and when they reproduce don’t get genetic variation bc asexual so the epigenetic provides it
Certain stresses increase epigenetic changes
Mating at range edges (assortative). Epigenetic change could be linked to dispersal traits that lead to evolution of greater dispersal ability
Range edges- species may not be at their environmental optimum so might be under stress which could trigger epigenetic change - phenotypic plasticity - maintain fitness is new environment
Epigenetic variation in Japanese and Bohemian knotweed
find study
Clonally propagating invasive
World’s largest female plant, all 1 genotype (japonica)
They hybridise with sachelinensis and spread clonal
AFLP restriction enzymes at particular point breaks up something into smaller fragments. How much overlap? If exactly the same then genetically (epigenetically) identical.
Found significant difference in epigenetic loci in 93% of cases
Found sig dif in genetic loci in 32% of cases
On the whole a lot less epigenetic differentiation than genetic?????????????????. Selection may be acting on epigenetic differentiation.
