Key readings Flashcards
Plants in alien environments - EICA
Blossey and Notzold (1995)
In alien environments plants tend to be more vigorous, taller and produce more seeds
- more favourable env and/ release from natural enemies?
Purple loosestrife introduced to north america. Took seed samples from there and places in the EU. Then grew. N America sample had increased vegetative growth and survival of root seeder was higher and larval weight was increased
- leaves are replaceable so dont need to invest as much in leaf defences. Larvae of leaf feeder not significantly different between 2 regions (switzerland and usa)
Dispersal traits
Shine et al 2011
Traits that enhance dispersal inevitably accumulate at expanding range edge, assortative mating at invasion/range front result in an evolutionary increase in dispersal rates in successive generations. Traits evolve because genes are differentially successful through space rather than time
If spatial selection favours faster dispersal we expect such fronts to be dominate by unusually fast dispersing individuals
- wing dimorphic crickets show more large wines at expanding front
- cane toad, 3-10 fold incr in daily dispersal rate of invasion front toads. Accelerated dispersal bc longer legs, frontal toads move more often, move further per move, and follow straighter paths and have greater endurance
How can we distinguish between natural selection and spatial sorting?
- both predict invasion fronts will often accelerate and be dominated by the fastest dispersing individuals. Simplest prediction to test involves expanding range fronts in which faster dispersal has not been favoured by classical natural selection - for this we predict lifetime reproductive success to be un/negatively correlated with dispersal rate –> difficult to test and experimental results unclear
However, effect of dispersal rates on viability often negative. locomotor traits that enhance dispersal can also cause spinal injuries and highly dispersive toads suffer higher mortality
Spatial sorting could also favour risk taking behaviours
Admixture
Rius and Darling (2014)
Admixture is not universally beneficial phenomenon. Selection is typically expected to favour locally adapted genotype and can act against admixed individuals
Fitness of F1 hybrids can differ considerably from other generations- later crosses from recombination. However, if colonisers gain sufficient transient fitness benefits through heterosis, this might buffer against demographic dangers of initial small pop size and reduce the long term risk of extinction
Likely there is a causal relationship between successful colonisation and multiple introductions. Admixture implies previously divergent evolutionary lineages arriving in the same place –> multiple sources of colonists to novel habitat. So admixture and higher propagule pressure relative to region that receive colonists from only one source. Difficult to isolated propagule pressure from admixture
Brazil invasion success of Pinus number of source pops and number of introduced individuals both strong predictors on colonisation success
Genetic diversity of Eu peaked not in glacial refugia (expected bc at centre of spp range), but rather where multiple divergent lineages likely admixed after recolonisation
Anolis lizards
Stuart et al (2014)
Small florida islands. Anolis carolinensis moved to higher perches following the invasion of Anolis sagrei and in response adaptively evolved larger toe pads after only 20 generations
To test raised offspring from invaded and uninvited islands identically. phenotype persisted suggesting genetically based divergence (though transgenerational plasticity cant be ruled out)
Could be because fo selective invasions by A.c.
- tested relatedness and india’s from same island related and islands largely genetically independent. No evidence that pop relatedness in A.c. was correlated with whether an island had been colonised or with distance between islands. Island populations independently founded from mainland.
All islands similar so no pre-adaptation
Did A.s. only colonise where A.c. already different? A.s. seems capable of colonising everywhere so unlikely
2 spp have never produced hybrids reportedly
