Lecture 15 – Invasions and Evolution
Evolution in Invasive Species
 Adaptive Evolution – Natural selection acting on existing or novel
(mutational or recombinational) genotypic variation.
 Can be rapid
 May be important at several different phases of the invasion process
Adaptation vs. Plasticity
Populations may differ significantly in many different ecological or morphological
attributes when exposed to different environmental conditions. It is important to
distinguish between traits that are the product of natural selection and adaptive
change, and those that are expressed through phenotypic plasticity.
Phenotypic plasticity
Environmentally induced variation in a trait, species may differ substantively in
behavior, physiology, ecology, etc when compared in a native environment and an
environment where they are invasive. This difference is due to the capacity of the
same genotype to express different phenotypes.
Adaptive change
In contrast to plasticity, natural selection produces different genotypes with
different phenotypes, each adapted to a given environments.
The gold standard for assessing adaptive evolution versus plasticity is the common
garden experiment, where multiple phenotypes are reared or grown under common
conditions. If the phenotypes are a product of selection, they will still be expressed
no matter the conditions. If they are plastic, they will revert to a homogenous form
as the environmental conditions are the same for each.
Plasticity
Mullein (pioneer’s toilet paper)
Distribution spans huge latitudinal and elevational range
Small prostrate plants at high elevation / latitude
Common garden / greenhouse experiment
At standard temperatures, no difference among populations
Plant morphology is plastic and varies depending on environmental conditions
Adaptive Evolution.
Replicated common gardens of St Johns Wort in Spain and Washington State
Reciprocal transplant experiment – a standard set of multiple American and
multiple Spanish cultivars planted at each garden
-American genotypes expressed less hypericin in both their native common
garden (Spain) and Washington State
Loosestrife Flowering Phenology
(Montague et al. 2007)
Plants from high latitude flowered earlier and did so at a smaller size under
common garden conditions and in situ in nature. At higher latitudes, a short
and cool growing season selects for plants to flower early and at a smaller size
so that the seeds will develop before frost comes.
Evolutionary Response of natives to Invaders
- Soapberry Bug (Carroll et al. 2005)
Use their beak to access and feed on seeds within a fruit.
In Australia fed on the native woolly rambutan
Balloon vine, a tropical American species invaded Australia in early 1960’s.
Soapberry bugs adopted it as a host, but only bugs with longer beaks could access
the seeds. As balloon vines became abundant, selection favored longer beaked bugs
driving the evolution of this trait.
- Red-bellied Snakes
Cane toad bufotoxin is lethal to predatory snakes imposing strong selection on
snakes to avoid cane toads as prey.
• In experiments, snakes from areas with established cane toad populations
exhibited significant aversion, snakes from outside of the cane toad range did
not.