invasive species

Loss of biodiversity

  • habitat loss #1 (on a list of reasons of loss of biodiversity)

  • invasive spp #2 (on a list)

  • huge economic cost

  • 50k non-indigenous spp established in the US with economic costs of 125 billion dollars per year

Genetics and invasive spp

  • info on source, number of introduced pops, and differentiation

  • Examine questions

    • how important is the amount of genetic variation present in introduced spp for their establishment and spread?

    • Evolution of native spp

    • Predictions about which spp likely to become invasive

Why are invasive spp successful?

  • Most not so successful: 1/100 become a pest

  • If bottlenecks harmful (inbreeding, loss of adaptive potential), how do invasive spp become successful?

    • Can be a mix from several source pops

    • more individuals and more release events, the more likely it is that a spp becomes invasive

    • in plants, vegetative reprod and selfing prevent inbreeding depression, loss of He

  • If local adaptations important, how can invasive spp replace native?

    • some spp better competitors bc evolved in a more competitive environment

    • absense of enemies: herbivors, predators

    • local adaptation may only be important during extreme events

Genetic analyses of introduced spp

  • molecular identification

  • ex. Asian swamp eels

    • large, can breathe out of water and disperse across land, drought tolerant

    • morphologically similar to other swamp eels

    • pops of eels in FL and GA are genetically distinct: 2-3 diff spp

Distribution of genetic variation

  1. Bottleneck, so introduced spp has less genetic variation than pops in the native range

  2. Admixture in introduced pops, so more variation than pops in the native range

Mechanisms of reproduction

  • can determine whether a plant is reproding sexually or asexually, the breeding system, and the ploidy level

  • ex. one strain of Caulerpa taxifolia differs from the native strain bc it reprods asexually, grows vigorously and is more resistant to cold temps

  • ^invasive in the Mediterranean

Establishment and spread of invasive spp

  • Propagule pressure

    • most important factor in predicting whether an alien spp will become established

    • Propagule: a dispersal vector - any disseminitive unit or part of an organism capable of independent growth (seed, spore, mycelial frag, tuber, root, shoot)

    • Includes the number of individuals introduced and the number of release events

    • an important factor on the basis of demography alone

    • may be important genetically bc more propagules decrease the size of the bottleneck, and propagules from different pops result in increased genetic variation

  • usually a lag time btwn initial colonization and rapid pop growth/expansion

  • often considered to be ecological, but is also expected if evolutionary change is an important part of colonization

  • many examples of rapid evolutionary change come from recently introduced pops

Hybridization as a stimulus for invasiveness

  • evolutionary novelty

    • hybridization can produce novel genotypes or phenotypes that do not occur in either of the parental taxa

    • transgressive segregation: hybridization produces phenotypes that are extreme or outside the range of either parent type

  • genetic variation

    • increase in heterozygosity and allelic diversity may provide more opportunity for natural selection to cause adaptive change

  • fixed heterosis

    • many invasive plant species have mechs that can fix genotypes at single or multiple loci that demonstrate heterosis

    • increased fitness via fixed heterozygosity

  • reduction of genetic load

    • in small isolated pops, deleterious alleles become fixed and over time they accumulate leading to the slow erosion of fitness

    • hybridization reduces this genetic load

Eradication, management, and control

  • best way to get rid of an invasive spp is to eliminate it before it becomes abundant, widespread, and has had time to evolve beneficial adaptations

  • but if this doesn’t happen, genetics has a role to play in managing invasive spp

Rat eradications

  • normally occur on isolated island pops

  • little change of recolonization

  • where no obvious barriers, can use genetics to look for pop structure and identify isolated reprod units

  • may be able to eradicate portions of a pop at a time if high genetic structure

  • also may allow you to determine whether an eradication has failed bc individuals were missed or the area was recolonized

  • South Georgia Island

    • Rats brought with whaling and sealing vessels

    • rats devastating the plant and bird life

    • huge island, so expensive to eradicate whole thing, but rat habitat limited to coastal areas that are separated by glaciers

    • genetics show that rat pops are highly structured

    • eradication of small areas starts 10 years ago

Genetics and biological control

  • sterile insect technique

    • introduce genotypes that are sterile or reduce fertility in invasive species