Igwe, Alexandria , McKenna, Mary .
Elemental Defense in Alyssum murale: Effect on a Specialist Herbivore, Pieris rapae.
Alyssum murale (Brassicaceae) is a nickel-hyperaccumulator from serpentine habitats in the Mediterranean region. The Elemental Defense Hypothesis (Martens & Boyd 1994) suggests that metal hyperaccumulators benefit by reduced herbivory on tissues with high levels of heavy metals. Generalist herbivores may gain protection against elemental defenses by a dilution effect;small amounts of dietary toxins may not have significant negative consequences.A previous study (Kissell and McKenna, 2008) showed that elemental defense does not protect A. murale seedlings from generalist herbivores (slugs,Gastropoda) under field conditions. This study examines the response of a specialist herbivore (Pieris rapae ) to elemental defense (Ni) in A. murale. We focused on two questions: Do high levels of soil nickel protect Alyssum murale against herbivory by a specialist herbivore (Pieris rapae)? and Does plant nickel concentration affect growth of the specialist herbivore Pieris rapae?A. murale seeds were germinated in soils at 0 ppm, 100 ppm, 500 ppm, and 2000 ppm Ni. Plants were transplanted after 4 months to grow singly in small pots at each nickel level for 8 weeks. Initial plant size (leaf number) was measured before placing 4 plants in a "no choice" array with one P. rapae larvae. Arrays were covered with a plastic lid containing a mesh top that prevented herbivores from escaping, but allowed airflow, light penetration, and watering. After one week,we removed the larvae for analysis and took final plant size measurements. We found high herbivory in controls; significantly fewer leaves remained after exposure to the herbivore for one week (p = 0.003). All treatments with nickel deterred herbivory. There was no difference in plant size (leaf number) after exposure to the herbivore for plants in 100 and 500 ppm Ni. Plants in soil with 2000 ppm Ni showed significantly greater leaf number after exposure to the herbivore (p=0.04), suggesting net increase in biomass over the one week period. High nickel concentrations appear to interfere with larval growth; high Ni levels resulted in smaller P. rapae larvae. In addition, fewer larvae were recovered from arrays with highest nickel levels. Future studies will include a wider group of generalist and specialist herbivores to explore the extent of nickel transfer from A. murale to higher trophic levels. It is important to gain a greater understanding of the interactions between Alyssum murale and insects in natural communities before permitting the introduction of this species for phytoremediation of contaminated soils.
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1 - Howard University, Biology Department, 415 College St NW, Washington, DC, 20059, USA
2 - HOWARD UNIVERSITY, Biology Department, 415 College St. N.W., Washington, DC, 20059, USA
Presentation Type: Poster:Posters for Sections
Location: Battelle South/Convention Center
Date: Monday, July 9th, 2012
Time: 5:45 PM