Document: SUS-3-46-7

Alligators, deer, and the evolutionary ecology of a native Louisiana iris.

MOPPER, S.* ¹, C.J.CRINER ¹, K.H.HASENSTEIN ¹, E.MOUTON ², M.A.TOBLER ¹, Y.WANG ¹ and P.A.VAN ZANDT ¹

Univeristy of Lousiana, Lafayette, LA 70504-2451 USA ¹
State of Louisiana Dept. of Wildlife and Fisheries, LA USA ²

Abstract:
Iris hexagona typically occurs in freshwater wetlands but a large population has colonized the saline soils of Marsh Island, Louisiana. Irises are bumble-bee pollinated and produce big blue flowers and huge seed pods. They also reproduce clonally through stout, branching rhizomes. We report here on field experiments, allozyme studies, and phytochemical analyses that suggest a link between alligators, deer, and the evolutionary ecology of I. hexagona. Most Marsh Island irises cannot reproduce sexually because of heavy flower predation by white-tailed deer. Alligators are abundant and prey on the deer, which avoid flowering plants on the water's edge. These edge plants develop normal seeds that can disperse via the island's bayous and tidal channels. Iris clonal patches vary in tolerance to salinity, which affects plant chemistry and resource allocation. Salinity increases iris seed production, and developing seeds contain high concentrations of abscisic acid (ABA), a plant growth regulator associated with stress tolerance. This maternal effect may increase germination success, because seeds from salinity-exposed plants germinate more readily than seeds from non-stressed plants. By eliminating iris flowers and sexual reproduction, deer can reduce genetic variation in the plant population and prevent maternally induced salinity tolerance. However, deer may also benefit irises because plants whose flowers were removed produced 24% more belowground biomass than unbrowsed plants. This could enhance iris survival on Marsh Island, where erosion is an important threat. Alligators, by discouraging floral predators, may help sustain a balance between sexual reproduction and rhizome allocation, and indirectly influence I. hexagona survival and adaptation in the salt marsh environment.

Keywords: : abscisic acid, belowground biomass, clonal reproduction, floral predation, germination success, salinity stress, maternal effects, sexual reproduction

This abstract is being presented at: 1:00 PM in session:
Oral Session #63: Evolutionary Ecology.