Abstract Detail

Ecology

Harvey, Alan [1], Dorfzaun, Alexandra [1], Corbin, Bradley [2].

Ecological role of post-floral nectaries in Richardia scabra (Rubiaceae).

Many species of plants use extrafloral nectaries (EFNs) to enlist the help of aggressive, territorial ants as bodyguards against herbivores. EFNs are usually separated physically or temporally from floral nectaries in most plants, presumably to minimize ant-pollinator encounters, nectar robbing by ants, or both. EFNs also tend to be located closest to that part of the plant most vulnerable to herbivory, which increases the potential for negative ant effects when flowers or fruits are the most vulnerable to herbivory. In Richardia scabra, the same floral nectaries that attract pollinators continue to secrete nectar for several days after the corolla abscises, at which point they are visited by several species of sugar-loving ants (as well as dozens of other species of insects). The tightly packed inflorescences usually have floral and post-floral nectaries (PFNs) active simultaneously, bringing ants and pollinators into close contact. We are investigating whether these PFNs are ecologically equivalent to EFNs, and whether the presence of ants might incur costs for the plant either directly through agonism towards pollinators or indirectly through nectar robbing. The main herbivores we observed on R. scabra were seed predators (pentatomid stink bugs and the minute seed weevil Asperauleutes tachygonoides) on R. scabra fruits. Plants with Tanglefoot™ barriers that excluded ants and other non-flying arthropods suffered significantly greater rates of seed damage than did control plants. Agonistic interactions between potential pollinators and ants were occasionally observed on leaves but not on flowers. On most local plant species with EFNs, the tiny rover ant Brachymyrmex patagonicus ignores or avoids other insects, but on R. scabra it actively attacks and repels A. tachygonoides. The total number of seeds per inflorescence did not differ between treatment and control plants, implying that ant aggression towards pollinators did not significantly reduce seed set. Ants visited PFNs but not floral nectaries in the same inflorescence. Thus, PFNs in R. scabra appear to be ecologically equivalent to EFNs, with little evidence of costs to the plant due to pollinator repulsion or nectar robbing by ants.

1 - Georgia Southern University, Biology, 4324 Old Register Road, Statesboro, GA, 30458, USA
2 - Mercer University , School of Medicine, 1250 E 66th Street , Savannah, GA, 31404, USA

Keywords:
mutualism
Post-floral nectaries
RIchardia scabra.

Presentation Type: Oral Paper
Session: 25, Ecology Section: Seed Ecophysiology
Location: 104/Savannah International Trade and Convention Center
Date: Tuesday, August 2nd, 2016
Time: 10:15 AM
Number: 25001
Abstract ID:695
Candidate for Awards:None