Alien tree's sugary S.O.S. exploited by thieving tramp ant: unidirectional benefit in an alien, tritrophic mΘlange

Date of Award

2019

Degree Name

M.S. in Biology

Department

Department of Biology

Advisor/Chair

Advisor: Chelse Prather

Abstract

For centuries, the invasive, extrafloral nectary-bearing tree, Triadica sebifera (Euphorbiaceae), was virtually free from natural enemies. In 2004, the Triadica-specific leaf-rolling moth Caloptilia triadicae (Lepidoptera: Gracillariidae) appeared in the invaded range. Simultaneously, populations of the destructive tawny crazy ant, Nylanderia fulva (Hymenoptera: Formicidae), spread cospatially across the southeast. Prior to this study, it was unknown if Triadica induced extrafloral nectar production as an indirect defense against Caloptilia, or if it formed a mutualistic association with - or was exploited by - Nylanderia. To examine these potential associations, and their implications for southern ecosystems, I conducted a series of lab, greenhouse, and field experiments in coastal Texas.In response to herbivory by Caloptilia, Triadica seedlings strongly induced extrafloral nectar production; percent leaf damage explained 57% of the variation in cumulative nectar volume (p < 0.0001). Additionally, nectar production was strongly tied to the life stage of Caloptilia, increasing rapidly with the onset of leaf-rolling and decreasing sharply after adult emergence. Large Caloptilia infestations reduced stem elongation in potted Triadica (R ▓ = 0.32, p < 0.0001), but had no effect on leaf production, biomass, or survivorship. In all trials, Nylanderia exploited available nectar resources without attacking Caloptilia larvae. Seedling nectar volume was significantly lower when ants were present (p = 0.008) while no differences in Caloptilia survivorship were observed (p = 0.56). Likewise, no differences in Caloptilia abundance or parasitism rates were observed when ants were excluded from Triadica saplings in the field (p-values > 0.8). These results suggest that Triadica supplies Nylanderia workers with a carbohydrate resource while sustaining heavy herbivore damage and that neither Triadica nor Caloptilia benefit indirectly from Nylanderia foraging. Therefore, Nylanderia appears to be the only beneficiary in this alien, tritrophic mΘlange.

Keywords

Ecology, Chinese tallow tree, Triadica sebifera, tawny crazy ant, Nylanderia fulva, Caloptilia triadicae, extrafloral nectar, induced defense, biological invasion, facultative mutualism

Rights Statement

Copyright © 2019, author

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