Evol Ecol Res 4: 79-90 (2002)     Full PDF if your library subscribes.

Macro-evolutionary trade-offs in the tephritid genus Urophora: benefits and costs of an improved plant gall

Berit Burkhardt and Helmut Zwölfer*

Department of Animal Ecology I, University of Bayreuth, D-95440 Bayreuth, Germany

Address all correspondence to Helmut Zwölfer, Schelmgraben 3, D-95473 Unternschreez (Haag), Germany.
e-mail: h.zwoelfer@freenet.de


The species of the tephritid genus Urophora differ greatly in the structure and function of the galls, which they induce on their Cardueae host plants. As this suggests the existence of trade-offs, we studied the benefits and costs of Urophora galls of different complexity using U. quadrifasciata, an oligophagous species with a primitive achene gall, and U. jaceana, a monophagous species with a complex multilocular ovariole-receptacle gall. Both Urophora species share Centaurea jacea as host plant and may co-exist in the same host populations without any sign of interspecific competition. Therefore, C. jacea was used in our tests as the standard host plant. We examined life-history data of the two species and tested the hypothesis that they respond in different ways to differences in host quality. Oviposition behaviour and larval development were studied on unfertilized and well-fertilized test plants grown under standardized nutrient regimes. The females of the specialist tephritid species, U. jaceana, had a much higher egg load, higher oviposition decisiveness, reduced time costs per deposited egg and they were able to select and adjust clutch size to the quality of the host plant. This oviposition behaviour maximized reproductive fitness, as even high larval densities in galls on well-fertilized hosts had no negative effect on larval weight. In addition, larvae in well-fertilized buds developed more biomass and produced females with a higher egg potential. Females of the generalist species, U. quadrifasciata, did not respond to differences in host quality. They could use flower heads during a broader temporal window, but had a lower reproductive reward per handling time and the larvae extracted much less energy and nutrients from the host. However, their development was distinctly faster, making a second generation per annum possible. Moreover, U. quadrifasciata has a much broader host range and is better adapted for long-distance dispersal, which has made it a very successful pioneer species in North America. The comparison of the two Urophora species shows that the evolution of a refined oviposition behaviour and the formation of a complex gall, which allows the import of nutrients via a newly formed vascular system, greatly increases the energy and nutrient rewards, as long as stable host populations can be exploited. On the other hand, the advanced gall type of Urophora involves higher costs of developmental time, univoltine generations and a high dependence on a specific host plant.

Keywords: effect of nitrogen, evolution of plant galls, host plant quality, host range, interspecific competition, oviposition behaviour, Tephritidae, Urophora.

IF you are connected using the IP of a subscribing institution (library, laboratory, etc.)
or through its VPN.


        © 2002 Helmut Zwölfer. All EER articles are copyrighted by their authors. All authors endorse, permit and license Evolutionary Ecology Ltd. to grant its subscribing institutions/libraries the copying privileges specified below without additional consideration or payment to them or to Evolutionary Ecology, Ltd. These endorsements, in writing, are on file in the office of Evolutionary Ecology, Ltd. Consult authors for permission to use any portion of their work in derivative works, compilations or to distribute their work in any commercial manner.

       Subscribing institutions/libraries may grant individuals the privilege of making a single copy of an EER article for non-commercial educational or non-commercial research purposes. Subscribing institutions/libraries may also use articles for non-commercial educational purposes by making any number of copies for course packs or course reserve collections. Subscribing institutions/libraries may also loan single copies of articles to non-commercial libraries for educational purposes.

       All copies of abstracts and articles must preserve their copyright notice without modification.