Plant Systematics and Evolution

, Volume 201, Issue 1–4, pp 131–138 | Cite as

The consequences of specialization for pollination in a rare South African shrub,Ixianthes retzioides (Scrophulariaceae)

  • Kim E. Steiner
  • V. B. Whitehead


Ixianthes retzioides is a rare South African shrub with large yellow oil-secreting flowers. Populations studied previously revealed low levels of reproductive success and the absence of a specialized oil-collecting pollinator. We report the discovery of a population in which the predicted specialist pollinator,Rediviva gigas, is present. The presence of this oil-collecting bee resulted in a mean fruit set per plant of 97.2 ± 8.3% (N = 9) and a mean seed set of 331.6 ± 162.6 (N = 52). This represents a 7.4-fold increase in fruit set and a 7.8-fold increase in seed set over a previously studied population lacking the specialist pollinator. The contrast between populations with and without the specialist pollinator dramatically illustrates the potential benefits and costs of specialization for pollination, respectively.

Key words

Scrophulariaceae Ixianthes Melittidae Rediviva Floral oil oil-collecting bees specialization for pollination reproductive success 


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  1. Anderson, W. R., 1979: Floral conservatism in neotropicalMalpighiaceae. — Biotropica11: 219–223.Google Scholar
  2. —, 1980: Cryptic self-fertilization in theMalpighiaceae. — Science207: 892–893.Google Scholar
  3. Buchmann, S. L., 1987: The ecology of oil flowers and their bees. — Annual Rev. Ecol. Syst.18: 343–369.Google Scholar
  4. Cane, J. H., Eickwort, G. C., Wesley, F. R., Spielholz, J., 1983: Foraging, grooming and mate-seeking behaviors ofMacropis nuda (Hymenoptera, Melittidae) and use ofLysimachia (Primulaceae) oils in larval provision and cell linings. — Amer. Midl. Naturalist110: 257–264.Google Scholar
  5. Cocucci, A. A., 1991: Pollination biology ofNierembergia (Solanaceae). — Pl. Syst. Evol.174: 17–35.Google Scholar
  6. Deacon, H. J., Jury, M. R., Ellis, F., 1992: Selective regime and time. — InCowling, R., (Ed.): The ecology of Fynbos, pp. 6–22. — Oxford: Oxford University Press.Google Scholar
  7. Houston, T. F., Lamont, B. B., Radford, S., Errington, S. G., 1993: Apparent mutualism betweenVerticordia nitens andV. aurea (Myrtaceae) and their oil-ingesting bee pollinators (Hymenoptera:Colletidae). — Austral. J. Bot.41: 369–380.Google Scholar
  8. Marloth, R., 1932: The Flora of South Africa.3. — Cape Town: Darter.Google Scholar
  9. Molau, U., 1981: The genusCalceolaria in NW South America. VI. The sectionsUrticopsis, Lobatae andMicranthera. — Nordic J. Bot.1: 165–185.Google Scholar
  10. Stebbins, G. L., Major, J., 1965: Endemism and speciation in the California flora. — Ecol. Monogr.35: 1–31.Google Scholar
  11. Steenis, C. G. G. J., Van, 1978: Rheophytes in South Africa. — Bothalia12: 543–546.Google Scholar
  12. Steiner, K. E., 1989: The pollination ofDisperis (Orchidaceae) by oil-collecting bees in southern Africa. — Lindleyana4: 164–183.Google Scholar
  13. —, 1992: Two newDiascia species (Scrophulariaceae) from the Little Karoo. — S. African J. Bot.58: 39–47.Google Scholar
  14. —, 1993: HasIxianthes (Scrophulariaceae) lost its special bee? — Pl. Syst. Evol.185: 7–16.Google Scholar
  15. —, 1994: Adaptive radiation for pollination in a South African orchid genus. — Amer. J. Bot.81: 189.Google Scholar
  16. —, 1988: The association between oil-producting flowers and oil-collecting bees in the Drakensberg of southern Africa. — Monogr. Syst. Bot. Missouri Bot. Gard.25: 259–277.Google Scholar
  17. —, —, 1991: Oil flowers and oil bees: further evidence for pollinator adaptation. — Evolution45: 1493–1501.Google Scholar
  18. Vogel, S., 1974: Ölblumen und ölsammelnde Bienen. — Trop. Subtrop. Pflanzenwelt7: 285–547.Google Scholar
  19. —, 1988: Die Ölblumensymbiosen — Parallelismus und andere Aspekte ihrer Entwicklung in Raum und Zeit. — Z. Zool. Syst. Evolutionsforsch.26: 341–362.Google Scholar
  20. —, 1991: Pollination of four sympatric species ofAngelonia (Scrophulariaceae) by oil-collecting bees in NE Brazil. — Pl. Syst. Evol.178: 209–222.Google Scholar
  21. Whitehead, V. B., Steiner, K. E., 1993: A newRediviva bee (Hymenoptera:Apoidea: Melittidae) that collects oil from orchids. — African Entomol.1: 159–166.Google Scholar

Copyright information

© Springer-Verlag 1996

Authors and Affiliations

  • Kim E. Steiner
    • 1
  • V. B. Whitehead
    • 2
  1. 1.Compton HerbariumNational Botanical InstituteClaremontRepublic of South Africa
  2. 2.South African MuseumCape TownRepublic of South Africa

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