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Competition induces adaptive shifts in caste ratios of a polyembryonic wasp


An important transition in insect life-history evolution was the shift from a solitary existence to living in groups comprising specialized castes. Caste-forming species produce some individuals that reproduce and others with worker functions that have few or no offspring1. Morphologically specialized castes are well known in eusocial species like ants and termites1, but castes have also evolved in less-studied groups like thrips, aphids and polyembryonic wasps2,3,4,5. Because selection acts at both the individual and the colony level, ratios of investment in different castes are predicted to vary with environmental factors like competition and resources6,7,8. However, experimental evidence for adaptive shifts in caste ratios is limited9 owing to the experimental difficulty of manipulating factors thought to influence caste ratios10,11,12,13, and because some species produce behaviourally flexible castes that switch tasks in response to colony needs14,15. Unlike other caste-forming species, the broods of polyembryonic wasps develop clonally, so that increased production of one caste probably results in decreased production of the other16. Here we show that the polyembryonic wasp Copidosoma floridanum alters caste ratios in response to interspecific competition. Our results reveal a distinct trade-off by C. floridanum between reproduction and defence, and show experimentally that caste ratios shift in an adaptive manner.

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Figure 1: Light micrograph of a C. floridanum precocious larva (a) and first instar reproductive larva (b).
Figure 2: The effects of multiparasitism by M. demolitor on caste formation by C. floridanum.
Figure 3: Mean number (± s.e.) of precocious larvae in hosts multiparasitized by M. demolitor and control hosts parasitized by C. floridanum only.

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  1. Robinson, G. E. Regulation of division of labor in insect societies. Annu. Rev. Entomol. 37, 637–665 ( 1992).

    Article  CAS  Google Scholar 

  2. Crespi, B. J. Eusociality in Australian gall thrips. Nature 359, 724–726 (1992).

    Article  ADS  Google Scholar 

  3. Stern, D. L. & Foster, W. A. The evolution of soldiers in aphids. Biol. Rev. 71, 27–79 (1996).

    Article  CAS  Google Scholar 

  4. Cruz, Y. P. A sterile defender morph in a polyembryonic hymenopterous parasite. Nature 294, 446–447 ( 1981).

    Article  ADS  Google Scholar 

  5. Grbic, M., Ode, P. J. & Strand, M. R. Sibling rivalry and brood sex ratios in polyembryonic wasps. Nature 360, 254– 256 (1992).

    Article  ADS  Google Scholar 

  6. Oster, G. & Wilson, E. O. Caste and Ecology in the Social Insects (Princeton Univ. Press, Princeton, 1978).

    Google Scholar 

  7. Herbers, J. M. On caste ratios in ant colonies: population responses to changing environments. Evolution 14, 575–585 (1980).

    Article  Google Scholar 

  8. Hasegawa, E. The optimal caste ratio in polymorphic ants: estimation and empirical evidence. Am. Nat. 149, 706–711 (1997).

    Article  Google Scholar 

  9. Passera, L., Roncin, E., Kaufmann, B. & Keller, L. Increased soldier production in ant colonies exposed to intraspecific competition. Nature 379, 630–631 ( 1996).

    Article  ADS  CAS  Google Scholar 

  10. Johnston, A. B. & Wilson, E. O. Correlates of variation in the major/minor ratio of the ant, Pheidole dentata (Hymenoptera: Formicidae). Ann. Entomol. Soc. Am. 78, 8–11 (1985).

    Article  ADS  Google Scholar 

  11. Hasegawa, E. Nest defense and early production of the major workers in the dimorphic ant Colobopsis nipponicus (Wheeler) (Hymenoptera: Formicidae). Behav. Ecol. Sociobiol. 33, 73–77 (1993).

    Article  Google Scholar 

  12. Wilson, E. O. The relation between caste ratios and division of labor in the ant genus Pheidole (Hymenoptera: Formicidae). Behav. Ecol. Sociobiol. 16, 89–98 ( 1984).

    Article  Google Scholar 

  13. Beshers, S. N & Traniello, J. F. The adaptiveness of worker demography in the attine ant Trachymyrmex septentrionalis. Ecology 75, 763–775 ( 1994).

    Article  Google Scholar 

  14. Gordon, D. M. Group-level dynamics in harvester ants: young colonies and the role of patrolling. Anim. Behav. 35, 833–843 (1987).

    Article  Google Scholar 

  15. Gordon, D. M. Dynamics of task switching in harvester ants. Anim. Behav. 38, 194–204 (1989).

    Article  Google Scholar 

  16. Strand, M. R. & Grbic, M. The development and evolution of polyembryonic insects. Curr. Top. Dev. Biol. 35, 121– 159 (1997).

    Article  CAS  Google Scholar 

  17. Strand, M. R. Oviposition behavior and progeny allocation of the polyembryonic wasp Copidosoma floridanum (Hymenoptera: Encyrtidae). J. Insect Behav. 2, 355–368 ( 1989).

    Article  Google Scholar 

  18. Ode, P. J. & Strand, M. R. Progeny and sex allocation decisions of the polyembryonic wasp, Copidosoma floridanum. J. Anim. Ecol. 64, 213–224 ( 1995).

    Article  Google Scholar 

  19. Browning, H. W. & Oatman, E. R. Intra- and interspecific relationships among some parasites of Trichoplusia ni. Environ. Entomol. 13, 551–556 (1984).

    Article  Google Scholar 

  20. Strand, M. R., Johnson, J. A. & Culin, J. D. Intrinsic, interspecific competition between the polyembryonic parasitoid, Copidosoma floridanum and solitary endoparasitoid Microplitis demolitor in Pseudoplusia includens. Entomol. Exp. Appl. 55, 275–284 ( 1990).

    Article  Google Scholar 

  21. Godfray, H. C. J. Parasitoids: Behavioral and Evolutionary Ecology (Princeton Univ. Press, Princeton, 1994).

    Google Scholar 

  22. Wheeler, D. E. The developmental basis of worker caste polymorphism in ants. Am. Nat. 138, 1218–1238 (1991).

    Article  Google Scholar 

  23. Grbic, M,, Nagy, L. M. & Strand, M. R. Development of polyembryonic insects: a major departure from typical insect embryogenesis. Dev. Genes Evol. 208, 69–81 (1998).

    Article  CAS  Google Scholar 

  24. Baehrecke, E. H., Aiken, J. M., Dover, B. A. & Strand, M. R. Ecdysteroid induction of embryonic morphogenesis in a parasitic wasp. Dev. Biol. 158, 275–287 (1993).

    Article  CAS  Google Scholar 

  25. Grbic, M., Rivers, D. & Strand, M. R. Caste formation in the polyembryonic wasp Copidosoma floridanum (Hymenoptera: Encyrtidae): in vivo and in vitro analysis. J. Insect Physiol. 43, 553–565 (1997).

    Article  CAS  Google Scholar 

  26. Strand, M. R. & Pech, L. L. Immunological basis for compatibility in parasitoid-host relationships. Annu. Rev. Entomol. 40, 31–56 (1995).

    Article  CAS  Google Scholar 

  27. Strand, M. R., Witherell, R. A. & Trudeau, D. Two Microplitis demolitor polyDNAvirus mRNAs expressed in hemocytes of Pseudoplusia includens contain a common cysteine-rich domain. J. Virol. 71, 2146– 2156 (1997).

    CAS  PubMed  PubMed Central  Google Scholar 

  28. Webb, B. A. in The Insect Viruses (eds Miller, L. K. & Ball, A. L.) 105– 139 (Plenum, New York, 1998).

    Book  Google Scholar 

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We thank J. Johnson for assistance during the study, M. Grbic for discussions, and M. Visser, F. Wackers and W. van der Putten for comments on an early draft of the manuscript. This work was supported by the NSF.

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Correspondence to Michael R. Strand.

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Harvey, J., Corley, L. & Strand, M. Competition induces adaptive shifts in caste ratios of a polyembryonic wasp. Nature 406, 183–186 (2000).

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