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Stage-structured cycles promote genetic diversity in a predator–prey system of Daphnia and algae


Competition theory predicts that population fluctuations can promote genetic diversity when combined with density-dependent selection1,2. However, this stabilizing mechanism has rarely been tested, and was recently rejected as an explanation for maintaining diversity in natural populations of the freshwater herbivore Daphnia pulex3. The primary limitation of competition theory is its failure to account for the alternative types of population cycles that are caused by size- or stage-dependent population vital rates—even though such structure both explains the fluctuating dynamics of many species4 and may alter the outcome of competition5. Here we provide the first experimental test of whether alternative types of cycles affect natural selection in predator–prey systems. Using competing Daphnia genotypes, we show that internally generated, stage-structured cycles substantially reduce the magnitude of selection (thereby contributing to the maintenance of genetic diversity), whereas externally forced cycles show rapid competitive exclusion. The change in selection is ecologically significant, spanning the observed range in natural populations3. We argue that structured cycles reduce selection through a combination of stalled juvenile development and stage-specific mortality. This potentially general fitness-equalizing mechanism may reduce the need for strong stabilizing mechanisms to explain the maintenance of genetic diversity in natural systems.

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Figure 1: Population and genotype dynamics in three externally driven environments.
Figure 2: Population and genotype dynamics in coupled predator–prey environments.
Figure 3: Selection coefficients for each treatment.
Figure 4: Population structure in coupled predator–prey environments and externally driven environments.


  1. 1

    Armstrong, R. A. & McGehee, R. Competitive exclusion. Am. Nat. 115, 151–170 (1980)

    MathSciNet  Article  Google Scholar 

  2. 2

    Huisman, J. & Weissing, F. J. Biodiversity of plankton by species oscillations and chaos. Nature 402, 407–410 (1999)

    ADS  Article  Google Scholar 

  3. 3

    Nelson, W. A. Competition in Structured Zooplankton Populations: Coupling Population Genetics and Dynamics Using Theoretical and Experimental Approaches. Ph.D. Thesis, Univ. Calgary (2004)

    Google Scholar 

  4. 4

    Murdoch, W. W. et al. Single-species models for many-species food webs. Nature 417, 541–543 (2002)

    ADS  CAS  Article  Google Scholar 

  5. 5

    de Roos, A. M., Persson, L. & McCauley, E. The influence of size-dependent life-history traits on the structure and dynamics of populations and communities. Ecol. Lett. 6, 473–487 (2003)

    Article  Google Scholar 

  6. 6

    Lynch, M. The limits to life history evolution in Daphnia . Evolution 38, 465–482 (1984)

    Article  Google Scholar 

  7. 7

    Lynch, M. The consequences of fluctuating selection for isozyme polymorphisms in Daphnia . Genetics 115, 657–669 (1987)

    CAS  PubMed  PubMed Central  Google Scholar 

  8. 8

    Mort, M. A. Bridging the gap between ecology and genetics: the case of freshwater zooplankton. Trends Ecol. Evol. 6, 41–45 (1991)

    CAS  Article  Google Scholar 

  9. 9

    Dufresne, F. & Hebert, P. D. N. Polyploidy and clonal diversity in an arctic cladoceran. Heredity 75, 45–53 (1995)

    Article  Google Scholar 

  10. 10

    Hebert, P. D. N. & Crease, T. J. Clonal diversity in populations of Daphnia pulex reproducing by obligate parthenogenesis. Heredity 51, 353–369 (1983)

    Article  Google Scholar 

  11. 11

    Weider, L. J. Spatial and temporal genetic heterogeneity in a natural Daphnia population. J. Plankton Res. 7, 101–123 (1985)

    Article  Google Scholar 

  12. 12

    Hebert, P. D. N. Niche overlap among species in the Daphnia carinata complex. J. Anim. Ecol. 46, 399–409 (1977)

    Article  Google Scholar 

  13. 13

    Loaring, J. M. & Hebert, P. D. N. Ecological differences among clones of Daphnia pulex Leydig. Oecologia 51, 162–168 (1981)

    ADS  Article  Google Scholar 

  14. 14

    Hebert, P. D. N. & Crease, T. J. Clonal coexistence in Daphnia pulex (Leydig): another planktonic paradox. Science 207, 1363–1365 (1980)

    ADS  Article  Google Scholar 

  15. 15

    Hardin, G. The competitive exclusion principle. Science 131, 1292–1298 (1960)

    ADS  CAS  Article  Google Scholar 

  16. 16

    Chesson, P. Mechanisms of maintenance of species diversity. Annu. Rev. Ecol. Syst. 31, 334–366 (2000)

    Article  Google Scholar 

  17. 17

    de Roos, A. M. & Persson, L. Competition in size-structured populations, mechanisms inducing cohort formation and population cycles. Theor. Popul. Biol. 63, 1–16 (2003)

    Article  Google Scholar 

  18. 18

    McCauley, E., Nisbet, R. M., de Roos, A. M., Murdoch, W. W. & Gurney, W. S. C. Structured population models of herbivorous zooplankton. Ecol. Monogr. 66, 479–501 (1996)

    Article  Google Scholar 

  19. 19

    McCauley, E. & Murdoch, W. W. Cyclic and stable populations: plankton as paradigm. Am. Nat. 129, 97–121 (1987)

    Article  Google Scholar 

  20. 20

    Persson, L., Bystram, P., Wahlstram, E., Andersson, J. & Hjelm, J. Interactions among size-structured populations in a whole lake experiment: size- and scale dependent processes. Oikos 87, 139–156 (1999)

    Article  Google Scholar 

  21. 21

    McCauley, E., Nisbet, R. M., Murdoch, W. W., de Roos, A. M. & Gurney, W. S. C. Large-amplitude cycles of Daphnia and its algal prey in enriched environments. Nature 402, 653–656 (1999)

    ADS  CAS  Article  Google Scholar 

  22. 22

    Spitze, K. Chaobrus predation and the life-history evolution in Daphnia pulex: temporal pattern of population diversity, fitness, and mean life-history. Evolution 45, 82–92 (1991)

    Article  Google Scholar 

  23. 23

    Carvalho, G. R. The clonal ecology of Daphnia magna (Crustacea: Cladocera) II: thermal differentiation among seasonal clones. J. Anim. Ecol. 56, 469–478 (1987)

    Article  Google Scholar 

  24. 24

    Mitchell, S., Carvalho, G. R. & Weider, L. J. Stability of genotype frequencies in an intermittent Daphnia magna population. Arch. Hydrobiol. Spec. Issues Adv. Limnol. 52, 185–194 (1998)

    Google Scholar 

  25. 25

    Kilham, S. S., Kreeger, D. A., Lynn, S. G., Goulder, C. E. & Herrera, L. COMBO: a defined freshwater culture medium for algae and zooplankton. Hydrobiologia 377, 147–159 (1998)

    CAS  Article  Google Scholar 

  26. 26

    Watson, S., McCauley, E. & Downing, J. A. Variation in algal community structure with enrichment. Can. J. Fish. Aquat. Sci. 49, 2605–2610 (1992)

    CAS  Article  Google Scholar 

  27. 27

    Hebert, P. D. N. & Beaton, M. J. Methodologies for Allozyme Analysis using Cellulose Acetate Electrophoresis (Helena Laboratories, Beaumont, Texas, 1993)

    Google Scholar 

  28. 28

    Yee, T. W. & Wild, C. J. Vector generalized additive models. J. Roy. Stat. Soc. B. 58, 481–493 (1996)

    MathSciNet  MATH  Google Scholar 

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We thank P. Hebert for his electrophoresis expertise and J. Fox for constructive comments on the original manuscript. The research was supported by grants from NSERC to E.M.

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Correspondence to William A. Nelson.

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The authors declare that they have no competing financial interests.

Supplementary information

Supplementary Methods

Derivation of the equation and statistical model used to calculate selection coefficients from continuous-time estimates of genotype proportions. (DOC 62 kb)

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Nelson, W., McCauley, E. & Wrona, F. Stage-structured cycles promote genetic diversity in a predator–prey system of Daphnia and algae. Nature 433, 413–417 (2005).

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