Ref ID : 765
John J. Gilbert; Control of morphotype frequency distributions in populations of the rotifer Asplanchna sieboldi: Factors influencing the production of the tocopherol-dependent cruciform and campanulate morphotypes. Ecology 62(5):1299-1310, 1981
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When the diet of A. sieboldi contains tocopherol and certain types of prey, such as congeners, females develop into one of two morphotypes-cruciform or campanulate. The frequency with which these morphotypes can be produced in a population is a function of: the probabilities that the daughters of amictic (asexual) cruciforms and campanulates will be cruciform and campanulate; the probabilities that cruciforms and campanulates will be amictic and mictic; and the birth rates of amictic cruciforms and campanulates. These reproductive parameters were determined from laboratory observations on individuals from populations maintained on a diet of A. brightwelli with d-alpha-tocopherol at 10E-7 mol/L. A Markovian model was developed and, when used with these data and intiated with a single amictic cruciform, showed that an equilibrium distribution of 34.8% amictic cruciforms, 51.0% mictic cruciforms, 8.5% amictic campanulates and 5.7% mictic campanulates was approached at a rapidly decelerating rate and finally attained after 15 generations. Varying the inputs to this model showed that very high equilibrium frequencies of campanulates could be produced if most campanulates were amictic and had predominantly campanulate daughters, even if almost all daughters of cruciform parents were cruciform, but could not be produced even by dramatically increasing either the probability of cruciforms bearing campanulate offspring or the reproductive rate of amictic campanulates relative to that of amictic cruciforms. The high proportions of campanulates often observed in natural populations could no be produced if the reproductive parameters of the amictic cruciforms and campanulates were similar to those determined in this study, unless the cruciforms were preferentially eliminated through cannibalism or predation. Shifts in the frequency distributions of cruciforms and campanulates, such as have been noted in natural populations, could be due to: preogressions to equilibrium distributions; variations in the types of prey available; changes in environmental factors that differentially affect the reproductive parameters of the two amictic morphotypes; different intensities of selective, intermorphotypic cannibalism; successions of invertebrate and vertebrate predators that differentially ingest the two morphotypes; and clonal replacements that alter characteristics of the two morphotypes affecting reproduction and survival.