Document: CAR-3-88-1

Population dynamics of species with haploid-diploid life cycles.

THORNBER, C.S.* and S.D.GAINES

University of California, Santa Barbara, CA 93106 USA ¹

Abstract:
Traditionally, investigations of population dynamics have focused upon species with diploid life cycles; the dynamics of species with more complex lifecycles (containing multiple separate individuals) have been mostly overlooked. Here, we examined the haploid-diploid cycle, one type of complex life cycle that obligately alternates between independent, free living haploids and diploids. The null model we constructed predicts that, given equal demographic rates for the two forms, populations will contain 59% haploids and 41% diploids at equilibrium, not the traditionally assumed 1:1 ratio. We compared our predictions with patterns found in the field by conducting surveys of populations of three intertidal macroalgal species. Two species are located on the western coast of North America, Mazzaella flaccida and M. splendens, and one is found on the western coast of South America, M. laminarioides. The pattern of haploid dominance exhibited by M. splendens (66%) is fairly similar to our null model prediction; however, the mean haploid abundances of M. flaccida (73%) and M. laminarioides (75%) were significantly greater. We found no indication of a geographical gradient or an effect of seasonality on the relative abundance of haploids. The overwhelming dominance of haploid individuals indicates that there may be significant ecological differences between the two forms. This may result from either a haploid advantage due to increased survivorship, or a haploid disadvantage due to decreased fecundity, or both.

Keywords: isomorphic life cycle, haploid, diploid, population dynamics, macroalgae

This abstract is being presented at: 2:00 PM in session:
Oral Session #63: Evolutionary Ecology.