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Ecological and Evolutionary Stability of Sperm-Dependent Parthenogenesis: Effects of Partial Niche Overlap between Sexual and Asexual Females

Lawrence R. Kirkendall and Nils Chr. Stenseth
Evolution
Vol. 44, No. 3 (May, 1990), pp. 698-714
DOI: 10.2307/2409446
Stable URL: http://www.jstor.org/stable/2409446
Page Count: 17
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Ecological and Evolutionary Stability of Sperm-Dependent Parthenogenesis: Effects of Partial Niche Overlap between Sexual and Asexual Females
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Abstract

Pseudogamous females reproduce parthenogenetically but require sperm. We analyze a density- and frequency-dependent model for the ecological and evolutionary stability of bisexual populations exposed to invasion by pseudogamous clones. In particular, we examine the effects of partial niche overlap and asymmetric competition between sexual and asexual forms. The model predicts that for a variety of relative fitness values for asexual females, pseudogamous forms can successfully invade bisexual populations. The probability of successful invasion increases as niche overlap decreases. Furthermore, invaded populations are often likely to be stable; for the parameter values analyzed, only combinations of nearly complete niche overlap and high asexual fitness will lead to extinction. Even such combinations will be stable under pronounced asymmetric competition. Asymmetric competition does not, however, affect the invadability of bisexual populations. The model predicts that stable populations cannot have more than three or four females per male; populations with more biased sex ratios are expected to be unstable. We analyze available sex ratio data for pseudogamous insects, fish, and salamanders, and find significant changes in roughly one-half of the asexual-dominated populations, but in only one sexual-dominated population. This analysis includes previously unpublished data on population sex ratios in a pseudogamous bark beetle, Ips acuminatus. Some asexual-dominated populations have far more than four females per male, contrary to predictions of the model.

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