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Sex Allocation Theory for Facultatively Sexual Organisms Inhabiting Seasonal Environments: The Importance of Bet Hedging


Gerber, Nina; Booksmythe, Isobel; Kokko, Hanna (2018). Sex Allocation Theory for Facultatively Sexual Organisms Inhabiting Seasonal Environments: The Importance of Bet Hedging. The American Naturalist, 192(2):155-170.

Abstract

Adaptive explanations for dormancy often invoke bet hedging, where reduced mean fitness can be adaptive if it associates with reduced fitness variance. Sex allocation theory typically ignores variance effects and focuses on mean fitness. For many cyclical parthenogens, these themes become linked, as only sexually produced eggs undergo the dormancy needed to survive harsh conditions. We ask how sex allocation and the timing of sex evolve when this constraint exists in the form of a trade-off between asexual reproduction and sexual production of dormant eggs—the former being crucial for within-season success and the latter for survival across seasons. We show that male production can be temporally separated from or co-occur with sex, depending on whether direct (time) or indirect (population density) cues of the season’s end are available and whether population growth is density dependent. Sex generally occurs late in the season but is induced earlier in unpredictable environments. When only indirect cues are available, the temporal spread of sex, and with it the production of dormant stages, is even larger and, given sufficient mortality, leads to endogenous population cycles in which frequent sex coincides with high densities. In all scenarios, algorithms maximizing geometric mean fitness have reduced fitness variance compared with a hypothetical non–bet hedger, confirming that the timing of male production and sex in facultative seasonal settings can be bet-hedging traits.

Abstract

Adaptive explanations for dormancy often invoke bet hedging, where reduced mean fitness can be adaptive if it associates with reduced fitness variance. Sex allocation theory typically ignores variance effects and focuses on mean fitness. For many cyclical parthenogens, these themes become linked, as only sexually produced eggs undergo the dormancy needed to survive harsh conditions. We ask how sex allocation and the timing of sex evolve when this constraint exists in the form of a trade-off between asexual reproduction and sexual production of dormant eggs—the former being crucial for within-season success and the latter for survival across seasons. We show that male production can be temporally separated from or co-occur with sex, depending on whether direct (time) or indirect (population density) cues of the season’s end are available and whether population growth is density dependent. Sex generally occurs late in the season but is induced earlier in unpredictable environments. When only indirect cues are available, the temporal spread of sex, and with it the production of dormant stages, is even larger and, given sufficient mortality, leads to endogenous population cycles in which frequent sex coincides with high densities. In all scenarios, algorithms maximizing geometric mean fitness have reduced fitness variance compared with a hypothetical non–bet hedger, confirming that the timing of male production and sex in facultative seasonal settings can be bet-hedging traits.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Institute of Evolutionary Biology and Environmental Studies
Dewey Decimal Classification:570 Life sciences; biology
590 Animals (Zoology)
Uncontrolled Keywords:Ecology, Evolution, Behavior and Systematics
Language:English
Date:1 August 2018
Deposited On:12 Feb 2019 10:15
Last Modified:25 Sep 2019 00:06
Publisher:University of Chicago Press
ISSN:0003-0147
OA Status:Green
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1086/697727

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