title: Higher rates of sex evolve during adaptation to more complex environments.
abstract: A leading hypothesis for the evolutionary maintenance of sexual reproduction proposes that sex is advantageous because it facilitates adaptation. Changes in the environment stimulate adaptation but not all changes are equivalent; a change may occur along one or multiple environmental dimensions. In two evolution experiments with the facultatively sexual rotifer Brachionus calyciflorus, we test how environmental complexity affects the evolution of sex by adapting replicate populations to various environments that differ from the original along one, two, or three environmental dimensions. Three different estimates of fitness (growth, lifetime reproduction, and population density) confirmed that populations adapted to their new environment. Growth measures revealed an intriguing cost of complex adaptations: populations that adapted to more complex environments lost greater amounts of fitness in the original environment. Furthermore, both experiments showed that B. calyciflorus became more sexual when adapting to a greater number of environmental dimensions. Common garden experiments confirmed that observed changes in sex were heritable. As environments in nature are inherently complex these findings help explain why sex is maintained in natural populations.
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada M5S 3B2 pepijn.luijckx@gmail.com.
authors.forename: Pepijn
authors.initials: P
authors.lastname: Luijckx
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada M5S 3B2.
authors.forename: Eddie Ka Ho
authors.initials: EK
authors.lastname: Ho
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada M5S 3B2.
authors.forename: Majid
authors.initials: M
authors.lastname: Gasim
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada M5S 3B2.
authors.forename: Suyang
authors.initials: S
authors.lastname: Chen
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada M5S 3B2.
authors.forename: Andrijana
authors.initials: A
authors.lastname: Stanic
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada M5S 3B2.
authors.forename: Connor
authors.initials: C
authors.lastname: Yanchus
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada M5S 3B2.
authors.forename: Yun Seong
authors.initials: YS
authors.lastname: Kim
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada M5S 3B2.
authors.forename: Aneil F
authors.initials: AF
authors.lastname: Agrawal
mesh_terms: D000064:Acclimatization; D000222:Adaptation, Physiological; D000818:Animals; D005075:Biological Evolution; D004777:Environment; D005260:Female; D056084:Genetic Fitness; D008297:Male; D012098:Reproduction / Q000502:physiology; D012403:Rotifera / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D054712:Salinity; D012723:Sex; D013696:Temperature
keywords: Fisher–Muller hypothesis; Hill–Robertson interference; adaptation; evolution of sex