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THE ECOLOGY AND GENETICS OF FITNESS IN CHLAMYDOMONAS. XIII. FITNESS OF LONG‐TERM SEXUAL AND ASEXUAL POPULATIONS IN BENIGN ENVIRONMENTS
Author(s) -
Renaut Sébastien,
Replansky Taissa,
Heppleston Audrey,
Bell Graham
Publication year - 2006
Publication title -
evolution
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.84
H-Index - 199
eISSN - 1558-5646
pISSN - 0014-3820
DOI - 10.1111/j.0014-3820.2006.tb01864.x
Subject(s) - biology , genetic fitness , epistasis , asexual reproduction , evolutionary biology , sexual reproduction , genetic load , genetics , genetic variation , gamete , evolution of sexual reproduction , sexual selection , meiosis , ecology , population , gene , sperm , demography , inbreeding , sociology
We measured the mean fitness of populations of Chlamydomonas reinhardtii maintained in the laboratory as obligately sexual or asexual populations for about 100 sexual cycles and about 1000 asexual generations. Sexuality (random gamete fusion followed by meiosis) is expected to reduce mutational load and increase mean fitness by combining deleterious mutations from different lines of descent. We found no evidence for this process of mutation clearance: the mean fitness of sexual populations did not exceed that of asexual populations, whether measured through competition or in pure culture. We found instead that sexual progeny suffer an immediate loss in fitness, and that sexual lines maintain genetic variance for fitness. We suggest that sexual populations at equilibrium with selection in a benign environment may be mixtures of several or many epistatic genotypes with nearly equal fitness. Recombination between these genotypes reduces mean fitness and creates genetic variance for fitness. This may provide fuel for continued selection should the environment change.