Variation in allocation to sexual and asexual reproduction among clones of cyclically parthenogenetic Daphnia pulex (Crustacea: Cladocera)

• Published in: Biological journal of the Linnean Society Vol. 71; no. 4; pp. 771 - 787
• Main Authors: INNES, D.J., SINGLETON, D.R.
• Format: Journal Article
• Language: English
• Published: Elsevier Science Ltd 01.12.2000; Blackwell Publishing Ltd
• Subjects: asexual reproduction; clones; cost of males; Daphnia pulex; extinction; females; genotype; habitats; males; microcosm; parthenogenesis; sex allocation; sex and evolution; sexual reproduction; microcosm; cost of males; sex allocation; sex and evolution
• ISSN: 0024-4066; 1095-8312
• DOI: 10.1006/bijl.2000.0474

Organisms reproducing by cyclical parthenogenesis combine the benefits of both sexual and asexual reproduction within the same life cycle. Few studies have examined the evolution of variation in the pattern of investment in parthenogenetic compared to sexual reproduction. Seven clones of Daphnia pulex (Crustacea: Cladocera) varying in allocation to sexual reproduction, as measured by the production of males, were raised in isolation and together in a microcosm to study the pattern of sexual reproduction and the effect of this variation on clone fitness. Sex allocation for clones raised together a microcosm was similar to their allocation when raised in isolation, suggesting a genetic basis to the variation. Three clones showed a cost of producing males that lead to their extinction after about 30 days due to the lack of females required for the clones to persist by parthenogenetic reproduction. The remaining four clones persisted until the end of the 72-day experiment. Clones with little or no allocation to males showed no increased allocation to sexual females. The seven clones showed a greater variation in estimated fitness through male and female function than in total estimated fitness. The clone with the greatest total fitness gained most of its fitness through male function but also had a relatively high fitness through female function. Although one clone produced only females it had the next highest fitness. The three clones that went extinct because of a high investment in males had estimated fitness as high as some clones that persisted in the microcosm because of a higher investment in parthenogenetic reproduction. The similarity in total fitness among clones suggests that Daphnia pulex populations in temporary habitats maintain a sex polymorphism where different genotypes vary in functional gender ranging from female to primarily male.