Sexual reproduction of Daphnia pulex in a temporary habitat |
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Authors: | David J Innes |
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Institution: | (1) Department of Biology, Memorial University of Newfoundland, St. John's, Newfoundland, A1B 3X9, Canada fax: (709)737‐3018, CA |
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Abstract: | Species of Daphnia (Crustacea: Cladocera) typically reproduce by cyclical parthenogenesis, in which a period of all-female parthenogenetic reproduction
is followed by sexual reproduction. Sex in Daphnia is determined by the environment, with factors such as temperature, photoperiod and crowding stimulating the production of
males and sexual females. Previous studies on Daphnia pulex from temporary pond habitats demonstrated the coexistence of male-producing and non-male-producing (NMP) females, as determined
under crowding in the laboratory. A strong genetic component to this sex allocation variation suggested that sex expression
in D. pulex is better described as a result of genotype-environment interaction. The present study examined the switch from parthenogenetic
to sexual reproduction in two temporary-pond populations of D. pulex. Both populations showed a very early investment in sexual reproduction, independent of population density, by producing
males very soon after the populations were reestablished from resting eggs in the early spring. Approximately 40% of the initial
broods were male. Additional evidence for gender specialization was obtained by observing the sex of two or three successive
broods for 85 individual females. Fifty-eight females produced successive broods of females, 13 females produced successive
broods of males and 14 females produced successive broods which included both male and female broods. Females that produced
successive female broods under natural conditions included a higher frequency of NMP females compared to a random sample of
females, confirming the existence of NMP females. Sexual females were observed in both populations after the first appearence
of males, suggesting that the presence of males may stimulate the production of sexual females. For D. pulex populations in a temporary environment, there appears to be an increased emphasis on sexual reproduction and a decreased
influence of the environment on sex determination, compared to Daphnia populations in more permanent habitats.
Received: 19 February 1996 / Accepted: 20 January 1997 |
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Keywords: | Sex allocation Daphnia pulex Parthenogenesis Sex determination Reproduction |
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