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Herbicides, Reservoirs, and Daphnia Reproduction: Is There a Cost to Male Production?

Stoeckel, James A
http://rave.ohiolink.edu/etdc/view?acc_num=miami1186153732

Abstract Details

2007, Doctor of Philosophy, Miami University, Zoology.
Herbicides and reservoirs are ubiquitous in the Midwestern United States. Reservoirs can act as storage units, slowly releasing herbicides into outflowing stream(s). Atrazine is the most widely used herbicide in the world. Previous studies yielded conflicting results regarding its ability to stimulate male production by Daphnia, an effect hypothesized to lower population growth rates. In this study, atrazine consistently flushed into Acton Reservoir during spring. The reservoir had positive and negative effects on atrazine exposure times: occasionally diluting atrazine below 10 µg L-1 but always extending exposure times to 5 and 3 µg L-1 thresholds. Release of atrazine-laden water by the reservoir also extended exposure times in the outflowing stream. Reservoir Daphnia exhibited excess male production during high atrazine exposure in 2003. However, in laboratory studies, Daphnia did not increase male production in response to atrazine, regardless of food availability, population growth phase, or exposure history. Laboratory populations of D. parvula invested in sexual reproduction while conditions were favorable for population growth, and returned to asexual reproduction under unfavorable conditions. Males were produced across a wide range of environmental conditions whereas ephippial females appeared only briefly. There was a cost to male production in terms of reduced carrying capacity, but not population growth rate. There were also windows within which Daphnia could increase male production without producing fewer parthenogenetic neonates. Increased male production seemed a significant disadvantage between clones only when level of investment in male production was high, and populations were at or near carrying capacity. Excess male production may be a common strategy of D. parvula clones rather than an indicator of endocrine disruption. Unlike atrazine, JHA (juvenile hormone analog) insecticides enhance male production by Daphnia and are likely to have other developmental effects on crustacean taxa. If JHAs are also stored and released by reservoirs, acute effects may be most important upstream of reservoirs, and chronic effects within and downstream of reservoirs. For ecologists, the ubiquity of reservoirs, coupled with annual flushing of agrochemicals from fields to streams, should elevate the importance of considering presence and location of reservoirs when assessing effects of land use on freshwater communities.
Maria Gonzalez (Advisor)
103 p.
Daphnia parvula; atrazine; Acton lake; reservoir; herbicide; retention; cost of male production; timing of sexual reproduction

Recommended Citations

Citations

  • Stoeckel, J. A. (2007). Herbicides, Reservoirs, and Daphnia Reproduction: Is There a Cost to Male Production? [Doctoral dissertation, Miami University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=miami1186153732

    APA Style (7th edition)

  • Stoeckel, James. Herbicides, Reservoirs, and Daphnia Reproduction: Is There a Cost to Male Production? 2007. Miami University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=miami1186153732.

    MLA Style (8th edition)

  • Stoeckel, James. "Herbicides, Reservoirs, and Daphnia Reproduction: Is There a Cost to Male Production?" Doctoral dissertation, Miami University, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=miami1186153732

    Chicago Manual of Style (17th edition)

miami1186153732
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© 2007, all rights reserved.
This open access ETD is published by Miami University and OhioLINK.