Evol Ecol Res 7: 325-333 (2005) Full PDF if your library subscribes.
Resolving an adaptive conundrum: reproduction in Caenorhabditis elegans is not sperm-limited when food is scarce
Nancy C. Goranson,* John P. Ebersole and Solange Brault
Department of Biology, University of Massachusetts Boston, 100 Morrissey Boulevard, Boston, MA 02125, USA
Author to whom all correspondence should be addressed.
Question: Has the less expensive gamete (sperm) really been selected as the limiting factor in a nematode’s reproduction, as laboratory studies have implied?
Hypothesis: Reproductive output of the self-fertilizing hermaphroditic nematode Caenorhabditis elegans is oocyte-limited in the worm’s natural environment: soil.
Organism: Sperm depletion and laying of unfertilized oocytes occurs in well-fed laboratory cultures of the self-fertilizing hermaphroditic nematode, Caenorhabditis elegans. This phenomenon has been much discussed as a possible contradiction to the usual expectation of selection for maximum fertility.
Methods: Caenorhabditis elegans were maintained in a variety of food regimes, not just the ad libitum Escherichia coli typical of laboratory cultures. Sperm production, oocyte production and body size were measured for nematodes cultured on agar with feeding treatments of serially diluted bacteria suspensions, before and during gamete formation. Body sizes were also measured for worms cultured in soil or compost microcosms.
Results: Reproduction was sperm-limited only for nematodes in the highest food treatments (106 or more E. coli cells per day); lower food treatments produced smaller worms with considerable excess sperm. Caenorhabditis elegans grown in natural soil or compost microcosms achieved the same sizes as those in treatments that showed oocyte limitation, not the large sizes of those typical of C. elegans in treatments that exhibited sperm limitation. Enriching soil or compost by adding E. coli produced appreciably larger C. elegans, but only if numbers of other invertebrates – potential predators/competitors of C. elegans – were minimized. Even with increased nutrients and reduced numbers of other invertebrates, only a few C. elegans in natural soil or compost were large enough to be consistent with sperm limitation.
Keywords: diet restriction, hermaphrodite, oocyte limitation, phenotypic plasticity, soil, sperm limitation, streptomycin.
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