Evol Ecol Res 17: 291-300 (2016) Full PDF if your library subscribes.
No evidence of sex reversal
by means of experimentally altered sex ratios in threespine stickleback
Theo C.M. Bakker
Institute for Evolutionary Biology and Ecology, University of Bonn, Bonn, Germany
Correspondence: T.C.M. Bakker, Institute for Evolutionary Biology and Ecology, University of Bonn, An der Immenburg 1, D-53121 Bonn, Germany. email: email@example.com
Background: Among fishes, sex reversal by abiotic or social factors is well documented even in species with genetic sex determination. All species of the family Gasterosteidae studied thus far show genetic sex determination, and natural sex reversal is most likely rare. In threespine stickleback (Gasterosteus aculeatus L.), exposure to sex hormones or endocrine disrupters can induce functional intersexuality or even sex reversal.
Hypothesis: In the presence of a shortage of reproductive males (i.e. a female-biased operational sex ratio), female threespine stickleback may become males.
Methods: A classical male-removal experiment, which induces sex reversal in many protogynous fishes. In six large male-removal tanks, each containing a full-sibling group, every time that a reproductive male appeared, it was removed. In the respective yoked-control tank (one control tank for each male-removal tank), a random fish was removed at the same time. The sex of all removed fish was determined by visual inspection of the gonads.
Results: Approximately 16 months after the appearance of the first reproductive male, the total number of fish (removed and remaining fish) in each male-removal and yoked-control tank showed no significant deviation from an even sex ratio (except for a single female-biased control tank). The male-removal and yoked-control tanks did not differ significantly in sex ratio. Threespine stickleback thus failed to show sex reversal under the applied male-removal regime.
Keywords: Gasterosteus aculeatus, male removal, sex determination, sex ratio, social cues, threespine stickleback.
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