Papers in the Biological Sciences


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Published in Biology Letters 9:4 (August 23, 2013), 4 pp.; doi: 10.1098/rsbl.2013.0113


Copyright © 2013 Steven K. Schwartz, William E. Wagner, Jr., and Eileen A. Hebets; published by the Royal Society. Used by permission.

Illustrative video is online at:


Monogyny (male monogamy) is found in a diverse assemblage of taxa, and recent theoretical work reveals that a male-biased sex ratio can favour the evolution of this relatively rare mating system. We integrate this theoretical framework with field observations and laboratory experiments involving the sexually size dimorphic fishing spider, Dolomedes tenebrosus, to test the prediction that this species exhibits monogyny. Field surveys revealed a male-biased sex ratio, likely resulting from different life-history strategies (early male maturation). Results from mating trials supported our prediction of monogyny as we discovered that males mate with a single female. Unexpectedly, however, we observed that mating results in obligate male death and genital mutilation. Additional field observations of released individuals suggest that males are not limited by their ability to encounter additional females. Controlled laboratory assays demonstrated that males discriminate among virgin and non-virgin female silk cues, consistent with predictions of first-male sperm precedence. In summary, we report a novel case of male self-sacrifice in a species that exhibits female-biased sexual size dimorphism, male-biased sex ratio, genital mutilation and a suggestion of first-male sperm precedence; all of which are consistent with theoretical predictions of the evolution of monogyny.

Includes Supplementary materials: Methods, Figures S1 & S2, & Table S1.

Data report (.xls format) attached below as supplemental file.