The evolution of genital complexity and mating rates in sexually size dimorphic spiders.
Genital diversity may arise through sexual conflict over polyandry, where male genital features function to manipulate female mating frequency against her interest. Correlated genital evolution across animal groups is consistent with this view, but a link between genital complexity and mating rates remains to be established. In sexually size dimorphic spiders, golden orbweaving spiders (Nephilidae) males mutilate their genitals to form genital plugs, but these plugs do not always prevent female polyandry. In a comparative framework, we test whether male and female genital complexity coevolve, and how these morphologies, as well as sexual cannibalism, relate to the evolution of mating systems.



Using a combination of comparative tests, we show that male genital complexity negatively correlates with female mating rates, and that levels of sexual cannibalism negatively correlate with male mating rates. We also confirm a positive correlation between male and female genital complexity. The macroevolutionary trajectory is consistent with a repeated evolution from polyandry to monandry coinciding with the evolution towards more complex male genitals.



These results are consistent with the predictions from sexual conflict theory, although sexual conflict may not be the only mechanism responsible for the evolution of genital complexity and mating systems. Nevertheless, our comparative evidence suggests that in golden orbweavers, male genital complexity limits female mating rates, and sexual cannibalism by females coincides with monogyny.
Institute of Biology, Research Centre of the Slovenian Academy of Sciences and Arts, Ljubljana, Slovenia. kuntner@gmail.com.|National Museum of Natural History, Smithsonian Institution, Washington, DC, USA. kuntner@gmail.com.
Matjaž
0000-0002-0057-2178
M
Kuntner
Institute of Biology, Research Centre of the Slovenian Academy of Sciences and Arts, Ljubljana, Slovenia.
Ren-Chung
RC
Cheng
Institute of Biology, Research Centre of the Slovenian Academy of Sciences and Arts, Ljubljana, Slovenia.
Simona
S
Kralj-Fišer
Department of Life Science, Tunghai University, Taichung, Taiwan.
Chen-Pan
CP
Liao
Zoological Institute, Biozentrum Grindel, University of Hamburg, Hamburg, Germany.
Jutta M
JM
Schneider
School of BioSciences, University of Melbourne, Victoria, 3010, Australia.
Mark A
MA
Elgar
D000818:Animals; D005075:Biological Evolution; D049628:Body Size; D005260:Female; D005837:Genitalia, Male / Q000502:physiology*; D008297:Male; D010641:Phenotype; D010802:Phylogeny; D012727:Sex Characteristics; D012726:Sexual Behavior, Animal / Q000502:physiology*; D013112:Spiders / Q000502:physiology*
Female gigantism; Nephila; Sexual conflict; Sexual selection; Sexual size dimorphism; Sexually antagonistic coevolution