Eunuchs are better fighters
Section snippets
Study System
We collected N. malabarensis spiders between December 2009 and January 2010 in Singapore: Labrador Park (1°15′58″N, 103°48′10″E), Pulau Ubin (1°24′30″N, 103°57′40″E) and Kent Ridge Park (1°17′10″N, 103°47′10″E). To examine rematings using the same genital organ, we needed spiders with known mating histories. Therefore, we collected subadults and reared them to adulthood in the laboratory (N♀ = 21, N♂ = 14). In addition to subadults, we collected adult females and males for contest trials (N♀ = 20, N♂ =
Results
In N. malabarensis, a male placed on the female’s web usually starts courtship by plucking the threads of the web, and attaching silk to it. If the female shows receptive behaviour, that is, she orients towards the male or comes out of the retreat the male eventually establishes physical contact and climbs onto her dorsal abdomen. The male then switches to her venter and attempts to insert one of the palps (see Supplementary Material, Video and Fig. S1). Figure 2 shows a detailed ethogram of
Discussion
Male N. malabarensis exhibit obligatory damage to their genitals during copulation either through direct or indirect amputation, the latter involving initial sclerite damage followed by subsequent, voluntary palpal removal. Their obligate genital amputation (direct or indirect), also termed the eunuch phenomenon, may be logical from the perspective of very limited sperm in each palp; new research shows that their palps can be charged only once because spermiogenesis in this species, as in
Acknowledgments
We thank Mark Elgar and an anonymous referee for their most helpful reviews, Jutta Schneider and Mariella Herberstein for commenting on our experimental design, and Ingi Agnarsson for commenting on the manuscript. Cene Fišer and Irena Kuntner kindly offered logistic help and Singapore National Parks supplied the research and collection permits. This work was funded by grants to M.K. from the Slovenian Research Agency (J1-2063) and the Raffles Museum for Biodiversity Research Fellowship,
References (49)
A game theoretical interpretation of male combat in the bowl and doily spider (Frontinella pyramitela)
Animal Behaviour
(1983)Evolution of sperm priority patterns in spiders
- et al.
Sexual cannibalism in the garden spider Araneus diadematus
Animal Behaviour
(1988) - et al.
Virgin doves and mated hawks: contest behaviour in a spider
Animal Behaviour
(2005) - et al.
A model for the evolutionary maintenance of monogyny in spiders
Journal of Theoretical Biology
(2008) - et al.
Monogyny and regulation of worker mating in the queenless ant Dinoponera quadriceps
Animal Behaviour
(1998) - et al.
Early birds are sexy: male age, dawn song and extrapair paternity in blue tits, Cyanistes (formerly Parus) caeruleus
Animal Behaviour
(2006) Phylogenetic placement of Echinotheridion (Araneae: Theridiidae); do male sexual organ removal, emasculation, and sexual cannibalism in Echinotheridion and Tidarren represent evolutionary replicas?
Invertebrate Systematics
(2006)Sexual selection for male sacrifice in the Australian redback spider
Science
(1996)First male sperm priority in the bowl and doily spider, Frontinella pyramitella (Walckenaer)
Evolution
(1982)
The evolution of male traits in social insects
Annual Review of Entomology
Costs and benefits of male–male competition in the orb weaving spider, Nephila clavipes
Behavioral Ecology and Sociobiology
Feeding and mating in the insectivorous Ceratopogoninae (Diptera)
Memoirs of the Entomological Society of Canada
Female Control: Sexual Selection by Cryptic Female Choice
Sperm competition and sexual selection in spiders and other arachnids
Female control of paternity in the sexually cannibalistic spider Argiope keyserlingi
Proceedings of the Royal Society B
Spontaneous male death during copulation in an orb-weaving spider
Proceedings of the Royal Society B
Safer sex with feeding females: sexual conflict in a cannibalistic spider
Behavioral Ecology
Emasculation to plug up females: the significance of pedipalp damage in Nephila fenestrata
Behavioral Ecology
Faithful without care: the evolution of monogyny
Evolution
Sexual selection research on spiders: progress and biases
Biological Reviews
Palpal loss, single palp copulation and obligatory mate consumption in Tidarren cuneolatum (Tullgren, 1910) (Araneae, Theridiidae)
Journal of Natural History
Tidarren argo sp nov (Araneae: Theridiidae) and its exceptional copulatory behaviour: emasculation, male palpal organ as a mating plug and sexual cannibalism
Journal of Zoology
A revision of Herennia (Araneae: Nephilidae: Nephilinae), the Australasian ‘coin spiders’
Invertebrate Systematics
Cited by (0)
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S. Zhang and D. Li are at the Department of Biological Sciences, National University of Singapore, 14 Sciences Drive 4, 117543 Singapore.