Male–male competition for females can significantly affect a male’s reproductive success and hence his fitness. Game theory predicts that an individual should avoid fighting when its future reproductive potential is high, but should fight forcefully when its future reproductive potential is insignificant. When mates are scarce, extreme competition and fatal fighting is expected. We recently showed that Nephilengys malabarensis eunuchs, i.e. sterile spider males that lost their genitals during copulation, become more aggressive during male–male contests. Here, we add crucial comparative data by exploring eunuch fighting behaviour in Nephilengys livida from Madagascar, specifically by testing the ‘better fighter hypotheses’ in a laboratory setting. Similar to N. malabarensis, N. livida copulations resulted in total male castration with the severed palp plugging the female genitals in 70.83% cases, which mostly (63.63%) prevented subsequent copulations. Unexpectedly, however, N. livida eunuchs exhibited lower aggressiveness than virgin males. We interpret these results in the light of different mating biology between the so far studied species known for the eunuch phenomenon, which might reflect differing plug effectiveness due to variation in genital anatomy in N. livida, N. malabarensis and Herennia multipuncta. However, detected differences in aggressive behaviour of N. livida versus N. malabarensis eunuchs might also be explained by the species’ ecology, with lower population densities resulting in a relaxed male–male competition making excessive aggression and mate guarding redundant. This study thus questions the generality of overt aggressiveness in mated males with no reproductive value, and highlights the importance of understanding the natural history of species in the question.
This is a preview of subscription content, log in to check access.
We thank three anonymous reviewers and Jutta Schneider for comments on the manuscript, Matjaž Gregorič for the spider collection and laboratory help; Živa Justinek for help with experiments and lab support; and Ingi Agnarsson, Sahondra Lalao Rahanitriniaina and Honore Rabarison for their help in field. This work was funded by the Slovenian Research Agency (grant J1-2063 to MK) and the National Geographic Society (grant 8655-09 to I. Agnarsson, M. Kuntner and T. Blackledge). SKF was supported by Humboldt fellowship for postdoctoral researchers and Humboldt return fellowship.
Innocent TM, Savage J, West SA, Reece SE (2007) Lethal combat and sex ratio evolution in a parasitoid wasp. Behav Ecol 8:709–715CrossRefGoogle Scholar
Innocent TM, West SA, Sanderson JL, Hyrkkanen N, Reece SE (2011) Lethal combat over limited resources: testing the importance of competitors and kin. Behav Ecol 22:923–931CrossRefGoogle Scholar
Jormalainen V (1998) Precopulatory mate guarding in crustaceans: male competitive strategy and intersexual conflict. Q Rev Biol 73:275–304CrossRefGoogle Scholar
Kasumovic MM, Bruce MB, Andrade MCB, Herberstein ME (2008) Spatial and temporal demographic variation drives within-season fluctuations in sexual selection. Evolution 62:2316–2325PubMedCrossRefGoogle Scholar
Kokko H, Rankin DJ (2006) Lonely hearts or sex in the city? Density-dependent effects in mating systems. Phil Trans R Soc B 1466:319–334CrossRefGoogle Scholar
Kralj-Fišer S, Gregorič M, Zhang SC, Li D, Kuntner M (2011a) Eunuchs are better fighters. Anim Behav 81:933–939CrossRefGoogle Scholar
Kralj-Fišer S, Schneider JM, Justinek Ž, Kalin S, Gregorič M, Kuntner M (2011b) Mate quality, not aggressive spillover, explains sexual cannibalism in a size dimorphic spider. Behav Ecol Sociobiol doi:10.1007/s00265-011-1262-7
Kuntner M (2005) A revision of Herennia (Araneae: Nephilidae: Nephilinae), the Australasian 'coin spiders'. Invertebr Syst 19:391–436CrossRefGoogle Scholar
Kuntner M (2007) A monograph of Nephilengys, the pantropical 'hermit spiders' (Araneae, Nephilidae, Nephilinae). Syst Entomol 32:95–135CrossRefGoogle Scholar
Kuntner M, Coddington JA, Hormiga G (2008) Phylogeny of extant nephilid orb-weaving spiders (Araneae, Nephilidae): testing morphological and ethological homologies. Cladistics 24:147–217CrossRefGoogle Scholar
Kuntner M, Kralj-Fišer S, Schneider JM, Li D (2009a) Mate plugging via genital mutilation in nephilid spiders: an evolutionary hypothesis. J Zool 277:257–266CrossRefGoogle Scholar
Kuntner M, Coddington JA, Schneider JM (2009b) Intersexual arms race? Genital coevolution in nephilid spiders (Araneae, Nephilidae). Evolution 63:1451–1463PubMedCrossRefGoogle Scholar
Kuntner M, Agnarsson I, Gregorič M (2009c) Nephilid spider eunuch phenomenon induced by female or rival male aggressiveness. J Arachnol 37:266–271CrossRefGoogle Scholar
Kuntner M, Agnarsson I (2011) Biogeography and diversification of hermit spiders on Indian Ocean islands (Nephilidae: Nephilengys). Mol Phylogenet Evol 59:477–488PubMedCrossRefGoogle Scholar
Maynard Smith J, Parker GA (1976) The logic of asymmetric contests. Anim Behav 24:159–175CrossRefGoogle Scholar
Moore JC, Obbard DJ, Reuter C, West SA, Cook JM (2008) Fighting strategies in two species of fig wasp. Anim Behav 76:315–322CrossRefGoogle Scholar
Murray MG, Gerrard R (1985) Putting the challenge into resource exploitation—a model of contest competition. J Theor Biol 115:367–389CrossRefGoogle Scholar
Parker GA (1970) Sperm competition and its evolutionary consequences in insects. Biol Rev Camb Philos Soc 45:525CrossRefGoogle Scholar
Poesel A, Kunc HP, Foerster K, Johnsen A, Kempenaers B (2006) Early birds are sexy: male age, dawn song and extrapair paternity in blue tits, Cyanistes (formerly Parus) caeruleus. Anim Behav 72:531–538CrossRefGoogle Scholar
Reece SE, Innocent TM, West SA (2007) Lethal male–male combat in the parasitoid Melittobia acasta: are size and competitive environment important? Anim Behav 74:1163–1169CrossRefGoogle Scholar
Reinhold K (2003) Influence of male relatedness on lethal combat in fig wasps: a theoretical analysis. Proc R Soc Lond Ser B Biol Sci 270:1171–1175CrossRefGoogle Scholar