Naturwissenschaften

, Volume 99, Issue 2, pp 95–101 | Cite as

Eunuchs as better fighters?

Original Paper

Abstract

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.

Keywords

Aggression Cannibalism Emasculation Guarding Plugging Nephilidae Nephilengys livida 

Supplementary material

114_2011_873_MOESM1_ESM.docx (26 kb)
ESMExperimental workflow. (DOCX 25 kb)

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Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  1. 1.Institute of Biology, Scientific Research CentreSlovenian Academy of Sciences and ArtsLjubljanaSlovenia
  2. 2.Biozentrum GrindelUniversity of HamburgHamburgGermany
  3. 3.National Museum of Natural HistorySmithsonian InstitutionWashingtonUSA
  4. 4.College of Life SciencesHubei UniversityWuhanChina

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