Li Daiqin’s paper with colleagues on genital amputation in the orb-web spider Nephilengys malabarensis has received considerable coverage, congratulations, Daiqin!
A large female Nephilengys malabarensis spider with the severed
copulatory organ (highlighted by the red square) of the smaller,
red-coloured male, embedded in her genitals.
Daiqin Li, J. Oh, S. Kralj-Fišer and M. Kuntner, 2012. Remote copulation: male adaptation to female cannibalism. Biology Letters, 01 Feb 2012; doi: 10.1098/rsbl.2011.1202.
“Sexual cannibalism by females and associated male behaviours may be driven by sexual conflict. One such male behaviour is the eunuch phenomenon in spiders, caused by total genital emasculation, which is a seemingly maladaptive behaviour. Here, we provide the first empirical testing of an adaptive hypothesis to explain this behaviour, the remote copulation, in a highly sexually cannibalistic orb-web spider Nephilengys malabarensis.
We demonstrate that sperm transfer continues from the severed male organ into female genitals after the male has been detached from copula. Remote copulation increases the total amount of sperm transferred, and thus probably enhances paternity. We conclude that the mechanism may have evolved in response to sexual cannibalism and female-controlled short copulation duration.”
And The Guardian used photos from Lee Qi Qi’s wikispaces page for the species.
The article has been covered by:
“Genital amputation, that is, genital damage or loss, seems maladaptive because it renders the amputee functionally sterile, but is nevertheless common in sexually dimorphic spiders. In these species, male genital amputation correlates with plugging of female genitals and with sexual cannibalism. Genital amputation in male spiders may be partial or full; the latter is known as the eunuch phenomenon. We tested two adaptive hypotheses about eunuch behaviour in an orb web spider, Nephilengys malabarensis: (1) the plugging hypothesis (i.e. broken male genitals (palps) effectively plug the female genitals) and (2) the better fighter hypothesis (i.e. eunuch males are better fighters than their intact rivals).
By staging mating trials, we documented genital amputation (occurrence and frequency), sexual cannibalism and genital organ reuse, morphologically examined plugs to infer their effectiveness, and conducted a series of maleemale contests to determine whether eunuch males were better fighters. Copulations always resulted in amputation of the palps: 87.5% of males became eunuchs directly during copulation and plugged females, while 12.5% of males first partially damaged the palps and then severed them after copulation. Sexual cannibalism and plugging effectiveness both reached 75%. Eunuchs guarded females, were highly aggressive and active, and initiated and won contests more often, whereas intact males and half-eunuchs showed significantly lower levels of guarding behaviour, aggression and general activity. Thus, both hypotheses are supported and we conclude that the eunuch phenomenon is adaptive.”