Segev, O., M. Ziv, and Y. Lubin. 2003. The male mating system in a desert widow spider. Journal of Arachnology 31: 379-393.

The male pedipalp in Ladrodectus revivensis are highly modified into copulatory organs that store sperm until intromission occurs. The embolus is the distal portion of the genital bulb, and it penetrates into the copulatory duct and spermatheca during copulation. A saddle-like obstruction on the embolus gets caught in the copulatory duct, rips off and mutilates the embolus leaving the male functionally infertile. Is this a maladaptation of the copulatory organ?

A widow spider population was monitored in a 25km2 area and 30 mated females, 3 adult males of unknown mating history, 10 subadult females, and 10 subadult males were collected. The genitalia of the respective specimens were isolated and analyzed.

The mutilation of the embolous, does in fact limit the number of matings that a male widow spider can have. When both pedipalps are used the males are effectively infertile. The broken off tip of the embolous does not prevent other males from copulating. However the broken tip does seal the female's spermathecal duct preventing the transmission of sperm from other males. This adaptation is quite spectacular considering that the lifespan of a male widow spider is not very long and they exhibit such high mortality rates in their attempt to seek a mate. With these characteristics it is optimal for the male to invest everything he has in his first mating, to ensure that the female will cede his sperm. Although the male is rendered infertile it is an advantageous tradeoff, considering multiple mating is not plausible.

(250 words)

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(posted March 19, 2009)