Sneaking behaviour is risky for spider males

Written by Thomas Hesselberg

Sunday, 17 February 2008

The poisonous redback spider (Latrodectus hasselti) showing its characteristic red pattern on the abdomen. Photo from Wikipedia.
In the mating game everything is allowed. A sneaking strategy can be observed in a wide range of species. It is usually smaller subdominant males that quickly seize opportunities to mate with unguarded females, for instance when dominant males are fighting among each other for access to the female. Such a strategy can be risky though as the dominant males, for obvious reasons, are not very tolerant towards sneaking males. However, scientists have discovered that for the redback spider (Latrodectus hasselti), the danger does not come from other males but from the female.

The redback spider is one of the easiest recognisable spiders in Australia with its characteristic red pattern on an otherwise black abdomen. It is related to the black widow and its poison can be dangerous for humans. The competition for female access is usually very high among redback males, although female redbacks are known to eat the males.

The group of scientists from the University of Toronto in Canada placed either one or two males of different weights at the edge of female webs built in the laboratory and recorded the ensuing behaviour with a video camera. The results showed that larger and therefore dominant males unexpectedly did not show pronounced aggression against their inferior competitors except occasional brief chases. Instead they invested their time in prolonged courtships, whereas the inferior males used a sneaking strategy with short or no courtship. In situations were only one male is present, even smaller males engage in prolonged courtships.

The scientists, furthermore, showed that females were more likely to kill and eat sneaking males after initial copulation, probably due to their shorter courtship, whereas dominant males were allowed to copulate several times.

Thus dominant males achieve a much higher paternity of the brood than subdominant males even without inter-male aggression. Though considering the high mortality for males while searching for webs, it may still be better for a smaller male to adopt a sneaking strategy when in webs with other large males. Passing the genes on to even a small proportion of the offspring is after all better than not mating at all.

Source:
Stoltz, J. A., Elias, D. O., Andrade, M. C. B. 2008. Females reward courtship by competing males
in a cannibalistic spider. Behavioral Ecology and Sociobiology 62, 689-697.

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