Sexual cannibalism is common amongst spiders. The female will often eat the male after copulation, but sometimes the female will eat the male during or even before mating. This behavior is costly in terms of reproduction, as it may jeopardize the chances of successful fertilization if a sufficient number of males are not present. An intriguing recent study, published in the journal Ethology, set out to investigate why this might be.
Researchers from the Experimental Station of Arid Zones evaluated the personalities and cannibalism behaviors of 80 virgin female wolf spiders (Lycosa hispanica). They predicted that more voracious females may be more aggressive and therefore less discriminating when approaching males. To test this, they first investigated voracity by observing the weight gain of the females after they were fed ad libitum. They found that some females had more docile feeding personalities, whereas others were more ravenous and gained weight quicker.
They then introduced the unmated females with males and observed their cannibalistic behaviors, which yielded surprising results. Interestingly, the more voracious spiders that gained more weight during the study were more likely to cannibalize the male, whereas the more docile spiders did not always engage in cannibalism. Furthermore, when the docile spiders did kill the males they were selective in doing so; they would mate with the males that appeared to be in a good condition, but killed those that appeared weaker. The voracious spiders were not so choosey and attacked males regardless of their apparent condition.
At first glance it may seem logical that more voracious spiders exert more cannibalism, but well-fed females have more resources in terms of nutrition which could then be invested in offspring. It therefore doesn’t make sense that they engage in behaviors that could jeopardize the chance of reproductive success. The more docile females on the other hand might be lacking in nutrition and may therefore be expected to prioritize eating before reproduction, as they may not have the resources to ensure healthy offspring.
These results support other studies which have suggested that animal personalities, sexual cannibalism and sexual selection are linked, and show that male selection on condition varies depending on female growth rate in these spiders.