The Effects of Kin Selection and Family on Juvenile Cannibalism in the Black Widow spider, Latrodectus hesperus

Below we have pasted the abstract from Katie's poster that won honorable mention for best Undergraduate poster at the national meetings of the Animal Behavior Society held July 2007 in Burlington, Vermont. 

Give 'em hell in Minnesota Kitchen!!

Cannibalism has been an active area of research in both behavior and ecology.  Due to their relatively strong cannibalistic tendencies, spiders have been a particularly popular focus for these studies.  Factors including relatedness, population density and material benefits have been shown to be important determinants of cannibalism in spiders.  However, the spiders that have been studied previously have been social, subsocial or wandering spiders.  Therefore, in this study we examine factors influencing the cannibalistic behavior of a solitary, web-building spider, the North American Black Widow (Latrodectus hesperus.  Here, we report evidence that kin selection influences the cannibalistic behavior of black widows.  Related spiderlings resided significantly closer to one another compared to unrelated individuals.  Despite having readier access to each other, related individuals took significantly longer to cannibalize one another than did their unrelated counterparts.  Cannibalism was not explained by a spiderling’s condition as estimated by offspring number/egg sac mass.  Finally, despite the fact that egg sac parameters did not explain cannibalism, family identity was a strong predictor of cannibalism.  Specifically, some families took, on average, 2-3 days to cannibalize a related individual, whereas other families took 3 weeks to cannibalize a related individual, suggesting that cannibalism has a significant underlying genetic basis.  This family effect proved to be so strong that when we included it in our model the effect of kin selection on cannibalism became non-significant.  We discuss the implications of these results giving particular attention to the fact that the black widow’s historical role as a solitary, desert predator has changed drastically in many urbanized areas of the desert Southwest, such that urban black widows now live in high-density populations, which are typified by heightened levels of social interactions.