Lindsay Miles & Patricia Trubl

Developing into a cannibal: the evolutionary ecology

of black widows from trophic eggs to sexual cannibals

Black widow spiders are well known for sexual cannibalism, but cannibalism in other life history stages is less studied.  Our lab has found Latrodectus hesperus spiderlings to be voracious cannibals among siblings immediately after hatching from the egg sac.  In fact, we have found that spiderlings will prey on related spiderlings and consume related eggs (see photos) at developmental stages prior to emerging from the egg sac.  Interestingly, cannibalism at these early stages shows great variation among families, with some families preying on siblings in a matter of a few days, and other families waiting several weeks before resorting to cannibalism.  We are interested in discovering the extent to which this family effect on cannibalism is a product of genes and/or the environment.  In particular, we are testing the hypothesis that a variable maternal environment (e.g. affecting maternal condition, egg sac size, and the condition of individual eggs) might influence cannibalism among siblings.  To do this, we are manipulating the condition of 20 females through lab feeding protocols, documenting the condition (area/mass) of 25 individual eggs per family, and tracking development and cannibalism rates among these families.  Our results will have implications for the urban ecology of black widows.  Given that urban populations of black widows are characterized by heightened prey abundance and associated increased competition for prey relative to desert populations, it remains unclear whether urban spiderlings should be more or less cannibalistic than their desert counterparts.  Preliminary field data, however, suggest that desert females create significantly bigger egg sacs with bigger eggs, but that egg condition does not differ between populations.  Perhaps this suggests that an optimal egg condition may exist wherein a female can minimize the extent to which her offspring feed upon each other.  Check back soon as we hope to have the full data set analyzed in time to present a poster at the 2011 January meetings of the Society for Integrative and Comparative Biology.