The behavior, ecology and evolution of the Western black widow (Latrodectus hesperus):  from desert predators to urban pests

I am excited to be working in conjunction with the Central Arizona Phoenix, Long Term Ecological Research (CAP-LTER) project. 

This is one of only a handful of these NSF-funded, long-term studies that is focused on the ecology of urban habitats. 

Below is an abstract of the work I am doing as a part of this group. 

The bite of a widow spider (Latrodectus spp., Theridiidae) has long been considered to be the most painful and dangerous of all North American spiders.  One result of urban expansion into desert habitats is that humans are encountering widow spiders more and more frequently.  Indeed, in Western cities such as Tucson and Phoenix, the local widow species, L. hesperus, is so common in and around homes that many residents, particularly those with small children, have begun contracting with pest control agencies to spray for widow spiders.  Despite the fact that many pesticides are currently labeled for use against spiders, pesticides are, in fact, largely ineffective at killing web-building spiders such as widows.  This is because widow spiders rarely leave their web and thus do not come into contact with toxins sprayed indiscriminately. 

The combination of a rise in widow population numbers in and around human homes and the ineffectiveness and dangers of widespread pesticide use to combat widow spiders suggest that it is of paramount importance to develop an alternative approach to controlling the abundance of these spiders in urban habitats.  The above-stated problem can be addressed in a similar manner to that of biological invasions by non-native, introduced species.  L. hesperus can be thought of as a novel species introduced somewhat suddenly to urban habitat in the West.  Thus, we can attempt to control the proliferation of widows in urban habitats in many of the same ways that we attempt to control the spread and establishment of invasive species. 

The aim of this project is to develop a thorough understanding of the interaction between widow behavior and population ecology that results in colonization and population establishment/growth in urban habitats.  The focus throughout this project will be on comparing the behavior, ecology and evolution of urban widow populations collected in Phoenix with populations from surrounding desert habitat.  What behavioral differences have arisen between these relatively recently diverged populations? For example, are spiders from urban environments, on average, bolder or shyer towards predators than spiders from desert habitats?  Is this boldness the result of different predation regimes experienced across the population types?  In other words, does the interaction between behavior (e.g. boldness towards predators) and ecology (e.g. degree of predation risk) explain the explosive success of urban widow spiders?  Similar questions will be asked regarding population differences in the behavioral ecology surrounding foraging, mating, agonism and parental care. 

Finally, what can genetic variation within and between these populations tell us about the success of urban populations?  The study of non-native species introductions has emphasized the importance of reduced genetic variation that typically accompanies the colonization of new habitats by only a few introduced individuals.  Do urban populations show evidence of low levels of genetic variation similar to that predicted for invasive species?  If so, this may explain local adaptation to urban environments. 

Male mate choice in black widows:

chemical and physical cues facilitate a male preference for high-condition females that never engage in pre-copulatory sexual cannibalism

Extensions of Bateman’s rule predict male mate choice should evolve as male investment in mating increases.  Spiders use chemical cues to avoid predators and locate mates, but it remains unclear whether males courting sexually cannibalistic females use chemical cues to make risk-sensitive mating decisions.  Here we test the prediction that cues of recent female foraging success (“fed cues”) encourage male courtship in the black widow spider (Latrodectus hesperus).  In addition, we test the prediction that previous foraging success reduces pre-copulatory sexually cannibalistic attacks by females.  Results show that males have a strong courtship preference for fed cues, and that this preference is maintained in the absence of the female and when structural cues from the female’s web architecture have been eliminated.  However, when well-fed females were switched to the webs of starved females and vice versa, males preferred courting well-fed females despite the lack of fed cue.  Male preferences for well-fed females appear adaptive as starved females were significantly more likely to attack males before mating.  We conclude by noting that sexual cannibalism offers a model system wherein chemical communication arms races between predator and prey have broad implications such as the effects on sexual selection described here.