For animals that live in association with humans, a key ecological question is how anthropogenic factors influence their behavior and life history. While major negative effects are obvious, subtle non-lethal responses to anthropogenic stimuli may provide insight into the features that lead to the success of species that thrive in habitats heavily impacted by humans. Anthropogenic influences impose novel selection pressures that shape the evolution of species that survive the stress they impose. These responses in turn can lead to changes in food webs, some of which can be detrimental to what humans desire such as the release of crop pests from natural enemies. Here we explored the influence of the herbicide atrazine on a variety of life history parameters exhibited by a wolf spider that is found in agroecosystems where this herbicide is commonly applied. During penultimate molt, male and female spiders were housed in containers treated with water, or a high or low dosage of atrazine. After completing the final molt, spiders were mated with another from the same treatment group. Spiders were then moved back into their respective containers until death. Time to complete molt, molt success, egg sac production and sac mass, and lifespan were recorded.
We found that exposure to atrazine delayed completion of the final molt and increased the probability that the spiders died during the molting process. We also found that longer exposure to the higher dosage of atrazine reduced the likelihood of producing an egg sac. There was also a marginally significant effect of atrazine on the mass of egg sacs; intriguingly the egg sacs produced by control females were the smallest. Spiders that were in the high dosage group of atrazine were also more likely to produce a second egg sac from the single mating. Finally, atrazine appears to have had a non-monotonic impact on the lifespan of these spiders. Those at the high dosage had the shortest average lifespan while the low dosage group had a longer average lifespan than the control group. These data suggest that the atrazine based herbicides that are routinely applied to agricultural fields are capable of impacting life history traits of these spiders and may therefore influence the community of predators and their effects on the food web in complex ways.