Spider body size and longevity after exposure to lead-polluted soil

Heavy metal pollution is pervasive in urban soils, and it can negatively
impact the fitness of arthropods. Arthropod populations can evolve to
become more tolerant or resistant to metals, but the mechanisms of these
processes are understudied. Here, we tested the hypotheses of fixed
adaptation and facultative adaptation in a lead (Pb)-exposure experiment
using the progeny of field-collected Pardosa
milvina spiders from urban (elevated soil Pb) and rural
(background soil Pb) habitats. We predicted that spiders from both
populations that were reared in the elevated Pb treatment would exhibit
decreased body size in comparison to individuals reared in background Pb
soil due to a facultative shift in metabolic investment from growth to Pb
resistance, or, alternatively, that urban spiders would exhibit no change
in body size across treatments, supporting fixed adaptation as a
consequence of a legacy effect of urban Pb pollution. We found no evidence
that exposure to elevated Pb soil had an effect on P. milvina’s
adult body size or survival, regardless of population origin. Our results
indicate that the amount of Pb accumulated by the spiders was not
sufficient to induce a measurable change in body size, or that there was a
fitness cost that was not measured in the experiment, such as changes in
fecundity or body condition. Overall, these findings do not provide
support for fixed or facultative adaptation to Pb pollution in P.
milvina; as such, future studies should investigate other possible
tradeoffs, including changes in egg size, body weight, and foraging
effort.